Page 113 - MNUmicrobiology practical 2025

General Microbiology & Immunology (PM 401) second level Semester 4 2024/2025

• Mechanism/reactions: In organisms that use oxygen as the terminal electron acceptor

in the electron transport chain, cytochrome oxidase transfers electrons to the oxygen.

In the test, the Oxidase reagent acts as the electron acceptor when it is oxidized, it

forms the colored compound Wurster’s blue. Wurster’s blue is a purple compound

that is readily visible and signifies a positive reaction. A positive reaction will usually

occur within 10-15 seconds and will be a bluish-purple color that progressively

becomes more purple.

• Procedure
1. Pick a good-sized amount of inoculum

(already incubated and grown) from a plate

culture or slant culture and place it on a piece

of filter paper FIRST.

2. Add one drop of the reagent.

3. TIME the reaction: a positive reaction will

occur within 20 seconds.

5- Sugar fermentation test

• Purpose: To distinguish carbohydrate fermenters from non-fermenters, to detect

and distinguish utilization of specific carbohydrates by the products formed.

• Media used: 0.5% to 1% carbohydrate broth- Dextrose (glucose), Lactose, or

Sucrose, Peptone, with Phenol Red and an inverted Durham tube for detection of

gas.

• Reagents and/or indicators: Phenol Red

General Microbiology & Immunology (PM 401) Practical note Page 102