Micro 8.12 Microbiology and Parasitology Problem-Solving

Question 1

1. An emergency department physician ordered a culture and sensitivity test on a catheterized urine specimen obtained from a 24-year-old female patient. A colony count was done, and the following results were obtained after 24 hours:
   Blood agar plate = >100,000 col/mL of gram-positive cocci resembling staphylococci
   MacConkey agar = No growth
   CNA plate = Inhibited growth
   Hemolysis = Neg
   Novobiocin = Resistant
   Catalase = +
   This isolate is:

A. Staphylococcus saprophyticus
B. Micrococcus luteus
C. Staphylococcus aureus
D. Streptococcus pyogenes

Answer 1

A. Staphylococcus saprophyticus

Question 2

2. An outbreak of S. aureus in the hospital nursery prompted the Infection Control Committee to proceed with an environmental screening procedure. The best screening media to use for this purpose would be:

A. CNA agar
B. THIO broth
C. Mannitol salt agar
D. PEA agar

Answer 2

C. Mannitol salt agar

Question 3

3. A 12-month-old boy who had a fever of 103°F and was listless was taken to the emergency department. He had been diagnosed with an ear infection 3 days earlier. A spinal tap was performed, but only one tube of CSF was obtained from the lumbar puncture. The single tube of CSF should be submitted first to which department?

A. Chemistry
B. Microbiology
C. Hematology
D. Cytology/Histology

Answer 3

B. Microbiology

Question 4

4. A 65-year-old female outpatient was requested by her physician to submit a 24-hour urine specimen for protein and creatinine tests. He also requested testing for mycobacteria in the urine. Should the microbiology laboratory accept this 24-hour specimen for culture?

A. Yes, if the specimen is kept on ice
B. Yes, if the specimen is for aerobic culture only
C. No, the specimen must be kept at room temperature
D. No, the specimen is unsuitable for the recovery of mycobacteria

Answer 4

D. No, the specimen is unsuitable for the recovery of mycobacteria

Question 5

5. A lymph node biopsy specimen obtained from a 30-year-old male patient was submitted to the microbiology laboratory for culture and AFB smear for mycobacteria. The specimen was fixed in formalin. This specimen should be:

A. Accepted for AFB smear preparation and cultured
B. Rejected
C. Held at room temperature for 24 hours and then cultured
D. Cultured for anaerobes only

Answer 5

B. Rejected

Question 6

6. A 49-year-old man who traveled to Mexico City returned with severe dysentery. His symptoms were fever; abdominal cramping; and bloody, mucoidal, frequent stools. In addition to this, many WBCs were seen in the Gram-stained smear. Stool culture gave
   the following results:
   Gram staining = gram-negative rods
   Lactose = +
   Indole = +
   Urease = Neg
   Lysine decarboxylase = Neg
   Motility = Neg
   What is the most likely organism?

A. Salmonella spp.
B. Proteus mirabilis
C. Escherichia coli
D. Enteroinvasive E. coli (EIEC)

Answer 6

D. Enteroinvasive E. coli (EIEC)

Question 7

7. An 80-year-old male patient was admitted to the hospital with a fever of 102°F. A sputum culture revealed many gram-negative rods on MacConkey agar and blood agar. The patient was diagnosed with pneumonia. The following biochemical results were obtained from the culture:
   H2S = Neg
   Citrate = +
   Motility = Neg
   Lactose = +
   Indole = +
   Urease = +
   VP = +
   Resistance to ampicillin and carbenicillin
   What is the most likely identification?

A. Klebsiella oxytoca
B. Proteus mirabilis
C. Escherichia coli
D. Klebsiella pneumoniae

Answer 7

A. Klebsiella oxytoca

Question 8

8. An immunocompromised 58-year-old female patient on chemotherapy received 2 units of packed RBCs. The patient died 3 days later, and the report from the autopsy revealed that her death resulted from septic shock. The blood bags were submitted for culture, and the following results were noted:
   GROWTH OF AEROBIC GRAM-NEGATIVE RODS ON BOTH MACCONKEY AND BLOOD AGARS
   Lactose = Neg
   Indole = Neg
   Urease = +
   Sucrose = +
   VP = Neg
   Motility 22°C = +
   Citrate = Neg
   H2S = Neg
   Motility 37°C = Neg
   What is the most likely identification?

