Influence of host and bacteriophage concentrations on the inactivation of food-borne pathogenic bacteria by two phages

To use bacteriophages (phages) to control food-borne pathogenic bacteria, it will be necessary to determine the conditions allowing optimal activity. To start exploring these conditions, a Salmonella phage (P7) and a Campylobacter phage (Cj6) were incubated with their respective hosts at 24 degrees C for up to 2 h at varying phage and host cell concentrations, and surviving host cells were enumerated. A quadratic polynomial equation was fitted to the inactivation data and contour maps of inactivation against log(10) phage and host concentrations were plotted. Inactivation of Salmonella by P7 seemed to be independent of the host concentration, with close to 100% inactivation occurring at a phage concentration of around 5 x 10(8) PFU mL(-1). For Campylobacter phage Cj6, there appeared to be an interaction of both phage and host concentrations. The data obtained were largely consistent with prior work indicating that, at low host cell concentrations, the proportion of cells killed is independent of the host cell concentration. The data indicate that biocontrol of pathogens present in low numbers in liquid foods is achievable, given a sufficiently high concentration of added phages, and that it is not necessary to know the concentration of pathogens to achieve this.