Medical Laboratory Technician Clinical Microbiology Questions and Answers

Question 1

A Gram stain performed on a purulent aspirate from a skin abscess reveals gram-positive cocci arranged in grape-like clusters.
Which of the following organisms is most likely responsible for the infection?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Enterococcus faecalis

Answer

Streptococcus pneumoniae

Question 2

MacConkey agar is a selective and differential medium used for isolating enteric bacteria. The selective agents that inhibit the growth of most gram-positive organisms are:

Accepted Answer

Bile salts and crystal violet

Answer

A high concentration of sodium chloride

Answer

Colistin and nalidixic acid

Answer

Phenylethyl alcohol

Question 3

A Kirby-Bauer susceptibility test for a *Staphylococcus aureus* isolate shows resistance to erythromycin and susceptibility to clindamycin, but with a flattening of the clindamycin zone of inhibition adjacent to the erythromycin disk. This characteristic "D" shape indicates:

Accepted Answer

Inducible clindamycin resistance

Answer

Beta-lactamase production

Answer

Intrinsic resistance to vancomycin

Answer

Tolerance to the antimicrobial agent

Question 4

A patient presents with prolonged, foul-smelling, fatty diarrhea (steatorrhea) after a camping trip where they drank unfiltered stream water. A microscopic examination of a stool sample is most likely to reveal which of the following?

Accepted Answer

Pear-shaped, binucleated trophozoites

Answer

Lemon-shaped cysts with a polar plug

Answer

Acid-fast positive oocysts

Answer

Flask-shaped ulcers upon colonoscopy

Question 5

An India ink preparation is performed on a cerebrospinal fluid (CSF) sample from an immunocompromised patient with suspected meningitis. This technique is used to visualize which feature for the presumptive identification of *Cryptococcus neoformans*?

Accepted Answer

The polysaccharide capsule

Answer

Germ tubes

Answer

Arthroconidia

Answer

Chlamydospores

Question 6

A gram-negative rod isolated from a urine culture grows as dry, pink colonies on MacConkey agar. The following biochemical test results are obtained:

Indole: Positive
Methyl Red: Positive
Voges-Proskauer: Negative
Citrate: Negative

What is the most probable identification of this organism?

Accepted Answer

Escherichia coli

Answer

Klebsiella pneumoniae

Answer

Proteus mirabilis

Answer

Pseudomonas aeruginosa

A Gram stain performed on a purulent aspirate from a skin abscess reveals gram-positive cocci arranged in grape-like clusters.Which of the following organisms is most likely responsible for the infection?

A Gram stain performed on a purulent aspirate from a skin abscess reveals gram-positive cocci arranged in grape-like clusters.
Which of the following organisms is most likely responsible for the infection?