Hemagglutination and colonization factors in enterotoxigenic and enteropathogenic Escherichia coli that cause diarrhea.

Controversy exists as to whether all strains of enterotoxigenic Escherichia coli must possess colonization factor antigen pili I or II (CFA/I, CFA/II) in order to be virulent for humans. Failure to detect CFA/I or CFA/II in enterotoxigenic strains from human diarrhea has been explained by some as due to plasmid loss and by others as evidence that CFA/I and CFA/II pili are not prerequisites for human virulence in all enterotoxigenic strains of E. coli. Seven enterotoxigenic and three enteropathogenic strains of E. coli that have been used in volunteer challenge studies were tested for CFA/I, CFA/II, and type 1 somatic pili after culture on solid agar and in broth. Six of the seven enterotoxigenic and two of the three enteropathogenic strains caused diarrhea in humans. Of these eight virulent strains, one produced CFA/I, and one had CFA/II. Threre remained four enterotoxigenic and two enteropathogenic strains that unequivocally caused diarrhea while lacking CFA/I or CFA/II. In such strains other organelles or surface properties must be operative to promote adhesion to and colonization of small intestinal mucosa. CFA/I and CFA/II are not prerequisites of virulence for all E. coli strains that cause diarrhea in humans.