Natural antimicrobial synergy against food spoilage and pathogenic bacteria

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Most naturally occurring antimicrobials have a long history of use in foods, often being used to satisfy cultural preferences or expectations regarding colour, flavour, and even shelf-life where access to suitable refrigeration has been unavailable. Work proposed will examine active components in some of the more potent materials from foods of plant origin to determine how these agents work to inhibit and kill spoilage and pathogenic bacteria. Once the mechanism of natural antimicrobial agent action is known, combinations of agents can be used to simultaneously inhibit bacteria at multiple targets, optimizing antimicrobial activity. Proposed work will focus on several natural antimicrobials from spice essential oils known to have effects often comparable in potency with conventional agents. These will include allyl isothiocyanate (AIT), cinnamaldehyde, eugenol and carvacrol. Previous work from this laboratory has shown differences in the action of cinnamaldehyde from eugenol and carvacrol. The primary antimicrobial target of AIT may further differ. Cinnamaldehyde has unique effects on cell division causing filament formation, whereas AIT may inhibit DNA synthesis. These issues will be explored in the proposed work, being mindful that principal inhibitory effects often translate ultimately into loss of cell membrane integrity. On the basis of known differences in antimicrobial action of these agents, combinations of those with potentially different mechanisms of action will be evaluated for their ability to cause increased sensitivity or overcome resistance to single agents. Novelty in the work derives from its use of recent information on differences in modes of antimicrobial action to test the hypothesis that microbial control can be achieved through additive or synergistic effects. Further, a less well recognized characteristic of the test antimicrobials is that based on what we currently know about their mechanism(s) of action, there is little likelihood that pathogens of concern will develop resistance in response to challenge by these agents. From this work it is expected that more effective use can be made of naturally occurring antimicrobials to reduce risk of foodborne illness and premature food spoilage.