Classification of pathogenic Escherichia coli according to serotype and the production of virulence factors, with special reference to colonization-factor antigens.

Multiple criteria are required to classify Escherichia coli isolates according to pathogenic grouping. There are three groups associated with intestinal illness. Acute watery diarrhea is the hallmark of enterotoxigenic E. coli, the majority of which belong to a small set of specific serotypes harboring plasmids encoding for the production of heat-stable enterotoxin and/or heat-labile enterotoxin and also for a fimbrial colonization-factor antigen. Bacterial dysentery is caused by specific, nonmotile Shigella-like E. coli serogroups identifiable by the property of tissue invasiveness. Specific virulence factors have not been defined for the traditional enteropathogenic E. coli serogroups, although the ability to colonize and overgrow the intestine appears to be of primary importance in this group. E. coli associated with extraintestinal infections generally belong to serogroups and serotypes other than those noted above; the virulence factors of these E. coli include polysaccharide capsular antigens, hemolysin, and fimbrial colonization factors that are antigenically complex and different from those of the enterotoxigenic E. coli.