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Unformatted text preview: RELATIONSHIPS BETWEEN THE NORMAL MICROBIOTA AND THE HOST Normal flora organisms are desirable because they can prevent the growth of large numbers of pathogens. This is called microbial antagonism and is mainly due to competition among microbes. If pathogens come along, normal flora may affect them in several ways: 1. Compete for nutrients 2. Produce substances harmful to the pathogens 3. Influence pH or oxygen levels in a way harmful to the pathogens When the balance is upset, pathogens which arrive or which have already been present but in numbers too small to cause disease take the opportunity to multiply. An example of this is the diarrhea or yeast infections often associated with taking antibiotics. The antibiotics may have a greater effect on the normal flora organisms than on the pathogens, thus upsetting the balance. In the mouth, streptococci (not the species that causes strep throat, but others) produce...
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- Fall '09