UAMS MICROBIOLOGY EXAM – QUESTIONS AND ANSWERS |
VERIFIED AND WELL DETAILED ANSWERS PLUS RATIONALES |
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1. A 45-year-old immunocompromised patient presents with a persistent cough, fever, and
patchy pulmonary infiltrates. Sputum Gram stain reveals beaded, partially acid-fast,
branching filamentous bacilli. Which of the following organisms is the most likely etiology?
A. Nocardia asteroides
B. Mycobacterium tuberculosis
C. Actinomyces israelii
D. Streptococcus pneumoniae
Nocardia species are aerobic, catalase-positive, partially acid-fast, branching filamentous
bacilli typically found in soil, causing opportunistic infections in immunocompromised hosts.
Mycobacterium tuberculosis is acid-fast but non-branching; Actinomyces israelii is anaerobic
and non-acid-fast; Streptococcus pneumoniae is an encapsulated gram-positive diplococcus.
2. A microbiology technologist observes beta-hemolytic colonies on a sheep blood agar plate
from a throat culture of a 7-year-old child. The isolate is catalase-negative and susceptible
to bacitracin (A disk). What is the definitive identification of this organism?
A. Streptococcus agalactiae
B. Streptococcus pyogenes
C. Enterococcus faecalis
D. Streptococcus pneumoniae
Streptococcus pyogenes (Group A Strep) is beta-hemolytic, catalase-negative, and susceptible
to bacitracin. Streptococcus agalactiae (Group B) is resistant to bacitracin and CAMP-
positive; Enterococcus faecalis is gamma or alpha-hemolytic and PYR-positive; Streptococcus
pneumoniae is alpha-hemolytic and optochin-susceptible.
3. During routine maintenance in a clinical microbiology laboratory, an automated blood
culture system flags a bottle from an asymptomatic patient as positive after 24 hours. The
Gram stain reveals small, pleomorphic gram-negative coccobacilli. The technologist
immediately alerts the supervisor and dons a high-efficiency particulate air (HEPA)
respirator because of the high risk of laboratory-acquired infection via aerosols. Which
agent is suspected?
,A. Escherichia coli
B. Brucella species
C. Pseudomonas aeruginosa
D. Staphylococcus aureus
Brucella species are extremely infectious via aerosols generated during laboratory processing,
presenting as small gram-negative coccobacilli. Escherichia coli, Pseudomonas aeruginosa,
and Staphylococcus aureus do not pose the same aerosol containment risk requiring
mandatory high-level respiratory precautions upon initial Gram stain review.
4. A stool specimen from an adult patient with severe, watery "rice-water" diarrhea is
cultured on thiosulfate-citrate-bile salts-sucrose (TCBS) agar. Yellow, sucrose-fermenting
colonies are observed. Which phenotypic characteristic best differentiates this pathogen
from other non-fermenting enteric organisms?
A. Positive oxidase reaction
B. Negative urease test
C. Resistance to novobiocin
D. Inability to grow in 6.5 percent sodium chloride
Vibrio cholerae grows as yellow colonies on TCBS agar due to sucrose fermentation and is
strongly oxidase-positive. While other enteric bacteria may share some traits, the combination
of growth on TCBS and a positive oxidase test is a cornerstone for identifying Vibrio species.
5. A 32-year-old man who recently returned from a camping trip in the southwestern
United States develops high fever, painful regional lymphadenopathy (buboes), and
conjunctivitis. A lymph node aspirate reveals bipolar-staining gram-negative bacilli
resembling safety pins. What is the primary vector for transmission of this pathogen?
A. Ixodes scapularis tick
B. Xenopsylla cheopis flea
C. Aedes aegypti mosquito
D. Triatoma infestans bug
Yersinia pestis is transmitted primarily through the bite of infected rodent fleas, such as
Xenopsylla cheopis, manifesting as bubonic plague. Ixodes transmits Borrelia and
Anaplasma; Aedes transmits dengue and Zika; Triatoma transmits Trypanosoma cruzi.
