The Cytotoxic Effect of Essential Oils from Origanum vulgare L. and/or Rosmarinus officinalis L. on Aeromonas hydrophila

This study aimed to evaluate the antibacterial activities of the essential oils from Origanum vulgare L. (OV) and Rosmarinus officinalis L. (RO), both singly and in combination at sub-inhibitory concentrations (1/4 MIC + 1/4 MIC), against Aeromonas hydrophila and to investigate the possible mechanisms underlying these activities. Used singly (OV: 2.5 mu L/mL; RO: 20 mu L/mL) or in a mixture (OV: 0.625 mu L/mL + RO: 5 mu L/L), these essential oils led to a significant decrease (p < 0.01) in bacterial viability after 24 h of exposure. A decrease in glucose consumption by A. hydrophila and release of cellular material were observed immediately after the addition of the essential oils, both singly and as a mixture, and continued for up to 6 h. Electron microscopy of cells exposed to the essential oils revealed severe changes in the plasma membrane, cytoplasmic appearance, and cell shape during the 6-h exposure period. OV and RO essential oils combined at sub-inhibitory concentrations could be rationally applied to inhibit the growth of A. hydrophila in food products, particularly minimally processed vegetables.