Page 58 - MNU microbiology theoritical 2025

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

According to their tolerance for acidity or alkalinity bacteria are
classified as:

1- Acidophiles “acid-loving”

• Acidity inhibits most microbial growth and is used
frequently for food preservation (e.g: pickling).

• Acidophilic organisms grow best at a pH of 0.1 - 5.4.

• Example

➢ Molds and yeast prefer pH between 5 and 6.

➢ Lactobacillus spp, (produces lactic acid)

2- Neutrophiles

• Most bacteria prefer neutral pH (6.5-7.5).

• Most bacteria that cause disease are in this class.

3- Alkaliphiles or “alkali-loving”

• Alkalinity inhibits microbial growth, but not commonly used for food

preservation.

• Organisms grow best at pH range 8-12.

Examples: Vibrio cholerae, grows best

at pH 9.0.

General Microbiology & Immunology (PM 401) theoretical handbook Page 47