A. Escherichia coli
B. Yersinia enterocolitica
C. Enterobacter cloacae
D. Citrobacter freundii

Answer 8

B. Yersinia enterocolitica

Question 9

9. A pediatric patient who had had been camping with his parents was admitted to the hospital with severe bloody diarrhea and complications of hemolytic uremic syndrome (HUS). Several stool specimens were submitted for culture and the following results noted:
   Gram staining = Many gram-negative rods, with no WBCs seen
   Blood agar = Normal flora
   MacConkey agar = Normal flora
   MacConkey agar with sorbitol = Many clear colonies (sorbitol negative)
   Hektoen agar = Normal flora Campy agar = No growth
   What is the most likely identification?

A. Yersinia spp.
B. E. coli O157:H7
C. Salmonella spp.
D. Shigella spp

Answer 9

B. E. coli O157:H7

Question 10

10. A 14-year-old patient presented to the emergency department; he had been to the doctor’s office 2 days ago with abdominal pain, diarrhea, and a low-grade fever. He was diagnosed at the emergency department with pseudoappendicular syndrome. Cultures from the stool containing blood and WBCs showed the following results:
    AEROBIC GRAM-NEGATIVE RODS ON MACCONKEY AGAR (CLEAR COLONIES)
    Campy agar = No growth
    Lactose = Neg
    Sucrose = +
    Citrate = Neg
    Indole = Neg
    VP = Neg
    H2S = Neg
    Motility 37°C = Neg
    Motility 22°C = +
    Hektoen agar = NF
    What is the most likely identification?

A. Yersinia enterocolitica
B. Salmonella spp.
C. Shigella spp.
D. Escherichia coli

Answer 10

A. Yersinia enterocolitica

Y. enterocolitica is responsible for diseases in younger persons. Blood and leukocytes can be present in stools. Patients (usually teens) exhibiting appendicitis-like symptoms with lactose-negative colonies growing on MacConkey agar (small colonies at 24 hours, but larger colonies at 48 hours if incubated at room temperature) should be tested for the growth of Y. enterocolitica.

Question 11

11. Culture of the sputum specimen from a 13-year-old patient with CF grew a predominance of short, gram-negative rods that tested oxidase negative. On MacConkey, chocolate, and blood agar plates, the organism appeared to have lavendergreen pigmentation. Further testing showed the following:
    Motility = +
    Glucose = + (oxidative)
    Lysine decarboxylase = +
    DNase = +
    Maltose = + (oxidative)
    Esculin hydrolysis = +
    What is the most likely identification?

A. Stenotrophomonas maltophilia
B. Acinetobacter spp.
C. Pseudomonas aeruginosa
D. Burkholderia (P.) cepacia

Answer 11

A. Stenotrophomonas maltophilia

Question 12

12. A patient with a human bite wound on the right forearm arrived at the clinic for treatment. The wound was inflicted 36 hours earlier, and a culture was taken by the physician on duty. After 48 hours, the culture results were as follows:
    GRAM-STAINING = GRAM-NEGATIVE STRAIGHT, SLENDER RODS
    Chocolate agar plate = “Pitting” of the agar by small, yellow, opaque colonies
    Oxidase = +
    Motility = Neg
    Catalase = Neg
    Glucose = +
    Growth in increased CO2 = + Growth at 42°C = Neg
    What is the most likely identification of this facultative anaerobe?

A. Pseudomonas aeruginosa
B. Acinetobacter spp.
C. Kingella kingae
D. Eikenella corrodens

Answer 12

D. Eikenella corrodens

E. corrodens is part of the normal flora of the human mouth and typically “pits” the agar. This organism is capnophilic (needing increased CO2).

Question 13

13. A dog bite wound to the thumb of a 20-year-old male patient became infected. Culture grew a gram-negative, slender rod, which was a facultative anaerobe. The following results were noted:
    Oxidase = +
    Catalase = +
    “Gliding” on the agar was noted.
    Motility = Neg
    Capnophilic = +
    What is the most likely identification?

A. Pseudomonas aeruginosa
B. Capnocytophaga canimorsus
C. Acinetobacter spp.
D. Proteus mirabilis

Answer 13

B. Capnocytophaga canimorsus

C. canimorsus is associated with septicemia or meningitis following dog bites. All Capnocytophaga strains are capnophilic, facultative anaerobic, gram-negative, slender or filamentous rods with tapered ends.

Question 14

14. A patient exhibits fever, chills, abdominal cramps, diarrhea, vomiting, and bloody stools 10 to 12 hours after eating. Which organisms will most likely grow from this patient’s stool culture?

A. Salmonella or Yersinia spp.
B. Escherichia coli O157:H7 or Shigella spp.
C. Staphylococcus aureus or Clostridium perfringens
D. Salmonella or Staphylococcus spp.

