Is the antimicrobial mechanism of action of essential oils against bacteria associated with channels similar to TRPV1 channels found in mammalian cells?

Abstract

Objectives: The aim of this investigation was to find out if the antimicrobial mechanism of action of Essential Oils (EOs) against Enterococcus spp. may be associated with channels similar to TRPV1 channels found in mammalian cells. A known antimicrobial combination of EOs compounds (Carvacrol 0.2µl and Cuminaldehyde 25µl) against E. faecium and capsaicin were used to investigate this hypothesis. The bacterial membrane has many porin proteins which act as hydrophilic transmembrane channels and allow small hydrophilic solutes to pass through them1, such channels may be the target for the antimicrobial mechanism of action of EOs in the Gram-positive bacterial cell wall. Methods: Transient receptor potential (TRP) channels, are a group of unique ion channels in mammalian cells, that are effected by a wide spectrum of physical and chemical stimuli2, including high temperature and low pH. Capsaicin the EO compound of chilli peppers is known to be a TRP channel antagonist in mammalian cells2,3 whilst AMG 517 specifically blocks TRP channels, and Ruthenium Red (RR) is a wide spectrum blocker for TRPV1 channels4,5. The Minimum Inhibitory Concentration (MIC) of capsaicin against Vancomycin Sensitive E. faecium (VSE) was defined by agar-broth dilution method, a checkerboard assay was conducted to determine the interactions of AMG517 and RR against E. faecium. A growth curve was also conducted to assess the effect of the EO blend in the presence of AMG517. Results: Capsaicin showed antibacterial activity against E. faecium with an MIC of 1.6mM. The checkerboard data demonstrated that AMG517 has no inhibitory effect on E. faecium and therefore was a good candidate to reverse the effect of EOs blend by potentially blocking channels that were similar to TRPV1. RR was antimicrobial at concentrations above 10µM, however, AMG517 above 60nM reverses the inhibitory effect of RR, demonstrating a competitive effect of AMG517 and RR towards a definite site in the bacterial cell wall. Growth curves showed no reverse effect of the EO blend in the presence of AMG517. Conclusions: This study does not support the existence of a TRPVI homologue in the bacterial cell. Future studies will investigate the genes related to transport channels in E. faecium, that are differentially regulated when exposed to the EO blend, in order to further understand the effect of the EOs on transport channels in bacteria.