Dynamics of Listeria monocytogenes and microbiome on fresh-cut cantaloupe and romaine lettuce during storage at refrigerated and abused temperatures

Recent listeriosis outbreaks and recalls associated with fresh produce have raised concern and demand from industry and consumers to mitigate the contamination risk of this foodborne pathogen during produce production. Temperature has been reported to be one of the main factors affecting Listeria monocytogenes (Lm) survival and proliferation on fresh-cut produce. However, knowledge on the relationship and impact of complex indigenous microbiome on Lm kinetics on fresh-cut produce during storage is still limited. In this study, the growth of Lm and total bacteria on fresh-cut cantaloupe and romaine lettuce stored at refrigerated and abused temperatures were measured by both cultural dependent and independent methods. Composition and dynamics of microbial communities on Lm inoculated and non-inoculated samples were analyzed by 16S rDNA high-throughput sequencing. Fresh-cut cantaloupe provided an optimal growth condition for Lm proliferation overtaking other indigenous microbes. Lm population also increased on fresh-cut lettuce, while the growth rate was lower than the total mesophilic bacteria, especially at refrigerated temperature. Microbial diversity of fresh-cut cantaloupe was significantly lower than fresh-cut romaine lettuce. Shannon index of microbial communities on cantaloupe reduced after storage, but it was not significantly changed on lettuce samples. Shift in microbiome on cantaloupe was mainly affected by Lm inoculation, while both inoculation and storage temperature played significant roles on lettuce microbiota. Multiple indigenous bacteria, such as Leuconostoc and Weissella spp., showed negative correlation to Lm abundance on romaine lettuce, which were determined to be potential anti-listeria species by a following bioassay.