Abstract
The survival on stainless steel of ten Salmonella isolates from food factory, clinical and veterinary sources was investigated. Stainless steel coupons inoculated with Salmonella were dried and stored at a range of temperatures and relative humidity (RH) levels representing factory conditions. Viability was determined from 1 to 22 days. Survival curves obtained for most isolates and storage conditions displayed exponential inactivation described by a log-linear model. Survival was affected by environmental temperatures and RH with decimal reduction times (DRTs) ranging from <1 day to 18 days. At 25 °C/15% RH, all isolates survived at levels of 103 to 105 cfu for >22 days. Furthermore, temperatures and RH independently influenced survival on stainless steel; increasing temperatures between 10 °C and 37 °C and increasing RH levels from 30–70% both decreased the DRT values. Survival curves displaying a shoulder followed by exponential death were obtained for three isolates at 10 °C/70% RH. Inactivation kinetics for these were described by modified Weibull models, suggesting that cumulative injury occurs before cellular inactivation. This study highlights the need to control temperature and RH to limit microbial persistence in the food manufacturing environment, particularly during the factory shut-down period for cleaning when higher temperature/humidity levels could be introduced.
Highlights
Salmonella are important foodborne pathogens that are able to cause cross-contamination of food products and are a leading cause of foodborne illness worldwide [1]
The results showed a marked decrease in Salmonella survival with a low temperature and high humidity combination, emphasising the need to further study the interaction between these two parameters
The aim of this study was to identify the combined effect of temperature and humidity on the survival on stainless steel of a range of Salmonella isolates from factory and veterinary sources, clinical isolates from outbreaks associated with pet food and reference strains
Summary
Salmonella are important foodborne pathogens that are able to cause cross-contamination of food products and are a leading cause of foodborne illness worldwide [1]. Salmonella occurs naturally in the environment and can pass via multiple routes in the food chain from producers to consumers. Salmonella contamination has been implicated in a range of food products, including poultry, fish eggs, dairy, vegetables and dry foods [2,3]. Despite the common misconception regarding the contamination of low water activity produce, these products are subject to microbial contamination and organisms, such as Salmonella, may survive [3,4,5]. The food manufacturing processes associated with some of these included thermal inactivation, suggesting that cross-contamination is likely to occur post-treatment with Salmonella that have become established in the manufacturing environment
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