Characterization of necrotizing Escherichia coli strains isolated from diarrheic children in Brazil

Seventeen strains of Escherichia coli were isolated during etiologic studies of diarrheic children in Brazil. Culture supernatants of these strains induced morphological changes in Vero cells similar to the alterations elicited by the cytotoxic necrotizing factor (CNF). Since CNF is considered a cell associated toxin normally undetectable in culture supernatants, we undertook this study to further characterize these Escherichia coli isolates. The strains were assayed for the presence of CNF in culture supernatants and sonic extracts, necrotizing activity, haemolysin production, mannose resistant haemagglutination (MRHA), eel surface hydrophobicity and serogrouping. All the isolates caused necrosis in rabbit skin and typical CNF1-induced morphological changes that could be observed assaying both the sonic extracts and culture supernatants. Haemolysin and hydrophobicity was found in 76% and 54% of the strains, respectively. Haemagglutination tests with erythrocytes of 6 distinct species showed that all the strains belonged to MRHA type III or IVa. Serogrouping showed that most of the strains (14/17) belonged to serogroup O6, two to serogroup O14 and one to serogroup O4. To conclude, we have shown that NTEC strains can be isolated from children with diarrhea in Brazil. These isolates produce CNF1 detectable in both culture supernatants and cell extracts and possess characteristics very similar to those of NTEC strains isolated in Europe.