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

Authors: Gu, Ganyu; KROFT, BRENDA - University Of Maryland; LICHTENDWALD, MARINA - Orise Fellow; Luo, Yaguang - Sunny; Millner, Patricia; Patel, Jitu; Nou, Xiangwu

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2022
Publication Date: 1/10/2022
Citation: Gu, G., Kroft, B., Lichtendwald, M., Luo, Y., Millner, P.D., Patel, J.R., Nou, X. 2022. Dynamics of Listeria monocytogenes and microbiome on fresh-cut cantaloupe and romaine lettuce during storage at refrigerated and abusive temperatures. International Journal of Food Microbiology. 364:109531. https://doi.org/10.1016/j.ijfoodmicro.2022.109531.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2022.109531

Interpretive Summary: In recent years, listeriosis outbreaks and recalls associated with fresh produce, like cantaloupe and leafy green, have raised increasing attention and highlighted the need for concerted effort to effectively control this foodborne pathogen in produce production and distribution systems. Fresh-cut produce is considered to be more vulnerable for the colonization and proliferation of foodborne pathogens due to damaged tissue and rich nutrient on cut surface. In this study, ARS scientists examined the dynamics of inoculated Lm and native microbiome on fresh-cut cantaloupe and romaine lettuce during storage at refrigerated and abused temperatures. The microbiota shifts were also compared with the patterns of Lm abundance to gain insights on the effects of indigenous microbiota on Lm growth. Data derived from the microbiome experiments could contribute to better understanding of the relationship between Lm and indigenous microbiomes on produce during storage. Certain species from produce, like romaine lettuce, have the capacity to potentially suppress the growth of Lm. High variance of microbiome on produce (difference among individual samples and significant temporal shift) are one of the main challenges to elucidate the exact impact of indigenous microbiome on Lm. This research benefits produce industries by understanding microbial dynamics of food ecosystems that can ultimately lead to safer, more efficient, and sustainable food-production practices.

Technical Abstract: Listeria monocytogenes (Lm) outbreaks and recalls associated with fresh produce in recent years have heightened concerns and demands from industry and consumers to more effectively mitigate the contamination risk of this foodborne pathogen on fresh produce. In this study, the growth of Lm and indigenous bacteria on fresh-cut cantaloupe and romaine lettuce held at refrigerated (4 °C) and abusive temperatures (10-24 °C) was determined by both culture dependent and independent methods. Composition and dynamics of bacterial communities on Lm inoculated and non-inoculated samples were analyzed by 16S rDNA high-throughput sequencing. Fresh-cut cantaloupe provided favorable growth conditions for Lm proliferation to overtake indigenous bacteria. The Lm population also increased on fresh-cut lettuce, but the growth rate was lower than that of the total mesophilic bacteria, especially at 4 °C. Microbial diversity of fresh-cut cantaloupe was significantly lower than that of fresh-cut romaine lettuce. The Shannon index of microbial communities on cantaloupe declined after storage, but it was not significantly changed on lettuce samples. Shifts in the bacterial microbiome on cantaloupe were mainly affected by Lm inoculation, while both inoculation and storage temperature played significant roles on lettuce bacterial communities. Multiple indigenous bacteria, such as Leuconostoc and Weissella spp., were negatively correlated with Lm abundance on romaine lettuce, and were determined by bioassay as potential anti-listerial species.