Shining Light on Microbial Interactions: A Luminescence-Assisted Milk-Based Medium to Study LAB–Salmonella Dynamics

The study of microbial dynamics is increasingly important as new control strategies, such as biopreservation, are becoming relevant to conservation of certain food categories, for instance raw milk dairy products. Lactic acid bacteria (LAB), widely used in the dairy industry, constitute a promising reservoir for the identification of strains with biopreservative potential, although few of the underlying mechanisms have been explored. In this study, a chemically defined medium mimicking raw milk's nutrient concentrations was optimized and used to design a high-throughput screening methodology using luminescent Salmonella strains as model contaminants, to investigate the role of nutritional interactions in LAB biopreservative activity in milk. Cocultured LAB- Salmonella pairs showed reduced luminescence compared to Salmonella grown alone, and for several pairs, restoration of luminescence was observed under nutrient-enriched conditions. These findings strongly suggest that resource competition contributes to LAB-mediated biopreservation and highlight potential model pairs to investigate the specific resources and mechanisms involved.