LAB 9 - Identifying Bacteria Through Enzyme Activity Testing

MICROBIOLOGY

Amylase

Enzyme that breaks down starch, detected by a clear zone on starch agar plate after iodine is added.

Protease

Enzyme that degrades casein protein, detected by a clear zone on skim milk plate.

Lipase

Enzyme that breaks down fats, detected by blue precipitation or depletion of fat droplets on spirit blue agar.

Tryptophanase

Enzyme that breaks down tryptophan into indole, detected by adding Kovac's reagent to tryptone broth.

Urease

Enzyme that breaks down urea, detected by a color change from yellow to bright pink on urea agar slant due to ammonia release.

Phenylalanine deaminase

Enzyme that breaks down phenylalanine, detected by a greenish precipitate after adding 10% ferric chloride to phenylalanine agar.

Kligler's Iron Agar

Medium containing 1.0% lactose, 0.1% glucose, and phenol red, used to detect glucose fermentation, lactose fermentation, and hydrogen sulfide production.

SIM

Semi-solid medium (0.7% agar) used to detect motility, hydrogen sulfide production, and tryptophan breakdown.

IMViC test

A series of four tests (Citrate, Indole, Methyl Red, Voges-Proskauer) used to differentiate E. coli from other gram-negative organisms.

Citrate

Part of the IMViC test, indicates the ability of an organism to utilize citrate as a carbon source.

Indole

Part of the IMViC test, indicates the ability of an organism to produce indole from tryptophan.

Methyl Red

Part of the IMViC test, indicates the ability of an organism to perform mixed acid fermentation.

Voges-Proskauer

Part of the IMViC test, indicates the ability of an organism to produce acetoin from glucose fermentation.

E. coli

A gram-negative organism that tests positive for indole and methyl red, and negative for citrate and Voges-Proskauer.

E. aerogenes

A gram-negative organism that tests negative for indole and methyl red, and positive for citrate and Voges-Proskauer.

Starch agar plate

Medium used to detect amylase activity by observing clear zones after iodine application.

Skim milk plate

Medium used to detect protease activity by observing clear zones due to casein degradation.

Spirit blue agar

Medium used to detect lipase activity by observing blue precipitation or depletion of fat droplets.

Tryptone broth

Medium used to detect tryptophanase activity by adding Kovac's reagent to observe indole production.

Urea agar slant

Medium used to detect urease activity by observing pH increase and color change due to ammonia release.

Phenylalanine agar

Medium used to detect phenylalanine deaminase activity by observing greenish precipitate after adding ferric chloride.