This study assessed the occurrence of an enhancing inhibitory effect of the combined application of Origanum vulgare L. essential oil and lactic acid against Staphylococcus aureus by the determination of Fractional Inhibitory Concentration (FIC) index and cell viability in meat broth and meat model. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the oil was 0.6 and 1.25 µL.mL-1, respectively. Lactic acid showed MIC and MBC of 2.5 and 5µL.mL-1, respectively. FIC indices of the combined application of the oil and lactic acid were 0.5 showing a synergic interaction. The essential oil and lactic acid showed similar (p>0.05) anti-S. aureus effect in meat broth over 96 h of exposure. Treatment with essential oil or lactic acid presented a smaller anti-staphylococcal effect in meat in comparison to meat broth. No significant difference (p>0.05) was found for the microbial counts in meat treated with each antimicrobial alone or in mixture. These results could arise as an interesting approach for the improvement of food preservation using more natural procedures, considering the current demand of consumer and sensory quality of foods.

Este estudo avaliou a ocorrência de um efeito inibitório potencializado quando da aplicação combinada do óleo essencial de O. vulgare e ácido acético sobre Staphylococcus aureus através da determinação Concentração Inibitória Fracional (FIC) e de ensaios de tempo de morte em caldo nutriente, caldo base carne e em um modelo alimentar (pedaços de carne). O ácido acético mostrou um valor de CIM e CBM de 0,6 e 1,25 µL.mL-1, respectivamente. Estudos prévios encontraram valores de CIM e CBM para o óleo essencial de O. vulgare sobre as cepas teste de S. aureus de 1,25 e 1,5 µL.mL-1, respectivamente. Valores de índices de CIF da mistura do óleo essencial e ácido acético na concentração de CIM x ½ foram £ 1,0 caracterizando uma interação de adição. Nenhum efeito sinérgico foi encontrado nos ensaios de tempo de morte. O efeito anti-estafilocócico dos antimicrobianos isolados ou em combinação (CIM x ½) foi menor quando aplicado em carne em comparação a sua adição em caldo nutriente e caldo carne. A efetiva combinação de óleos essenciais e outros agentes preservativos pode ser reconhecida como uma alternativa promissora para a indústria de alimentos, podendo viabilizando a diminuição de doses de antimicrobianos aplicadas para inibir o crescimento microbiano em alimentos.

This study evaluated the occurrence of an enhancing inhibitory effect of the combined application of Origanum vulgare L. essential oil and acetic acid against Staphylococcus aureus by the determination of Fractional Inhibitory Concentration (FIC) index and kill-time assay in nutrient broth, meat broth and in a food model (meat pieces). Acetic acid showed MIC and MFC of 0.6 and 1.25 µL.mL-1, respectively. For O. vulgare essential oil MIC and MBC were 1.25 and 2.5 µL.mL-1, respectively. FIC indexes of the mixture of essential oil and acetic acid at MIC x ½ were £ 1.0, showing an additive effect. No synergy was found at kill-time study. Anti-staphylococcal effect of the antimicrobials alone or in mixture (MIC x ½) was lower in meat than in nutrient and meat broths. The effective combination of essential oils and organic acids could appear as an attractive alternative for the food industry, as the doses to inhibit the microbial growth in foods can be lowered.