Study of food borne pathogens in poultry

Campylobacter and Salmonella are the two main causative agents of bacterial foodborne disease in humans and are a significant public health problem worldwide. In the poultry industry, broilers frequently become colonized by Campylobacter species. As a consequence, Campylobacter can enter the poultry meat supply chain by posing a significant risk to human health. Several “generally recognized as safe” (GRAS) chemicals, such as chlorine and acidified sodium chlorite are used in processing plants to mitigate the load of Campylobacter on point-of-use chicken meat. However, contamination of chicken meat in the food chain remains a significant public health issue and its control is critical for the poultry industry. My research has investigated the physiological, morphological, and cellular responses of Campylobacter jejuni following exposure to chicken meat sanitizers and how this affects bacterial virulence potential. In many countries, chlorine is commonly used as a biocide in processing plants to reduce bacterial loads. In Chapter 2, the effectiveness of chlorine on the inactivation of C. jejuni was investigated. The results revealed the majority of the isolates exhibited minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC) values of 128 ppm for chlorine, which is higher than the concentration (8ppm) recommended for use in the Australian poultry industry. Experiments performed in Chapter 2 also demonstrated that the efficacy of chlorine is significantly influenced by organic matter as well as bacterial load. The morphological effect of exposure to chlorine was also investigated using scanning and transmission electron microscopy. C. jejuni exposed to chlorine showed changes in shape (coccoid, or elongated), cellular degeneration, and shriveled bacterial cells. The present study suggests that, although chlorine is effective in reducing C. jejuni contamination, the current protocol used in the Australian poultry industry is unable to eliminate completely. Acidified sodium chlorite (ASC) has been previously shown to have greater bacteriocidal capacity compared with chlorine and is most commonly recommended for post-spin chill applications. In Chapter 3, the cellular response of C. jejuni following exposure to ASC was studied. The data showed that 7.03 ppm of ASC was sufficient to inactivate C. jejuni. Interestingly, the effects of ASC were independent of organic matter presence and bacterial load. C. jejuni exposed to ASC could not be resuscitated indicating that this sanitizer induced irreversible cellular damage. Analysis of the C. jejuni transcriptome post-exposure to sanitizer revealed that chlorine induced an adaptive stress response mechanism, which aids in survivability under oxidative stress. ASC, however, induced higher oxidative damage by inhibiting all vital metabolic pathways resulting in cellular death. This study suggests that ASC would be a better alternative to chlorine in reducing C. jejuni contamination in chicken meat. The presence of sub-lethally injured food-borne pathogens such as C. jejuni and Salmonella Typhimurium in the chicken meat juice of thawed or raw poultry packages is a significant risk. In Chapter 4, the survivability, invasion potential, and virulence gene expression of C. jejuni and S. Typhimurium following exposure to chlorine and acidified sodium chlorite (ASC) during storage in chicken meat juice (CMJ) were investigated. The results revealed that CMJ facilitated the survival of both C. jejuni and S. Typhimurium following exposure to chlorine but not ASC. Both chlorine and ASC reduced bacterial invasiveness, motility, and culturability of C. jejuni but not S. Typhimurium. The gene expression data revealed the upregulation of bacterial stress response and virulence genes in C. jejuni (ropB, sobB, flaG, flaA, cadF, racR) and S. Typhimurium (rpoH, rpoS, hilA, fimH, spvR, avrA) over storage time, indicating an increase in virulence potential. Moreover, the data suggested that sub-lethally injured C. jejuni and S. Typhimurium in CMJ remain a significant risk in the food chain due to the likelihood of cross-contamination while handling chicken meat. The understanding of the in-vivo virulence potential sub lethally injured C. jejuni is crucial in evaluating public health risks. In Chapter 5, the virulence of sub-lethally injured C. jejuni during prolonged storage in chicken meat juice in C57BL/6 mice was evaluated. The results revealed that tissue colonization and invasion of C. jejuni were significantly reduced following exposure to ASC. The reduced expression levels of inflammatory cytokine genes, (IL6, IL23, and IL10), Toll-like receptor genes (TLR2, and TLR4), and host stress response genes (CRP, MBL, and NF-B) in mice infected with C. jejuni exposed to chlorine or ASC suggested the reduced virulence potential of sublethally injured C. jejuni . Exposure to chlorine results in sublethal injury of C. jejuni and S. Typhimurium which allows for their persistence in the food supply chain. ASC, however, induces substantial bacterial cell damage which bacteria have limited or no ability to recover from which would contribute to reducing bacterial foodborne pathogens in the food supply chain. A re-evaluation of current Australian protocols is warranted to improve the safety of the chicken meat supply chain.Thesis (Ph.D.) -- University of Adelaide, School of Animal and Veterinary Sciences, 202

Comparison of peroxyacetic acid and acidified sodium chlorite at reducing natural microbial contamination on chicken meat pieces

ABSTRACT: The spin-chill process at poultry processing plants involves the immersion of chicken carcasses in cold water (<5°C) often containing sodium hypochlorite which significantly contributes to the reduction of bacterial loads. Cutting carcasses into pieces, however, has been linked with increases in Campylobacter and Salmonella counts. Here, the efficacy of PAA and ASC on reducing bacteria on skin-on, bone-in thigh cuts was investigated. Three concentrations of ASC (60, 112, and 225 ppm) and PAA (50, 75, 100 ppm) were used. Thighs were dipped into sanitizer and tested for total viable bacterial counts, Campylobacter load, and prevalence of Salmonella. The efficacy of PAA and ASC was also compared with chlorine (8 ppm). All sanitizers exhibited a greater log reduction compared with water. PAA at both 75 and 100 ppm resulted in significantly higher log reductions compared with the water only. PAA at 100 ppm and 225 ppm ASC were the most effective at reducing Campylobacter. All wash treatments reduced the proportion of Salmonella positive samples, but the greatest reduction was observed for 225 ppm ASC. Both concentrations of ASC resulted in a greater reduction in total viable counts compared with chlorine