AP-Micro Microbiology: Bacteriology: Gram-Negative Identification 3

Question 1

Which gram-negative organism is the causative agent of cat-scratch disease?

Accepted Answer

Bartonella henselae

Answer

Bartonella henselae, transmitted via cat scratches or flea feces, causes cat-scratch disease presenting with regional lymphadenopathy.

Question 2

On MacConkey agar, Salmonella colonies appear:

Accepted Answer

Colorless (non-lactose fermenter)

Answer

Salmonella is a non-lactose fermenter and appears colorless/transparent on MacConkey agar because it does not lower the pH to trigger the neutral red indicator.

Question 3

Which feature of Klebsiella pneumoniae is responsible for its mucoid colony appearance?

Accepted Answer

Polysaccharide capsule

Answer

Klebsiella pneumoniae produces a thick polysaccharide capsule that gives colonies a mucoid, string-test-positive appearance.

Question 4

The CAMP test is used to identify Listeria monocytogenes, but which gram-negative organism uses a similar beta-hemolysin enhancement mechanism in its own identification?

Accepted Answer

Haemophilus influenzae in satellite phenomenon

Answer

The satellite phenomenon uses beta-hemolysin from S. aureus to provide factor V (NAD) that supports H. influenzae growth around the streak, analogous to CAMP enhancement.

Question 5

Which gram-negative pathogen is most associated with waterborne outbreaks and produces a cholera toxin that activates adenylyl cyclase?

Accepted Answer

Vibrio cholerae

Answer

Vibrio cholerae produces cholera toxin (CT), which ADP-ribosylates Gs protein, permanently activating adenylyl cyclase and causing massive secretory diarrhea.

AP Practice Test

AP Practice Test

AP-Micro Microbiology: Bacteriology: Gram-Negative Identification 3