Infectious Disease - Infectious Agents - Practice Questions

Question 1

Most agents of infection can be detected and identified by their DNA content. Which of the following groups would not be satisfactorily detected this way?

a. Gram-positive bacteria
b. Fungi
c. Viruses
d. Protozoa
e. Gram-negative bacteria

Answer 1

c. Viruses

Question 2

The initial step in the process of many bacterial infections is adherence of the organism to mucous membranes. The bacterial component that mediates adherence is the:

a. Lipid A
b. Nucleoid
c. Peptidoglycan
d. Pilus
e. Plasmid

Answer 2

d. Pilus

Question 3

In the Gram stain procedure, bacteria are exposed to 95% alcohol or to an acetone/alcohol mixture. The purpose of this step is:

a. To adhere the cells to the slides
b. To retain the purple dye within all the bacteria
c. To disrupt the outer cell membrane so the purple dye can leave the bacteria
d. To facilitate the entry of the purple dye into the gram-negative cells
e. To form a complex with the iodine solution

Answer 3

c. To disrupt the outer cell membrane so the purple dye can leave the bacteria

Question 4

In the process of studying how bacteria cause disease, it was found that a rare mutant of a pathogenic strain failed to form a capsule. Which one of the following statements is the most accurate in regards to this unencapsulated mutant strain?

a. It was nonpathogenic primarily because it was easily phagocytized
b. It was nonpathogenic primarily because it could not invade tissue
c. It was nonpathogenic primarily because it could only grow anaerobically
d. It was highly pathogenic because it could secrete larger amounts of exotoxin
e. It was highly pathogenic because it could secrete larger amounts of endotoxin

Answer 4

a. It was nonpathogenic primarily because it was easily phagocytized

Question 5

Of the following components, which one exhibits the most antigenic variation?

a. Capsule
b. Lipid A of endotoxin
c. Peptidoglycan
d. Ribosome
e. Spore

Answer 5

a. Capsule

Question 6

β-Lactamases are an important case of antibiotic resistance. Which one of the following is the most common site where β-lactamases are located?

a. Attached to DNA in the nucleoid
b. Attached to pili on the bacterial surface
c. Free in the cytoplasm
d. Within the capsule
e. Within the periplasmic space

Answer 6

e. Within the periplasmic space

Question 7

Which one of the following is the most accurate description of the structural differences between gram-positive and gram-negative bacteria?

a. Gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer
b. Gram-positive bacteria have an outer lipid-rich membrane whereas gram-negative bacteria do not
c. Gram-positive bacteria from a sex pilus that mediates conjugation, whereas gram-negative bacteria do not
d. Gram-positive bacteria have capsules, whereas gram-negative bacteria do not

Answer 7

a. Gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer

Question 8

Bacteria that cause nosocomial (hospital-acquired) infections often produce extracellular substances that allow them to stick firmly to medical devices, such as intravenous catheters. Which one of the following is the name of this extracellular substance?

a. Axial filament
b. Endotoxin
c. Flagella
d. Glycocalyx
e. Porin

Answer 8

d. Glycocalyx

Question 9

The figure depicts a bacterial growth curve. In which one of the phases are antibiotics such as penicillin most likely to kill bacteria?

A. Lag phase

B. Log phase

C. Stationary phase

D. Death phase

Answer 9

B. Log phase

Question 10

The properties of bacteria change as they pass through the cell cycle and adopt different patterns of growth in liquid or on solid media. Which of the following growth states or patterns produces the highest level of clinically significant phenotypic antibiotic tolerance?

A. Growth in colonies on agar

B. Exponential growth in liquid

C. Stationary growth in liquid

D. Lag phase in liquid

E. Biofilm growth

Answer 10

E. Biofilm growth

Question 11

Sterile instruments are an essential requirement for surgery. Which of the following methods should be used to sterilize a retractor used in abdominal surgery?

A. Ionizing radiation

B. Immersion in glutaraldehyde

C. Dry heat delivered in an oven

D. Moist heat delivered in an autoclave

E. Exposure to gaseous ethylene oxide

Answer 11

D. Moist heat delivered in an autoclave

Question 12

Upon activation, macrophages increase their consumption of oxygen. How does this respiratory burst affect replication of bacteria within the phagosome or near the macrophage?

A. It inhibits bacterial replication as a result of the formation of reactive oxygen species

B. It promotes intracellular bacterial replication because of the availability of oxygen for aerobic respiration

C. It inhibits bacterial replication because of the resulting high intracellular pH

Answer 12

A. It inhibits bacterial replication as a result of the formation of reactive oxygen species

Question 13

Pseudomonas aeruginosa is a major cause of nosocomial infections because of its ability to survive in a variety of environmental conditions, such as on IV tubing, in the respiratory tract, and even in distilled water. This is an indication of it being a highly fastidious microorganism.

A. True

B. False

Answer 13

B. False

Question 14

A 65-y/o woman has a long-term central venous catheter for intravenous therapy. She develops fever and subsequently has multiple blood cultures positive for Staphylococcus epidermidis. All the isolates have the same colony morphology and antimicrobial susceptibility pattern suggesting they are the same strain. A Staphylococcus epidermidis biofilm is thought to be present on the catheter. Which one for the following statements about such an infection is correct?

A. The biofilm is likely to wash off the catheter

B. Production of an extracellular polysaccharide inhibits growth of the bacteria, limiting the infection

C. The bacteria in the biofilm are likely to be more susceptible to antimicrobial therapy because they have decreased rates of metabolism

D. The quorum sensing ability of the bacteria in the biofilm results in increased susceptibility to antimicrobial therapy

E. The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy and it is likely the catheter will have to be removed to cure the infection

Answer 14

E. The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy and it is likely the catheter will have to be removed to cure the infection

Question 15

The emergence of antibiotic-resistant bacteria, especially in enteric gram-negative rods, is a medically important phenomenon. This most commonly occurs by a process that involves a sex pilus and the subsequent transfer of plasmids carrying one or more transposons. Which one of the following is the name that best describes this process?

a. Conjugation
b. Transduction
c. Transformation
d. Translocation
e. Transposition

Answer 15

a. Conjugation

Question 16

Which statement is the most accurate regarding transposons?

a. They encode enzymes that degrade the ends of the bacterial chromosome
b. They are short sequences of DNA that often encode enzymes that mediate antibiotic resistance
c. They are short sequences of RNA that silence specific regulatory genes
d. They are a family of transfer RNAs that enhance mutations at “hot spots” in the bacterial genome

Answer 16

b. They are short sequences of DNA that often encode enzymes that mediate antibiotic resistance

Question 17

• Corynebacterium diphtheriae* causes the disease diphtheria by producing diphtheria toxin. The gene encoding the toxin is integrated into the bacterial genome during lysogenic conversion. The toxin gene was acquired by which process?
  a. Conjugation
  b. Transduction
  c. Transformation
  d. Translocation
  e. Transposition

Answer 17

b. Transduction

Question 18

Regarding bacterial pathogenicity islands, which of the following statements is correct?

a. They are only found in gram-positive bacteria
b. They play an important role in the pathogenesis of toxin-induced diseases
c. They play a major role in quorum sensing (bacterial communication)
d. They prevent phagocytosis of bacterial organisms
e. They can only be transferred by Transposons

Answer 18

b. They play an important role in the pathogenesis of toxin-induced diseases

Question 19

An 11—y/o boy develops a mild fever and pain in his upper arm. An X-ray of his arm shows a lytic lesion (dissolution) in the upper part of the humerus with periosteal elevation over the lesion. The patient is taken to surgery, where the lesion is debrided (dead bone and pus removed). Culture from the lesion yields a gram—positive coccus that is coagulase positive. Which of the following is the most likely causative agent?

A. Staphylococcus epidermidis

B. Streptococcus pyogenes

C. Streptococcus agalactiae

D. Streptococcus pneumoniae

E. Staphylococcus saprophyticus

F. Staphylococcus aureus

Answer 19

F. Staphylococcus aureus

Question 20

7 days ago, a 27 y/o woman returned from Central America, where she had spent the summer working in a clinic for indigenous people. 4 days ago, she developed an erythematous sunburn-like rash. She also has had headache, muscle aches, and abdominal cramps with diarrhea. Her blood pressure is 70/40 mm Hg. Pelvic examination shows, she is having her menstrual period with a tampon in place, but no other abnormal findings. Her kidney function tests (serum urea nitrogen and creatinine) are abnormal, indicating mild renal failure. A blood smear for malaria is negative. Her illness is likely to be caused by which of the following?

A. A toxin that results in greatly increased levels of intracellular cyclic adenosine monophosphate (cAMP)

B. A toxin that degrades sphingomyelin

C. A toxin that binds to the class II major histocompatibility complex (MHC II) of an antigen presenting cell and the V-beta region of a T cell

D. A two component toxin that forms pores in white blood cells and increases cation permeability

E. A toxin that blocks elongation factor 2 (EF2)

Answer 20

C. A toxin that binds to the class II major histocompatibility complex (MHC II) of an antigen presenting cell and the V-beta region of a T cell

Question 21

A 16 y/o bone marrow transplant patient has a central venous line that has been in place for 2 weeks. He also has a urinary tract catheter, which has been in place for 2 weeks as well. He develops fever while his white blood cell count is very low and before the transplant has engrafted. Three blood cultures are done, and all grow a significant gram positive, coagulase negative bacterium. Which of the following is the most likely causative organism?

A. Staphylococcus aureus

B. Staphylococcus saprophyticus

C. Staphylococcus epidermidis

D. Streptococcus agalactiae

E. Streptococcus pyogenes

Answer 21

C. Staphylococcus epidermidis

Question 22

Which of the following statements regarding the role of Protein A in the pathogenesis of infections caused by Staphylococcus aureus is correct?

