Purpose: The objective of this study was to identify the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of different antimicrobial EO-containing micelles against foodborne pathogens.
Methods: Surfactants (Tween® 20, Surfynol® 485W, sodium dodecyl sulfate (SDS), and CytoGuard® LA20) were dispersed in sterile distilled water to different concentrations; eugenol and carvacrol (0.05-9.0% w/v) were added to surfactant solutions and stirred until completely emulsified. The micelle solutions were filter sterilized using a membrane filter (0.2 μm pore diameter). Antimicrobial activity of micelles was determined by addition of different concentrations of 2X micelle solutions to a 96-well plate. Escherichia coli O157:H7 and Salmonella Saintpaul in 2X tryptic soy broth (TSB; 5.0 log CFU/ml target inoculum) were then added to micelle-loaded wells. OD630 of test wells was measured before and after incubation at 35°C for 24 hr. After baseline adjustment, test wells showing <0.05 increase in OD630 were considered inhibitory; the lowest concentration of antimicrobial micelle producing pathogen inhibition was identified as the MIC for each EO/surfactant system. One hundred (100) μl from pathogen-inhibiting samples were spread on tryptic soy agar (TSA)-loaded Petri dishes and incubated for 24 hr at 35°C. The concentrations of micelle solution that produced ≥3.0 log CFU/ml reduction of the inoculated pathogen were classified as bactericidal; the lowest concentration of EO-micelle was deemed the MBC. All assays were performed in triplicate (n = 3).
Results: The lowest MIC of antimicrobial-bearing micelles against pathogens was observed in 0.5% SDS+ 0.1125% carvacrol while the lowest MBC was observed in 0.0625% CytoGuard LA20 + 0.0016% eugenol or carvacrol.
Significance: Antimicrobial micelle systems containing plant-derived EO may be useful delivery systems for the decontamination of fresh and/or fresh-cut produce.