Norwegian Sheep Are an Important Reservoir for Human-Pathogenic Escherichia coli O26:H11

Abstract

A previous national survey ofEscherichia coliin Norwegian sheep detectedeae-positive (eae⁺)E. coliO26:H11 isolates in 16.3% (80/491) of the flocks. The purpose of the present study was to evaluate the human-pathogenic potential of these ovine isolates by comparing them withE. coliO26 isolates from humans infected in Norway. All humanE. coliO26 isolates studied carried theeaegene and shared flagellar type H11. Two-thirds of the sheep flocks and 95.1% of the patients harbored isolates containingarcAallele type 2 andespKand were classified as enterohemorrhagicE. coli(EHEC) (stxpositive) or EHEC-like (stxnegative). These isolates were further divided into group A (EspK2 positive), associated withstx_2-EDL933andstcE_O103, and group B (EspK1 positive), associated withstx_1a. Although thestxgenes were more frequently present in isolates from patients (46.3%) than in those from sheep flocks (5%), more than half of the ovine isolates in the EHEC/EHEC-like group had multiple-locus variable number of tandem repeat analysis (MLVA) profiles that were identical to those seen instx-positive human O26:H11 isolates. This indicates that EHEC-like ovine isolates may be able to acquirestx-carrying bacteriophages and thereby have the possibility to cause serious illness in humans. The remaining one-third of the sheep flocks and two of the patients had isolates fulfilling the criteria for atypical enteropathogenicE. coli(aEPEC):arcAallele type 1 andespKnegative (group C). The majority of these ovine isolates showed MLVA profiles not previously seen inE. coliO26:H11 isolates from humans. However, according to their virulence gene profile, the aEPEC ovine isolates should be considered potentially pathogenic for humans. In conclusion, sheep are an important reservoir of human-pathogenicE. coliO26:H11 isolates in Norway.