Effectiveness of Bdellovibrio bacteriovorus to contain Escherichia coli on milk and temperature impact on predation dynamics

Abstract

We tested the predation of B. bacteriovorus against Escherichia coli in milk samples in three different experiments. In Experiment 1, the growth and predatory activity of B. bacteriovorus against E. coli in milk stored at 4°C were evaluated. In Experiment 2, the predatory activity of B. bacteriovorus against E. coli in the milk matrix was compared to the optimal one in the medium of choice. In Experiment 3, the influence of the native milk microbial community on the predation of B. bacteriovorus against E. coli experimentally added or indigenous grown at 4°C was tested. The predator increased at 4°C by about 1 Log in the first 48 hours and caused E. coli decrease by about 2 Log after 24 hours. The predator at 30°C reduced E. coli faster (3 Log after 6 hours) than at 4°C (2 Log after 24 hours). B. bacteriovorus at 30°C preyed on E. coli more in the nutrient broth than in the milk, with the most significant difference by about 4 Log after 48 hours. In raw milk contaminated only by the predator, it increased by about 1 Log after 48 hours at 4°C, suggesting that it preyed on indigenous microorganisms. B. bacteriovorus could find application in raw milk used as food or raw material during storage at 4°C to reduce the microbial load of spoilage and Shigatoxin-producing E. coli (STEC) strains of E. coli and therefore increase its shelf-life and healthiness.