Micrology 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 gave the
   following results 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
   Catalase = Positive
   Novobiocin = Resistant

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 Staphylococcus aureus in the
   nursery department 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 listless 12-month-old boy with a fever of
   103°F 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 obtained from a 30-year-old
   male patient was submitted to the microbiology
   laboratory for a culture and AFB smear for
   mycobacteria. The specimen was fixed in
   formalin. This specimen should be:
   A. Accepted for AFB smear 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 a bad case of dysentery. His
   symptoms were fever; abdominal cramping; and
   bloody, mucoidal, frequent stools. In addition to
   this, many WBCs were seen on the Gram stain
   smear. Stool culture gave the following results:

Gram stain: Gram-negative rods
Lactose = +
Indole = +
Lysine decarboxylase
= Neg
Urease = 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
   Lactose = +
   Urease = +
   Citrate = +
   Indole = +
   VP = +
   Motility = Neg
   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
   chemotherapy patient received 2 units of packed
   RBCs. The patient died 3 days later, and the report
   from the autopsy revealed that her death was due
   to septic shock. The blood bags were cultured, and
   the following results were noted:

GROWTH OF AEROBIC GRAMNEGATIVE RODS ON
BOTH MACCONKEY AND BLOOD AGARS:
Lactose = Neg
Sucrose = +
Citrate = Neg
Indole = Neg
VP = Neg
H2S = Neg
Urease = +
Motility 22°C = +
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 with severe bloody diarrhea
   who had been camping with his parents was
   admitted to the hospital with complications of
   hemolytic uremic syndrome (HUS). Several stool
   specimens were cultured with the following results
   noted:
   Gram stain smear = 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 Campy agar = No growth
   flora
   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 emergency department patient had
    been to the doctor’s office 2 days previously with
    abdominal pain, diarrhea, and a low-grade fever.
    He was diagnosed 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

Question 11

11. A sputum culture from a 13-year-old cystic
    fibrosis patient grew a predominance of short,
    gram-negative rods that tested oxidase negative.
    On MacConkey, chocolate, and blood agar plates,
    the organism appeared to have a lavender-green
    pigment. Further testing showed:
    Motility = +
    DNase = +
    Glucose = + (oxidative) Maltose = + (oxidative)
    Lysine decarboxylase = + Esculin hydrolysis = +

What is the most likely identification?
A. Stenotrophomonas maltophilia
B. Acinetobacter baumannii
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:
    Gram-stain smear = 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 baumannii
C. Kingella kingae
D. Eikenella corrodens

Answer 12

D. Eikenella corrodens

Question 13

13. A dog bite wound to the thumb of a 20-year-old
    male patient became infected. The culture grew a
    gram-negative, slender rod, which was a facultative
    anaerobe. The following results were noted:

Oxidase = +
Motility = Neg
Catalase = +
Capnophilic = +
“Gliding” on the agar was noted.

What is the most likely identification?
A. Pseudomonas aeruginosa
B. Capnocytophaga canimorsus
C. Acinetobacter baumannii
D. Proteus mirabilis

Answer 13

B. Capnocytophaga canimorsus

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. E. coli O157:H7 or Shigella spp.
    C. Staphylococcus aureus or Clostridium perfringens
    D. Salmonella or Staphylococcus spp.

Answer 14

B. E. coli O157:H7 or Shigella spp.

Question 15

15. When testing for coagulase properties,
    staphylococci isolates from a 67-year-old male
    diabetic patient showed a positive tube test (free
    coagulase). 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 Staphylococcus aureus was cultured
    from an ulcer obtained from the leg of a diabetic
    79-year-old female patient. The organism showed
    resistance to methicillin. Additionally, this isolate
    should be 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 a 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

Question 18

18. Which organism is the most often recovered grampositive cocci (catalase negative) from a series of
    blood cultures obtained from individuals 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 (modified
    Thayer–Martin)
    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 (modified
Thayer–Martin)

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. E. coli
    Microbiol

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
    Mycobacterium tuberculosis?

A. Niacin = + Nitrate Photochromogenic
reduction = + = Neg
B. Niacin= Neg Optochin = + Catalase = +
C. PYR = + Urease = + Bacitracin = +
D. Ampicillin = Penicillin =
Resistant Resistant

Answer 22

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

Question 23

23. Which biochemical tests should be performed in
    order 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 burn patient. Which of the
    following is the best choice of tests to differentiate
    Pseudomonas 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

Question 25

25. A Haemophilus spp., recovered from a throat
    culture 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. H. ducreyi
    B. H. parahaemolyticus
    C. H. haemolyticus
    D. H. aegyptius

Answer 25

C. H. haemolyticus

Question 26

26. Large gram-positive bacilli (boxcar shaped) were
    recovered from a blood culture taken from a
    70-year-old female diabetic patient. The following
    results were recorded:
    Aerobic growth = Neg Anaerobic growth = +
    Spores = Neg Motility = Neg
    Lecithinase = + Hemolysis = β (double zone)
    GLC (volatile acids) = acetic acid and butyric acid
    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 ONPG = +
    Glucose (open) OF = + Urease = Neg
    Glucose (closed) OF = Neg Catalase = +
    Indole = + Oxidase = +
    Motility = Neg Pigment = Yellow
    42° C growth = Neg

What is the correct identification?
A. Pseudomonas aeruginosa
B. Chryseobacterium meningosepticum
C. Acinetobacter baumannii
D. E. coli

