Isolation and characterisation of lytic bacteriophages against Pseudomonas spp., a novel biological intervention for preventing spoilage of raw milk

Thirteen novel lytic bacteriophages against 13 Pseudomonas strains were isolated from local sewage and initially identified by morphology using a transmission electron microscope. PP1 and PP5 were identified as Pedoviridae and Cystoviridae, respectively; while the other 11 phages were identified as Leviviridae. Most phages showed high infectivity at either 4 °C or 25 °C, and the optimum pH range for phage infectivity was pH 5–7. A strong antimicrobial effect of the phage cocktail was evidenced by a 2-log reduction in Pseudomonas cell number of UHT milk inoculated with Pseudomonas, and a 1-log reduction in the psychrotrophic bacteria and total bacteria counts of raw milk at 4 °C over 5 d. A similar result was obtained at 25 °C over 8 h. Results indicated that the 13 phages with different morphological and physiological characteristics may have a potential application as biological preservative agent in raw milk.