Interactions between indigenous microflora and pathogens on produce generally have not been well studied. Indigenous LAB can be antagonistic due to organic acid production, generation of H2O2, bacteriocin production, or competition for nutrients. Naturally present in low numbers on vegetables, they can reach high numbers in MAP where high levels of CO2 are employed. MAP gas combinations may be manipulated to encourage growth of these antagonists, which may indirectly control growth of spoilage organisms or pathogens. Research has shown that growth of some organisms can result in enhanced growth of others. Salmonella spp. co-inoculated with a soft-rot bacterium or Pseudomonas spp. on potato, carrot, and pepper grew significantly better than when inoculated alone . Pathogens may grow on biofilms naturally formed on produce, where the environment may be altered such that it is more favorable for microbial growth compared to the direct produce surface. Work has shown that L. monocytogenes can grow on multi-species biofilms on meat; comparable studies have not yet been performed on produce. Biofilms have been found to constitute between 10 and 40% of bacterial populations on endive and parsley, and more work is needed to determine the extent of biofilm development and microbial interactions at the biofilm surface on other whole produce .
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