A. It is responsible for the rash in toxic shock syndrome

B. It converts hydrogen peroxide into water and oxygen

C. It is a potent enterotoxin

D. It is directly responsible for lysis of neutrophils

E. It is a bacteria surface protein that binds to the Fc portion of IgG1

Answer 22

E. It is a bacteria surface protein that binds to the Fc portion of IgG1

Question 23

A 48 y/o man is admitted to the hospital because of stupor. He is homeless and lives in an encampment with other homeless people who called the authorities when he could not be easily aroused. The patient suffers from Alcohol Use Disorder with a score of 9. His temperature is 38.5 C and his blood pressure is 125/80 mm Hg. He moans when attempts are made to arouse him. He has positive Kernig and Brudzinski signs, suggesting meningeal irritation. Physical examination and chest x-ray show evidence of left lower lobe lung consolidation. An endotracheal aspirate yields rust-colored sputum. Examination of a Gram-stained sputum smear shows numerous polymorphonuclear cells and numerous gram-positive lancet shaped diplococci. On lumbar puncture, the cerebrospinal fluid is cloudy and has a white blood cell count of 570/microL with 95% PMNs. Based on this information, the likely diagnosis is pneumonia and meningitis due to:

A. Staphylococcus aureus

B. Streptococcus pyogenes

C. Streptococcus pneumoniae

D. Enterococcus faecalis

E. Staphylococcus epidermidis

Answer 23

C. Streptococcus pneumoniae

Question 24

A 48 y/o man is admitted to the hospital because of stupor. He is homeless and lives in an encampment with other homeless people who called the authorities when he could not be easily aroused. The patient suffers from Alcohol Use Disorder with a score of 9. His temperature is 38.5 C and his blood pressure is 125/80 mm Hg. He moans when attempts are made to arouse him. He has positive Kernig and Brudzinski signs, suggesting meningeal irritation. Physical examination and chest x-ray show evidence of left lower lobe lung consolidation. An endotracheal aspirate yields rust-colored sputum. Examination of a Gram-stained sputum smear shows numerous polymorphonuclear cells and numerous gram-positive lancet shaped diplococci. On lumbar puncture, the cerebrospinal fluid is cloudy and has a white blood cell count of 570/microL with 95% PMNs. Based on this information, the likely diagnosis is pneumonia and meningitis due to, this infection might have been prevented by:

A. Prophylactic intramuscular benzathine penicillin every 3 weeks

B. A 23 valent capsular polysaccharide vaccine

C. A vaccine against serogroups A, C, Y and W135 capsular polysaccharide

D. A vaccine of polyribosylribitol capsular polysaccharide linked to a protein

E. Oral penicillin V daily

Answer 24

C. A vaccine against serogroups A, C, Y and W135 capsular polysaccharide

Question 25

An 8 y/o boy develops a severe sore throat. On exam, a grayish-white exudate is seen on the tonsils and pharynx. The differential diagnosis includes group A streptococcal infection, Epstein-Barr virus (EBV) infection, severe adenovirus infection, and diphtheria. (*Neisseria gonorrhea* pharyngitis would also be included if sexual abuse is suspected). The cause of the boy’s pharyngitis is most likely: A. A catalase-negative gram-positive coccus that grows in chains B. A single stranded positive-sense RNA virus C. A catalase-positive gram-positive coccus that grows in clusters D. A coagulase-negative gram-positive coccus that forms biofilms E. A double stranded RNA virus

Answer 25

A. A catalase-negative gram-positive coccus that grows in chains

Question 26

A primary mechanism responsible for the pathogenesis of group A Strep. is: A. A net increase in intracellular cyclic adenosine monophosphate B. Action of M protein C. Action of IgA1 protease D. Action of Lipid A E. Inactivation of elongation factor 2

Answer 26

B. Action of M protein

Question 27

*Enterococci* can be distinguished from nonenterococcal Group D streptococci on the basis of which of the following characteristics? A. Gamma hemolysis B. Esculin hydrolysis C. Growth in 6.5% NaCl D. Growth in the presence of bile E. Gram stain morphology

Answer 27

C. Growth in 6.5% NaCl

Question 28

The main reason why methicillin-resistant *Staphylococcus aureus* (MRSA) strains are resistant to methicillin and nafcillin is: A. They produce beta-lactamases that degrade antibiotics B. They have altered penicillin-binding proteins that have reduced binding of the antibiotics C. They have mutant porin proteins that prevent the antibiotics from entering the bacteria D. They have plasmid-encoded export proteins that remove the drug from the bacteria

Answer 28

B. They have altered penicillin-binding proteins that have reduced binding of the antibiotics

Question 29

A pore-forming exotoxin produced by *Staphylococcus* *aureus* that kills cells and is important in the severe, rapidly spreading necrotizing lesions caused by the MRSA strains is: A. Coagulase B. Enterotoxin C. Exfoliatin D. P-V leucocidin E. Staphyloxanthin

Answer 29

D. P-V leucocidin

Question 30

Superantigen production by *Staphylococcus aureus* is involved in the pathogenesis of which one of the following diseases? A. Impetigo B. Osteomyelitis C. Scalded Skin syndrome D. Septicemia E. Toxic shock syndrome

Answer 30

E. Toxic shock syndrome

Question 31

Which one of the following best describes the pathogenesis of rheumatic fever? A. An exotoxin produced by Streptococcus pyogenes that acts as a Superantigen damages cardiac muscle B. And exotoxin produced by *Streptococcus pyogenes* that ADP-ribosylates a G protein damages joint tissue C. Antibody to the capsular polysaccharide of *Streptococcus pyogenes* cross-reacts with joint tissue and damages it D. Antibody to the M protein of *Streptococcus pyogenes* cross-reacts with cardiac muscle and damages it E. Endotoxin produced by *Streptococcus pyogenes* activates macrophages to release cytokines that damage cardiac muscle

Answer 31

D. Antibody to the M protein of *Streptococcus pyogenes* cross-reacts with cardiac muscle and damages it

Question 32

The Jones family of 4 had a delicious picnic lunch last Sunday. It was a warm day, and the food sat in the sun for several hours. Alas, 3 hrs later, everyone came down with vomiting and non-bloody diarrhea. In the ED, it was found that Mrs. Jones, who prepared the food, had a paronychia on her thumb. Which one of the following is the most likely culprit? A. *Enterococcus faecalis* B. *Staphylococcus aureus* C. *Staphylococcus epidermidis* D. *Streptococcus agalactiae* E. *Streptococcus pyogenes*

Answer 32

B. *Staphylococcus aureus*

Question 33

Your patient is a 2-week old infant who was well until 2 days ago, when she stopped feeding and became irritable. She now has a fever to 38°C, developed a petechial rash all over her body, and is very difficult to arouse. In the ED, a blood culture and spinal tap are done. Gram stain of the spinal fluid showed gram-positive cocci in chains. Culture of the spinal fluid on blood agar revealed beta-hemolytic colonies that grew in the presence of bacitracin. Which of the following is the most likely causative organism? A. *Staphylococcus aureus* B. *Streptococcus agalactiae* C. *Streptococcus mutans* D. *Streptococcus pneumoniae* E. *Streptococcus pyogenes*

Answer 33

B. *Streptococcus agalactiae*

Question 34

Which one of the following is an important virulence factor of *Bacillus anthracis*? A. Protective antigen B. Lipopolysaccharide C. Pili D. A toxin that inhibits EF-2 E. Lecithinase

Answer 34

A. Protective antigen

Question 35

A food commonly associated with *Bacillus cereus* food poisoning is A. Fried rice B. Baked potato C. Hot freshly steamed rice D. Green beans E. Honey

Answer 35

A. Fried rice

Question 36

Tetanus toxin (tetanospasmin) diffuses to terminals of inhibitory cells in the spinal cord and brain stem and blocks which of the following? A. Release of acetylcholine B. Activation of G-protein coupled receptors C. Release of inhibitory glycine and gamma-aminobutyric acid D. Release of PA E. Activation of acetylcholine esterase

Answer 36

C. Release of inhibitory glycine and gamma-aminobutyric acid

Question 37

Which of the following food items is most frequently associated with infant botulism? A. Corn syrup B. Canned infant formula C. Liquid multivitamins D. Honey E. Jarred baby food

Answer 37

D. Honey

Question 38

A 65 y/o woman is brought to the ED complaining of double vision and difficulty talking. Within the past 2 hours she noted a dry mouth and generalized weakness. Last night she served home-canned greens beans as part of the meal. She tasted the beans before they were boiled. None of the other family members are ill. On exam, there is symmetrical descending paralysis of cranial nerves, upper extremities, and trunk. Which of the following is the correct diagnosis? A. Tetanus B. Diphtheria C. Botulism D. *Staph. aureus* food poisoning E. *Bacillus cereus* food poisoning F. Anthrax

Answer 38

C. Botulism

Question 39

A 24 y/o man suffers major soft tissue injury and open fractures of his right leg after a bicycle accident. One day later, he has a temperature of 38C, increased heart rate, sweating and restlessness. On exam, the leg is swollen and tense with thin, dark serous fluid draining from the wounds. The skin of the leg is cool, pale, white and shining. Crepitus can be felt in the leg. His hematocrit is 20% (approximately 50% of the normal) while his circulating hemoglobin is normal. His serum shows free hemoglobin. Which of the following is the most likely causative agent? A. *Clostridium tetani* B. *Staphylococcus aureus* C. *Bacillus anthracis* D. *Clostridium perfringens* E. *Clostridium botulinum* F. *Bacillus cereus*

Answer 39

D. *Clostridium perfringens*

Question 40

67 y/o man had surgery for a ruptured sigmoid colon diverticulum with an abscess. A repair was done and the abscess was drained. He was treated with intravenous gentamicin and ampicillin. 10 days later and 4 days after being discharged from the hospital, the patient developed malaise, fever, and cramping abdominal pain. He had multiple episodes of diarrhea. His stool was positive for occult blood and the presence of PMNs. On sigmoidoscopy, the mucosa was erythematous and appeared to be inflamed, and there were many raised white to yellowish plaques 4-8 mm in diameter. Which of the following is the most likely cause of this patient’s problem? A. *Staphylococcus aureus* enterotoxin B. *Bacillus cereus* toxin C. *Clostridium difficile* toxins D. *Clostridium perfringens* toxin E. *Clostridium botulinum* toxin

Answer 40

C. *Clostridium difficile* toxins

Question 41

An 8 y/o boy is brought to the office with a severe sore throat. On examination, a grayish exudate is seen over the tonsils and pharynx. The differential diagnosis of severe pharyngitis such as this includes group A streptococcal infection, Epstein-Barr virus (EGV) infection, *Neisseria gonorrhoeae* pharyngitis, and diphtheria. The cause of the boy’s pharyngitis is most likely: A. A gram-negative bacillus B. A single-stranded positive-sense RNA virus C. A catalase—positive gram-positive coccus that grows in clusters D. A club-shaped gram-positive bacillus E. A double stranded RNA virus

Answer 41

D. A club-shaped gram-positive bacillus

Question 42

In reference to diphtheria, the primary mechanism in the pathogenesis is: A. A net increase in intracellular cyclic adenosine monophosphate B. Action of pyrogenic exotoxin (a Superantigen) C. Inactivation of acetylcholine esterase D. Action of enterotoxin A E. Inactivation of EF-2

