Lecture 15

Question 1

What is the Catalase Test, and which microorganisms test positive or negative?

Answer 1

The Catalase test is used to identify bacteria that produce the catalase enzyme, which breaks down hydrogen peroxide into water and oxygen. Bacteria that use oxygen for respiration typically produce catalase.

Procedure: A drop of 3% hydrogen peroxide is placed on a microscope slide. A colony from a bacterial agar culture is added to the slide.
Positive result: Bubbles of oxygen appear (catalase-positive).
Negative result: No bubbles appear (catalase-negative).

Question 2

What is an example of a catalase positive and negative

Answer 2

Catalase-positive: Staphylococci
Catalase-negative: Streptococci, Enterococci

Question 3

What is the Oxidase Test, and which microorganisms test positive or negative?

Answer 3

The Oxidase test determines whether a bacterium produces cytochrome c oxidase, an enzyme involved in aerobic respiration.

Procedure: The presence of cytochrome c oxidase oxidizes the reagent, leading to the formation of indophenols that turn purple. If the enzyme is absent, the reagent remains colorless.
Positive result: Purple color (oxidase-positive).
Negative result: No color change (oxidase-negative).

Question 4

What is an example of oxidase positive and negative

Answer 4

Oxidase-positive: Aeromonas, Pseudomonas
Oxidase-negative: Enterobacteriaceae