Infectious Disease - Infectious Agents - Practice Questions Flashcards
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
c. Viruses
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
d. Pilus
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
c. To disrupt the outer cell membrane so the purple dye can leave the bacteria
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
a. It was nonpathogenic primarily because it was easily phagocytized
Of the following components, which one exhibits the most antigenic variation?
a. Capsule
b. Lipid A of endotoxin
c. Peptidoglycan
d. Ribosome
e. Spore
a. Capsule
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
e. Within the periplasmic space
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
a. Gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer
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
d. Glycocalyx
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

B. Log phase
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
E. Biofilm growth
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
D. Moist heat delivered in an autoclave
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
A. It inhibits bacterial replication as a result of the formation of reactive oxygen species
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
B. False
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
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
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
a. Conjugation
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
b. They are short sequences of DNA that often encode enzymes that mediate antibiotic resistance
- 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
b. Transduction
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
b. They play an important role in the pathogenesis of toxin-induced diseases
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
F. Staphylococcus aureus
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)
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
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
C. Staphylococcus epidermidis
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
E. It is a bacteria surface protein that binds to the Fc portion of IgG1
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
C. Streptococcus pneumoniae
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
C. A vaccine against serogroups A, C, Y and W135 capsular polysaccharide