Answer 42

E. Inactivation of EF-2

Question 43

A 20-year-old college student goes to the student health center because of dysuria, frequency, and urgency on urination for 24 hours. She has recently become sexually active. On urinalysis, many polymorphonuclear cells are seen. The most likely organism responsible for these symptoms and signs is: A. *Staphylococcus aureus* B. *Streptococcus agalactiae* C. *Staphylococcus saprophyticus* D. *Pseudomonas aeruginosa* E. *Escherichia coli*

Answer 43

E. *Escherichia coli*

Question 44

Which of the following test methods is the **least** sensitive procedure for diagnosis of colitis caused by Shiga-toxin–producing *Escherichia coli*? A. Culture on sorbitol MacConkey agar B. Toxin testing using an enzyme immunoassay C. Cell culture cytotoxin assay using Vero cells D. Polymerase chain reaction for detection of the genes that encode Shiga toxin

Answer 44

A. Culture on sorbitol MacConkey agar

Question 45

A 27-year-old woman is admitted to the hospital because of fever, with increasing anorexia, headache, weakness, and altered mental status of 2 days’ duration. She works for an airline as a cabin attendant, flying between the Indian subcontinent and other places in Southeast Asia and the West Coast of the United States. She has been constipated for the past 3 days. Her temperature is 39°C, heart rate is 68 beats/min, blood pressure is 120/80 mm Hg, and respirations are 18 breaths/min. She knows who she is and where she is but does not know the date. She is picking at the bedclothes. Rose spots are seen on her trunk. The remainder of the physical examination is normal. Blood cultures are done, and an intravenous line is placed. Blood cultures from the patient grow a non–lactose-fermenting gram-negative bacillus. Which of the following is likely to be a constituent of this organism? A. antigen 157, H antigen 7 (O157:H7) B. Vi antigen (capsule; virulence antigen) C. antigen 139 (O139) D. Urease E. K1 (capsular type 1)

Answer 45

B. Vi antigen (capsule; virulence antigen)

Question 46

A 55-year-old homeless man with alcoholism presents with severe multilobar pneumonia. He requires intubation and mechanical ventilation. A Gram stain of his sputum reveals numerous polymorphonuclear leukocytes and gram-negative rods that appear to have a capsule. The organism is a lactose fermenter on MacConkey agar and is very mucoid. It is nonmotile and oxidase negative. Which of the following is most likely to be causing this man’s illness? A. *Serratia marcescens* B. *Streptococcus pneumoniae* C. *Proteus mirabilis* D. *Klebsiella pneumoniae* E. *Pseudomonas aeruginosa*

Answer 46

D. *Klebsiella pneumoniae*

Question 47

A 37-year-old woman with a history of urinary tract infections comes to the emergency department with burning on urination along with frequency and urgency. She says her urine smells like ammonia. The cause of her urinary tract infection is likely to be ## Footnote A. *Enterobacter aerogenes* B. *Proteus mirabilis* C. *Staphylococcus saprophyticus* D. *Escherichia coli* E. *Serratia marcescens*

Answer 47

B. *Proteus mirabilis*

Question 48

A 5-year-old girl attended a birthday party at a local fast food restaurant. About 48 hours later, she developed cramping abdominal pain and a low-grade fever and had five episodes of loose, bloody stools. She is taken to a local emergency department the next evening because the diarrhea has continued, and she now appears pale and lethargic. On presentation, she has a temperature of 38°C, and she is hypotensive and tachycardic. The abdominal examination reveals tenderness in the lower quadrants. Laboratory work is remarkable for a serum creatinine of 2.0 mg/dL, a serum hemoglobin of 8.0 mg/dL, thrombocytopenia, and evidence of hemolysis. What is the most likely pathogen causing this child’s illness? A. EHEC B. *Salmonella typhimurium* C. EPEC D. *Salmonella typhi* E. *Staphylococcus aureus* F. *Bacillus cereus*

Answer 48

A. EHEC

Question 49

A 37-year-old woman with a history of urinary tract infections comes to the emergency department with burning on urination along with frequency and urgency. She says her urine smells like ammonia. Which of the following is a unique feature of the causative agent? A. Production of a capsule B. Secretion of a red pigment C. Swarming behavior on solid agar D. Biofilm production E. Coagulase production

Answer 49

C. Swarming behavior on solid agar

Question 50

An 18-year-old student has abdominal cramps and diarrhea. Growth on Hektoen agar indicates that the causative agent belongs to either the *Salmonellae* or *S**higellae* families. Which of the following would be the best criterion to distinguish those two organism? A. Production of urease B. Motility in the medium C. Inability to ferment lactose D. Fermentation of glucose E. Capsule production F. Spore formation

Answer 50

B. Motility in the medium

Question 51

A 36 y/o man recently traveled to the Caribbean for a 2-week vacation. He developed acute watery diarrhea and abdominal pain with a low grade fever during the second week of his vacation, a day before he returns home. Upon his return, he immediately seeks medical help because he still fills quite sick. As part of an epidemiological study, a stool sample is taken and examined for the production of a specific toxin that leads to an increase in cAMP in Enterocytes. Which of the following is the most likely causative agent for this patient’s illness? A. EIEC B. ETEC C. EPEC D. EHEC E. EAEC

Answer 51

B. ETEC

Question 52

A 4-year-old boy from Kansas City who recently started attending preschool and after-school daycare is brought to his pediatrician for a diarrheal illness characterized by fever to 38.2°C, severe lower abdominal pain, and initially watery diarrhea. His mother became concerned because the stools are now blood tinged 24 hours into the illness, and the child appears quite ill. The mother reports that two other children who attend the same after-school daycare have recently had diarrheal disease, one of whom likewise had bloody stools. Which of the following is the most likely pathogen causing the illness in these children? A. ETEC B. *Salmonella typhi* C. *Shigella sonnei* D. *Salmonella typhimurium* E. *Yersinia enterocolitica*

Answer 52

C. *Shigella sonnei*

Question 53

An 18-year-old male resident of Arizona came to the emergency department (ED) complaining of fever, pain in his left groin, and diarrhea for the past 2 days. On examination, he was afebrile, had a pulse rate of 126 beats/min, a respiratory rate of 20 breaths/min, and a blood pressure of 130/80 mm Hg. Left groin swelling and tenderness were noted. A groin muscle strain was diagnosed, attributed to a fall 2 days earlier. He was treated with nonsteroidal anti-inflammatory drugs and released. The next day, the patient reported feeling weak, had difficulty breathing, and collapsed while taking a shower. He was transported to a hospital ED and pronounced dead shortly after arrival. Cultures of blood samples obtained in the ED were most likely positive for which one of the following organisms? A. *Bacillus anthracis* B. *Clostridium perfringens* C. *Staphylococcus aureus* D. *Streptococcus pyogenes* E. *Yersinia pestis* F. *Salmonella typhi*

Answer 53

E. *Yersinia pestis*

Question 54

*Yersinia pestis* entered North America through San Francisco in the 1890s, carried by rats on ships that had sailed from Hong Kong, where a plague epidemic had occurred. The current reservoir for *Y. pestis* in the United States is: A. Urban feral cats B. Urban rats C. Domestic cows D. Coyotes E. Rural wild rodents

Answer 54

E. Rural wild rodents

Question 55

A 4-year-old girl in rural Bangladesh develops profuse (8 L/day) diarrhea with ensuing dry mucous membranes, loss of skin elasticity and rapid heart rate. What is the most effective initial treatment strategy for her? A. Intravenous doxycycline B. Oral rehydration therapy C. Iron supplementation

Answer 55

B. Oral rehydration therapy

Question 56

A family of four ate dinner together one evening, and the chicken was undercooked. Within 3 days, three members of the family developed fever, myalgia, abdominal cramps and diarrhea. Stool cultures grew *Campylobacter jejuni*. Which of the following growth conditions would have been used to isolate *Camyplobacter jejuni*? A. Thiosulfate-citrate-bile-sucrose medium incubated at 37°C in 5% oxygen and 10% CO2 B. MacConkey agar and Hektoen enteric afar incubated at 37°C in ambient air C. 5% sheep blood agar incubated at 42°C in ambient air D. Medium containing vancomycin, polymixin B, and trimethoprim incubated at 42°C in 5% oxygen and 10% CO2

Answer 56

D. Medium containing vancomycin, polymixin B, and trimethoprim incubated at 42°C in 5% oxygen and 10% CO2

Question 57

A 54-year-old man develops a gastric ulcer that is visible on endoscopy. A biopsy specimen is taken from the site of ulceration. A presumptive diagnosis can be reached most rapidly by inoculating part of the specimen on which of the following? A. A medium used to detect urease incubated at 37°C B. A medium containing vancomycin, polymyxin B, and trimethoprim incubated at 42°C C. MacConkey agar incubated at 37°C D. Blood agar medium incubated at 42°C

Answer 57

A. A medium used to detect urease incubated at 37°C

Question 58

A 17-year-old girl with cystic fibrosis has a slight increase in her frequent cough and production of mucoid sputum. A sputum specimen is collected and plated on routine culture medium, producing mucoid colonies and a grape-like odor, with predominant recovery of Gram-negative bacilli. This microorganism can most likely be found in the patient’s airway A. Tightly adherent to epithelial cells B. Within epithelial cells C. In a biofilm

Answer 58

C. In a biofilm

Question 59

All of the following are virulence factors associated with *Neisseria gonorrhoeae* except: A. Pili B. Porins C. Lipooligosaccharide D. sIgA protease E. Polysaccharide capsule

Answer 59

E. Polysaccharide capsule

Question 60

A 25-year-old woman presents with septic arthritis of the knee. The fluid aspirate grows a gram-negative diplococcus on chocolate agar after 48 hours of incubation. The isolate is oxidase positive and oxidizes glucose but not maltose, lactose, or sucrose. You suspect infection with: A. *Neisseria meningitidis* B. *Staphylococcus aureus* C. *Haemophylus ducreyi* D. *Neisseria gonorrhoeae* E. *Haemophilus influenzae*

Answer 60

D. *Neisseria gonorrhoeae*

Question 61

An 18-year-old woman who reports unprotected sex with a new partner 2 weeks previously develops fever and left lower quadrant abdominal pain with onset in association with her menstrual period. On pelvic examination in the emergency department, she has bilateral tenderness when the uterus is palpated. A mass 2–3 cm in diameter is felt on the left, suggestive of tubo-ovarian abscess. Subsequently, *Neisseria gonorrhoeae* is cultured from her endocervix. The diagnosis is gonococcal pelvic inflammatory disease. A common sequela of this infection is: A. Cancer of the cervix B. Arthritis C. Pneumonia D. Meningitis E. Toxic shock

