Heterogeneous virulence of enteroaggregative Escherichia coli strains isolated from children in southwest Nigeria

Enteroaggregative Escherichia coli (EAEC) has been implicated in acute and persistent diarrhea, and most strains harbor a member of a partially-conser ved plasmid family (called pAA). We studied EAEC isolated from Nigerian chi ldren aged <5 years to elucidate the roles of plasmid and chromosomal EAEC loci. We tested a total of 131 EAEC strains isolated from acute diarrhea ca se patients and control subjects for hybridization with 8 pAA plasmid-deriv ed and 2 chromosomal gene probes, for several in vitro phenotypes and for r esistance to antimicrobial agents. Using by multiple logistic regression, w e found genes encoding the AAF/II fimbriae to be strongly associated with d iarrhea in this population. EAEC strains appear to be of heterogeneous viru lence, and data suggest that AAF/II may be a marker for pathogenic strains.