Answer 14

B. Escherichia coli O157:H7 or Shigella spp.

Question 15

15. When testing for coagulase properties, staphylococci isolates from a 67-year-old male patient with diabetes showed a positive tube test (free coagulase) result. The organism should be identified as:

A. Staphylococcus aureus
B. Staphylococcus haemolyticus
C. Staphylococcus saprophyticus
D. Micrococcus luteus

Answer 15

A. Staphylococcus aureus

Question 16

16. An isolate of S. aureus was cultured from an ulcer obtained from the leg of a 79-year-old female patient with diabetes. The organism showed resistance to methicillin. This isolate should be additionally tested for resistance or susceptibility to:

A. Erythromycin
B. Gentamicin
C. Vancomycin
D. Kanamycin

Answer 16

C. Vancomycin

Question 17

17. An isolate recovered from a vaginal culture obtained from a 25-year-old female patient who is 8 months pregnant is shown to be gram-positive cocci, catalase negative, and β-hemolytic on blood agar. Which tests are needed for further identification?

A. Optochin, bile solubility, PYR
B. Bacitracin, CAMP, PYR
C. Methicillin, PYR, trehalose
D. Coagulase, glucose, PYR

Answer 17

B. Bacitracin, CAMP, PYR

Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.

Question 18

18. Which organism is the most often recovered gram-positive coccus (catalase negative), displaying α-, β-, or γ-hemolysis on blood agar from a series of blood culture specimens obtained from patients with endocarditis?

A. Streptococcus agalactiae
B. Clostridium perfringens
C. Enterococcus faecalis
D. Pediococcus spp.

Answer 18

C. Enterococcus faecalis

Question 19

19. A presumptive diagnosis of gonorrhea can be made from an exudate from a 20-year-old emergency department patient if which of the following criteria are present?

A. Smear of urethral exudate (male only) shows typical gram-negative, intracellular diplococci; growth of oxidase-positive, gram-negative diplococci on selective agar (MTM)
B. Smear from vaginal area shows gram-negative diplococci; growth of typical colonies on blood agar
C. Smear from rectum shows typical gram-negative diplococci; no growth on chocolate agar
D. Growth of gram-negative cocci on MacConkey agar and blood agar

Answer 19

A. Smear of urethral exudate (male only) shows typical gram-negative, intracellular diplococci; growth of oxidase-positive, gram-negative diplococci on selective agar (MTM)

Question 20

20. “Clue cells” are seen on a smear of vaginal discharge obtained from an 18-year-old female emergency department patient. This finding, along with a fishy odor (amine) after the addition of 10% KOH, suggests bacterial vaginosis caused by which organism?

A. Staphylococcus epidermidis
B. Streptococcus agalactiae
C. Gardnerella vaginalis
D. Escherichia coli

Answer 20

C. Gardnerella vaginalis

Question 21

21. A 1-month-old infant underwent a spinal tap to rule out bacterial meningitis. The CSF was cloudy, and the smear showed many pus cells and short gram-positive rods. After 18 hours, many colonies appeared on blood agar that resembled Streptococcus spp. or L. monocytogenes. Which of the following preliminary tests should be performed on the colonies to best differentiate L. monocytogenes from Streptococcus spp.?

A. Hanging-drop motility (25°C) and catalase
B. PYR and bacitracin
C. Oxidase and glucose
D. Coagulase and catalase

Answer 21

A. Hanging-drop motility (25°C) and catalase

Question 22

22. Acid-fast-positive bacilli were recovered from the sputum of a 79-year-old man who had been treated for pneumonia. Which of the following test reactions after 3 weeks of incubation on Löwenstein-Jensen agar are consistent with M. tuberculosis?

A. Niacin = +
Nitrate reduction = +
Photochromogenic = Neg

B. Niacin= Neg
Optochin = +
Catalase = +

C. PYR = +
Urease = +
Bacitracin = +

D. Ampicillin = Resistant
Penicillin = Resistant

Answer 22

A. Niacin = +
Nitrate reduction = +
Photochromogenic = Neg

M. tuberculosis is niacin positive and nonphotochromogenic. This organism takes up to 3 weeks to grow on selective agar.

Question 23

23. Which biochemical tests should be performed to identify colorless colonies growing on MacConkey agar (swarming colonies on blood agar) from a catheterized urine specimen?

