Characterizing Environmental Background Microflora and Assessing Their Influence on Listeria Persistence in Dairy Processing Environment

<i>Listeria monocytogenes</i> (<i>Lm</i>) may persist in food processing environments (FPEs) alongside diverse background microflora. While microbial communities in FPEs can influence <i>Lm</i> survival, their role in supporting or suppressing its growth remains unclear. This study aimed to characterize the microflora in floor swabs and air samples collected from a dairy processing facility across three seasons and assess their potential impact on the growth of a <i>Lm</i> test strain previously isolated from a dairy processing environment. A total of 167 environmental isolates, representing 30 bacterial genera, were identified. <i>Pseudomonas</i> was consistently prevalent across all sample types. Seasonal shifts in bacterial genera were observed, with differences in microbial composition and relative abundance between production lines with and without <i>Listeria innocua</i> occurrence. Microflora distribution appeared more influenced by environmental and operational factors than by spatial proximity. Co-culture growth assays revealed no competitive exclusion of the <i>Lm</i> test strain, and no zones of inhibition were observed in antimicrobial assays using cell-free extract and dialyzed cell-free extract from environmental isolates against <i>Lm</i>. These findings suggest that <i>Lm</i> could potentially establish itself within mixed microbial communities in dairy processing environments, emphasizing the complexity of microbial interactions in FPEs and their potential role in <i>Lm</i> persistence.