Induction of the Viable but Non-Culturable State in Salmonella Contaminating Dried Fruit

Appl Environ Microbiol. 2021 Nov 3:AEM0173321. doi: 10.1128/AEM.01733-21. Online ahead of print.ABSTRACTSalmonella can become viable but non-culturable (VBNC) in response to environmental stressors but the induction of the VBNC state in Salmonella contaminating ready-to-eat dried fruit is poorly characterized. Dried apples, strawberries and raisins were mixed with a five-strain cocktail of Salmonella at 4% volume per weight of dried fruit at 109 CFU/g. The inoculated dried fruit were then dried in desiccators at 25°C until the water activity (aw) approximated that of the uninoculated dried fruit. However, Salmonella could not be recovered after drying, not even after enrichment, suggesting a population reduction of approx. 8 log CFU/g. To assess the potential impact of storage temperature on survival, dried apples were spot-inoculated with the Salmonella cocktail, dried under ambient atmosphere at 25°C and stored at 4 and 25°C. Spot-inoculation permitted recovery of Salmonella on dried apple after drying, with the population of Salmonella decreasing progressively on dried apples stored at 25°C until it was undetectable after about 46 days, even following enrichment. The population decline was noticeably slower at 4°C, with Salmonella being detected until 82 days. However, fluorescence microscopy and laser scanning confocal microscopy with the LIVE-DEAD BacLight Bacterial Viability system at timepoints at which no Salmonella could be recovered on growth med...
Source: Applied and Environmental Microbiology - Category: Microbiology Authors: Source Type: research

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