VIRULENCE DETERMINANTS IN NONTOXINOGENIC ESCHERICHIA-COLI 0157 STRAINS THAT CAUSE INFANTILE DIARRHEA

Ten sorbitol-fermenting Escherichia coli O157 strains that cause infan tile diarrhea and are positive in the fluorescence actin staining test were determined to be negative for Shiga-like toxin (SLT) genes. We a mplified their complete eae genes, contrasting them with those of SLT- producing E. coli O157 by restriction fragment length polymorphism ana lysis and nucleotide sequence analysis of a 400-bp stretch of the 3' e nd of eae. The data substantiated the presence of two eae genotypes wi thin serogroup O157, one resembling eae of enteropathogenic E. coli (E PEC) strain E2348/69, found in nontoxinogenic E. coli O157 strains, an d the other resembling eae of EHEC strain EDL 933, found in toxinogeni c E. coli O157 strains. Another EPEC-specific virulence determinant wa s also shown to be large plasmids harboring EPEC adherence factor sequ ences. The SLT-negative E. coli O157 strains described here fall under the heading of EPEC, which serves as an explanation for their virulen ce in infants, and represent a third pathogroup within serogroup O157.