Inhibitory effect of carvacrol nanoemulsions on Staphylococcus aureus and its biofilms

Abstract

Staphylococcus aureus is a leading cause of foodborne illnesses, partly due to its pronounced capacity for biofilm formation. This study aims to evaluate the antibacterial and antibiofilm effects of carvacrol encapsulated within a nanoemulsion against S. aureus. The minimum mitigation concentration, bacterial growth curves, and cell membrane characteristics were the key parameters examined. Carvacrol nanoemulsions demonstrated superior antibacterial activity compared to pure carvacrol, with a minimum inhibitory concentration of 0.125 mg/mL. Remarkable leakage of intracellular components such as nucleic acids, proteins, and alkaline phosphatases was noted following the exposure of S. aureus to carvacrol nanoemulsions, thereby suggesting significant impairment of the integrity of bacterial cell membranes and cell walls. Carvacrol nanoemulsions effectively disrupted the biofilm formation process in 96-well microtiter plates, and successfully eradicated mature biofilms of S. aureus at minimum concentrations of 0.25 mg/mL and 0.5 mg/mL, respectively. A similarly robust antibiofilm effect of carvacrol nanoemulsions was also achieved on stainless steel surfaces in a dose- and time-dependent manner. This was likely due to the suppression of bacterial surface hydrophobicity. This study underscores the potential application of carvacrol nanoemulsions as a means to combat S. aureus in both planktonic and biofilm states, contributing to microbial food safety control.