Antibacterial activity of essential oils from Citrus hystrix (makrut lime) against respiratory tract pathogens

Abstract

Many essential oils have antibacterial activity with a potential use in medicine. Citrus hystrix DC, or makrut lime, contains two essential oils, makrut leaf oil and makrut (fruit peel) oil, of which we determined the inhibitory effect against respiratory pathogens and evaluated their active components. Gas chromatography-mass spectrometry was used to analyse the chemical composition of the essential oils. The antibacterial activities were tested by disc-diffusion and broth microdilution methods against 411 isolates of groups A, B, C, F, G streptococci, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus (methicillin-resistant and -sensitive S. aureus) and Acinetobacter baumannii, obtained from patients with respiratory tract infections. Makrut leaf oil and makrut oil were both effective against all the pathogens with minimal inhibitory concentration (MIC) ranges of 0.06-68 mg/ml and 0.03-17.40 mg/ml, respectively. Citronellal was found to be the major component (80.04%) in makrut leaf oil and had the lowest MIC. In contrast, makrut oil consisted of several components (limonene 40.65%, terpinene-4-ol 13.71%, -terpineol 13.20%), and the most active component was -terpineol, followed by terpinene-4-ol, and limonene. These results suggest that makrut leaf oil, makrut oil, and their components (citronellal, -terpineol, terpinene-4-ol) may be alternative natural source medicine to prevent and treat many bacterial diseases.