Phosphates have been approved for use in meat products primarily to protect flavor and increase yields. It also is known that phosphates have antimicrobial properties. The objective of this study was to compare the effects of different phosphates in a model system. Minimum inhibitory concentrations (MICs) of selected food-grade phosphates added to early-exponential-phase cells of Staphylococcus aureus ISP40 8325 in a synthetic medium were determined to be 0.1% for sodium ultraphosphate and sodium polyphosphate glassy and 0.5% for sodium acid pyrophosphate, sodium tripolyphosphate and tetrasodium pyrophosphate. Thus, the MIC values for the very long chain-length phosphates were lower than the MIC values for shorter chain-length phosphates. Leakage of intracellular nucleotides was observed both spectrophotometrically (release of A260-absorbing material) and microscopically (appearance of gelatinous cellular aggregates). Treatment of the gelatinous cellular aggregates with DNase, RNase and proteinase indicat...