CHARACTERISTICS OF ESCHERICHIA-COLI STRAINS BELONGING TO ENTEROPATHOGENIC ESCHERICHIA-COLI SEROGROUPS ISOLATED IN ITALY FROM CHILDREN WITH DIARRHEA

Fifty-five Escherichia coli strains belonging to enteropathogenic E. c oli (EPEC) serogroups were examined for phenotypic and genetic factors associated with virulence. The strains were isolated in Italy from ch ildren with diarrhea and identified as EPEC by clinical laboratories u sing commercially available antisera, O:H serotyping showed that 35 st rains (27 of O26, O111, and O128 serogroups) belonged to 11 serotypes considered to be classical EPEC O:H serotypes. The other 20 isolates w ere classified as 15 nonclassical EPEC O:H serotypes. All the potentia l EPEC virulence factors associated with bacterial adhesion (localized adherence, fluorescent-actin staining test positivity, presence of th e attaching and effacing [eaeA] gene), the production of verotoxin, an d the positivity with the enterohemorrhagic E. coli probe were signifi cantly more frequent among isolates belonging to classical than noncla ssical serotypes, Strains displaying an aggregative adhesion and hybri dizing with the enteroaggregative DNA probe were found in serogroups O 86, O111, and O126, Verotoxin-producing isolates belonged to serogroup s O26, O111, and O128, Only one of the isolates hybridized with the EP EC adherence factor (EAF) probe, but 33 strains gave positive results with the eae probe, confirming that the former is more suitable in epi demiological studies in European countries. These results indicate tha t up to 75% of strains identified as EPEC by commercial antisera may p ossess potential virulence properties and/or belong to classical EPEC O:H serotypes and suggest that O grouping is still a useful diagnostic tool for presumptive identification of diarrheagenic E. coli in clini cal laboratories.