, 6. Which of the following biochemical test results is characteristic of Klebsiella
pneumoniae, distinguishing it from most other members of the Enterobacteriaceae family?
A. Motile and indole-positive
B. Non-motile and urease-positive
C. Oxidase-positive and citrate-negative
D. Hydrogen sulfide positive and methyl red positive
Klebsiella pneumoniae is characteristically non-motile and typically produces positive results
for urease and Voges-Proskauer tests, while being indole-negative and methyl red-negative.
Indole-positivity and motility rule out typical Klebsiella strains.
7. A cerebrospinal fluid (CSF) specimen from a neonate with meningitis shows gram-
negative bacilli that grow on chocolate agar supplemented with hemin (X factor) and NAD
(V factor), but fail to grow on sheep blood agar alone due to the absence of nurse colonies.
What is the identification?
A. Neisseria meningitidis
B. Haemophilus influenzae
C. Escherichia coli
D. Listeria monocytogenes
Haemophilus influenzae requires both X and V factors for growth, which are available on
chocolate agar but deficient on unlysed sheep blood agar. Neisseria meningitidis is a gram-
negative diplococcus; Escherichia coli grows readily on blood agar; Listeria monocytogenes is
a gram-positive rod.
8. An obligate intracellular bacterium is suspected in a patient presenting with atypical
pneumonia. The organism cannot be cultured on standard cell-free bacteriologic media and
lacks a classic peptidoglycan cell wall, containing cholesterol in its cell membrane instead.
Which organism fits this description?
A. Legionella pneumophila
B. Mycoplasma pneumoniae
C. Chlamydia psittaci
D. Streptococcus pneumoniae
Mycoplasma pneumoniae lacks a cell wall and incorporates sterols into its cell membrane,
necessitating specialized media like SP4 or Eaton agar for culture. Legionella requires
VERIFIED AND WELL DETAILED ANSWERS PLUS RATIONALES |
GUARANTEED PASS | LATEST EXAM UPDATE | EXAM PREP |
STUDY GUIDE | PRACTICE TEST| DOWNLOAD INSTANT PDF
1. A 45-year-old immunocompromised patient presents with a persistent cough, fever, and
patchy pulmonary infiltrates. Sputum Gram stain reveals beaded, partially acid-fast,
branching filamentous bacilli. Which of the following organisms is the most likely etiology?
A. Nocardia asteroides
B. Mycobacterium tuberculosis
C. Actinomyces israelii
D. Streptococcus pneumoniae
Nocardia species are aerobic, catalase-positive, partially acid-fast, branching filamentous
bacilli typically found in soil, causing opportunistic infections in immunocompromised hosts.
Mycobacterium tuberculosis is acid-fast but non-branching; Actinomyces israelii is anaerobic
and non-acid-fast; Streptococcus pneumoniae is an encapsulated gram-positive diplococcus.
2. A microbiology technologist observes beta-hemolytic colonies on a sheep blood agar plate
from a throat culture of a 7-year-old child. The isolate is catalase-negative and susceptible
to bacitracin (A disk). What is the definitive identification of this organism?
A. Streptococcus agalactiae
B. Streptococcus pyogenes
C. Enterococcus faecalis
D. Streptococcus pneumoniae
Streptococcus pyogenes (Group A Strep) is beta-hemolytic, catalase-negative, and susceptible
to bacitracin. Streptococcus agalactiae (Group B) is resistant to bacitracin and CAMP-
positive; Enterococcus faecalis is gamma or alpha-hemolytic and PYR-positive; Streptococcus
pneumoniae is alpha-hemolytic and optochin-susceptible.
3. During routine maintenance in a clinical microbiology laboratory, an automated blood
culture system flags a bottle from an asymptomatic patient as positive after 24 hours. The
Gram stain reveals small, pleomorphic gram-negative coccobacilli. The technologist
immediately alerts the supervisor and dons a high-efficiency particulate air (HEPA)
respirator because of the high risk of laboratory-acquired infection via aerosols. Which
agent is suspected?
