Serotypes, Virulence Genes, and Intimin Types ofShiga Toxin (Verotoxin)-ProducingEscherichia coliIsolatesfrom Cattle in Spain and Identification of a New Intimin VariantGene(eae-ξ)

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Abstract
A total of 514 Shiga toxin-producingEscherichia coli(STEC) isolates from diarrheic and healthy cattle in Spain were characterized in this study. PCR showed that 101 (20%) isolates carriedstx1genes, 278 (54%) possessedstx2genes, and 135 (26%) possessed bothstx1andstx2. Enterohemolysin (ehxA) and intimin (eae) virulence genes were detected in 326 (63%) and in 151 (29%) of the isolates, respectively. STEC isolates belonged to 66 O serogroups and 113 O:H serotypes (including 23 new serotypes). However, 67% were of one of these 15 serogroups (O2, O4, O8, O20, O22, O26, O77, O91, O105, O113, O116, O157, O171, O174, and OX177) and 52% of the isolates belonged to only 10 serotypes (O4:H4, O20:H19, O22:H8, O26:H11, O77:H41, O105:H18, O113:H21, O157:H7, O171:H2, and ONT:H19). Although the 514 STEC isolates belonged to 164 different seropathotypes (associations between serotypes and virulence genes), only 12 accounted for 43% of isolates. Seropathotype O157:H7stx2eae-γ1ehxA(46 isolates) was the most common, followed by O157:H7stx1stx2eae-γ1ehxA(34 isolates), O113:H21stx2(25 isolates), O22:H8stx1stx2ehxA(15 isolates), O26:H11stx1eae-β1ehxA(14 isolates), and O77:H41stx2ehxA(14 isolates). Forty-one (22 of serotype O26:H11) isolates had intiminβ 1, 82 O157:H7 isolates possessed intimin γ1, three O111:H- isolates had intimin type γ2, one O49:H- strain showed intimin type δ, 13 (six of serotype O103:H2) isolates had intimin type ε and eight (four of serotype O156:H-) isolates had intimin ζ. We have identified a new variant of theeaeintimin gene designated ξ (xi) in two isolates of serotype O80:H-. The majority (85%) of bovine STEC isolates belonged to serotypes previously found for human STEC organisms and 54% to serotypes associated with STEC organisms isolated from patients with hemolytic uremic syndrome. Thus, this study confirms that cattle are a major reservoir of STEC strains pathogenic for humans.

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