Action mechanism of small and large molecule surfactant-based clove oil nanoemulsions against food-borne pathogens and real-time detection of their subpopulations

Flow cytometry exactly discriminated three subpopulations, i.e., viable, damage and sublethal cells of L. monocytogenes, S. aureus and E. coli when treated at their MIC values. Purity gum ultra (PGU) a large molecule surfactant-based CO nanoemulsion exerted significant impact on cellular subpopulations of L. monocytogenes and S. aureus, with more membrane-damaged cells. On the other hand, when compared with bulk CO the results showed minimum membrane damage and more viable cells, whereas PGU CO nanoemulsion showed minimum effect on cellular subpopulation and represented more viable than damaged cells in case of E. coli. Similarly, Tween 80 a small molecule surfactant-based CO nanoemulsion showed limited overall activity against three tested microorganisms with more viable cells. We conclude that it was due to sequestration of CO constituents in interfaces, less availability in aqueous phase and finally inhibit bactericidal activity. Moreover, both CO and CO nanoemulsions showed membrane damage as primary inactivation mechanism of tested bacterial cells.