Classification of bacteria based on Oxygen requirement- Dr C R Meera

Based on requirement of oxygen for growth, bacteria can be classified into the following groups.

·       Obligate Aerobes: are strict aerobes. Can grow only in the presence of oxygen (21%). Eg. Mycobacterium tuberculosis, Pseudomonas aeroginosa

·       Obligate Anaerobes: are strict anaerobes. Grow only in the complete absence of oxygen. Oxygen presence is toxic and lethal to their growth. Eg: Clostridium perfringens, Clostridium boyulinum.

·       Aerotolerant Anaerobes: Some anaerobic bacteria can tolerate low levels of oxygen and are called nonstringent or aerotolerant anaerobes.  Oxygen is actually not required for their growth but not harmful if present. Eg: Propionibacterium acnes

·       Facultative anaerobes: They can grow well in both aerobic and anaerobic conditions. They do not require oxygen for growth, but may use it for energy production if available.  e.g., Enterobacteriaceae group, Staphylococcus aureus

·       Microaerophiles: Require low levels of oxygen for growth. They can neither tolerate normal levels of oxygen in air nor can live in complete oxygen absence. These groups of bacteria can grow under reduced oxygen (5% to 10%) and increased carbon dioxide (8% to 10%) concentration.  Eg: Campylobacter jejuni, Helicobacter pylori

             Their growth when inoculated into semisolid media is as shown in the diagram.