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Microbiology: Bacteriology: Gram-Negative Identification Flashcards

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Read the first 7 Microbiology: Bacteriology: Gram-Negative Identification flashcards as text

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

    Answer: Bartonella henselae

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

  2. On MacConkey agar, Salmonella colonies appear:

    Answer: Colorless (non-lactose fermenter)

    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.

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

    Answer: Polysaccharide capsule

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

  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?

    Answer: Haemophilus influenzae in satellite phenomenon

    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.

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

    Answer: Vibrio cholerae

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

  6. A curved, gram-negative rod with a single polar flagellum isolated from a patient with bloody diarrhea after eating undercooked chicken is most likely:

    Answer: Campylobacter jejuni

    Campylobacter jejuni is the most common bacterial cause of foodborne diarrhea in the US, transmitted via undercooked poultry, and is curved/comma-shaped.

  7. Which identification test differentiates Neisseria meningitidis from Neisseria gonorrhoeae?

    Answer: Maltose fermentation

    N. meningitidis ferments both glucose and maltose, while N. gonorrhoeae ferments only glucose; this maltose fermentation test is the key differentiator.