A comparative study of the antimicrobial activity of the leaf essential oils of chemo-varieties of Clausena anisata (Willd.) Hook. f. ex Benth

Abstract

The emergence of multiple drug resistance to human pathogenic organisms has necessitated a search for new antimicrobial substances from various sources including plants. The present study was carried out as part of this search using the essential oils of the leaves of three chemo-varieties of Clausena anisata (Willd.) Hook. f. ex Benth. namely, estragole, trans-anethole and feniculin-containing chemo-varieties. The oils were screened against six bacteria ( Escherichia coli, Staphylococcus aureus, Salmonella typhi, Shigella sp., Proteus sp. and Pseudomonas aeruginosa) and three fungi ( Candida albicans, Aspergillus niger and Aspergillus parasiticus) isolated from clinical specimen using the disc sensitivity test. Microbes which showed significant sensitivity were further assayed with various concentrations of the active extracts in a dilution sensitivity test. The microorganisms were also assayed against seven broad spectrum antibiotics: penicillin G, amoxycillin, ampicillin, tetracycline, ceftizoxime, fosfomycin and urotractin. Results from the disc sensitivity test showed that the estragole-rich oil exhibited significant antimicrobial activity against E. coli (16.3 ± 0.3 mm) and Shigella sp. (17.2 ± 0.4 mm). The trans-anethole-rich oil exhibited less significant activity (11.4 ± 0.7 mm and 12.1 ± 0.3 mm respectively) whereas the feniculin-rich oil, acting alone and in combination with the trans-anethole-rich oil did not show any significant activity against the all microbes tested. Only the neat oils and their 1:2 dilutions showed visible inhibition of microbial growth in the dilution sensitivity test. The estragole-rich oil gave minimum inhibitory concentrations of 3.7, 6.7 and 13.2 mg/ml against C. albicans, S. aureus and E. coli respectively with corresponding ED 50 values of 1.3, 2.1 and 1.2 mg/ml. The trans-anethole-rich oil gave a minimum inhibitory concentration of 1.8 mg/ml against C. albicans with an ED 50 of 0.2 mg/ml. The findings suggest a significant antimicrobial activity of these plant essential oils though of lower efficacy compared to ampicillin. The results further suggest that such plant essential oils could potentially be exploited in the development of novel antibiotics.