Answer 61

B. Arthritis

Question 62

A 38-year-old vice squad police officer comes to the emergency department and is diagnosed with recurrent disseminated gonococcal infection. Cultures of his urethra and knee fluid yield *Neisseria gonorrhoeae*. He has previously had five episodes of disseminated gonococcal infection. The patient should be evaluated for A. Selective IgA deficiency B. A polymorphonuclear cell chemotactic defect C. Deficiency of a late-acting complement component C5, C6, C7, or C8 D. Absent lymphocyte adenosine deaminase activity E. Myeloperoxidase deficiency

Answer 62

C. Deficiency of a late-acting complement component C5, C6, C7, or C8

Question 63

The inhabitants of a group of small villages in rural sub-Saharan Africa experienced an epidemic of meningitis. Ten percent of the people died, most of them younger than the age of 15 years. The microorganism that most likely caused this epidemic was: A. *Streptococcus agalactiae* (Group B) B. *Escherichia coli* K1 C. Non-typable *Haemophilus influenzae* D. *Neisseria* meningitidis serogroup A E. *Legionella pneumophila*

Answer 63

D. *Neisseria* meningitidis serogroup A

Question 64

One major advantage of the conjugate meningococcal vaccines compared with the polysaccharide vaccine is A. Stimulation of mucosal secretory IgA B. Fewer side effects C. A T cell–dependent response to vaccine is induced D. Inclusion of serogroup B

Answer 64

C. A T cell–dependent response to vaccine is induced

Question 65

A 3-month-old infant is brought to the pediatric emergency department in severe respiratory distress. The child appears dehydrated, and there is a prominent peripheral lymphocytosis. The chest radiograph reveals perihilar infiltrates. The child’s grandmother, who watches the infant now that the mother has returned to work, has had a dry hacking cough for about 2 weeks. The most likely causative agent is A. *Haemophilus influenzae* type b B. *Bordetella pertussis* C. *Streptococcus agalactiae* D. *Streptococcus pneumoniae* E. *Legionella pneumophila*

Answer 65

B. *Bordetella pertussis*

Question 66

Which of the following is not a recognized virulence factor of *Bordetella pertussis*? A. Heat-labile toxin B. Filamentous hemagglutinin C. Tracheal cytotoxin D. Pertussis toxin E. Pertactcin

Answer 66

A. Heat-labile toxin

Question 67

An 18-month-old boy has been playing with a child who develops *Haemophilus influenzae* meningitis. The boy’s parents consult his pediatrician, who says she is comfortable that the child will be fine because he has been fully immunized with the polyribitol ribose phosphate (PRP)–protein conjugate vaccine. For what reason is it necessary to immunize infants of 2 months to 2 years of age with polysaccharide–protein conjugate vaccines? A. The conjugate protein is diphtheria toxoid, and the goal is for the infant to develop simultaneous immunity to diphtheria. B. 2 months to 2 years of age do not immunologically respond to polysaccharide vaccines that are not conjugated to a protein. C. The conjugate vaccine is designed for older children and adults as well as infants. D. Maternal (transplacental) antibodies against *Haemophilus influenzae* are gone from the infant’s circulation by 2 months of age. E. Complement components C5-C9 don’t develop until the age of 2 years

Answer 67

B. 2 months to 2 years of age do not immunologically respond to polysaccharide vaccines that are not conjugated to a protein.

Question 68

A 3-month-old infant is brought to the pediatric emergency department in severe respiratory distress. The child appears dehydrated, and there is a prominent peripheral lymphocytosis. The chest radiograph reveals perihilar infiltrates. The child’s grandmother, who watches the infant now that the mother has returned to work, has had a dry hacking cough for about 2 weeks. The factor responsible for the profound lymphocytosis is: A. A hemagglutinin B. A polysaccharide capsule C. An A/B structured toxin D. A heat-labile toxin E. A neuraminidase

Answer 68

C. An A/B structured toxin

Question 69

A 65-year-old man comes to the emergency department feeling feverish and “really tired.” He has a chronic cigarette cough, but this has dramatically increased in the past week and he has been producing whitish sputum. The previous day he had a temperature of 38°C and watery diarrhea. Physical examination reveals inspiratory and expiratory wheezes and rales over the right lower lung field. Chest radiography shows a patchy right lower lobe infiltrate. The most likely causative agent of this patient’s ailment is: A. *Streptococcus pneumoniae* B. *Legionella pneumophila* C. *Haemophilus influenzae* D. *Mycoplasma pneumoniae* E. *Neisseria meningitidis*

Answer 69

B. *Legionella pneumophila*

Question 70

Charcoal is present in buffered charcoal yeast extract agar used to isolate *Legionella pneumophila* to: A. Provide the growth factors ordinarily provided by free-living amoebas present in environmental water B. Serve as a carbon source for the growth of *Legionella pneumophila* C. Prevent hemolysis of the red blood cells in the medium D. Provide a dark background E. Act as a detoxifying agent

Answer 70

E. Act as a detoxifying agent

Question 71

Pontiac fever is a severe form of pneumonia caused by which of the following organisms? A. *Legionella pneumophila* B. *Streptococcus pneumoniae* C. *Haemophilus influenzae* D. *Salmonella typhi* E. *Acinetobacter baumanii*

Answer 71

A. *Legionella pneumophila*

Question 72

Humans become infected with *Legionella pneumophila* by: ## Footnote A. Kissing a person who is a *Legionella* carrier B. Breathing aerosols from environmental water sources C. Receiving a mosquito bite D. Consuming undercooked pork E. Not washing their hands properly

Answer 72

B. Breathing aerosols from environmental water sources

Question 73

All of the following statements about lymphogranuloma venereum (LGV) are correct except A. Chronic LGV proctitis can lead to rectal strictures and fistula formation. B. The disease is more common in northern latitudes. C. There may be marked systemic symptoms, including fever, nausea, vomiting, headache, and meningismus. D. Chronic inflammation with LGV can lead to lymphatic obstruction. E. Inguinal lymph nodes may become enlarged and matted, draining pus through the skin. F. A few days or weeks after exposure, the disease manifests itself as a genital papule or vesicle.

Answer 73

B. The disease is more common in northern latitudes.

Question 74

Which of the following methods are considered the diagnostic tests of choice for urogenital infections caused by *Chlamydia trachomatis*? A. Serology using complement fixation B. Cell culture using cycloheximide containing McCoy cells C. Direct fluorescent antibody testing on urethral and cervical specimens D. Nucleic acid amplification methods E. Enzyme immunoassays performed on genital tract specimens

Answer 74

D. Nucleic acid amplification methods

Question 75

The following statements about trachoma are correct except: A. It follows chronic or recurrent eye infection with *Chlamydia trachomatis*. B. Millions of people worldwide have trachoma. C. Trachoma is readily prevented by a chlamydial vaccine. D. Progression of trachoma can be slowed by intermittent treatment with azithromycin. E. Trachoma involves scarring of the conjunctiva, eyelid deformities, and eyelash injury to the cornea.

Answer 75

C. Trachoma is readily prevented by a chlamydial vaccine.

Question 76

*Chlamydia pneumoniae* pneumonia most resembles infection caused by which of the following organisms? A. *Streptococcus pneumoniae* B. *Mycoplasma pneumoniae* C. *Haemophilus influenzae* D. *Chlamydia trachomatis* E. *Mycobacterium tuberculosis*

Answer 76

B. *Mycoplasma pneumoniae*

Question 77

An adolescent girl came to the clinic because of a new and unusual vaginal discharge. She had recently become sexually active and had two new partners during the previous month. On pelvic examination, a purulent discharge was seen at the opening of her endocervical canal. Which of the following statements about this patient is most correct? A. A serologic test for syphilis is not indicated because her symptoms are not those of syphilis. B. A Gram stain of her endocervical specimen would show *Chlamydia trachomatis* inside polymorphonuclear cells. C. The differential diagnosis includes infection with *Neisseria gonorrhoeae*, *Chlamydia trachomatis*, or both. D. The endocervical specimen should be analyzed for herpes simplex. E. Initial treatment is with ampicillin.

Answer 77

C. The differential diagnosis includes infection with *Neisseria gonorrhoeae*, *Chlamydia trachomatis*, or both.

Question 78

Your patient is a 40 y/o man with a urethral discharge. Gram stain of the pus reveals many neutrophils but no bacteria. You suspect this infection may be caused by *Chlamydia trachomatis*. Which one of the following is the lab result that best supports your clinical diagnosis? A. Gram stain of the pus reveals small gram-positive rods B. The organism produces beta-hemolytic colonies on blood agar plates when incubated aerobically C. The organism produces alpha-hemolytic colonies on blood agar plates when incubated anaerobically D. Fluorescent antibody staining of cytoplasmic inclusions in epithelial cells in the exudate E. Fourfold or greater rise in antibody titer against *C. trachomatis*

Answer 78

D. Fluorescent antibody staining of cytoplasmic inclusions in epithelial cells in the exudate

Question 79

Regarding *Chlamydiae*, which one of the following is the most accurate? A. Lifelong immunity usually follows an episode of disease caused by these organisms B. The reservoir host for the three species of *Chlamydiae* that cause human infection is humans C. Their life cycle consists of elementary bodies outside of cells and reticulate bodies within cells D. They can only replicate within cells because they lack the ribosomes to synthesize their proteins E. The vaccine against C. pneumoniae contains the capsular polysaccharides as the immunogen conjugated to a carrier protein

Answer 79

C. Their life cycle consists of elementary bodies outside of cells and reticulate bodies within cells

Question 80

Which one of the following is the drug of choice for STIs (urethritis, cervicitis) caused by *Chlamydia trachomatis*? A. Ampicillin B. Azithromycin C. Ciprofloxacin D. Metronidazole E. Rifampin

Answer 80

B. Azithromycin

Question 81

Which of the following statements about *Ehrlichiae* and ehrlichiosis is most correct? A. Dogs and mice are reservoirs. B. Mosquitoes are the vectors. C. Ampicillin is the treatment of choice. D. Culture is a good method to confirm the diagnosis. E. *Ehrlichiae* are typically found in lymphocytes.

