Lack of induction of direct protection or cross-protection in Staphylococcus aureus by sublethal concentrations of Origanum vulgare L. essential oil and carvacrol in a meat-based medium.

The capacity of Origanum vulgare L. essential oil (OVEO) and its majority compound, carvacrol (CAR), to induce direct tolerance and cross-tolerance in Staphylococcus aureus against high temperature (45 °C), lactic acid (pH 5.2) and NaCl (10 g/100 mL) was assessed. Overnight exposure of S. aureus to sublethal concentrations (1/2 MIC, 1/4 MIC) of either OVEO or CAR in meat broth revealed no induction of direct protection. S. aureus cells pre-adapted to OVEO or CAR showed no induction of cross-protection to high temperature, lactic acid or NaCl. Cells subjected to 24 h cycles of adaptation in increasing amounts (1/2 MIC to 2 × MIC) of OVEO or CAR showed no increase in direct tolerance. These results revealed a lack of induction of direct protection or cross-protection in S. aureus exposed to sublethal amounts of OVEO or CAR in meat-based broth, as determined by monitoring cell survival and growth behavior.