Comparative analysis of the effects of Origanum vulgare essential oil and carvacrol nanoemulsified and non-nanoemulsified forms against Salmonella Typhimurium strains

This study investigates the potential of Origanum vulgare L. (OVEO), carvacrol (CAR), and their nanoemulsions (nOVEO and nCAR) in subinhibitory concentrations as antimicrobial agents against S. typhimurium strains in vitro and in situ. The minimum inhibitory concentrations (MIC) ranged from 0.59 to 0.60 mg/mL for the nanoemulsions and 0.68 to 1.5 mg/mL for their non-nanoemulsified counterparts. Growth kinetics analysis showed that all treatments at 1/4 MIC, 1/2 MIC, and MIC reduced the growth rate and prolonged the lag phase. Flow cytometry analysis revealed that these treatments caused permeabilization of the cell membranes, with OVEO standing out for its highest effect on membrane rupture, even at subinhibitory concentrations. Regarding adhesion prevention, the nanoemulsions demonstrated equal or greater efficacy compared to non-nanoemulsified compounds, with >44.12 % inhibition even at the lowest tested concentration. In chicken fillets inoculated with a four-strain S. typhimurium cocktail, a reduction in bacterial counts was observed throughout the experiment. The highest reduction (0.82 ± 0.08 log CFU/g) was recorded on the eighth day of treatment with nOVEO at 2xMIC (2.86 mg/mL). Therefore, this study investigates the complexity of OVEO and CAR, highlighting their antimicrobial potential at different action targets against Salmonella, including biofilm adhesion inhibition and their application in contaminated food matrices. Additionally, it reveals that the reduction in droplet size in nanoemulsions can enhance the antimicrobial action of the essential oils, increasing their applicability and contributing significantly to food safety.