Foodborne illness associated with fresh, ready-to-eat produce continues to be a significant challenge to public health. In this study, we created a phyllosphere-associated lactic acid bacteria (PLAB) library and screened it via a high-throughput in vitro fluorescent assay to identify bacteria capable of inhibiting the growth of the pathogenic bacterium Salmonella enterica. One isolate, 14B4, inhibited the growth of S. enterica by >45-fold in vitro; it was able to grow and persist on the surfaces of cantaloupe melons at both ambient (25°C) and refrigerator (5°C) temperatures. Isolate 14B4 inhibited the growth of S. enterica on the surfaces of cantaloupes by >3 log when incubated at 25°C for 24 h and by >4 log when the cantaloupes were stored at 5°C for 3 days and the temperature was shifted to 25°C for 2 days. Genomic DNA sequence analysis of isolate 14B4 revealed that it was Lactococcus lactis and that it did not contain any known antibiotic biosynthesis gene clusters, antibiotic resistance genes, or genes encoding any known virulence factors. Organic acid analysis revealed that L. lactis produces substantial amounts of lactic acid, which is likely the inhibitory substance that reduced the growth of Salmonella on the cantaloupes.
L. lactis isolate 14B4 inhibited the growth of Salmonella on cantaloupe rinds.
Storage of contaminated rinds at 5°C increased the growth inhibition by 1 log.
L. lactis isolate 14B4 is a potentially safe and effective biological control agent.