Salmonella survival in low aw environment

Since the early 1970’s a number of large Salmonella outbreaks have been associated with low aw food products, including chocolate, cereal, peanut butter, spices, and powdered infant formula. This research is design to help the food industry to determine Salmonella survival in the production environment and thus understand the potential risk of cross contamination to the product. The studies sought to assess the survival of 9 isolates of Salmonella on stainless steel surfaces, the influence of different serotypes on survival and the comparison of the survival rate within the same serotype. The following isolates were used for the experiments: S. Agona, S. Napoli, S. Enteritidis, S. Tennessee, S. Muenchen, S. Typhimurium (whey powder), S. Typhimurium DT104, S. Typhimurium NCTC 12023, S. Typhimurium, NCTC (PHLS), NC000 74-17. The stainless steel surfaces were inoculated with 10 7 cfu of each Salmonella isolate and placed in a controlled environment: relative humidity 33% and temperature 230C. The number of microorganisms surviving on the stainless steel surfaces was assessed at various time points from 1 hour to 30 days. Differential survival was observed for different serotypes of Salmonella. The highest survival rate was associated with S. Agona, S. Enteritidis, and S. Typhimurium DT104 where, after 30 days, the number of microorganisms on the surfaces ranged from 4.0 logs cfu to 4.5 logs cfu. There was 1 log cfu survival of S. Typhimurium NCTC (PHLS), NC000 74-17 after 10 days in experimental conditions, therefore differences within the same serotype were observed. The average number of Salmonella surviving after 30 days ranged from 2.5 logs cfu to 3.5 logs cfu. The results of the studies could provide insight into potential growth and survival mechanisms for Salmonella in dry processing environments. These results will be incorporated into a Campden BRI guidance document on the survival of Salmonella in dry process environments with relation to strain, temperature, humidity, water and soiling, which would help the industry to control Salmonella endurance in the environment and thus in the final product.