Serotypes and virulence factors of Shiga toxin-producing Escherichia coli isolated from healthy Norwegian sheep.

Aims: To characterize a number of Shiga toxin-producing Escherichia coli (STEC) isolates from sheep and to discuss the potential of these isolates as human pathogens. Methods and Results: Twelve different O-groups and seven different H-types were identified by standard serotyping methods. The most common serotypes were O5:NM, O6:H10, O91:NM and O128:NM. Polymerase chain reaction (PCR) was used for the detection of virulence factor genes. Of 102 isolates, 86·3% carried stx ₁ and 83% of these were also positive in the stx _1OX3 -specific PCR. stx ₂ was carried by 55·9% of the isolates and 77·2% of these were also positive in the stx _2d -specific PCR. The Vero cell assay showed high toxin production in 70·6% of the isolates. None of the isolates carried eae . Conclusions: The study supports the animal–host relationship suggested in other studies with STEC serogroups O5, O91 and O128 strongly associated with sheep. Most sheep STEC carry stx _1OX3 (except O91) and the dominating stx ₂ variant is stx _2d . One stx profile clearly dominates within a serotype. Significance and Impact of the Study: In spite of the predominance of certain sheep-associated STEC, sheep cannot be excluded as carriers of human pathogenic STEC. [ABSTRACT FROM AUTHOR]