Until recently, the antibacterial activity of essential oils has been primarily evaluated through direct contact methods between the pathogen and the antimicrobial agent through diffusion and dilution methods, however the role of essential oils in the vapour phase as antimicrobial agents is gaining increasing significance.
This method was developed on the premise that essential oil vapours exert critical biological activity. These methods offer rapid screening protocols for the antimicrobial assessment of plant essential oils. It has been suggested that essential oils in the vapour phase possess the greatest degree of antimicrobial activity since the active constituents are highly volatile in nature and thus, the vapour is therefore the contributing attribute for its biological activity. Each individual constituent has differing volatility, therefore when the mixtures are introduced into a free, non-saturated state in a closed micro-environment; the volatile constituents begin to disperse at differing rates in the vapour phase within the headspace according to their degree of volatility until they reach equilibrium.
Preliminary research involving the essential oils of citronella yielded promising results when tested against a selection of Gram-positive bacteria and Gram-negative bacteria. The use of such extracts can be explored especially in the development of cost-effective treatments of respiratory illness, specifically of those caused by bacterial or fungal infection. Preliminary tests exhibit complete inhibition of the growth of certain bacterial strains.