Answer 81

A. Dogs and mice are reservoirs.

Question 82

A middle-aged sportsman, a resident of Oklahoma, took a hike through a rural wooded and brushy area near his home. The next morning, he noticed and removed a large (\>1 cm) tick from his upper arm. About 1 week later, he experienced a gradual onset of fever and malaise. He now seeks medical attention because he is concerned about a possible infection transmitted by the tick. Which of the following diseases is most likely to be acquired from a tick? A. Epidemic Typhus B. Rocky Mountain spotted fever C. Diphtheria D. Q-fever E. Cat scratch fever

Answer 82

B. Rocky Mountain spotted fever

Question 83

One week after deer hunting in a wooded area, a 33-year-old man developed fever to 39°C with headache and malaise. Over the subsequent 24 hours, he developed nausea, vomiting, abdominal pain, and diarrhea. On day 4, he developed a rash, initially around the wrists and ankles, which then progressively evolved, involving the arms, trunk, palms, and soles. Initially the rash was macular, but it quickly evolved into maculopapules, some with central petechiae. Rocky Mountain spotted fever caused by *Rickettsia rickettsii* was diagnosed. Which of the following statements about Rocky Mountain spotted fever is correct? A. The vectors of *Rickettsia rickettsii* are human body lice B. A rash consistently appears by day 4 of illness. C. *Rickettsia rickettsii* forms inclusions in monocytes. D. The patient’s antibody response may not occur until after the second week of illness. E. The highest incidence of this disease is in the Rocky Mountain states.

Answer 83

D. The patient’s antibody response may not occur until after the second week of illness.

Question 84

A group of urban teenagers visited a sheep ranch in a large Western state for a 2-week experience. While they were there, many of the pregnant ewes delivered lambs to the delight of the closely observing teenagers. About 10 days later, three of the teenagers developed flulike illnesses characterized by malaise, cough, and fever. One had an infiltrate on chest radiography, indicating pneumonia. The three teenagers had different doctors, but the physicians each drew a blood specimen and submitted it to the city health department for serologic testing. All three specimens were positive for Q fever. Public health investigators determined that all of the teenagers had been to the sheep ranch. When the investigators contacted the ranch, they were told that there was no Q fever there and that no one who lived at the ranch had been sick. The most likely explanation for the teenagers’ illnesses and the lack of illness at the ranch is: A. There was no Q fever at the ranch, and it was acquired elsewhere. B. The people at the ranch had been previously immunized against Q fever. C. The teenagers acquired Q fever at the ranch, and the people who lived there had all previously had Q fever and were now immune to it. D. The teenagers had other illnesses, and the positive Q fever serology result was unrelated. E. The public health laboratory had errors in the Q fever serologic tests.

Answer 84

C. The teenagers acquired Q fever at the ranch, and the people who lived there had all previously had Q fever and were now immune to it.

Question 85

Which of the following statements about epidemic typhus is most correct? A. The disease occurs primarily in sub-Saharan Africa. B. It is transmitted by ticks. C. Mice are the reservoir. D. Historically, the disease occurs in times of prosperity. E. Recrudescence can occur many years after the initial infection.

Answer 85

E. Recrudescence can occur many years after the initial infection.

Question 86

The histopathological hallmark of infection caused by *Rickettsia rickettsiae* is which one of the following? A. Morulae within granulocytes B. Morulae within monocytes C. Granulomatous inflammation D. Intracellular vacuoles E. Perivascular lymphocytes

Answer 86

E. Perivascular lymphocytes

Question 87

The recommended treatment for Q-fever endocarditis is A. Emergent surgery; antibiotics are not effective B. Levofloxacin monotherapy for 6 weeks C. 18 months of combination therapy with doxycycline and hydroxychloroquine D. Penicillin and gentamicin combination therapy using IgG titers to determine duration E. Immediate vaccination

Answer 87

C. 18 months of combination therapy with doxycycline and hydroxychloroquine

Question 88

A disease characterized by malaise, headache, rigors, and fever developed in members of several families living in an unheated war-damaged house in an Eastern European country. Erythematous 2–6 mm macular red rashes appeared on the peoples’ trunks and later on their extremities. Some of the people had coughs. One elderly person, although sick, was much less sick than other adults. The people huddled together to keep warm; body lice were common. Which of the following statements is most correct? A. The disease that these people had is common in the Rocky Mountain states. B. The elderly person may have had acute epidemic typhus many years ago and recrudescent typhus now. C. Fleas from rodents in the house were spreading *Rickettsia typhi*. D. The primary host of the body louse infecting the people is the rat. E. The disease could have been prevented with one of the childhood vaccines

Answer 88

B. The elderly person may have had acute epidemic typhus many years ago and recrudescent typhus now.

Question 89

Morulae (intracellular inclusions in leukocytes) are characteristic of which of the following diseases? A. Rocky Mountain spotted fever B. Ehrlichiosis C. Lyme disease D. Trachoma E. Q-fever F. Typhus

Answer 89

B. Ehrlichiosis

Question 90

The most useful drug to treat ehrlichiosis is A. Doxycycline B. Penicillin G C. Trimethoprim–sulfamethoxazole D. Gentamicin E. Nitrofurantoin

Answer 90

A. Doxycycline

Question 91

Your patient is a 40 y/o woman with a sudden onset of fever over 40°C, severe headache, and a petechial rash over most of her body including the palms. Blood cultures are negative. Unfortunately, despite antibiotic therapy and other support, she dies the following day. An autopsy is performed, and immunohistochemical analysis of several tissue samples reveals intracellular organisms in endothelial cells. Which one of the following is the most likely causative agent? A. *Ehrlichia chaffeensis* B. *Anaplasma phagocytophilum* C. *Rickettsia rickettsii* D. *Rickettsia prowazekii* E. *Coxiella burnetii*

Answer 91

C. *Rickettsia rickettsii*

Question 92

Regarding Q-fever, which one of the following is most accurate? A. The causative organism is transmitted by tick bite B. The natural habitat of the causative agent is the white-footed mouse C. The diagnosis is made primarily by Gram stain and culture on chocolate agar D. Occupations that predispose people to Q-fever include veterinarians and abattoir workers E. Patients with Q-fever often have a petechial rash involving the palms.

Answer 92

D. Occupations that predispose people to Q-fever include veterinarians and abattoir workers

Question 93

Which of the following statements about bacillary angiomatosis is most correct? A. It is caused by *Bacillus anthracis*. B. It is typically confined to the skin. C. The major differential diagnosis is Kaposi sarcoma. D. The etiologic agent can be grown in 1–2 days in routine culture on sheep blood agar. E. Dogs are the reservoir for the etiologic agent.

Answer 93

D. The etiologic agent can be grown in 1–2 days in routine culture on sheep blood agar.

Question 94

A 23-year-old, otherwise healthy woman presents with a 3-day history of low-grade fever and headache. Examination reveals enlarged and slightly tender lymph nodes near her left elbow and in the left axilla. Approximately 2 weeks earlier, she had visited a friend whose cat had scratched her on the left arm; the site later developed a reddish papule. Which of the following statements about this disease is correct? A. Characteristic histopathology in response to infection is acute, neutrophilic inflammation. B. The diagnosis is based on a suggestive history and physical examination. C. β-Lactam/β-lactamase inhibitor combinations are the agents of choice for treatment. D. The diagnosis is based on negative routine bacterial cultures of pus aspirated from involved lymph nodes. E. The disease rapidly leads to sepsis even in immunocompetent people.

Answer 94

B. The diagnosis is based on a suggestive history and physical examination.

Question 95

Your patient in the pediatric intensive care unit is a 2 week old boy with a high fever and signs of meningitis. Gram stain of the spinal fluid reveals small gram-positive rods. Colonies on blood agar show a narrow zone of beta-hemolysis. Which one of the following is the most likely cause of his neonatal meningitis? A. *Rickettsia rickettsia* B. *Listeria monocytogenes* C. *Chlamydophila pneumoniae* D. *Coxiella burnetii* E. *Streptococcus pneumoniae*

Answer 95

B. *Listeria monocytogenes*

Question 96

*Listeria monocytogenes* is frequently a foodborne pathogen because: A. It can survive at 4°C. B. It survives under conditions of low pH. C. It survives in the presence of high salt concentrations. D. It is adapted to a number of mammalian hosts E. All of the above are correct.

Answer 96

E. All of the above are correct.

Question 97

Movement of *Listeria monocytogenes* inside of host cells is caused by A. Inducing host cell actin polymerization B. The formation of pili (fimbriae) on the *Listeriae* surface C. Pseudopod formation D. The motion of *Listeriae* flagella E. Tumbling motility F. All of the above is correct

Answer 97

A. Inducing host cell actin polymerization

Question 98

Initiation of infection by *Mycoplasma pneumoniae* begins with A. Elaboration of a polysaccharide capsule that inhibits phagocytosis B. Secretion of a potent exotoxin C. Endocytosis by ciliated respiratory epithelial cells D. Adherence to respiratory epithelial cells mediated by P1 adhesin E. Phagocytic uptake by alveolar macrophages

Answer 98

D. Adherence to respiratory epithelial cells mediated by P1 adhesin

Question 99

A 25-year-old medical student has contact with a patient who has pneumonia with fever and cough. Four days later, the medical student develops fever and cough, and chest radiographs show consolidation of the right lower lobe. Routine bacterial sputum culture results are negative. Pneumonia caused by *Mycoplasma pneumoniae* is considered. All of the following are methods to confirm the clinical suspicion except: A. PCR amplification of *Mycoplasma pneumoniae* DNA in sputum B. Culture of sputum for *Mycoplasma pneumoniae* C. Gram stain of sputum smear D. Culture of a lung aspirate for *Mycoplasma pneumoniae* E. Enzyme immunoassay test of acute and convalescent sera

Answer 99

C. Gram stain of sputum smear

Question 100

*Mycoplasma pneumoniae* is an important cause of atypical pneumonia. Regarding this organism, which one of the following is the most accurate? A. Amoxicillin is the drug of choice for pneumonia cause by this organisms. B. Antibodies in a patient’s serum will agglutinate human red blood cells at 4°C but not at 37°C. C. Gram stain of the sputum reveals small gram-negative rods D. It is an obligate intracellular parasite that can only grow within human cells in the clinical lab. E. People with cystic fibrosis are predisposed to pneumonia caused by this organism.

