Antimicrobial actions of glycerol fatty-acid esters for oral streptococci

Objective: Mono-glycerol esters of short-chain fatty acids have been found to have antimicrobial actions for a variety of pathogens. Methods: Responses of the oral pathogen Streptococcus mutans to monocaprylin (C8 fatty acid ester), monocaprin (C10), monolaurin (C12) and monomyristin (C14) were assessed to determine if the esters have potential for use as anticaries agents. Results: Monocaprin was highly effective for sensitizing glycolysis of intact cells to acidification, as indicated by the results of standard pH drop experiments with thick suspensions of cells given excess glucose. Minimum pH values at which glycolysis occurred in the presence of 1 mM monocaprin were approximately 4.9 compared to a value of 3.7 for control suspensions. A level of some 18 mM monocapyrlin was required for the same response, while the higher esters were at best minimally effective. Acid sensitization appeared to be related to membrane disruption rather than inhibition of the proton-translocating F-ATPase. Monocaprin was not a potent inhibitor of the enzyme of permeabilized cells, assayed in terms of phosphate release from ATP, but the higher esters were with 50% inhibitory levels of about 2 mM. Moreover, monocaprin did not inhibit the F-ATPase of intact cells. Monocaprin proved also to be lethal for S. mutans with 99.99% killing by 1 mM monocaprin after 10 minutes exposure. The other esters were much less effective for killing. Conclusion: Overall, the results indicate that these esters, especially monocaprin, are effective antimicrobials against S. mutans and have potential as anticaries agents. Supported by USPHS awards P01DE11549, R01DE06127 and T35DE07189.