Fate of Listeria monocytogenes and Escherichia coli O157:H7 in the presence of natural background microbiota on conventional and organic lettuce

Foodborne illnesses due to the consumption of contaminated raw vegetables is a continuing food safety concern. The limited efficacy of chlorine products to disinfect in fresh-cut industries, has led to study other methods or strategies to improve the safety of processed fresh-cut products. It has been reported that the presence of competing microorganisms on the surfaces of fresh produce can contribute to the reduction of pathogens. The aim of this study was to evaluate the interactions between the natural background microbiota of shredded conventional and organic lettuce and Listeria monocytogenes and Escherichia coli O157:H7. The effect of different initial load of background microbiota ('low', 'medium' and 'high') was tested for its ability to reduce L. monocytogenes and E. coli O157:H7 populations on shredded lettuce during storage at 10 ± 1 °C for 8 days. After the different pre-conditioning steps in order to obtain different initial loads of microbiota, in general, we observed that varying its size had no effect on L. monocytogenes and E. coli O157:H7 survival/growth during the storage period. Only differences on the survival/growth of L. monocytogenes and E. coli O157:H7 inoculated onto organic and conventional lettuce, respectively at the end of storage period at 10 °C were found. These results highlight the necessity for corrective measures to avoid contamination of fresh-cut vegetables with foodborne pathogens.

► This is the first report on the effect of microbiota from conventional and organic lettuce on L. monocytogenes and E. coli. ► Different initial loads of microbiota were obtained after pre-conditioning steps. ► Natural microbiota occasionally affected growth of foodborne pathogens on lettuce.