Answer 100

B. Antibodies in a patient’s serum will agglutinate human red blood cells at 4°C but not at 37°C.

Question 101

Which one of the following is the drug of choice for atypical pneumonia caused by *M. pneumoniae*? A. Amoxicillin B. Azithromycin C. Ceftriaxone D. Gentamicin E. Vancomycin

Answer 101

B. Azithromycin

Question 102

Three months ago, a 53-year-old woman had surgery and chemotherapy for breast cancer. Four weeks ago, she developed a cough occasionally productive of purulent sputum. About 2 weeks ago, she noted a slight but progressive weakness of her left arm and leg. On chest examination, rales were heard over the left upper back when the patient breathed deeply. Neurologic examination confirmed weakness of the left arm and leg. Chest radiography showed a left upper lobe infiltrate. Contrast-enhanced computed tomography showed two lesions in the right hemisphere. Gram stain of a purulent sputum specimen showed branching gram-positive rods that were partially acid fast. Which of the following organisms is the cause of this patient’s current illness? A. *Actinomyces israelii* B. *Corynebacterium diphtheriae* C. *Mycoplasma pneumoniae* D. *Nocardia asteroides* E. *Streptococcus pneumoniae*

Answer 102

D. *Nocardia asteroides*

Question 103

Which one of the following is the drug of choice to treat a patient infected with *Nocardia asteroides*? A. Penicillin G B. Trimethoprim–sulfamethoxazole C. Gentamicin D. Amphotericin B E. A third-generation cephalosporin

Answer 103

B. Trimethoprim–sulfamethoxazole

Question 104

Infections caused by *Bacteroides* species can be treated with all of the following antibiotics except: A. Ampicillin B. Clindamycin C. Metronidazole D. Penicillin E. Cefoxitin

Answer 104

D. Penicillin

Question 105

An 18-year-old man develops fever with pain in the right lower quadrant of his abdomen. After initial evaluation, he is taken to the operating room. During surgery, a ruptured appendix with an abscess is found. *Bacteroides* *fragilis* is cultured from the abscess fluid. Which of the following factors promote abscess formation by *B. fragilis*? A. Lipopolysaccharide B. Capsule C. Superoxide dismutase D. Pili E. Leukocidin toxin

Answer 105

B. Capsule

Question 106

The drug of choice for treatment of infections caused by *Actinomyces* species is: A. Tigecycline B. Cefoxitin C. Metronidazole D. Imipenem E. Penicillin

Answer 106

E. Penicillin

Question 107

A patient who has not maintained good dentition presents with induration and swelling of the mandibular area. On examination, you note purulent material draining from a small opening. The material appears yellowish, and there are some visible granules. You perform a Gram stain, and pleomorphic gram-positive rods with short branches are noted along with cells suggestive of acute and chronic inflammation. You suspect which of the following organisms? A. *Bacteroides fragilis* B. *Streptococcus mutans* C. *Clostridium perfringens* D. *Actinomyces israelii* E. *Staphylococcus aureus*

Answer 107

D. *Actinomyces israelii*

Question 108

Your patient is a 75 y/o woman with fever and a painful nodule on her forearm. She also has a nonproductive cough that she says is worse than her usual smoking-related cough. She is taking high-dose corticosteroids (prednisone) for an autoimmune disease. Chest x-ray reveals a nodular lesion in the right upper love. A biopsy of the nodule on her arm was obtained. Gram stain of the specimen showed filaments of gram-positive rods. The rods were also weakly acid-fast. Regarding the causative organism, which one of the following is most accurate? A. Culture of the organisms should be done under anaerobic conditions. B. The natural habitat of the organism is the soil. C. It produces an exotoxin that inhibits protein synthesis by ADP-ribosylation D. Sulfur granules are often seen in the skin lesion E. The vaccine against this organism contains the capsular polysaccharide as the immunogen.

Answer 108

B. The natural habitat of the organism is the soil.

Question 109

Your patient is a 20-y/o man who was in a fist fight in a bar about 3 weeks ago. He took a punch that broke his left second molar. He now has a 3-cm inflamed area on the skin overlying the broken tooth that is draining pus. A Gram stain of the pus reveals gram-positive filamentous rods. The rods did not appear red in the acid-fast stain. Regarding the causative organism, which of of the following is most accurate? A. Infections caused by this organism occur primarily in the Ohio and Mississippi River Valley area B. The natural habitat of the organism is the soil C. This organism is resistant to both penicillin and aminoglycosides D. Sulfur granules are often seen in the pus located at the orifice of the sinus tract in the skin lesion E. The vaccine against this organism contains a toxoid as the immunogen.

Answer 109

D. Sulfur granules are often seen in the pus located at the orifice of the sinus tract in the skin lesion

Question 110

Which of the following statements regarding interferon-γ release assays (IGRAs) is correct? A. They are useful for evaluating immunocompromised patients for active tuberculosis. B. They detect antigens present in all *Mycobacterium* species. C. They are not available yet for testing in the United States. D. They are performed using molecular probes that detect organism DNA. E. They are used as alternatives to the tuberculin skin test to evaluate for latent tuberculosis.

Answer 110

E. They are used as alternatives to the tuberculin skin test to evaluate for latent tuberculosis.

Question 111

You observe a 40-year-old man begging on a street in a town in India. He has clawing of the fourth and fifth digits with loss of distal parts of the digits of both hands, strongly suggesting leprosy. The causative agent of this disease: A. Is susceptible to isoniazid and rifampin B. Grows in parts of the body that are cooler than 37°C C. Can be cultured in the laboratory using Middlebrook 7H11 medium D. Is seen in high numbers in biopsies of tuberculoid leprosy lesions E. Commonly infects people in Texas because armadillos are hosts of *M. leprae*

Answer 111

B. Grows in parts of the body that are cooler than 37°C

Question 112

The definition of extensively drug-resistant (XDR) Tuberculosis includes: A. Resistance to isoniazid B. Resistance to a fluoroquinolone C. Resistance to capreomycin, amikacin or kanamycin D. Resistance to rifampin E. All of the above

Answer 112

E. All of the above

Question 113

Which of the following statements about the purified protein derivative (PPD) and the tuberculin skin test is most correct? A. It is strongly recommended that medical and other health science students have PPD skin tests every 5 years. B. Persons immunized with BCG rarely, if ever, convert to positive PPD skin test results. C. The intradermal skin test is usually read 4 hours after being applied. D. A positive tuberculin test result indicates that an individual has been infected with *M. tuberculosis* in the past and may continue to carry viable mycobacteria. E. A positive PPD skin test result implies that a person is immune to active tuberculosis

Answer 113

D. A positive tuberculin test result indicates that an individual has been infected with *M. tuberculosis* in the past and may continue to carry viable mycobacteria.

Question 114

A 10-year-old child has a primary pulmonary *M. tuberculosis* infection. Which of the following features of tuberculosis is most correct? A. In primary tuberculosis, an active exudative lesion develops and rapidly spreads to lymphatics and regional lymph nodes. B. The exudative lesion of primary tuberculosis often heals slowly. C. If tuberculosis develops years later, it is a result of another exposure to *M. tuberculosis*. D. In primary tuberculosis, all of the infecting *M. tuberculosis* organisms are killed by the patient’s immune response. E. In primary tuberculosis, the immune system is primed, but the PPD skin test result remains negative until there is a second exposure to *M. tuberculosis*.

Answer 114

A. In primary tuberculosis, an active exudative lesion develops and rapidly spreads to lymphatics and regional lymph nodes.

Question 115

*Mycobacterium marinum* most often causes disease among which group of individuals? A. Young children exposed to dirt B. People that keep pet fish C. Homeless people D. AIDS patients E. People who shear sheep

Answer 115

B. People that keep pet fish

Question 116

A 31-year-old woman is admitted to the hospital with a 7-week history of increasing malaise, myalgia, nonproductive cough, and shortness of breath. She has daily fevers of 38–39°C and a recent 5-kg weight loss. She had a negative chest radiograph when she emigrated from China 7 years ago. The patient’s grandmother died of tuberculosis when the patient was an infant. A current chest radiograph is normal; results of other tests show a decreased hematocrit and liver function test abnormalities. Liver and bone marrow biopsies show granulomas with giant cells and acid-fast bacilli. She is probably infected with which one of the following? A. *Mycobacterium leprae* B. *Mycobacterium fortuitum* C. *Mycobacterium ulcerans* D. *Mycobacterium marinum* E. *Mycobacterium tuberculosis*

Answer 116

E. *Mycobacterium tuberculosis*

Question 117

A 31-year-old woman is admitted to the hospital with a 7-week history of increasing malaise, myalgia, nonproductive cough, and shortness of breath. She has daily fevers of 38–39°C and a recent 5-kg weight loss. She had a negative chest radiograph when she emigrated from China 7 years ago. The patient’s grandmother died of tuberculosis when the patient was an infant. A current chest radiograph is normal; results of other tests show a decreased hematocrit and liver function test abnormalities. Liver and bone marrow biopsies show granulomas with giant cells and acid-fast bacilli. Besides TB, it is very important that she also be evaluated for: A. HIV/AIDS B. Typhoid fever C. Liver abscess D. Lymphoma E. Malaria

Answer 117

A. HIV/AIDS

Question 118

Your patient is a 25 y/o homeless man who reports of a cough for the past month. The cough is now productive of several tablespoons of blood-streaked sputum per day. The sputum is not foul-smelling. He has lost 10 pounds but says he doesn’t eat regularly. On physical exam, temp is 38°C, and coarse rales are heard in the apex of the left lung. An acid-fast stain of the sputum reveals acid-fast rods. Culture of the sputum shows no growth at 7 days, but buff-colored colonies are visible at 21 days. Of the following organisms, which one is most likely to be the cause of this infection? A. *Mycobacterium fortuitum* B. *Mycobacterium leprae* C. *Mycobacterium marinum* D. *Mycobacterium tuberculosis*

Answer 118

D. *Mycobacterium tuberculosis*

Question 119

Your patient is a 70 y/o man with progressive weakness in both legs that began about a week ago. He reports back pain and fever for the past month. MRI of the spine reveals destruction of the seventh thoracic vertebra and a paravertebral mass. Surgical decompression and debridement is performed. Histological exam of the mass reveals caseating granulomas and Langerhans’ giant cells. Gram stain reveals no organisms, but an acid-fast stain shows red rods. Culture shows no growth at 7 days but growth is seen at 28 days. Of the following, which one is the most likely cause? A. *Mycobacterium fortuitum* B. *Mycobacterium leprae* C. *Mycobacterium marinum* D. *Mycobacterium tuberculosis*

Answer 119

D. *Mycobacterium tuberculosis*

Question 120

Your patient is a 30 y/o woman who is HIV positive. Her CD4 count is low. She now has the findings of pulmonary tuberculosis, but the causative agent turns out to be *Mycobacterium avium-intracellulare* (MAI). What is the most likely route that she acquired her infection? A. Through respiratory droplets from another MAI infected patient B. Through direct skin contact from another MAI infected patient C. Through contaminated soil or water D. Through a contaminated blood transfusion or shared needle from an MAI infected patient E. Through sexual contact

Answer 120

C. Through contaminated soil or water

Question 121

Your patient is a 20 y/o man with a single, slowly expanding non-painful scaly lesion in his chest for the past 2 months. The lesion is non-pruritic, and he has lost sensation at the site of the lesion. He is otherwise well. He recently emigrated from Central America. An acid-fast stain of a scraping of the lesion is positive. Which one of the following diseases is he most likely to have? A. Cutaneous tuberculosis B. Fish tank granuloma C. Lepromatous leprosy D. Scrofula E. Tuberculoid leprosy F. Pott’s disease

Answer 121

E. Tuberculoid leprosy

Question 122

A 47-y/o man presents with slowly progressive arthritis in his knees. He enjoys hiking in the coastal areas of Northern California, where the prevalence of *Borrelia burgdorferi* in the Ixodes ticks is known to be 1–3% (considered low). The patient is concerned about Lyme disease. He never noticed a tick on his body and did not see an expanding red rash. The result of an EIA for Lyme borreliosis is positive. What should be done now? A. A biopsy specimen of the synovium of a knee joint should be examined for *Borrelia burgdorferi*. B. The patient should be given an antibiotic to treat Lyme disease. C. PCR on the patient’s plasma should be done to detect *Borrelia burgdorferi*. D. A serum specimen should be submitted for immunoblot assay to detect antibodies reactive with *Borrelia burgdorferi* antigens. E. Culture of synovial fluid on blood and chocolate agar.

