Synergistic antimicrobial effect of lactocin AL 705 and nisin combined with organic acid salts against Listeria innocua 7 in broth and a hard cheese

Summary The effectiveness of antimicrobial mixtures against Listeria innocua 7, used as a L. monocytogenes surrogate, was investigated in broth and a food system. Synergistic effects were found for nisin (Nis), potassium sorbate ( PS ), calcium propionate ( CP ) and sodium lactate ( SL ), Nis +  PS being the most effective binary mixture that exhibited listericidal activity in broth. To assess the effect of adding lactocin AL 705 ( AL 705) to Nis + organic acid salt combinations, tridimensional isobolograms were generated. Sub‐ MIC combinations of the antimicrobials exerted bactericidal activity against L. innocua 7 after AL 705 addition to the binary mixtures. However, when applied on Sardo cheese contaminated with L. innocua 7 (initial inoculum 4.45 ± 0.06 CFU g −1 ), only Nis +  PS  +  AL 705 produced count reductions respect to the control, reaching 3.04 ± 0.35 CFU g −1 counts after 15 days at 15 °C. Ternary combinations containing AL 705 showed potential to reduce antimicrobial usages for L. innocua 7 inhibition.