Re: How can anaerobic bacteria live in the oral cavity and respiratory tract ?

Anaerobic bacteria do not grow (and may or may not die) in the presence of oxygen. The presence of oxygen in a micro environment can be measured by what is called the redox potential. It is common to find microorganisms living together in small micro environments in nature. Within these communities some microorganism members utilize oxygen while others do not. This is called symbiotic relationships. The anaerobic bacteria grow only when the REDOX falls below a set potential or in other words the other organisms have used all or most of the oxygen present in the microenvironment. In some cases, such as in tissue, there is an injury or bruise and the blood flow is restricted reducing the oxygen concentration. A good example of this is a deep puncture wound. This area may become infected with a variety or microorganisms which quickly use up all of the oxygen. Then, many of the microorganisms switch their metabolism to anaerobic. These organisms are sometimes called facultatively anaerobic (meaning sometimes) as compared to obligately (meaning all the time) aerobic (requiring oxygen) or anaerobic (requiring no oxygen). Also, the true anaerobic (obligately anaerobic) bacteria begin to reproduce. An example is Clostridium tetani (causative agent of Tetanus) or Clostridium perfringens (one of the causative agents in gangrene). Reference Dr. Richter