Competitive exclusion (CE) is the prophylactic treatment of young animals with suspensions of enteric bacteria obtained from healthy adults. It is a highly effective method of controlling gut colonization by Salmonella and other enteric pathogens, particularly when cultures are administered to animals shortly after birth while the ecology of the gastrointestinal (GI) tract is relatively naive. The mechanism by which CE cultures confer protection is not clearly understood but may involve one or more of the following factors: 1) blockage of potential attachment sites; 2) production of bacteriocins by endogenous bacterial species; 3) maintenance of gut pH by volatile fatty acids; and 4) competition for nutrients.
In many countries, the use of undefined mixed bacterial cultures for competitive exclusion is acceptable, but in the United States, the Food and Drug Administration (FDA) restricts the use of such cultures as undefined drugs. Use of continuous-culture technology (i.e., continuous-flow chemostats) has allowed for the selection, testing, and maintenance of defined CE cultures, and has led to the development of an efficacious CE culture, called CF3, for use in controlling Salmonella in poultry. Similar products are being developed for use in controlling Salmonella and enterotoxigenic E. coli in swine.
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