The enteropathogenic role of cytotoxic necrotizing factor (CNF)-producing Escherichia coli
was investigated by searching cnf genes among 2074 isolates from 200 children with and 200 without acute diarrhea in Brazil. Fourteen (7%) cases versus 10 (5%) control children carried at least one cnf positive isolate (P
= 0.50) and most isolates expressed CNF type 1. DNA sequences of virulence factors of extraintestinal pathogenic E. coli
(ExPEC) were detected in 78.6% of CNF1-producing isolates. Besides not being associated with human acute diarrhea, the CNF1-producing isolates here identified may represent potential ExPEC transitorily composing the normal intestinal flora.