Answer 122

D. A serum specimen should be submitted for immunoblot assay to detect antibodies reactive with *Borrelia burgdorferi* antigens.

Question 123

A 23-year-old man presented with a maculopapular rash over much of his trunk but not in his mouth or on his palms. Because secondary syphilis was considered in the differential diagnosis, an RPR test was done, and the result was positive at a 1:2 dilution. However, the FTA-ABS test result was negative. Which of the following diseases can be ruled out? A. Secondary syphilis B. Atypical measles C. Coxsackie virus infection D. Acute HIV 1 infection E. Allergic drug reaction

Answer 123

A. Secondary syphilis

Question 124

Nontreponemal serological tests: A. Are useful in definitively identifying a *Treponema pallidum* infection. B. Measure antibodies against *Treponema pallidum*. C. Can be used to monitor antibiotic treatment of tertiary syphilis. D. Measure antibodies against lipids released from damaged cells. E. Are useful in diagnosing a disseminated gonococcal infection.

Answer 124

D. Measure antibodies against lipids released from damaged cells. (e.g. cardiolipin)

Question 125

Which of the following animals is a possible source of *Leptospira interrogans*? A. Alligators B. Ducks C. Frogs D. Catfish E. Swine

Answer 125

E. Swine

Question 126

A 27-year-old medical resident was admitted to the hospital because of sudden onset of fever to 39°C and headache. Two weeks previously, he had vacationed in rural Oregon, where he had frequently gone swimming in an irrigation canal that bordered land where cows were pastured. Blood tests done shortly after admission indicated renal function abnormality and elevated bilirubin and other liver function test results. Routine blood, urine, and CSF culture results were negative. Leptospirosis is suspected. Which of the following would be most likely to confirm this diagnosis? A. Testing acute and convalescent phase sera using the RPR test B. Culture of urine on human diploid fibroblast cells C. Testing serum by dark-field examination for the presence of leptospires D. Testing acute and convalescent phase sera for antileptospiral antibodies E. Culture of CSF on blood and chocolate agar F. Gram stain of CSF and blood

Answer 126

D. Testing acute and convalescent phase sera for antileptospiral antibodies

Question 127

A 28-year-old woman who is 10 weeks pregnant presents to the obstetrics clinic for prenatal care. She has a history of treatment for syphilis 7 years previously. The results of serologic tests for syphilis are as follows: nontreponemal test, RPR, nonreactive; treponemal test (TP-PA), reactive. Which of the following statements is most correct? A. The mother’s previous treatment for syphilis was effective. B. The baby is at high risk for congenital syphilis. C. The mother needs to be treated again for syphilis. D. The mother needs a lumbar puncture and a VDRL test of her CSF for neurosyphilis.

Answer 127

A. The mother’s previous treatment for syphilis was effective.

Question 128

A 42-year-old woman went camping in the Sierra Nevada Mountains, where she slept for two nights in an abandoned log cabin. After the second night, a tick was found on her shoulder. Six days later, she developed fever to 38°C, which lasted for 4 days. Ten days later, she had another similar episode of fever. Examination of a blood smear stained with Wright stain showed spirochetes suggestive of *Borrelia* species. Which of the following statements about relapsing fever is correct? A. Each relapse is associated with an antigenically distinct variant. B. Blood smears should be made when the patient is afebrile. C. *Borreliae* do not pass transovarially from one generation to the next in ticks. D. The main reservoir for the *Borrelia* is deer. E. *Borrelia* is resistant to penicillin and tetracycline.

Answer 128

A. Each relapse is associated with an antigenically distinct variant.

Question 129

A 12-year-old Boy Scout went to summer camp for 2 weeks in late August at a site located just outside Mystic, Connecticut. When he returned home, his mother noticed a bull’s-eye-shaped rash on the back of her son’s left calf. Shortly after Labor Day, the boy developed a flu-like illness that resolved after 4 days of bed rest. Three weeks later, the boy complained to his mother that his body hurt all over whenever he moved. This prompted a visit to the pediatrician, who ordered an infectious disease workup. What is the most likely source of the boy’s infection? A. Respiratory transmission from another sick camper B. Ingestion of urine-contaminated water from a stream C. The bite of a mosquito harboring a parasite D. Ingestion of fecally contaminated food E. The bite of an infected tick

Answer 129

E. The bite of an infected tick

Question 130

Which of the following organisms principally infects the liver and kidneys? A. *Leptospira interrogans* B. *Staphylococcus aureus* C. *Escherichia coli* D. *Enterococcus faecalis* E. *Treponema pallidum*

Answer 130

A. *Leptospira interrogans*

Question 131

Your patient is a 20 y/o man with an erythematous, macular, non-painful rash on the right arm for the past 4 days. The rash is approximately 10 cm in diameter. He also has a fever to 100°F and a mild headache. He reports hiking on several weekends recently in New York State. You suspect the rash is erythema migrans and that he has Lyme disease. Which one of the following is the best approach to confirm your clinical diagnosis? A. Detect IgM antibodies in an ELISA assay B. Determine the titer in a VDRL test C. Gram stain and culture on blood agar incubated aerobically D. Gram stain and culture on blood agar incubated anaerobically E. Grow on human cells in cell culture and identify with fluorescent antibody

Answer 131

A. Detect IgM antibodies in an ELISA assay

Question 132

Which one of the following antibiotics is the most appropriate to treat infection with Lyme disease? A. Azithromycin or Trimethoprim-sulfamethoxazole B. Doxycycline or amoxicillin C. Gentamicin or amikacin D. Metronidazole or clindamycin E. Penicillin G or levofloxacin

Answer 132

B. Doxycycline or amoxicillin

Question 133

Regarding syphilis, which one of the following is most accurate? A. The characteristic lesion of primary syphilis is a painful vesicle on the genitals B. In secondary syphilis, the number of organisms is low, so the chance of transmitting the disease to others is low C. In secondary syphilis, both the rapid plasma reagin (RPR) and the fluorescent treponemal antibody-absorbed (FTA-ABS) tests are usually positive D. The antibody titer in the FTA-ABS test typically declines when the patient has been treated adequately E. In congenital syphilis, no antibody is formed against *Treponema pallidum* because the fetus is tolerant to the organism

Answer 133

C. In secondary syphilis, both the rapid plasma reagin (RPR) and the fluorescent treponemal antibody-absorbed (FTA-ABS) tests are usually positive

Question 134

A college student returns from a trip around the Caribbean over Spring Break complaining of painful headaches and severe bone pain accompanied by nausea, vomiting and high fever. He reports being bitten by mosquitos throughout his trip. The virus infecting this student requires which of the following cellular factors for completing the viral replication cycle? A. DNA polymerase B. Ribosomes C. DNA dependent RNA polymerase D. Interferon E. RNA dependent DNA polymerase

Answer 134

B. Ribosomes (host ribosomes)

Question 135

Viruses in the Adenoviridae, Parvoviridae, and Papillomaviridae families are extremely stable. They are resistant to heat, detergents, and chlorination. What common factor provides these viruses with such stability? A. All contain double-stranded DNA genomes B. None have membrane-derived envelopes C. All have helical nucleocapsids D. All have naked icosahedral nucleocapsids E. The viral glycoproteins are heavily glycosylated

Answer 135

D. All have naked icosahedral nucleocapsids

Question 136

After the attachment and entry of a virus into a host cell, what is the next step in the replication of human viruses? ## Footnote A. Transcription of “late” genes B. Transcription of “early” genes C. Synthesis of capsid proteins D. Uncoating of viral genome E. Release of virions

Answer 136

D. Uncoating of viral genome

Question 137

Which of the following must be made by all RNA virus-infected cells in order for viral progeny to be produced? A. RNA complementary to the viral genome B. Viral mRNA C. Viral glycoproteins D. Phospholipids E. Both A and B

Answer 137

E. Both A and B

Question 138

Infection with human immunodeficiency virus (HIV) is suspected in a 28-year-old man who has recently lost weight, complains of intermittent fever and chills, and is suffering from pneumonia and oral thrush. Detection of which enzyme in the patient’s blood would be indicative of infection with this retrovirus: A. DNA-dependent DNA polymerase B. DNA-dependent RNA polymerase C. RNA-dependent DNA polymerase D. RNA-dependent RNA polymerase E. Thymidine kinase

Answer 138

C. RNA-dependent DNA polymerase

Question 139

Influenza virus type A produces a mild, self-limited febrile illness in the general population. However, worldwide epidemics have occurred at different times in history due to rapid changes in viral genetic makeup. Which of the following is the most important reason why these sporadic worldwide epidemics occur? A. Random mutation due to an error prone RNA dependent RNA polymerase B. Reassortment of segments of the RNA genome within a cell infected by two different strains of influenza C. Neuraminidase develops the ability to attach to sialic acid receptors, becoming more infectious D. Hemagglutinin develops the ability to destroy a component of mucin, becoming more infectious E. RBCs agglutinate with certain strains

Answer 139

B. Reassortment of segments of the RNA genome within a cell infected by two different strains of influenza

Question 140

Viral infection of cells in culture and in animals often cause cytopathic effects due to damage of the host cell. Which of the processes of viral replication is most likely to damage the host cell? A. Reverse transcription of retroviral RNA B. Viral uncoating C. Release of enveloped viruses D. Viral entry into host cells by fusion E. Release of nonenveloped “naked” viruses

