Fecal samples collected from 470 slaughtered reindeer 6 to 7 months of age were screened by real-time PCR (after enrichment) for Shiga toxin genes (stx) and then for Escherichia coli serogroup O157. Shiga toxin genes were found frequently (>30% of samples), and serogroup O157 was detected in 20% of the stx-positive samples. From these samples, a total of 25 E. coli O157:H- isolates (nonmotile but PCR positive for fliCH7) were obtained. Twenty-four of these E. coli O157:H- isolates did not ferment sorbitol and originated from one geographic area. These 24 isolates belonged to the multilocus sequence type 11, typical for Shiga toxin-producing E. coli (STEC) O157:H7 and O157:H-, and harbored genes stx1a, stx2c, eae, and hlyA; the stx2c subtype has been associated with high virulence. In contrast, one E. coli O157:H- isolate (multilocus sequence type 11) did ferment sorbitol, lacked Shiga toxin genes, but was positive for eae, hlyA, and sfpA. This isolate closely resembled an STEC that has lost its Shiga toxin genes. Additional examination revealed that reindeer can be colonized by various other STEC isolates; 21 non-O157 STEC isolates belonged to four multilocus sequence types, harbored stx1a (8 isolates) or stx2b (13 isolates), and in the stx2b-positive isolates the recently described new allelic variants (subAB2-2 and subAB2-3) for subtilase cytotoxin were identified. Hence, slaughtered semidomesticated Finnish reindeer might constitute a little known reservoir for STEC O157:H7/H- and other serogroups, and the risk of direct or indirect transmission of these pathogens from reindeer to humans and domestic livestock must not be overlooked.
Keywords: Multilocus sequence typing; Phenotypic and genotypic traits; Reindeer fecal samples; Shiga toxin–producing Escherichia coli O157.