AP-Micro Microbiology: Bacteriology: Gram-Negative Identification 2

Question 1

Which enzyme produced by Neisseria gonorrhoeae helps it evade complement-mediated killing?

Accepted Answer

IgA protease

Answer

N. gonorrhoeae secretes IgA protease, which cleaves secretory IgA and also helps evade host mucosal immunity and complement.

Question 2

Which gram-negative rod is the most common cause of nosocomial urinary tract infections?

Accepted Answer

Escherichia coli

Answer

E. coli accounts for approximately 80% of community-acquired and 50%+ of nosocomial urinary tract infections.

Question 3

A gram-negative, oxidase-positive, non-fermenting rod growing at 42°C with a fruity odor is most likely:

Accepted Answer

Pseudomonas aeruginosa

Answer

Pseudomonas aeruginosa is oxidase-positive, non-fermenting, grows at 42°C, and produces pyocyanin and a characteristic grape-like odor.

Question 4

The Voges-Proskauer (VP) test detects which end-product of glucose fermentation?

Accepted Answer

Acetoin

Answer

The VP test detects acetoin (acetylmethylcarbinol), an intermediate in the butanediol fermentation pathway.

Question 5

Which gram-negative organism characteristically produces a green metallic sheen on EMB agar?

Accepted Answer

Escherichia coli

Answer

Strong acid fermenters like E. coli produce a metallic green sheen on Eosin Methylene Blue (EMB) agar due to dye precipitation.

AP Practice Test