Antimicrobial and cytotoxicity properties of the crude extracts and fractions of Premna resinosa (Hochst.) Schauer (Compositae): Kenyan traditional medicinal plant

Antibacterial and antifungal activities were investigated by disc diffusion and micro dilution techniques. Antituberculous activity was investigated using BACTEC MGIT 960 system while cytotoxicity was analyzed by MTT assay on Vero cells (Methanolic crude extract) and HEp-2 cells (fractions). Finally, phytochemicals were profiled using standard procedures.

P. resinosa had high antituberculous activity with a MIC of <6.25 μg/ml in ethyl acetate fraction. The antibacterial activity was high and broad spectrum, inhibiting both Gram positive and Gram negative bacteria. Dichloromethane fraction had the best antibacterial MIC of 31.25 μg/ml against Methicillin-resistant S. aureus while Ethyl acetate fraction had the highest zone of inhibition of 22.3 ± 0.3 against S. aureus. Its effects on tested fungi were moderate with petro ether fraction giving an inhibition of 10.3 ± 0.3 on C. albicans. The crude extract and two fractions (petro ether and methanol) were not within the acceptable toxicity limits, however dichloromethane and ethyl acetate fractions that exhibited higher activity were within the acceptable toxicity limit (CC₅₀ < 90). The activity can to some extent be associated to alkaloids, flavonoids, terpenoids, anthraquinones and phenols detected in this plant extracts.

Our findings demonstrate that P. resinosa has high selective potential as a source of novel lead for antituberculous, antibacterial and antifungal drugs. Of particular relevance is high activity against MRSA, S. aureus, C. albicans and MTB which are great public health challenge due to drug resistance development and as major sources of community and hospital based infections.