Listeria monocytogenes is a foodborne pathogen that causes high rates of hospitalization and mortality in people infected. Contamination of fresh, ready to eat produce by this pathogen is especially troubling because of the ability of this bacterium to grow on produce under refrigeration temperatures. In this study, we created a library of over 8,000 plant phyllosphere-associated bacteria and screened them for the ability to inhibit the growth of L. monocytogenes in an in vitro fluorescence-based assay. One isolate, later identified as Bacillus amyloliquefaciens ALB65, was able to inhibit the fluorescence of L. monocytogenes by >30-fold in vitro. B. amyloliquefaciens ALB65 was also able to grow, persist, and reduce the growth of L. monocytogenes by >1.5 log CFU on cantaloupe melon rinds inoculated with 5 × 103 CFU at 30°C and was able to completely inhibit its growth at temperatures below 8°C. DNA sequence analysis of the B. amyloliquefaciens ALB65 genome revealed six gene clusters that are predicted to encode genes for antibiotic production; however, no plant or human virulence factors were identified. These data suggest that B. amyloliquefaciens ALB65 is an effective and safe biological control agent for the reduction of L. monocytogenes growth on intact cantaloupe melons and possibly other types of produce.
IMPORTANCE Listeria monocytogenes is estimated by the Centers for Disease Control and Prevention and the U.S. Food and Drug Administration to cause disease in approximately 1,600 to 2,500 people in the United States every year. The largest known outbreak of listeriosis in the United States was associated with intact cantaloupe melons in 2011, resulting in 147 hospitalizations and 33 deaths. In this study, we demonstrated that Bacillus amyloliquefaciens ALB65 is an effective biological control agent for the reduction of L. monocytogenes growth on intact cantaloupe melons under both pre- and postharvest conditions. Furthermore, we demonstrated that B. amyloliquefaciens ALB65 can completely inhibit the growth of L. monocytogenes during cold storage (<8°C).