A. Indole, phenylalanine deaminase, and urease
B. Glucose, oxidase, and lactose utilization
C. Phenylalanine deaminase and bile solubility
D. H2S and catalase

Answer 23

A. Indole, phenylalanine deaminase, and urease

Question 24

24. A gram-negative nonfermenter was isolated from a culture taken from a patient who had suffered burns. Which of the following is the best choice of tests to differentiate P. aeruginosa from Acinetobacter spp.?

A. Growth on MacConkey agar, catalase, growth at 37°C
B. Oxidase, motility, growth at 42°C
C. Growth on blood agar, oxidase, growth at 35°C
D. String test and coagulase test

Answer 24

B. Oxidase, motility, growth at 42°C

P. aeruginosa has a distinctive grape odor. The best tests to differentiate it from Acinetobacter spp. are growth at 42°C, oxidase, and motility.

Question 25

25. A Haemophilus species recovered from a throat culture specimen obtained from a 59-year-old male patient undergoing chemotherapy required hemin (X factor) and NAD (V factor) for growth. This species also hemolyzed horse erythrocytes on blood agar. What is the most likely species?

A. Haemophilus ducreyi
B. Haemophilus parahaemolyticus
C. Haemophilus haemolyticus
D. Haemophilus aegyptius

Answer 25

C. Haemophilus haemolyticus

H. haemolyticus requires both X and V factors for growth and lyses horse erythrocytes.

Question 26

26. Large gram-positive bacilli (boxcar shaped) were recovered from a blood culture specimen taken from a 70-year-old female patient with diabetes. The following results were recorded:
    Aerobic growth = Neg
    Spores = Neg
    Lecithinase = +
    GLC (volatile acids) = acetic acid and butyric acid
    Anaerobic growth = +
    Motility = Neg
    Hemolysis = β (double zone)
    What is the most likely identification?

A. Clostridium perfringens
B. Fusobacterium spp.
C. Bacteroides spp.
D. Clostridium sporogenes

Answer 26

A. Clostridium perfringens

Question 27

27. Anaerobic gram-negative rods were recovered from the blood of a patient after gallbladder surgery. The bacteria grew well on agar containing 20% bile but were resistant to kanamycin and vancomycin. What is the most likely identification?

A. Clostridium perfringens
B. Bacteroides fragilis group
C. Prevotella spp.
D. Porphyromonas spp.

Answer 27

B. Bacteroides fragilis group

Question 28

28. In breakpoint antimicrobial drug testing, interpretation of susceptible (S), intermediate (I), and resistant (R) refers to testing antibiotics by using:

A. The amount needed to cause bacteriostasis
B. Only the specific concentrations necessary to report S, I, or R
C. An MIC of 64 µg/mL
D. A dilution of drug that is one tube less than the toxic level

Answer 28

B. Only the specific concentrations necessary to report S, I, or R

Question 29

29. A CSF sample obtained from a 2-week old infant with suspected bacterial meningitis grew gram-negative rods on blood and chocolate agars. The following results were noted:
    MacConkey agar = No growth
    Glucose (open) OF = +
    Glucose (closed) OF = Neg
    Indole = +
    Motility = Neg
    42°C growth = Neg
    ONPG = +
    Urease = Neg
    Catalase = +
    Oxidase = +
    Pigment = Yellow
    What is the correct identification?

A. Pseudomonas aeruginosa
B. Elizabethkingia (Chryseobacterium) meningosepticum
C. Acinetobacter spp.
D. Escherichia coli

Answer 29

B. Elizabethkingia (Chryseobacterium) meningosepticum

Question 30

30. During the summer break, several elementary school teachers, all middle-aged, from the same school district attended a 3-day seminar in Chicago. Upon returning home, three female teachers from the group were hospitalized with pneumonia, flulike symptoms, and a nonproductive cough. Routine testing of sputum samples revealed normal flora. Further testing with buffered CYE agar with L-cysteine and α-ketoglutarate in 5% CO2 produced growth of opaque colonies that stained faintly, showing thin gram-negative rods. What is the most likely identification?

A. Legionella pneumophila
B. Haemophilus influenzae
C. Eikenella corrodens
D. Streptococcus pneumoniae

Answer 30

A. Legionella pneumophila

Question 31

31. A vancomycin-resistant gram-positive coccobacillus resembling the S. viridans group was isolated from the blood of a 42-year-old female patient undergoing bone marrow transplantation. The PYR and leucine aminopeptidase (LAP) tests were negative. The
    following results were noted:
    Catalase = Neg
    Esculin hydrolysis = Neg
    Hippurate hydrolysis = Neg
    CAMP = Neg
    Gas from glucose = +
    6.5% salt broth = Neg
    What is the correct identification?

