Secondary Assays for Bacterial Characterization

Vocabulary flashcards covering bacterial secondary characterization assays, including the Indole, TSI, and API tests.

Indole test

A biochemical test used to determine a bacterial species' ability to convert or break down tryptophan into indole.

Indole

A compound that regulates bacterial physiology, including spore formation, plasmid stability, and drug resistance.

COVAX reagent

A chemical reagent added (about five drops) to an overnight liquid culture to detect indole production, forming a bright or subtle pink band at the top of an indole-positive culture.

TSI test

The Triple Sugar Iron test, which utilizes agar slants with a pH indicator to assess bacterial sugar fermentation (glucose, lactose, sucrose) and hydrogen sulfide gas production.

Enteric bacteria

Gram-negative bacteria residing in the intestines or gut, such as Salmonella and Shigella, commonly identified using TSI slants.

Hydrogen sulfide gas ($H_2S$)

A gas produced by certain bacteria during sugar breakdown in a TSI slant, indicated by a dark black color change in the agar.

API test

The Analytical Profile Index test, a broad multi-panel test strip containing 20 test wells/capsules used for rapid biochemical characterization of bacterial species.

Mineral oil (API test)

A layer added to specific API test wells (ADH, LDC, ODC, H2S, and URE) to seal out oxygen and establish an anaerobic environment.

API index number

A seven-digit code derived from numerical values assigned to positive reactions across the 20 API wells, which is used with a key to identify exact bacterial species.

Escherichia coli (E. coli)

A gram-negative bacterium that tests positive for indole production and ferments all three sugars in a TSI slant with non-$H_2S$ gas production.

Salmonella

A gram-negative enteric bacterium that tests negative for indole production and produces hydrogen sulfide gas in a TSI slant.

Pseudomonas

A gram-negative bacterium that tests negative for indole production when treated with COVAX reagent.