Genes encoding Shiga toxin and the intimin receptor detected in faecal samples collected from wild canids

Abstract

Background: Enteropathogenic Escherichia coli (EPEC) and Shiga toxin-producing E. coli (STEC) are diarrheagenic E. coli that can cause disease in humans. The pathotype EPEC leads to the attaching and effacing lesion, causing damage to the microvilli following to diarrhea. STEC pathotypes produces cytotoxins, which in humans are responsible for hemorrhagic colitis or hemolytic uremic syndrome. Animals are the reservoirs of these pathotypes, especially ruminants. However, other animal’s species can be associated as carriers of EPEC and STEC strains. The aim of this study was to analyze wild canid crab-eating fox (Cerdocyon thous) as potential natural carriers of STEC and EPEC E. coli. Materials, Methods & Results: Seven fecal samples were analyzed from the crab-eating fox of free-living, captured in a peri-urban area. Samples were collected from the rectal ampulla, and the animals were clinic evaluated, being considered healthy at the captured moment. The feces were inoculated on medium MacConkey agar, and then the plates were incubated at 37°C for 24 h. All colony forming units (CFU) were collected by plate washing with ultrapure water (2 mL) and posterior freezing at -20°C. The total bacterial DNA from the CFU collected was extracted, followed by PCR assay to search for three genes: stx1, stx2 (responsible for the synthesis of the Shiga toxin) and tir, which encodes the translocated intimin receptor, related to the A/E lesion formation. Three samples were detected as positive, being one animal detected as carrier of the stx2 gene (STEC strain), while two animals were identified as carrier of the tir gene (EPEC strains).The stx1 gene was not identified on the samples. Also, in the samples, only the presence of one gene studied at a time was observed. Therefore, we have found out that the crab-eating fox can act as reservoirs of STEC and EPEC strains. Discussion: The carrier’s animals of STEC and EPEC strains do not have receptors for the Shiga toxin, serving as asymptomatic vehicle. The wild canids collected and positives to STEC and EPEC E. coli strains analyzed here, did not shown any clinical signs, wherefore they have the potential of being a source of pathogens to other animals and even humans. The observation of this additional wild species, the crab-eating fox, as carriers of STEC and EPEC reinforces the importance of monitoring wild species and the need for caution because of the potential zoonosis. Nevertheless, there are other species of wild animals that were described as rarely-carriers of these pathogens, like deer, wild ruminants and birds. These E. coli pathotypes, potentially foodborne zoonotic pathogens, are acquired by humans from food and water contaminated, by oral-fecal route, or by direct contact with carries animals and their feces. The human contact with wild animals is getting ordinary; because of that, wild animals, like wild canids, may constitute a considerable risk to animal and humans health, mostly by the transmission of these bacteria strains to the environment. In conclusion, the identification of genes encoding Shiga toxin and the intimin receptor in wild canids feces highlight that STEC and EPEC pathogens could be spread by these wild animals. We reinforce that STEC and EPEC pathogens could be naturally carried by wild animals, such as the crab-eating fox, and therefore, is needed further research for better understanding their potential effect, and also the interaction between the pathogen and the host.