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What is currently known about the molecular mechanisms of colonisation resistance.

Anaerobes are the main bacteria which inhabit the digestive tract. They have adapted their development to many environmental factors such as host secretions, corresponding to control mechanisms which allow a relative stability of microflora in healthy humans. These control mechanisms include the control of endogenous and exogenous bacterial populations which corresponds to bacterial antagonism occurring in the digestive tract of mammals and represents one of its main functions. The main antagonism to study is colonisation resistance since this function of the gut microflora is responsible for the prevention of many intestinal diseases. However, only a few things are currently known about this function and the main questions which need attention are: (1) which bacteria are responsible for colonisation resistance? and (2) what are the molecular mechanisms involved in such a function? In order to answer these questions, we need to study simplified models based on gnotobiotic animals. Two models are currently being studied in France. One corresponds to the colonisation resistance of C. perfringens which seems to be linked to the in vivo secretions of an antimicrobial substance by a Ruminococcus species. The other corresponds to the colonisation resistance of C. difficile whose mechanisms are different and seem to be linked to an interaction between mucin and microflora.