Growth of Listeria monocytogenes and Salmonella spp. on ready to eat fresh-cut lettuce: microbiological counts and combase predictor

Introduction: Consumption of fresh produce has been recognized as an important vehicle for the transmission of human pathogens. The consumption of these foods has been increasing among consumers who prefer healthy diets and provide an appropriate meal for the current lifestyles. Consumption of pre-washed leafy green salads has been increasing in parallel with consumer demand for convenient foods. In spite of their healthy and convenient aspects, microbiological safety should be a concern as growth of pathogens may occur during refrigerated storage in particular at abuse temperature conditions often observed at household level. Methodology: Individual packages of pre-washed lettuce salad were inoculated with a cocktail of Salmonella or Listeria monocytogenes strains. Counts of the pathogens were followed during storage at different temperatures simulating refrigeration temperature abuse conditions observed in domestic settings. Growth under the same conditions was predicted using the ComBase Predictor software. Results: Growth of Listeria monocytogenes and Salmonella spp. was observed on salads stored at temperatures above 5.5ºC and 7ºC, respectively. Higher growth rates were determined when ComBase Predictor was used. Conclusion and Relevance: Listeria monocytogenes and Salmonella spp. can grow in fresh-cut lettuce even at short abuse of refrigeration temperature during storage. ComBase Predictor can be a useful tool to estimate the risk of consumption of lettuce stored at abuse temperatures at household level.