AUTHOR=Pracser Nadja , Voglauer Eva M. , Thalguter Sarah , Pietzka Ariane , Selberherr Evelyne , Wagner Martin , Rychli Kathrin 

TITLE=Exploring the occurrence of Listeria in biofilms and deciphering the bacterial community in a frozen vegetable producing environment

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1404002

DOI=10.3389/fmicb.2024.1404002

ISSN=1664-302X

ABSTRACT=<p>The establishment of <italic>Listeria (L.) monocytogenes</italic> within food processing environments constitutes a significant public health concern. This versatile bacterium demonstrates an exceptional capacity to endure challenging environmental conditions in the food processing environment, where contamination of food products regularly occurs. The diverse repertoire of stress resistance genes, the potential to colonize biofilms, and the support of a co-existing microbiota have been proposed as root causes for the survival of <italic>L. monocytogenes</italic> in food processing environments. In this study, 71 sites were sampled after cleaning and disinfection in a European frozen vegetable processing facility, where <italic>L. monocytogenes</italic> in-house clones persisted for years. <italic>L. monocytogenes</italic> and <italic>L. innocua</italic> were detected by a culture-dependent method at 14 sampling sites, primarily on conveyor belts and associated parts. The presence of biofilms, as determined by the quantification of bacterial load and the analysis of extracellular matrix components (carbohydrates, proteins, extracellular DNA) was confirmed at nine sites (12.7%). In two cases, <italic>L. innocua</italic> was detected in a biofilm. Furthermore, we explored the resident microbial community in the processing environment and on biofilm-positive sites, as well as the co-occurrence of bacterial taxa with <italic>Listeria</italic> by 16S rRNA gene sequencing. <italic>Pseudomonas</italic>, <italic>Acinetobacter</italic>, and <italic>Exiguobacterium</italic> dominated the microbial community of the processing environment. Using differential abundance analysis, amplicon sequence variants (ASVs) assigned to Enterobacterales (<italic>Enterobacter</italic>, <italic>Serratia</italic>, unclassified <italic>Enterobacteriaceae</italic>) and <italic>Carnobacterium</italic> were found to be significantly higher abundant in <italic>Listeria</italic>-positive samples. Several <italic>Pseudomonas</italic> ASVs were less abundant in <italic>Listeria</italic>-positive compared to <italic>Listeria</italic>-negative samples. <italic>Acinetobacter, Pseudomonas</italic>, <italic>Janthinobacterium</italic>, <italic>Brevundimonas</italic>, and <italic>Exiguobacterium</italic> were key players in the microbial community in biofilms, and <italic>Exiguobacterium</italic> and <italic>Janthinobacterium</italic> were more relatively abundant in biofilms. Further, the microbial composition varied between the different areas and the surface materials.</p>