Colonization factor antigens I and II and type 1 somatic pili in enterotoxigenic Escherichia coli: relation to enterotoxin type

Abstract

Enterotoxigenic E. coli (ETEC) isolates from 36 persons with acute traveler''s diarrhea from whom no other pathogens were recovered were tested (after no more than 3 subcultures) for the presence of colonization factor antigens I and II (CFA/I and CFA/II) and type 1 somatic pili. CFA/I or CFA/II was identified in 7 of 10 strains with heat-labile and heat-stable enterotoxins (LT+/ST+), but in only 2 of 12 LT-/ST+ (P < 0.05) and 0 of 14 LT+/ST- (P < 0.02) strains. CFA pili were not found among 74 nonenterotoxigenic E. coli strains. Type 1 somatic pili were demonstrable in 42% of the 36 ETEC and in 49% of the 74 nonenterotoxigenic E. coli isolates. The 9 ETEC isolates bearing a CFA were serially subcultured on 10 consecutive days and retested for CFA and toxin. After 5 subcultures only 1 strain had lost a CFA; after 10 passages 3 strains were negative; 2 lost CFA/I and 1 lost CFA/II. The strain that lost CFA/II became negative for both LT and ST and lacked 48 and 60 megadalton plasmids. The 2 strains that lost CFA/I became negative for ST; plasmid analysis revealed no plasmid loss. Disappearance of the CFA/I phenotype without loss of a plasmid can be explained by phase variation, as exhibited by type 1 somatic pili, or by rearrangement of base sequences in the CFA/I plasmid genome. If purified pili vaccines are to provide broad-spectrum protection against ETEC diarrhea, the search must be intensified to identify the antigens responsible for adhesion to intestinal mucosa in the many ETEC strains that lack CFA/I and CFA/II.