Stability of listerial bacteriophage A511 in bovine milk fat globules

Abstract Raw milk and milk fractions were analysed for their activity against the bacteriophage A511. The whole milk was separated into fat, casein and whey. Fat was fractionated further into butter serum, butter oil, butter milk and milk fat globule membrane. Bacteriophage was inoculated and was enumerated at different time periods (0, 24, 48, 72 and 96 h). Results (plaque-forming units, PFU) showed that raw milk reduced phage counts 2.4 log10 PFU mL-1. Among milk fractions, fat and whey were the most active fractions, reducing the phage titre 2.6 and 2.1 log10 PFU mL-1, respectively, compared with 0.8 log10 PFU mL-1 in casein. Fat fractions also influenced phage stability. The main effect was attributed to the milk fat globule membrane (2.1 log10 PFU mL-1 reduction) followed by butter milk and butter serum (1.0 log10 PFU mL-1 reduction). Butter oil showed no effect on phage stability.