Trisodium Phosphate Increases Sensitivity of Gram-Negative Bacteria to Lysozyme and Nisin

Cell suspensions of Campylobacter jejuni, Escherichia coli, Pseudomonas fluorescens, and Salmonella enteritidis exposed to sublethal concentrations (0.5 to 5 mM) of trisodium phosphate (TSP) for 10 min showed greatly increased susceptibility to lysozyme (10 μg ml−1) and/or nisin (1 μM). Under optimal conditions at 37°C, reductions in viable count after 30 min were up to six log cycles. At 4°C, C. jejuni showed greater resistance than at 37°C, and maximal cell kills (95%) were reduced by more than two log cycles. Cells dried on the surface of chicken skin were more resistant than suspended cells to TSP–lysozyme and TSP–nisin treatments; nevertheless, at 37°C, kills varied from approximately 95% for S. enteritidis cells with nisin (30 μM) or lysozyme (100 μg ml−1) to >99.9% for C. jejuni and E. coli cells with nisin. Under the experimental conditions used, nisin also reduced viable counts of skin-attached Staphylococcus aureus by >99.9%. The results suggest that the high TSP concentrations (approximately 10% wt/vol, 0.25 M) needed for successful decontamination of gram-negative bacteria, on the surface of poultry and other foodstuffs, may be substantially reduced by following TSP treatment with exposure to low lysozyme or nisin concentrations.