Answer 140

E. Release of nonenveloped “naked” viruses

Question 141

Which of the following statements regarding viral envelopes is the most correct? A. All viral envelopes contain glycoproteins for viral entry into host cells B. All viral envelopes contain both viral and host proteins C. All viral envelopes are derived from the cellular plasma membrane D. Viral envelopes provide protection against heating and drying E. Viral envelopes are strong inducers of innate immune responses

Answer 141

A. All viral envelopes contain glycoproteins for viral entry into host cells

Question 142

Interferons are an important part of the host defense against viral infections. What is interferon’s principal mode of action? a. It is present in the serum of healthy individuals, providing a viral surveillance role b. It coats viral proteins and blocks their attachment to cells c. It induces synthesis of one or more cellular proteins that inhibit translation or transcription d. It protects the virus-infected cell that produced it from cell death

Answer 142

c. It induces synthesis of one or more cellular proteins that inhibit translation or transcription

Question 143

The skin is an impenetrable barrier to virus entry, but a few viruses are able to breach this barrier and initiate infection of the host. Which of the following is an example of a virus that enters through skin abrasions? a. Adenovirus b. Rotavirus c. Rhinovirus d. Papillomavirus e. Influenza virus

Answer 143

d. Papillomavirus

Question 144

Which of the following viruses is the most common cause of neonatal infections in the United States? a. Zika virus b. Rubella c. Hepatitis C d. Cytomegalovirus e. HIV

Answer 144

d. Cytomegalovirus

Question 145

Many viruses use the respiratory tract as the route of entry to initiate infections. Which of the following virus groups does not? a. Adenovirus b. Coronavirus c. Hepadnavirus d. Paramyxovirus e. Poxvirus

Answer 145

c. Hepadnavirus

Question 146

Which of the following is not a viral strategy for immune evasion? ## Footnote a. Inhibition of proteasomal activity b. Blocking formation of MHC-I c. Producing miRNAs to block apoptosis d. Release of type-1 interferons e. Producing miRNAs that block type-1 interferon production

Answer 146

d. Release of type-1 interferons

Question 147

Which of the following are associated with immunopathology? a. Stromal keratitis b. Cytokine storm c. Rash d. A and C only e. All of the above

Answer 147

e. All of the above

Question 148

Regarding the mode of action of interferon, which one of the following is the most accurate? a. It acts by inhibiting the virion protease. b. It acts by inhibiting the virion polymerase. c. It acts by inducing a ribonuclease that degrades viral mRNA. d. It acts by binding to the extracellular virion, thereby preventing entry into the cell. e. It acts against viruses with a DNA genome but not against viruses that have RNA as their genome.

Answer 148

c. It acts by inducing a ribonuclease that degrades viral mRNA.

Question 149

Regarding immunologic aspects of viral diseases, which one of the following is most accurate? a. Antibodies protect against some viral diseases by inhibiting the synthesis of mRNA by the RNA polymerase in the virion. b. IgG plays a major role in neutralizing virus infectivity during the primary infection. c. IgA exerts an antiviral effect by preventing virus from infecting the mucosal cells of the respiratory and gastrointestinal tracts. d. IgE can prevent viral infection by activating complement, which leads to the production of the membrane attack complex. e. Interleukin-2 is important in protecting uninfected cells from viral infection by inhibiting the release of virus from infected cells.

Answer 149

c. IgA exerts an antiviral effect by preventing virus from infecting the mucosal cells of the respiratory and gastrointestinal tracts.

Question 150

Which one of the following phrases accurately describes virus-neutralizing antibodies? a. Directed against viral protein determinants on the outside of the virus particle b. Appear in the host sooner after viral infection than interferon c. Directed against viral nucleic acid sequences d. Induced only by disease-causing viruses e. Of little importance to immunity to viral infection

Answer 150

a. Directed against viral protein determinants on the outside of the virus particle

Question 151

Regarding viral vaccines, which one of the following is the MOST accurate? a. Killed vaccines induce a longer lasting response than do live, attenuated vaccines. b. Killed vaccines are no longer used in this country because they do not induce secretory IgA. c. Killed vaccines induce a broader range of immune responses than do live, attenuated vaccines. d. Killed vaccines are safer to give to immunocompromised patients than are live, attenuated vaccines.

Answer 151

d. Killed vaccines are safer to give to immunocompromised patients than are live, attenuated vaccines.

Question 152

Induction of passive-active immunity is useful in the prevention of which one of the following sets of two viral diseases? a. Hepatitis A and dengue b. Hepatitis B and rabies c. Influenza and varicella d. Mumps and yellow fever e. Rubella and measles

Answer 152

b. Hepatitis B and rabies

Question 153

Individuals who have had an anaphylactic reaction to egg proteins should NOT receive which one of the following vaccines? a. Hepatitis A vaccine b. Hapatitis B vaccines c. Influenza vaccines d. Polio vaccine e. Rabies vaccine

Answer 153

c. Influenza vaccines

Question 154

Protection of the unimmunized individual based on immunization of a sufficient number of other members of the population is a description of which one of the following? a. Active immunity b. Herd immunity c. Passive immunity d. Passive-active immunity e. Post-exposure immunity

Answer 154

b. Herd immunity

Question 155

A component of the cell membrane of most fungi is: A. cholesterol. B. chitin. C. ergosterol. D. peptidoglycan. E. keratin.

Answer 155

C. ergosterol.

Question 156

A component of the cell wall of most fungi is: A. cholesterol. B. chitin. C. ergosterol. D. peptidoglycan. E. keratin

Answer 156

B. chitin.

Question 157

A patient presents to the dermatology clinic with discolored, deformed and brittle toe nails. He is prescribed extended treatment with Terbinafine (Lamisil). What is the mechanisms of action of the antimicrobial used to treat this patient? A. Inhibits DNA replication B. Interferes with ergosterol synthesis C. Alters lipoteichoic acid metabolism D. Stops DNA synthesis E. Inhibits 50S ribosomal RNA

Answer 157

B. Interferes with ergosterol synthesis

Question 158

After vacationing in the desert areas of New Mexico, a 40-year-old Filipino man develops a respiratory infection with cough, fever, headache, pulmonary infiltrates, and has red, painful lesions (erythema nodosum) on both shins. He is diagnosed with San Joaquin Valley fever. Which of the following is NOT a characteristic of the etiological agent? A. Can be transmitted person to person B. Dimorphic fungus C. Endemic to the Southwest region of the US D. Can become systemic E. Spherules are found at 25°C

Answer 158

E. Spherules are found at 25°C

Question 159

A 72-year-old man presented with a 2-week history of odynophagia (pain on swallowing). The patient had previously received a diagnosis of diffuse panbronchiolitis, and had been receiving long-term treatment with macrolide antibiotics. Upper endoscopy revealed, white, mucosal, plaquelike lesions on the esophagus. Microscopic examination revealed ovoid yeast and pseudohyphae. What is the most likely causative agent? A. *Aspergillus fumigatus* B. *Cryptococcus neoformans* C. *Staphylococcus aureus* D. *Candida albicans* E. *Coccidioides immitis*

Answer 159

D. *Candida albicans*

Question 160

A 4 year old girl in day care was brought to the clinic because of several lesions on her arm. They were reddish and round, slightly raised and scaling. There were a few pinpoint pustules around the edge of the lesions. The girl had no other lesions except the ones on the arm and had no other symptoms. Ringworm was suspected and a skin superficial sample was taken. What should be done first for an initial diagnosis of the lesion? A. Gram stain B. Microscopy of skin sample with 10% KOH C. Grow it on blood agar at room temperature D. Perform India ink stain or PAS stain E. Grow it on Sabouraud's agar

Answer 160

B. Microscopy of skin sample with 10% KOH

Question 161

While in a medical mission trip to Africa a male presents to the clinic with multiple pruritic, warty cauliflower like lesions in the foot. You learn the patient has had the lesions for a while and is not in pains. Microscopy reveals muriform bodies that resemble pigmented yeast cells. Which of the following clinical syndromes most likely accounts for this presentation? A. Zygomycosis B. Sporotrichosis C. Deep dermatophytosis D. White piedra E. Chromoblastomycosis

Answer 161

E. Chromoblastomycosis

Question 162

A high school wrestler develops a superficial lesion as shown in the photograph. Which description or terms are frequently used to describe this type of infection?

Answer 162

A. and C.

Question 163

Which statement regarding dermatophytosis is correct? A. Chronic infections are commonly associated with zoophilic dermatophytes such as *Microsporum canis* B. Acute infections are commonly associated with zoophilic dermatophytes such as *Microsporum canis* C. Chronic infections are commonly associated with anthropophilic dermatophytes such as *Microsporum canis* D. Acute infections are commonly associated with anthropophilic dermatophytes such as *Microsporum canis*

Answer 163

B. Acute infections are commonly associated with zoophilic dermatophytes such as *Microsporum canis*

Question 164

Which Statement regarding sporotrichosis is correct? A. the etiological agent is an encapsulated yeast B. It is a nosocomial disease C. Most patients are immunocompromised D. The etiological agent is a dimorphic fungus E. Most common clinical presentation are indolent macules

Answer 164

D. The etiological agent is a dimorphic fungus

Question 165

Onychomycoses are difficult to treat mostly because: A. Dermatophytes are resistant to multiple antimycotic agents B. Once the diagnosis is made the patient requires surgery C. Poor penetration of the nail bed by antimycotics D. Poor patient compliance due to adverse effects E. Antimycotic drug interactions with statins

Answer 165

C. Poor penetration of the nail bed by antimycotics

Question 166

A new rapid diagnostic assay for *Campylobacter jejuni* is under development. Preliminary assessment of the assay using standard stool specimens yielded 9 positive results from 10 known infected patients. Which of the following is true about the new assay: A. The specificity is 10% B. The sensitivity is 10% C. The specificity is 90% D. The sensitivity is 90%

Answer 166

D. The sensitivity is 90%

Question 167

A 23-year-old woman presents to her doctor complaining of 1 day of increased urinary frequency, dysuria and sensation of incomplete voiding. A urine culture is performed with subsequent MALDI-TOF analysis. This diagnostic tool identifies microorganisms based on which of the following?

Answer 167

C. 16s rRNA sequencing

Question 168

A 56-year-old male who underwent colonic resection three days ago develops a fever. His wound is red and tender with some purulent discharge. A swab of the wound is collected and inoculated on blood agar. A rapid latex agglutination test is used for presumptive identification of the pathogen. This diagnostic tool identifies microorganisms based on which of the following?

Answer 168

A. Antibody-antigen interaction