A. Leuconostoc spp.
B. Enterococcus spp.
C. Staphylococcus spp.
D. Micrococcus spp.

Answer 31

A. Leuconostoc spp.

Question 32

32. A catalase-negative, gram-positive coccus resembling staphylococci (clusters on the Gram-stained smear) was recovered from three different blood culture specimens obtained from a 60-year-old patient diagnosed with endocarditis. The following test results were noted:
    PYR = Neg
    Esculin hydrolysis = Neg
    Vancomycin = Sensitive
    LAP = Neg (V)
    6.5% Salt broth = Neg
    CAMP test = Neg
    What is the correct identification?

A. Leuconostoc spp.
B. Gemella spp.
C. Enterococcus spp.
D. Micrococcus spp.

Answer 32

B. Gemella spp.

Question 33

33. Several clinical culture specimens obtained from an immunocompromised patient with prior antibiotic treatment grew aerobic gram-positive cocci. The organism was vancomycin resistant and catalase negative. Additional testing proved negative for enterococci. What other groups of organisms might be responsible?

A. Leuconostoc spp. and Pediococcus spp.
B. Streptococcus pyogenes and Streptococcus agalactiae
C. Micrococcus spp. and Gemella spp.
D. Clostridium spp. and Streptococcus bovis

Answer 33

A. Leuconostoc spp. and Pediococcus spp.

Question 34

34. A catalase-positive, gram-positive coccus (clusters on the Gram-stained smear) grew pale yellow, creamy colonies on 5% sheep blood agar. The specimen was recovered from pustules on the face of a 5-year-old girl with impetigo. The following test reactions indicate which organism?
    Glucose = + (Fermentation)
    PYR = Neg
    Lysostaphin = Sensitive
    Oxidase = Neg
    Bacitracin = Sensitive

A. Micrococcus spp.
B. Streptococcus spp.
C. Enterococcus spp.
D. Staphylococcus spp.

Answer 34

D. Staphylococcus spp.

Question 35

35. A wound (skin lesion) specimen obtained from a newborn grew predominantly β-hemolytic colonies of gram-positive cocci on 5% sheep blood agar. The newborn infant was covered with small skin eruptions that gave the appearance of a “scalding of the skin.” The gram-positive cocci proved to be catalase positive. Which tests should be performed next for appropriate identification?

A. Optochin, bile solubility, PYR
B. Coagulase, glucose fermentation, DNase
C. Bacitracin, PYR, 6.5% salt broth
D. CAMP, bile-esculin, 6.5% salt broth

Answer 35

B. Coagulase, glucose fermentation, DNase

S. aureus is the cause of “scalded skin” syndrome in newborn infants. The production
of a potent exotoxin (exfoliatin) causes the epidermis to slough off, leaving the newborn’s skin with a red, raw texture or a burned, scalded look.

Question 36

36. A 20-year-old female patient presented to the emergency department complaining of abdominal pain, fever, and a burning sensation during urination. An above-normal WBC count, along with pus cells and bacteria in the urine specimen, prompted the physician to order a urine culture. The colony count reported for this patient revealed greater than100,000 col/mL of a nonhemolytic, catalase-negative, gram-positive organism on 5% sheep blood agar. The following test results indicate which organism?
    PYR = +
    6.5% Salt broth = + growth
    Bacitracin = Neg
    Bile esculin = +
    Optochin = Neg

A. Enterococcus faecalis
B. Streptococcus pyogenes
C. Streptococcus agalactiae
D. Streptococcus bovis

Answer 36

A. Enterococcus faecalis

Question 37

37. A sputum specimen from an 89-year-old male patient with suspected bacterial pneumonia grew a predominance of gram-positive cocci displaying α-hemolysis on 5% sheep blood agar. The colonies appeared donut shaped and mucoidy and tested negative for catalase. The most appropriate tests for a final identification are:

A. Coagulase, glucose fermentation, lysostaphin
B. Penicillin, bacitracin, CAMP
C. Optochin, bile solubility, PYR
D. Bile esculin, hippurate hydrolysis

Answer 37

C. Optochin, bile solubility, PYR

Question 38

38. A tissue biopsy specimen of the stomach was obtained from a 38-year-old male patient diagnosed with gastric ulcers. The specimen was transported immediately and processed for culture and histology. At 5 days, the culture produced colonies of gram-negative (curved) bacilli on chocolate and Brucella agar with 5% sheep blood. The cultures were held at 35°C to 37°C in a microaerophilic atmosphere. The colonies tested positive for urease. The most likely identification is:

