What Is an Anaerobic Infection?

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  • Written By: Jillian O Keeffe
  • Edited By: PJP Schroeder
  • Last Modified Date: 29 September 2019
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Anaerobic infections are illnesses caused by microbes that do not need oxygen to grow. They can cause abscesses, lung disease, gangrene, and other illnesses. Anaerobic bacteria naturally live on human skin and mucosal membranes, such as the mouth, intestine, and vagina. These usually harmless organisms may invade the body and cause disease if the skin or mucosal membranes are broken. Anaerobic microbes affect many parts of the body and can sometimes be fatal.

There are three types of anaerobic bacteria. An obligate anaerobe is completely intolerant of oxygen, a microaerophilic microbe can handle low levels of oxygen but prefers to grow without oxygen, and a facultative anaerobic grows equally well in the presence or absence of oxygen. Different types grow better in different conditions, but even obligate anaerobes can live for up to three days in an atmosphere containing oxygen.

Most often, an anaerobic infection is caused by a mixture of microbes and not just one species. Sometimes, aerobic bacteria, which need oxygen to live, also grow at the same infected site. Common causes of anaerobic infections include Bacteriodes, which causes abdominal infections; the Clostridium group, which can result in gangrene, botulism, or colitis; and Propionibacterium, which grows around medical devices in the body.


Some people are more likely to contract anaerobic infections, such those who have had surgery or trauma or those who have had a foreign object such as a shunt or a cardiac device inserted in the body. Someone with diabetes, colitis, or who is immunocompromised is also more at risk than the general public. For these reasons, hospital patients are more likely to become infected.

A doctor can recognize a likely anaerobic infection by the unpleasant gas produced by the bacteria. The infected area also commonly contains a lot of pus, and the tissue around the infection can have an abscess or appear to be dead. To confirm a patient has an anaerobic infection, the doctor sends a sample of the pus or other bodily fluids to the lab for testing. As anaerobes are commonly found on skin, special care must be taken to avoid sampling harmless anaerobic microbes that could be mistaken for the cause of infection.

The microbiological culture confirmation of a suspected anaerobic infection can take up to five days. A doctor may therefore place a patient straight onto an antibiotic regimen before the test results come back. Some anaerobic bacteria are resistant to penicillin, so other antibiotics must be used in those cases. He or she can also try to halt the spread of infection by draining the pus from the infection and debriding the infected area, which involves removing dead and infected cells.


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