Abstract

This study aimed to determine the antimicrobial activity and strength of kill of Himalayan oregano oil (HOO) across a range of dilutions typically formulated for potential topical use in healthcare settings, using bioluminescent constructs of bacterial pathogens as real time biosensors for rapid bactericidal monitoring. Escherichia coli, Pseudomonas aeruginosa and Methicillin sensitive Staphylococcus aureus, previously genetically modified by addition of the luxCDABE operon to express bioluminescence, were used as reporters of viable metabolically active cells to show a real time in situ antimicrobial effect of oregano oil. On the other hand, for genetically non-modified methicillin resistant S. aureus and Candida albicans, viable count method was used to assess the antimicrobial effect of oregano oil. Minimal inhibitory concentration of Himalayan oregano oil (HOO) and its major components, carvacrol and thymol, were found to be between 0.03 and 0.16%. High positive correlation was obtained between viable count and bioluminescence. These findings suggest that bioluminescence has the capability to replace the plate culture method for evaluating the efficacy of antimicrobial products. HOO may have the potential as a natural potent bactericide in the health care setting, as it has demonstrated bactericidal action towards pathogens in a short time (40-220 s). This is the first in vitro method used to assess the antimicrobial activity of oregano oil using lux reporter gene technology as an accurate measure of kill rates which is captured in real-time with high reproducibility and fidelity of responses such that comparisons are accurate.

Key words: Oregano oil, bioluminescence, viable count, lux operon, antimicrobial.

Abbreviation

pA, Height in picoamperes; HOO, Himalayan oregano oil; MOO, Mediterranean oregano oil; MIC, minimum inhibitory concentration; RLU, relative light unit; CFU, colony forming unit.