,A. Escherichia coli
B. Brucella species
C. Pseudomonas aeruginosa
D. Staphylococcus aureus
Brucella species are extremely infectious via aerosols generated during laboratory processing,
presenting as small gram-negative coccobacilli. Escherichia coli, Pseudomonas aeruginosa,
and Staphylococcus aureus do not pose the same aerosol containment risk requiring
mandatory high-level respiratory precautions upon initial Gram stain review.
4. A stool specimen from an adult patient with severe, watery "rice-water" diarrhea is
cultured on thiosulfate-citrate-bile salts-sucrose (TCBS) agar. Yellow, sucrose-fermenting
colonies are observed. Which phenotypic characteristic best differentiates this pathogen
from other non-fermenting enteric organisms?
A. Positive oxidase reaction
B. Negative urease test
C. Resistance to novobiocin
D. Inability to grow in 6.5 percent sodium chloride
Vibrio cholerae grows as yellow colonies on TCBS agar due to sucrose fermentation and is
strongly oxidase-positive. While other enteric bacteria may share some traits, the combination
of growth on TCBS and a positive oxidase test is a cornerstone for identifying Vibrio species.
5. A 32-year-old man who recently returned from a camping trip in the southwestern
United States develops high fever, painful regional lymphadenopathy (buboes), and
conjunctivitis. A lymph node aspirate reveals bipolar-staining gram-negative bacilli
resembling safety pins. What is the primary vector for transmission of this pathogen?
A. Ixodes scapularis tick
B. Xenopsylla cheopis flea
C. Aedes aegypti mosquito
D. Triatoma infestans bug
Yersinia pestis is transmitted primarily through the bite of infected rodent fleas, such as
Xenopsylla cheopis, manifesting as bubonic plague. Ixodes transmits Borrelia and
Anaplasma; Aedes transmits dengue and Zika; Triatoma transmits Trypanosoma cruzi.
, 6. Which of the following biochemical test results is characteristic of Klebsiella
pneumoniae, distinguishing it from most other members of the Enterobacteriaceae family?
A. Motile and indole-positive
B. Non-motile and urease-positive
C. Oxidase-positive and citrate-negative
D. Hydrogen sulfide positive and methyl red positive
Klebsiella pneumoniae is characteristically non-motile and typically produces positive results
for urease and Voges-Proskauer tests, while being indole-negative and methyl red-negative.
Indole-positivity and motility rule out typical Klebsiella strains.
7. A cerebrospinal fluid (CSF) specimen from a neonate with meningitis shows gram-
negative bacilli that grow on chocolate agar supplemented with hemin (X factor) and NAD
(V factor), but fail to grow on sheep blood agar alone due to the absence of nurse colonies.
What is the identification?
A. Neisseria meningitidis
B. Haemophilus influenzae
C. Escherichia coli
D. Listeria monocytogenes
Haemophilus influenzae requires both X and V factors for growth, which are available on
chocolate agar but deficient on unlysed sheep blood agar. Neisseria meningitidis is a gram-
negative diplococcus; Escherichia coli grows readily on blood agar; Listeria monocytogenes is
a gram-positive rod.
8. An obligate intracellular bacterium is suspected in a patient presenting with atypical
pneumonia. The organism cannot be cultured on standard cell-free bacteriologic media and
lacks a classic peptidoglycan cell wall, containing cholesterol in its cell membrane instead.
Which organism fits this description?
A. Legionella pneumophila
B. Mycoplasma pneumoniae
C. Chlamydia psittaci
D. Streptococcus pneumoniae
Mycoplasma pneumoniae lacks a cell wall and incorporates sterols into its cell membrane,
necessitating specialized media like SP4 or Eaton agar for culture. Legionella requires
