Comparison of antimicrobial spectrum and mechanisms of organic virgin coconut oil and lauric acid against bacteria

Abstract

Organic virgin coconut oil (VCO) contains almost 50% lauric acid (LA). As lauric acid exhibits antimicrobial activity against some bacteria, VCO is thought to also possess antibacterial properties. However, it is unclear whether the antimicrobial activity of VCO is comparable to that of LA. The present study was performed to examine whether VCO demonstrates antimicrobial activity against species of gram-positive bacteria (i.e. Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactie, Streptococcus sanguinis, Streptococcus salivarius, and Streptococcus mutans) as well as LA by disk diffusion antibacterial test. Although LA has antimicrobial activity against S. aureus, S. pyogenes, S. agalactie, S. mutans and S. sanguinis, VCI has antimicrobial activity against S. pyogenes, S. agalactiae, S. mutans, and S. sanguinis, but not S. aureus. Furthermore, the antimicrobial activities of VCO against several Streptococcus species were weaker than those of LA. We further compared the antimicrobial activities of VCO and LA against Streptococcus pyogenes by antimicrobial test involving the inhibition of microbial growth in broth medium. While >4.4 mM VCI was capable of exhibiting an antimicrobial effect against S. pyogenes, the same effect was demonstrated by as little as 0.18 mM LA. Furthermore, >0.88 mM LA, but not VCO, was able to eliminate S. pyogenes completely. We also confirmed that LA could eliminate bacteria within 10 minutes, and the number of bacteria did not increase for 2 hours. On the other hand, the addition of VCI did not decrease the number of bacteria. In addition, scanning electron microscopic (SEM) analysis indicated that the antimicrobial activity of LA is mediated by a bactericidal mechanism, whereas VCO function by inducing bacteriostasis. Taken together, we found that VCO has antimicrobial properties against some strains of bacteria belonging to the genus Streptococcus, but not Staphylococcus aureus of some gram-negative bacteria. These findings suggest that the antimicrobial spectrum of VCO differs from that of LA. We also found that the antimicrobial effect of VCO is mediated by bacteriostasis, and not a bactericidal mechanism as observed for LA.