Lab 14 - Multiple Test Media Flashcards

Multiple Test Media

• Multiple test media contains more than one substrate and indicator, allowing for the observation of multiple reactions in a single test.

Triple Sugar Iron (TSI) Agar

• Tests the bacterium's ability to utilize glucose, sucrose, and lactose.

• Indicator: Phenol red (yellow indicates acid production from sugar utilization).

• Detects cysteine desulfurase activity, indicated by hydrogen sulfide (H2S) production.

• Indicator: Iron (black precipitate indicates H2S production).

• Inoculation: Stab the bottom of the tube and streak the slant.

• Key Abbreviations:

  • K: Alkaline

  • A: Acid

  • G: Gas production

  • S: Hydrogen sulfide production

• Interpretation:

  • Butt (bottom of the tube) and slant (top of the tube) colors are evaluated.

  • Yellow butt: Glucose utilization.

  • Yellow slant: Sucrose and/or lactose utilization.

  • Black butt: Hydrogen sulfide production.

  • Red slant and butt: Negative for glucose, lactose, and sucrose utilization.

  • Gas production is indicated by air bubbles or cracks in the media; if gas is present, glucose HAD to have been utilized.

Sulfur Indole Motility (SIM) Agar

• Tests for:

  • Cysteine desulfurase activity (hydrogen sulfide production).

    • Indicator: Iron (blackening of the media).

  • Tryptophanase activity (indole production).

    • Detected using Kovac's reagent (pink color indicates a positive result).

  • Motility (presence of flagella).

• Inoculation: Stab down to the center of the tube.

• Interpretation:

  • Sulfur reduction: Blackening of the media indicates H2S production.

  • Indole production: Add Kovac's reagent; pink color indicates indole production.

  • Motility: Growth spreading away from the stab line indicates motility.