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Microbiology Basics Flashcards

7 cards from real CMLA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. The catalase test differentiates which two groups of Gram-positive cocci?

    Answer: Staphylococcus vs. Streptococcus

    Staphylococci are catalase-positive (produce bubbles with hydrogen peroxide) while Streptococci are catalase-negative, making this the first key differentiation test.

  2. Which of the following viruses requires a helper virus to replicate?

    Answer: Hepatitis D virus

    Hepatitis D virus (delta agent) is a defective RNA virus that requires the surface antigen of Hepatitis B virus (HBsAg) for its own replication and packaging.

  3. A wet mount preparation showing motile, pear-shaped organisms with two nuclei is most consistent with:

    Answer: Giardia lamblia

    Giardia lamblia trophozoites appear pear-shaped with bilateral symmetry, two nuclei, and characteristic tumbling motility on wet mount preparations.

  4. Which sterilization method is most appropriate for heat-sensitive items such as plastic tubing?

    Answer: Ethylene oxide gas

    Ethylene oxide (EO) gas sterilizes at low temperatures, making it ideal for heat-sensitive materials like plastics, rubber, and electronic devices.

  5. When performing a Gram stain, what is the correct sequence of reagents?

    Answer: Crystal violet → iodine → decolorizer → safranin

    The correct Gram stain sequence is: crystal violet (primary stain), Gram's iodine (mordant), alcohol/acetone (decolorizer), then safranin (counterstain).

  6. Which laboratory safety level (BSL) is required for working with Mycobacterium tuberculosis?

    Answer: BSL-3

    Mycobacterium tuberculosis requires BSL-3 containment, which includes respiratory protection (N95 respirators), negative-pressure rooms, and HEPA filtration due to airborne transmission risk.

  7. What term describes bacteria that grow best at oxygen concentrations lower than atmospheric but not completely anaerobic conditions?

    Answer: Microaerophiles

    Microaerophiles require oxygen for growth but at concentrations (typically 2–10%) lower than atmospheric (21%), such as Campylobacter and Helicobacter pylori.