Abstract: The aim of this study was to investigate the antibacterial activity of essential oils against respiratory pathogens in vapour phase. In vitro antibacterial activity against three Grampositive strains (Staphylococcus aureus, Streptococcus pneumoniae and Hemolytic streptococcus) and three Gram-negative strains (Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa) was evaluated by disc volatilization method.The antibacterial tests indicated that Gram-positive bacteria were sensitive to all thirteen essential oils.Particularly linalyl oil,peppermint oil and litsea cubeba oil showed the best activities,which expressed the minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) at 250 μL/L.While Gram-negative microorganism were less sensitive and P.aeruginosa was the least inhibited,the most effective essential oil was rosemary oil against Gram-negative microorganism,which held MIC and MBC at 1000 μL/L.Therefore,It was concluded that the investigated essential oils in vapour phase are significant in control of common Gram-positive respiratory pathogens.

Key words: essential oil, vapor-phase antimicrobial effect, respiratory pathogens