Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected aw and pH

To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound. Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (aw; 0·99 or 0·97) and pH (5·5 or 4·5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at aw 0·99, and pH 5·5 to 100-ppm thymol or carvacrol for the four studied bacteria at aw 0·97 and pH 4·5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the aw and the pH tested. Synergistic binary mixtures with fractional inhibitory concentration index