[Characteristics of E.coli O157 strains isolated in Poland from clinical material and food samples].

E. coli belonging to the O157 serological group are among the organisms isolated most frequently out of all the so called entero-hemorrhagic E. coli strains (EHEC). Since several years they have been isolated also in Poland. The purpose of the present study was determination on selected phenotypic and genotypic properties of E. coli O157 strains isolated in our country from clinical material samples and from food. The serotype of the strains was determined, together with the following properties regarded as pathogenicity markers of verotoxic E. coli strains such as absence of beta-glucuronidase activity and sorbitol fermentation ability, as well as production of verotoxins SLT I and/or SLT II and entero-hemolysin. Besides that, by the PCR method the fragments of the genes coding for verotoxins, intimin and enterohaemolysin were amplified. The products of PCR were analysed by the restriction enzyme analysis (RFLP). All verotoxic E. coli O157 strains isolated in Poland were analysed by the pulsed field gel electrophoresis of genomic DNA (PFGE). The studied group comprised E. coli O157 strains, among them 40 strains were isolated from human faeces and 5 from food. The remaining strains were the reference E. coli O157:H7 EDL 933 and G 5244 strains and strains from NIH collection. The obtained results showed that the tested strains were a very varying population. 21 of them (all isolated from food, 11 from faeces and 5 reference strains) belonged to serotype O157:H7, five were not peritrichous O157:NM and the remaining ones had other ciliary antigen than H7. All strains isolated from food, reference strains and only 3 O157:NM strains isolated from humans were verotoxic. The strains from food and two reference strains produced only SLT II, 2 of 3 strains isolated from humans and one reference strain also produced only SLT II and the other produced both verotoxins. Apart from these 13 verotoxic strains all remaining strains caused sorbitol fermentation.