Context matters: environmental microbiota from ice cream processing facilities affected the inhibitory performance of two lactic acid bacteria strains against Listeria monocytogenes

Using biocontrol microorganisms to complement sanitation of dairy processing facilities may enhance the control of pathogenic Listeria monocytogenes. However, it remains unknown whether the microbiota of dairy processing facilities affects the antilisterial activity of biocontrol strains. We tested two lactic acid bacteria (LAB) strains (Enterococcus faecium PS01155 and Enterococcus lactis PS01156) for their antilisterial potential in the context of microbiomes collected from three ice cream processing facilities (A, B, and C). Antilisterial ability was assessed by co-culturing LAB strains with eight L. monocytogenes strains in the presence of microbiota for 3 days at 15°C, followed by quantification of the most probable number of attached L. monocytogenes. We observed no significant reduction of the L. monocytogenes concentration in the samples co-cultured with LAB strains in the presence of environmental microbiota collected from ice cream processing facilities, compared to a positive control containing only the L. monocytogenes cocktail and the environmental microbiomes. The attachment of LAB strains to an abiotic surface was assessed by co-culturing LABs with microbiomes at 15°C for 3 days, followed by characterization of attached microbiota composition using amplicon sequencing. All treatment samples that contained microbiomes from dairy processing facilities had a high relative abundance of Pseudomonas. Further, the presence of Pseudomonas isolated from the microbiome from facility B significantly reduced the antilisterial ability of E. faecium PS01155.