Answer 29

B. Chryseobacterium meningosepticum

Question 30

30. During the summer break, several middle-aged
    elementary school teachers 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 using 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 Streptococcus
    viridans group was isolated from the blood of a
    42-year-old female patient undergoing a bone
    marrow transplant. The PYR and leucine
    aminopeptidase (LAP) tests were negative. The
    following results were noted:
    Catalase = Neg
    CAMP = Neg
    Esculin hydrolysis = Neg
    Gas from glucose = +
    Hippurate hydrolysis = Neg 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 cultures obtained from a 60-year-old patient
    diagnosed with endocarditis. The following test
    results were noted:
    PYR = Neg
    LAP = Neg (V)
    Esculin hydrolysis = Neg 6.5% Salt broth = Neg
    Vancomycin = Sensitive 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. An immunocompromised patient with prior
    antibiotic treatment grew aerobic gram-positive
    cocci from several clinical specimens that were
    cultured. 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 Gram stain 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) Oxidase = Neg
    PYR = Neg Bacitracin = Sensitive
    Lysostaphin = 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
    follow for the 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

Question 36

36. A 20-year-old female patient entered the
    emergency clinic 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
    emergency physician to order a urine culture. The
    colony count reported for this patient revealed
    >100,000 col/mL of a nonhemolytic, catalasenegative, gram-positive organism on 5% sheep
    blood agar. The following test results indicate
    which organism?
    PYR = +
    Bile Esculin = +
    6.5% Salt broth = + growth
    Bacitracin = Neg
    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
    alpha-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–37°C in a microaerophilic atmosphere.
    The colonies tested positive for urease. The
    most likely identification is:
    A. E. 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
    beta-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)
    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
    Corynebacterium diphtheriae when examining the
    sore throat of an exchange student from South
    America. What is the appropriate media 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. A 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 spp.
    B. Gardnerella vaginalis
    C. Staphylococcus aureus
    D. Staphylococcus saprophyticus

Answer 41

B. Gardnerella vaginalis

Question 42

42. A 50-year-old male transplant patient was
    experiencing neurological difficulties after a
    pulmonary infection. A spinal tap revealed a
    cloudy CSF with a 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

Question 43

43. A 22-year-old pregnant woman (third trimester)
    entered the emergency department complaining
    of diarrhea, fever, and other flulike symptoms.
    Blood cultures were ordered along with a urine
    culture. After 24 hours, the urine culture was
    negative, but the blood cultures 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 = Catalase = +
    Tumbling)
    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 prior. 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 Vancomycin = Sensitive
    Colistin = Resistant Lecithinase = Neg
    Lipase = Neg
    Nitrate = Neg
    Indole = Neg
    Urease = Neg
    Catalase = 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 (nonspore
    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 = +
    Nitrate = + Catalase = +
    Kanamycin = Sensitive Vancomycin = Sensitive
    Colistin = Resistant Major acid from PYG broth
    by GLC = Propionic acid

What is the correct identification?
A. 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
    Urease = Neg
    Lipase = Neg
    Catalase = Neg
    Lecithinase = 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 Vancomycin = Resistant
    Colistin = Resistant
    Growth on 20%
    bile plate = +
    Pigment = Neg
    Indole = V (Neg)
    Nitrate = Neg
    Urease = 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 Vancomycin = Resistant
    Colistin = Sensitive
    Nitrate = Neg
    Indole = +
    Catalase = Neg
    Lipase = Neg
    Urease = Neg
    Growth on 20% bile agar = 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 (×3) for bacteria
    as well as for AFB revealed no pathogens. A
    fungal culture was also ordered that 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. 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 for relief from the itching.
    A culture 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 in color. Other observations
    were:
    Hyphae = Septate
    Urease = +
    Macroconidia = Cigar shaped, thin walled with 1–6 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

C. Candida albicans

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 revealed a budding yeast. The
    following tests performed from Sabouraud
    dextrose agar (after 3 days of growth) showed:
    Germ tube = Neg growth Birdseed agar = Brown
    Urease = +
    Pseudohyphae = Neg
    Blastospores =+ Chlamydospores = Neg
    Arthrospores = Neg
    Assimilation agar = + (dextrose, sucrose, maltose)

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, Epstein–Barr virus, and hepatitis.
    Which of the following viral serological tests
    should help with a possible diagnosis?
    A. CMV
    B. Echovirus
    C. Respiratory syncytial virus
    D. Measles virus

Answer 53

A. CMV

Question 54

54. A nursing student working in the emergency
    department accidentally stuck herself with a needle
    after removing it from an intravenous set taken
    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 2–4 weeks
    B. Immediately test the patient and the student for
    HIV 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 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
    sexually transmitted disease (STD). Examination
    showed extensive lesions in the genital area.
    Chlamydia spp. testing, Neisseria gonorrhoeae,
    and Gardnerella vaginalis cultures were negative.
    Rapid plasma reagin (RPR) testing was also
    negative. What is the next line of testing?
    A. Darkfield examination
    B. Herpes simplex testing
    C. Trichomonas spp. testing
    D. Group B streptococcal testing

Answer 55

B. Herpes simplex testing

Question 56

56. A patient is being seen in the emergency
    department for a low-grade fever, headache, and
    general malaise after returning from Africa on a
    photographic safari. The physician has requested
    blood 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 8–10 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 hominis
    B. Polymorphonuclear leukocytes
    C. Cyclospora cayetanensis
    D. Large yeast cells

Answer 57

C. Cyclospora cayetanensis