Microbiology Flashcards

An oxidase-positive, non-lactose-fermenting gram-negative rod produces a blue-green pigment and a grape-like odor. What is the most likely identification?

Answer: Pseudomonas aeruginosa

P. aeruginosa produces pyocyanin and has a characteristic fruity grape odor.

A small gram-negative coccobacillus grows on chocolate agar but only around an X and V factor strip on a nutrient agar plate. What is the organism?

Answer: Haemophilus influenzae

H. influenzae requires both hemin (X) and NAD (V) factors.

A gram-negative diplococcus from a urethral discharge is oxidase positive and produces acid from glucose only. What is the likely identification?

Answer: Neisseria gonorrhoeae

N. gonorrhoeae oxidizes glucose only, while N. meningitidis uses glucose and maltose.

A lactose-negative Enterobacterales isolate swarms on blood agar and is H2S positive, urease positive, and indole negative. Which organism is it?

Answer: Proteus mirabilis

P. mirabilis swarms, is H2S and urease positive, and is indole negative, unlike P. vulgaris.

On Hektoen enteric agar, which colony appearance suggests Salmonella rather than Shigella?

Answer: Green colonies with black centers

Salmonella produces H2S, giving black centers, while Shigella is H2S negative.

A curved gram-negative rod from stool grows at 42°C under microaerophilic conditions and is hippurate hydrolysis positive. What is it?

Answer: Campylobacter jejuni

C. jejuni is thermophilic, microaerophilic, and the hippurate-positive Campylobacter.

Which medium is recommended for culturing Bordetella pertussis from a nasopharyngeal swab?

Answer: Regan-Lowe agar

Regan-Lowe (charcoal-horse blood with cephalexin) supports B. pertussis growth.