Hostrelated susceptibility factors

By definition, anaerobic bacteria cannot survive in air. However it has now been proven that a large number of anaerobic bacteria can survive partial pressures of oxygen ranging from 15 to 60 mmHg, and even much more for some of them (Bacteroides fragilis)8-10.

The tissue redox potential is a better index than the oxygen pressure to assess the development capacity of anaerobic bacteria in tissue. The redox potential actually measures the aptitude of a tissue to produce electrons. It is usually expressed in millivolts. A normal redox potential is +120 mV and is the most important mechanism to fight anaerobic bacteria infection7,14,19. If the redox potential is reduced, bacteria develop even if the pressure of oxygen in the tissue is around the normal range. Circumstances reducing the redox potential include: ischemia, tissue necrosis, development of associated aerobic bacteria.

Many other conditions or circumstances encourage the development of anaerobic infections: vascular disease (vascular atheromata, diabetic micro-angiopathy, vasculitis, etc.); vasoconstrictor drugs, cold and shock; trauma and surgery; haematoma and compressive oedema; foreign bodies; aerobic bacteria; and neoplastic proliferation. It is well known that anaerobic infection can develop jointly with cancer - it is not unusual for C. septicum infections to be the revealing sign of a cancer (rectocolon cancer in particular).

Lastly, some general systemic factors can encourage anaerobic infections: malnutrition, alcoholism, immunosuppressive treatments, granulocytopenia, etc.

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