TRISODIUM PHOSPHATE INCREASES SENSITIVITY OF GRAM-NEGATIVE BACTERIA TO LYSOZYME AND NISIN

Cell suspensions of Campylobacter jejuni, Escherichia coli, Pseudomona s fluorescens, and Salmonella enteritidis exposed to sublethal concent rations (0.5 to 5 mM) of trisodium phosphate (TSP) for 10 min showed g reatly increased susceptibility to lysozyme (10 mu g ml(-1)) and/or ni sin (1 mu M) Under optimal conditions at 37 degrees C, reductions in v iable count after 30 min were up to six log cycles. At 4 degrees C, C. jejuni showed greater resistance than at 37 degrees C, and maximal ce ll kills (95%) were reduced by more than two log cycles. Cells dried o n the surface of chicken skin were more resistant than suspended cells to TSP-lysozyme and TSP-nisin treatments; nevertheless, at 37 degrees C, kills varied from approximately 95% for S. enteritidis cells with nisin (30 mu M) or lysozyme (100 mu g 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 aureu s by >99.9%. The results suggest that the high TSP concentrations (app roximately 10% wt/vol, 0.25 M) needed for successful decontamination o f gram-negative bacteria, on the surface of poultry and other foodstuf fs, may be substantially reduced by following TSP treatment with expos ure to low lysozyme or nisin concentrations.