In vitro combined effect of oregano essential oil and caprylic acid against salmonella serovars, escherichia coli O157:H7, staphylococcus aureus and listeria monocytogenes

Abstract

In vitro inhibition of foodborne pathogens via action of natural antimicrobials - caprylic acid (CA) and essential oil from Origanum vulgare L. (OEO) with high carvacrol content (72%) was evaluated. For 15 Salmonella strains the minimum inhibitory concentration (MIC) determined by broth microdilution method ranged between 3.67-4.33 ixl·ml- 1 for CA and between 0.48-0.57 ixl·ml- 1 for OEO. For 7 Listeria monocytogenes strains the MIC ranged between 2.17-2.83 |xl·ml -1 for CA and between 0.52-0.58 ixl·ml- 1 for OEO. Type strains of Escherichia coli O157:H7 and Staphylococcus aureus were tested, too, with MIC of CA 3.60 ixl·ml- 1 and 3.20 ixl·ml- 1 and MIC of OEO 0.51 ixl·ml- 1 and 0.48 ixl·ml- 1, respectively. Furthermore, it was found that the MIC of CA can be decreased by even low addition (0.05%) of citric or acetic acid and to a lesser extent by lactic acid, whereas the MICs of OEO did not notably decrease. Combined application of CA and OEO determined by FIC index led only to an additive effect (0.5 ≤ FIC ≤ 1). Combination of natural additives OEO, CA and eventually acetic or citric acid seems to have the potential to be an effective mixture for inhibition of foodborne pathogens, predominantly Salmonella spp. and L. monocytogenes, even in only slightly acidic food.