Phenotypic diversity of enterotoxigenic Escherichia coli strains from a community-based study of pediatric diarrhea in Periurban Egypt

No past studies of diarrhea in children of the Middle East have examined in detail the phenotypes of enterotoxigenic Escherichia coli (ETEC) strains, which are important pathogens in this setting During a prospective study co nducted from November 1993 to September 1995 with 242 children under 3 year s of age with diarrhea living near Alexandria, Egypt, 125 episodes of diarr hea were positive for ETEC;ETEC strains were available for 98 of these epis odes, from which 100 ETEC strains were selected and characterized on the ba sis of enterotoxins, colonization factors (CFs), and O:H serotypes. Of thes e representative isolates, 57 produced heat-stable toxin (ST) only, 34 prod uced heat-labile toxin (LT) only, and 9 produced both LT and ST. Twenty-thr ee ETEC strains expressed a CF, with the specific factors being CF antigen TV (CFA/IV; 10 of 23; 43%), CFA/II (5 of 23; 22%), CFA/I (3 of 23; 13%), PC FO166 (3 of 23; 13%), and CS7(2 of 23; 9%). No ETEC strains appeared to exp ress CFA/III, CS17, or PCFO159. Among the 100 ETEC strains, 47 O groups and 20 H groups were represented, with 59 O:H serotypes. The most common O ser ogroups were O159 (13 strains) and O43 (10 strains). O148 and O21 were each detected in five individual strains, O7 and O56 were each detected in four individual strains, O73, O20, O86, and O114 were each detected in three in dividual strains, and O23, O78, O91, O103, O128, and O132 were each detecte d in two individual strains. The most common H serogroups were H4 (16 strai ns), 12 of which were of serogroup O159; H2 (9 strains), all of which were O43; H18 (6 strains); H30 (6 strains); and H28 (5 strains); strains of the last three H serogroups were all O148. Cumulatively, our results suggest a high degree of clonal diversity of disease-associated ETEC strains in this region. As a low percentage of these strains expressed a CF,it-remains poss ible that other adhesins for which we either did not assay or that are as y et undiscovered are prevalent in this region. Our findings point out some p otential barriers to effective immunization against ETEC diarrhea in this p opulation and emphasize the need to identify additional protective antigens commonly expressed by ETEC for inclusion in future vaccine candidates.