Virulence properties of atypical EPEC strains

Virulence properties of 31 atypical enteropathogenic Escherichia coli (EPEC ) strains isolated from cases of diarrhoea were examined. All except two st rains adhered to HEp-2 cells in a localised adherence-like (LAL) pattern. W ith the exception of two strains, all were fluorescent actin staining (FAS) positive. Gentamicin HEp-2 invasion assay studies showed that all strains were invasive, Transmission electron microscopy of infected HEp-2 cells sho wed the characteristic attaching and effacing lesion and invasion of the cu ltured cells. Of the nine strains that hybridised with a DNA probe for a-ha emolysin, five were haemolytic within 3 h of incubation, while the remainin g strains were haemolytic only after incubation for 24 h, Three strains pro duced enterohaemolysin on blood agar, None of the 31 strains of E. coli ind uced fluid accumulation in the rabbit intestinal loop assay or displayed cy totoxic effects in HeLa and Vero cells. All the strains belonging to seroty pes O26:H11, O26:H- and O119:H2 expressed intimin beta, whereas all the str ains from serotype O55:H7 expressed intimin gamma, The strains belonging to serogroup O111 expressed a non-typable intimin, The participation of intim in in LAL was supported by adhesion inhibition experiments in which antibod ies to intimin significantly reduced the level of LAL.