Animals as a source of Escherichia coli pathogenic for human beings

Symptoms of SLT E coli-induced enteric disease in human beings include watery diarrhea, hemorrhagic diarrhea, and, in some cases, HUS. The most frequent serotype associated with HUS is O157:H7, although several other serotypes have also been implicated. These organisms produce SLT-I, SLT-II, or both toxins. Factors other than SLT are implicated as virulence attributes, such as adhesins and enterohemolysins, but roles for these factors in the pathogenicity of these organisms have not been defined. Colonization mechanisms for enterohemorrhagic E coli have not been defined, nor is there a defined set of characteristics by which enterohemorrhagic E coli pathogenic for human beings can be identified. Because virulence attributes are ill-defined, experimental animal models are useful in studies of pathogenicity. Gnotobiotic pigs, infant rabbits, streptomycin-treated mice, and one-day-old chickens have been used. Although the epidemiologic evidence implicating cattle as a source of zoonotic SLT E coli is strong, there is a paucity of direct evidence documenting this relationship. Until we have a better set of criteria with which to identify SLT E coli that are human pathogens, we are probably limited to epidemiologic criteria. Cattle excrete a variety of SLT E coli that includes many serotypes, in addition to O157:H7, that have been associated with disease in human beings. Surveys of the incidence of O157:H7 indicate a low incidence of these organisms in healthy cattle. However, much of these data have been derived from surveys of clinically normal cattle in daries.(ABSTRACT TRUNCATED AT 250 WORDS)