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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. Which staining technique differentiates bacteria based on cell wall peptidoglycan thickness?

    Answer: Gram stain

    The Gram stain exploits differences in peptidoglycan layer thickness: thick walls in Gram-positive bacteria retain crystal violet, while Gram-negative bacteria decolorize and take up safranin.

  2. A culture plate shows hemolysis where red blood cells are completely lysed, leaving a clear zone around colonies. This is classified as:

    Answer: Beta hemolysis

    Beta hemolysis indicates complete lysis of red blood cells, producing a clear, transparent zone around the colony on blood agar.

  3. Which organism is responsible for causing tuberculosis?

    Answer: Mycobacterium tuberculosis

    Mycobacterium tuberculosis is the causative agent of tuberculosis and is identified by its acid-fast staining property due to mycolic acids in its cell wall.

  4. What is the purpose of a Mueller-Hinton agar plate in microbiology?

    Answer: Performing antimicrobial susceptibility testing

    Mueller-Hinton agar is the standard medium used for disk diffusion (Kirby-Bauer) antimicrobial susceptibility testing per CLSI guidelines.

  5. Which component of a bacterial cell is the primary target of penicillin?

    Answer: Cell wall peptidoglycan synthesis

    Penicillin inhibits transpeptidase enzymes involved in cross-linking peptidoglycan strands during cell wall synthesis, causing cell lysis.

  6. A urine culture grows >100,000 CFU/mL of a single organism. This finding is most consistent with:

    Answer: Significant bacteriuria

    A colony count of ≥100,000 CFU/mL of a single organism in a clean-catch midstream urine sample is the threshold for significant bacteriuria indicating a urinary tract infection.

  7. Which media is selective and differential for isolation of Salmonella and Shigella from stool specimens?

    Answer: SS (Salmonella-Shigella) agar

    SS agar is both selective (inhibits most normal flora with bile salts and brilliant green) and differential (non-lactose fermenters appear colorless) for enteric pathogens Salmonella and Shigella.