Rosmarinus officinalis L. essential oil and the related compound 1,8-cineole do not induce direct or cross-protection in Listeria monocytogenes ATCC 7644 cultivated in meat broth

Listeria monocytogenes has the capability of adapting to 1 or more antimicrobial compounds or procedures applied by the food industry to control the growth and survival of microorganisms in foods. In this study, the effects of Rosmarinus officinalis essential oil (EO) and the related compound 1,8-cineole on the inhibition of the growth and survival of L.?monocytogenes ATCC 7644 were determined. The ability of the R.?officinalis EO and 1,8-cineole to induce direct and cross-protection of bacteria against various stresses (lactic acid, pH?5.2; NaCl, 3?g/100?mL; high temperature, 45?°C) was also determined. At all concentrations tested (minimum inhibitory concentration (MIC), ? MIC, and ? MIC), both compounds inhibited the cell viability of L.?monocytogenes over 120?min of exposure. Overnight exposure of L.?monocytogenes to sublethal amounts of either the R.?officinalis EO or 1,8-cineole in meat broth revealed no induction of direct or cross-protection against lactic acid, NaCl, or high temperature. Similarly, cells subjected to 24?h cycles of adaptation with increasing amounts (? MIC to 2× MIC) of the EO and 1,8-cineole showed no increase in direct tolerance, as they were able to survive in growth medium containing up to ? MIC of either substance. These results show the antimicrobial efficacy of R.?officinalis EO and 1,8-cineole for use in systems, particularly as anti-L.?monocytogenes compounds.