The spread, persistence and survival of salmonella and campylobacter in the domestic kitchen
This thesis investigates the exposure risk of Salmonella and Campylobacter following the preparation of a chicken salad in domestic kitchens.
Methods were first devised, developed and validated to maximise recovery of cells, including those sub-lethally damaged, in order to accurately assess exposure routes.
Isolation rates of Campylobacter were maximised by delaying the addition of rifampicin and polymyxin and prolonging the incubation period of broths. It was found that isolation of Salmonella was improved when sulphamandelate was added to the pre-enrichment broth.
Pilot work, utilising these improved isolation methodologies, was then carried out in a test domestic kitchen to determine likely exposure routes and commonly contaminated sites during the preparation of a meal by 30 participants. Using the techniques refined in the pilot study, the food preparation practices of 70 participants were studied preparing the same salad in their home. A total of 609 samples were taken and contamination by Campylobacter was found to be relatively common with 13% of participants contaminating the kitchen or the prepared salad. The raw chicken breasts used to prepare the salad were the most significant source of contamination; 90% were contaminated with high numbers of Campylobacter, 6% were contaminated with Salmonella. Commonly contaminated items included the salads and wiping cloths. The most common exposure routes were due to the inadequate washing / drying of hands, chopping boards and knifes.
In order to accurately assess the risks associated with the widespread contamination of Campylobacter spp., their ability to survive on simulated kitchen work-surfaces was compared with Salmonella spp.. Salmonella was found to survive significantly better than Campylobacter after two hours of air drying (P: 0.001). Differences in the ability of some Campylobacter strains to survive air drying were also found to be significant.
It is suggested that the results of this thesis could be used to determine exposure assessment and quantitative risk assessment in the domestic kitchen in order to prioritise and target food safety messages.