Page 56 - MNU microbiology theoritical 2025

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

2- Facultative anaerobes

• Growth of microorganism is best near the surface, where oxygen is
available, but occurs throughout the tube.

• e.g most bacteria fall into this group as E. coli

3- Obligate anaerobes

• Oxygen is toxic to microorganisms, and there is no growth near the

surface.

• e.g Clostridium sp

4- Aerotolerant anaerobes
• Growth of microorganism occurs evenly throughout the tube but is

not better at the surface because the organisms do not use oxygen.

• e.g Streptococcus pyogenes

5- Microaerophiles
• They are aerobic organisms that do not tolerate atmospheric

concentrations of oxygen- growth occurs only in a narrow band of

optimal oxygen concentration.

• e.g Spirillum volutans

General Microbiology & Immunology (PM 401) theoretical handbook Page 45