Diarrheagenic Escherichia coli and Virulence Determinants

Escherichia coli is normally the most common facultative anaerobe in the large bowel and usually nonpathogenic for man. However, some E. coli strains which cause distinct syndromes of diarrhea diseases have been proved to be pathogenic. These organisms are one of the most common causes of food poisoning in Japan. In developing countries, these pathogens are known to be main causative agents of diarrhea which is the major cause of infantile morbidity and mortality. These E. coli strains are divided into four groups: enteropathogenic E. coli (EPEC), enter-oinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC), and enterohemorrhagic E. coli (EHEC). The four groups are distinguished on the basis of pathogenic, clinical, and epidemiologic features. Moreover, the fifth group of diarrheagenic E. coli, termed enteroaggregative E. coli (EAggEC), has been recently proposed. The strains of EAggEC exhibit characteristic patterns of adherence when bound to cultured epithelial cells. But the epidemiologic significance of EAggEC as diarrheal pathogens has not been yet determined. Although the features of the four groups are different, they have certain underlying commonalities with respect to pathogenesis as follows. (1) Critically virulent properties are encoded in plasmids. (2) Characteristic interactions with intestinal mucosa occurred. (3) Enterotoxins or cytotoxins are produced. In this review, microbiological features and etiological significances of these strains, are described.