Genotypic Characterization of Shigella Species Isolated from Abattoirs in the North West Province, South Africa Using PCR Analysis

Abstract

Foodborne pathogens pose a serious threat to food safety especially in developing countries where hygiene facilities are not well developed and operational practices in abattoirs and retail shops are often poor. Shigella species are known to cause foodborne complications in humans including shigellosis that is not only characterized by destruction of the epithelium of the colon but usually results to an inflammatory response. The transmission of Shigella species to humans most often results through the consumption of contaminated food, meat and water. The aim of this study was to isolate and identify Shigella species from carcass of cattle in some abattoirs in the North West Province, South Africa and determine the virulence gene profiles of the isolates using PCR assays. A total of 97 carcass swabs were obtained from the abattoirs that were sampled. Swabs were properly labeled and transported on ice to the laboratory for analysis. The swabs were washed in 2% (w/v) peptone water and plated on Salmonella-Shigella agar. Standard identification tests (Gram staining, oxidase test, TSI test and 16S rRNA) were used to confirm the identities of 97 (one from each sample) presumptive isolates. Large proportions (85% to 100%) of the isolates from Rustenburg and Zeerust were oxidase positive. None of the isolates produced hydrogen sulphide gas on TSI medium but utilize glucose as a source of carbon. A large proportion (75.3%) of the isolates was positively identified as Shigella species based on PCR analysis. The number of isolates confirmed as Shigella species was higher in Zeerust (54.8%) than in Rustenburg (45.2%). Shigella species were most often isolated from samples that were collected outside than inside the carcass. Generally a large proportion (74.0%) of the isolates possessed the IpaH gene while64.4% of these isolates were positive for the IpaBCD gene that encodes for the invasion plasmid antigen. An analysis of the isolates from the different sampling sections indicated that 46.3% and 55.3% of the isolates from Zeerust possessed the IpaH and the IpaBCD genes, respectively while 53.7% and 44.7% of the isolates from Rustenburg possessed these genes. The detection of virulent Shigella species in beef carcasses demonstrates the need for a continued surveillance of this pathogen in meat in order to ensure the implementation of improved food safety measures.