Prevalence and diversity of Shiga toxin genes in Canada geese and water in western Lake Erie Region

Shiga toxin-producing Escherichia coli (STEC) poses a major health risk by causing gastrointestinal illness and has been isolated from wild birds, including Canada geese (Branta canadensis). The major virulence factor for STEC infection is Shiga toxin. This study was designed to evaluate the occurrence and diversity of the Shiga toxin gene (stx) in Canada geese in the western Lake Erie region. Samples were collected from the Ottawa National Wildlife Refuge (ONWR) at Oak Harbor, Ohio from June to December, 2012, and occurrence of the stx gene was determined using polymerase chain reaction (PCR). Genetic diversity of stx variants among the fecal samples was examined using denaturing-gradient gel electrophoresis (DGGE). The Shiga toxin gene 2 (stx2) variant were detected in 20.8% (n = 77) of the geese fecal samples and 7% (n = 71) of the water samples. DGGE and clustering analysis showed a low stx2 diversity and single genetic lineage of all the stx2 fragments. All the stx2 sequences from excised DGGE bands were similar to those from a toxin form of high potency (stx2a) and those from reported outbreak-causing serotypes (E. coli O157:H7, O165:H25, and O111:H-). Detection of stx from Canada geese suggested that viable Shiga toxin-producing Escherichia coli may be present. Further investigations, such as bacterial isolation, are suggested to better understand potential public health hazards in Lake Erie recreational areas, the role of Canada geese as a reservoir of Shiga toxin-producing Escherichia coli, and dissemination of these pathogenic bacteria.