Characterization of microbial communities in floor drain biofilms and drain waters in a Listeria monocytogenes-contaminated food processing environment. Microbial communities of dairy plant floor drains

Sanitation protocols are applied on a daily base in food processing facilities to avoid contamination of food with spoilage organisms or food-borne pathogens. Biofilms, water and food residues in drains can serve as reservoirs for microbial contamination. Floor drains in food production environments have thus been described as hotspots for (re)contamination of food posing a significant risk on food safety. To control the occurrence of opportunistic pathogens such as Listeria monocytogenes, drain water (DW) samples are frequently used as sample matrix for hygiene monitoring. Besides of the drain water microcosm, drains are usually colonized by biofilms due to the high content of organic matter and stagnant flow conditions. The microbiome of a drain biofilm (DB) however, could be very different from the microbiome of drain water. To better understand the exchange of microbial communities between both niches, the bacterial communities of four floor drains (FD) were characterized using 16S rRNA gene pyrosequencing in a L. monocytogenes-positive food processing environment. L. monocytogenes was confirmed following the protocols of ISO11290 and by quantitative PCR. Pyrosequencing of microbial communities of DW and DB samples yielded 50,611 reads. Sequences were clustered into 641 operational taxonomic units (OTUs), affiliating to 16 phyla dominated by Proteobacteria, Firmicutes and Bacteroidetes. The most abundant OTUs represented either cheese- (Lactococcus lactis) or fermentation- and food spoilage-associated phylotypes (Pseudomonas mucidolens, Pseudomonas fragi, Leuconostoc citreum, and Acetobacter tropicalis). The microflora in each sampling area was composed heterogeneously, suggesting the presence of indigenous microbial communities in each processing compartment. The microbiota of drain biofilms was largely different from the microbiota of the drain water. A sampling approach based only on drain water may thus only provide reliable information on planktonic bacterial cells but might not allow conclusions on the bacterial composition of the microbial flora in biofilms. However, DW serves as suitable sample type for Listeria environmental monitoring as L. monocytogenes quantities were higher in the water phase in contrast to DB.