Quiz 2

Slide 1: Kirby-Bauer Test

Purpose: To determine the susceptibility of bacteria to antibiotics (antimicrobial sensitivity testing).

Inoculation:

  • Spread a bacterial lawn on a Mueller-Hinton agar plate.

  • Place antibiotic-impregnated discs on the agar.

Reading Results:

  • Measure the zone of inhibition (clear area around discs).

  • Compare zone sizes to a standard chart to determine susceptibility (resistant, intermediate, or sensitive).

Slide 2: IMViC Tests Overview

Purpose: A series of tests to differentiate Enterobacteriaceae species (e.g., E. coli vs. Enterobacter).

Tests:

  1. Indole Test:

    • Inoculation: Grow bacteria in tryptone broth.

    • Reagents: Add Kovac’s reagent after incubation.

    • Result: Red layer = positive; no color change = negative.

  2. Methyl Red (MR) Test:

    • Inoculation: Grow bacteria in MR-VP broth.

    • Reagents: Add methyl red.

    • Result: Red = positive (acidic fermentation); yellow = negative.

  3. Voges-Proskauer (VP) Test:

    • Inoculation: Use MR-VP broth.

    • Reagents: Add alpha-naphthol and KOH.

    • Result: Red = positive (acetoin production); no change = negative.

  4. Citrate Test:

    • Inoculation: Streak and stab Simmons citrate agar.

    • Result: Blue = positive (citrate used); green = negative.

Slide 3: TSIA (Triple Sugar Iron Agar) Test

Purpose: To determine sugar fermentation, gas production, and hydrogen sulfide (H₂S) production in gram-negative bacteria.

Inoculation:

  • Stab the butt and streak the slant of a TSIA tube.

Reading Results:

  • Color Changes:

    • Yellow slant/butt = glucose and lactose/sucrose fermentation.

    • Yellow butt/red slant = glucose fermentation only.

    • Red slant/butt = no fermentation.

  • Gas Production: Cracks or bubbles in the agar.

  • H₂S Production: Black precipitate in the butt.

Slide 4: SIM (Sulfide, Indole, Motility) Test

Purpose: To test for H₂S production, indole production, and bacterial motility.

Inoculation:

  • Stab inoculate the SIM medium.

Reading Results:

  1. H₂S Production:

    • Black precipitate = positive.

    • No precipitate = negative.

  2. Indole Test:

    • Add Kovac’s reagent.

    • Red layer = positive; no color change = negative.

  3. Motility:

    • Diffuse growth radiating from the stab line = positive.

    • Growth confined to the stab line = negative.