Survival and death kinetics of Salmonella strains at low relative humidity, attached to stainless steel surfaces.

Salmonella is a major pathogen of concern for low water activity foods and understanding its persistence in dry food processing environments is important for producing safe food. The studies sought to assess the survival of 15 isolates of Salmonella on stainless steel surfaces. Additionally, the aim was to select a suitable model to describe and understand the strains' survival kinetics. Salmonella isolates were dried onto stainless steel surfaces, placed in controlled temperature (25°C) and humidity (33%) conditions and their viability assessed at times from 1h to 30days. The highest survival rate was associated with S. Typhimurium DT104, S. Muenchen, and S. Typhimurium (NCTC 12023), where, after 30days, the reduction ranged from 1.3log10 cfu/surface to 1.6log10 cfu/surface. The lowest survival was linked to a S. Typhimurium strain used in European Standard disinfectant approval tests and S. Typhimurium isolated from whey powder. For most of the strains, following an initial reduction in viability in the first hours (<72h), no further reduction was seen over the 30day period; therefore a 2-population Weibull model was fitted to model the survival kinetics. The overall survival was neither serotype nor time related. All strains had two different subpopulations, one more resistant to desiccation than the other. The results indicate the possibility of the long term survival of Salmonella on environmental surfaces (at least 30days) and suggest the most suitable model to describe and predict survival kinetics. The results also identify strains that may be used to study stress response mechanisms and potential factory control measures in future studies.