A. Escherichia coli
B. Helicobacter pylori
C. Enterococcus faecalis
D. Streptococcus bovis

Answer 38

B. Helicobacter pylori

Question 39

39. A catalase-positive, gram-positive short rod was recovered from the blood of a prenatal patient. The organism appeared on 5% sheep blood as white colonies surrounded by a small zone of β-hemolysis. The following tests were performed, indicating the patient was infected with which organism?
    Motility = + (tumbling on wet prep) room temperature
    Motility = + (umbrella-shape on semisolid agar) room temperature
    Glucose = + (fermentation)
    Bile esculin = +
    Voges Proskauer = +

A. Listeria monocytogenes
B. Streptococcus agalactiae
C. Streptococcus pyogenes
D. Lactobacillus spp.

Answer 39

A. Listeria monocytogenes

Question 40

40. An emergency department physician suspected C. diphtheriae when examining the sore throat of an exchange student from South America. What is the appropriate medium for the culture of the nasopharyngeal swab obtained from the patient?

A. Chocolate agar
B. Thayer-Martin agar
C. Tinsdale medium
D. MacConkey agar

Answer 40

C. Tinsdale medium

Question 41

41. A 25-year-old pregnant patient complained of vaginal irritation. Cultures taken for STDs proved negative. The Gram-stained vaginal smear revealed many epithelial cells with gram-variable short rods (coccobacilli) covering the margins. What is the most likely cause of the vaginosis?

A. Group B streptococci
B. Gardnerella vaginalis
C. Staphylococcus aureus
D. Staphylococcus saprophyticus

Answer 41

B. Gardnerella vaginalis

Question 42

42. A 50-year-old male transplant recipient was experiencing neurological difficulties after a pulmonary infection. A spinal tap revealed a cloudy CSF with the Gram-stained smear revealing gram-positive long-beaded bacilli. An acid-fast smear showed filamentous partially acid-fast bacilli. What is the most likely identification of the organism?

A. Nocardia asteroides
B. Mycobacterium avium
C. Mycobacterium bovis
D. Legionella spp.

Answer 42

A. Nocardia asteroides

N. asteroides is a gram-positive, beaded, long bacillus and is partially acid fast. It is an intracellular pathogen that grows in human cells. Immunocompromised patients are susceptible to infections, especially pulmonary infections, which then disseminate to other organs, often proving fatal.

Question 43

43. A 22-year-old pregnant woman (third trimester) presented to the emergency department complaining of diarrhea, fever, and other flulike symptoms. Blood culture, along with a urine culture, were ordered. After 24 hours, the urine culture was negative, but the blood culture revealed a gram-positive, short rod that grew aerobically on blood agar. The colonies were small and smooth, resembling a Streptococcus spp. with a small narrow zone of β-hemolysis. The following test results indicate which organism?
    Motility = + (Wet mount = Tumbling)
    Catalase = +
    Glucose = + (Acid)
    Esculin hydrolysis = +

A. Listeria monocytogenes
B. Streptococcus pneumoniae
C. Streptococcus agalactiae
D. Corynebacterium spp

Answer 43

A. Listeria monocytogenes

Question 44

44. Anaerobic gram-positive, spore-forming bacilli were recovered from the feces of a chemotherapy patient with severe diarrhea. The patient had undergone antibiotic therapy 1 week earlier. The fecal culture produced growth only on the CCFA plate. No aerobic growth of normal flora was seen after 48 hours. The following results were
    noted:
    Kanamycin = Sensitive
    Colistin = Resistant
    Lipase = Neg
    Indole = Neg
    Catalase = Neg
    Vancomycin = Sensitive
    Lecithinase = Neg
    Nitrate = Neg
    Urease = Neg
    Spores = +
    CCFA agar = Growth of yellow, “ground-glass” colonies that fluoresce chartreuse (yellow-green)
    What is the correct identification?

A. Clostridium perfringens
B. Clostridium tetani
C. Clostridium sordellii
D. Clostridium difficile

Answer 44

D. Clostridium difficile

Question 45

45. Anaerobic gram-positive diphtheroids (non–spore formers) were cultured from two separate blood culture bottles (at 5 days) obtained from a 25-year-old patient admitted to the hospital with dehydration, diarrhea, and other flulike symptoms. Four other blood culture bottles did not grow any organisms at 7 days and were discarded. The following results were obtained from the recovered anaerobe:
    Indole = +
    Kanamycin = Sensitive
    Colistin = Resistant
    Nitrate = +
    Catalase = +
    Vancomycin = Sensitive
    Major acid from PYG broth by GLC = Propionic acid
    What is the correct identification?

