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Bacterial Classification Flashcards

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  1. The CAMP test is used to presumptively identify which organism based on enhanced hemolysis near Staphylococcus aureus?

    Answer: Listeria monocytogenes and Streptococcus agalactiae

    Both Streptococcus agalactiae (Group B Strep) and Listeria monocytogenes produce a positive CAMP reaction with S. aureus.

  2. Which characteristic defines bacteria in the phylum Firmicutes?

    Answer: Low G+C content Gram-positive cell wall

    Firmicutes are Gram-positive bacteria with low G+C content in their DNA, including Staphylococcus, Streptococcus, and Clostridium.

  3. A bacterium requires a NaCl concentration of at least 10% to grow. This organism would be classified as a:

    Answer: Halophile

    Halophiles require high salt concentrations for growth, with extreme halophiles needing 15–30% NaCl.

  4. Which of the following best explains why Mycoplasma species cannot be Gram-stained effectively?

    Answer: They lack a cell wall entirely

    Mycoplasma species have no cell wall, so the Gram stain procedure, which relies on cell wall retention of crystal violet, cannot classify them.

  5. The oxidase test detects the presence of cytochrome c oxidase and is used to differentiate:

    Answer: Pseudomonas (oxidase+) from Enterobacteriaceae (oxidase−)

    Members of Enterobacteriaceae are oxidase-negative, while Pseudomonas and Neisseria are oxidase-positive.

  6. Alphaproteobacteria include organisms notable for their evolutionary relationship to mitochondria. Which free-living genus is most closely related to the mitochondrial ancestor?

    Answer: Rickettsia

    Rickettsia species are obligate intracellular Alphaproteobacteria most closely related to the ancestral mitochondrial endosymbiont.

  7. Which of the following describes the zoonotic classification of Brucella species?

    Answer: Zoonotic Gram-negative coccobacilli acquired from infected animals

    Brucella are Gram-negative coccobacilli that infect animals (cattle, goats, pigs) and cause brucellosis in humans through contact with infected animals or products.