Page 115 - MNUmicrobiology practical 2025

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

sulfanilic acid to form a complex i.e. nitrite-sulfanilic acid which then reacts with

an α-naphthylamine to give a red precipitate

• Result and Interpretation

1. Nitrate Reduction Positive: (Red after sulfanilic acid + alpha-naphthylamine; no
color after zinc)

2. Negative Nitrate Reduction: (No color after sulfanilic acid + alpha-naphthylamine)

7- Ammonia production

Objective: to test the ability of the organism to degrade the organic nitrogen in the

protein into ammonia.

Procedure:

• Incubate tube of 4% peptone water with organism

• Incubate at 37 c for 2, 4, 7 days

• Add nesseler’s reagent.

• Appearance of yellow, orange or brown color

indicate positive test.

8- Gelatin hydrolysis

• Purpose: To determine the production of gelatinase.

• Media: Nutrient Gelatin Deep (12- 15% gelatin)

• Mechanism/reactions: Gelatinase causes the breakdown and liquefaction of

gelatin→polypeptides→amino acids.

General Microbiology & Immunology (PM 401) Practical note Page 104