A. Eggerthella (Eubacterium) lentum
B. Propionibacterium acnes
C. Actinomyces spp.
D. Peptostreptococcus spp.

Answer 45

B. Propionibacterium acnes

Question 46

46. Anaerobic gram-positive bacilli with subterminal spores were recovered from several blood cultures obtained from a patient diagnosed with a malignancy of the colon. The following results were recorded:
    Indole = Neg
    Catalase = Neg
    Urease = Neg
    Lecithinase = Neg
    Lipase = Neg
    Double-zone of Beta hemolysis = Neg
    Growth on blood agar = Swarming colonies
    What is the correct identification?

A. Clostridium septicum
B. Clostridium perfringens
C. Clostridium sordellii
D. Propionibacterium acnes

Answer 46

A. Clostridium septicum

Question 47

47. Anaerobic gram-negative bacilli were recovered from fluid obtained from drainage of a postsurgical abdominal wound. The following test results were recorded:
    Kanamycin = Resistant
    Colistin = Resistant
    Growth on 20% bile plate = +
    Indole = V (Neg)
    Urease = Neg
    Vancomycin = Resistant
    Pigment = Neg
    Nitrate = Neg
    Lipase = Neg
    What is the correct identification?

A. Prevotella spp.
B. Bacteroides fragilis group
C. Porphyromonas spp.
D. Clostridium spp.

Answer 47

B. Bacteroides fragilis group

Question 48

48. Anaerobic, nonpigmented, gram-negative rods were recovered from an anaerobic blood agar plate after 48 hours of incubation. The Gram-stained smear showed thin bacilli with pointed ends. The colonies on blood agar had the appearance of dry, irregular, white breadcrumb-like morphology with greening of the agar. The following reactions were noted:
    Kanamycin = Sensitive
    Colistin = Sensitive
    Indole = +
    Lipase = Neg
    Growth on 20% bile agar = Neg
    Vancomycin = Resistant
    Nitrate = Neg
    Catalase = Neg
    Urease = Neg
    What is the correct identification?

A. Fusobacterium nucleatum
B. Bacteroides fragilis
C. Clostridium perfringens
D. Peptostreptococcus spp.

Answer 48

A. Fusobacterium nucleatum

Question 49

49. A 2-month-old infant in good health was scheduled for a checkup at the pediatrician’s office. After arriving for the appointment, the mother noted white patches on the baby’s tongue and in his mouth. The baby constantly used a pacifier. What is the most likely organism causing the white patches?

A. Cryptococcus neoformans
B. Candida albicans
C. Aspergillus fumigatus
D. None of these options

Answer 49

B. Candida albicans

Question 50

50. A 69-year-old male patient who was a cigarette smoker visited the doctor’s office complaining of a cough and congestion of the lungs. Routine cultures of early morning sputum for bacteria and AFB revealed no pathogens. A fungal culture grew the following on Sabouraud dextrose agar after 3 days:
    Hyphae = Septate with dichotomous branching
    Spores = Produced by conidial heads with numerous conidia
    Colonies = Velvety or powdery, white at first, then turning dark greenish to gray (reverse = white to tan)
    Vesicle = Holding phialides usually on upper two-thirds only
    What is the most likely identification?

A. Aspergillus niger
B. Lichthemia (Absidia) spp.
C. Mucor spp.
D. Aspergillus fumigatus

Answer 50

D. Aspergillus fumigatus

Question 51

51. A young male patient with a fungus of the feet visited the podiatrist seeking relief from the itching. A culture specimen was sent to the microbiology laboratory that grew after 8 days on Sabouraud dextrose agar. Colonies were powdery pink with concentric and radial folds, with the reverse side showing brownish-tan to red. Other observations were as follows:
    Hyphae = Septate
    Urease = +
    Macroconidia = Cigar shaped, thin walled with 1 to 6 cells
    Microconidia = Round and clustered on branched conidiophores
    Red pigment on cornmeal (1% dextrose) = Neg
    In vitro hair perforation = +
    The most likely identification is:

A. Trichophyton mentagrophytes
B. Trichophyton rubrum
C. Candida albicans
D. Aspergillus niger

Answer 51

A. Trichophyton mentagrophytes

Question 52

52. A 79-year-old female nursing home patient was admitted to the hospital with a fever and central nervous system dysfunction. Routine blood work and blood cultures were ordered. After 48 hours, the blood cultures showed budding yeast. The following tests performed from Sabouraud dextrose agar (after 3 days of growth) showed:
    Germ tube = Neg growth
    Urease = +
    Blastospores =+
    Arthrospores = Neg
    Assimilation agar = + (dextrose, sucrose, maltose)
    Birdseed agar = Brown
    Pseudohyphae = Neg
    Chlamydoconidia (spores) = Neg
    What is the most likely identification?

