The identification and characterisation of Salmonella enterica subspecies enterica serovars that exist in pigs and pork in Northern Ireland

Abstract

Salmonella enterica subspecies enterica can infect both humans and animals alike, with the most common route being the ingestion of food/water/faecal matter contaminated with Salmonella bacterium. As Salmonella can comfortably survive and replicate within the intestinal tracts of all domestic meat producing animals it is important to control the Salmonella prevalence in such animals and to ensure they are slaughtered and processed in a correct safe and hygienic fashion. This, in turn, should limit the possible contamination of the final meat product. This thesis attempts to assess the prevalence and diversity of Salmonella serovars within pork and pigs slaughtered in Northern Ireland.

This study of abattoir pigs and pork conducted between January 2006 and July 2007 determined Salmonella Typhimurium (41) and Salmonella Rissen (29) as the most prevalent Salmonella enterica serovar within the NI pig population. Salmonella serovars Derby, Panama, Orion, Dublin and Meleagridis were also isolated throughout the sampling period. S. Typhimurium phage typing analysis identified six distinctive types within the 41S. Typhimurium consisting of phage types; DT193, DT104, U288, DT104b, DT120,DT110 and one S. Typhimurium that proved to be untypable. Overall 85.4% of all S. Typhimurium were classified as multidrug resistant while Xba1-PFGE analysis subdivided select S. Typhimurium into three distinct clusters. Antibiotic resistance was established to be low amongst S. Rissen with all 29 isolates displaying resistance to tetracycline. A combination of Xba1-PFGE and plasmid profiling subdivided the 29 S. Rissen into three distinct genotypes.

The characteristics of S. Typhimurium and S. Rissen were investigated by both adhesion and invasion assays while the effect of environmental stresses (temperature, pH, high osmolarity and starvation) had on antibiotic resistance was assessed for three clinical important antibiotics (tetracycline, streptomycin and trimethoprim/sulfamethoxazole). The adhesion and invasion assays concluded that although S. Rissen adhered to Caco-2 tissue culture cells in greater numbers that S. Typhimurium DT104 invasion was significantly lower. The environmental stress analysis identified starvation as the stress factor that had the greatest effect on the susceptibility to the three test antibiotics and that of three antibiotics tested the effectiveness of streptomycin was most reduced when applied to the environmentally stressed test Salmonella.

Date of Award	Apr 2013
Original language	English
Sponsors	Safefood, the Food Safety Promotion Board
Supervisor	Patrick Naughton (Supervisor) & James Dooley (Supervisor)