A. Candida albicans
B. Cryptococcus laurentii
C. Cryptococcus neoformans
D. Candida tropicalis

Answer 52

C. Cryptococcus neoformans

Question 53

53. A dehydrated 25-year-old male patient was admitted to the hospital with symptoms similar to those of chronic fatigue syndrome. Serological testing proved negative for recent streptococcal infection, EBV, and hepatitis. Which of the following viral serological tests should help with a possible diagnosis?

A. CMV
B. Echovirus
C. RSV
D. Measles virus

Answer 53

A. CMV

Question 54

54. A nursing student working in the emergency department accidentally suffered a needlestick after removing an intravenous set from a suspected drug user. The best course of action, after reporting the incident to her supervisor, is to:

A. Test the student for HIV virus if flulike symptoms develop in 2 to 4 weeks
B. Immediately test the patient and the student for HIV by using an EIA or ELISA test
C. Perform a Western blot assay on the student’s serum
D. Draw blood from the student only and freeze it for further testing

Answer 54

B. Immediately test the patient and the student for HIV by using an EIA or ELISA test

Question 55

55. A 30-year-old female patient complained of vaginal irritation and symptoms (fever, dysuria, and inguinal lymphadenopathy) associated with STDs. Examination showed extensive lesions in the genital area. Chlamydia spp. testing, N. gonorrhoeae, and G. vaginalis cultures were negative. RPR testing was also negative. What is the next line of testing?

A. Darkfield examination
B. HSV testing
C. Trichomonas spp. testing
D. Group B streptococci testing

Answer 55

B. HSV testing

Question 56

56. A patient is being seen in the emergency room for a low-grade fever, headache, and general malaise after returning from a photographic safari in Africa. The physician has requested blood analysis for malaria; the laboratory would like to have patient information regarding:

A. Specific travel history and body temperature every 4 hours
B. Liver function tests and prophylactic medication history
C. Transfusion history and body temperature every 4 hours
D. Prophylactic medication history and specific travel history

Answer 56

D. Prophylactic medication history and specific travel history

Question 57

57. Examination of a modified acid-fast–stained fecal smear reveals round structures measuring approximately 8 to 10 µm, some of which are stained and some of which are not. They do not appear to show any internal morphology. The patient is symptomatic with diarrhea, and the cause may be:

A. Blastocystis spp.
B. Polymorphonuclear leukocytes
C. Cyclospora cayetanensis
D. Large yeast cells

Answer 57

C. Cyclospora cayetanensis

Question 58

58. A patient has been diagnosed as having amebiasis but continues to be asymptomatic. The physician has asked for an explanation and recommendations regarding follow-up. Suggestions should include:

A. Consideration of Entamoeba histolytica versus Entamoeba dispar
B. A request for an additional three stools for culture
C. Initiating therapy, regardless of the patient’s asymptomatic status
D. Performance of barium x-ray studies

Answer 58

A. Consideration of Entamoeba histolytica versus Entamoeba dispar

Question 59

59. Although a patient is strongly suspected of having giardiasis and is still symptomatic, three routine stool examinations (O&P examination) have been performed correctly and reported as negative. Biopsy confirmed the patient had giardiasis. Reasons for these findings may include:

A. The patient was coinfected with several bacterial species
B. Giardia lamblia (G. intestinalis, G. duodenalis) tends to adhere to the mucosal surface and more than three stool examinations may be required to confirm a suspected infection
C. The organisms present did not stain with trichrome stain, and therefore the morphology is very atypical
D. Special diagnostic procedures, such as the Knott concentration and nutrient-free agar cultures, should have been used

Answer 59

B. Giardia lamblia (G. intestinalis, G. duodenalis) tends to adhere to the mucosal surface and more than three stool examinations may be required to confirm a suspected infection

Question 60

60. A transplant recipient is currently receiving steroids. The patient is now complaining of abdominal pain and has symptoms of pneumonia and positive blood cultures with gram-negative rods. The individual has been living in the United States for 20 years but grew up in Central America. The most likely parasite causing these symptoms is:

A. Trypanosoma brucei rhodesiense
B. Giardia lamblia (G. intestinalis, G. duodenalis)
C. Strongyloides stercoralis
D. Schistosoma japonicum

Answer 60

C. Strongyloides stercoralis