Bioactivity guided fractionation of potent antiacne plant extract against Propionibacterium acnes

Abstract

Propionibacterium acnes (P. acnes) is a commensal anaerobic, Gram positive bacterium that belongs to the normal microflora. P. acnes play an important role in the pathogenesis of various skin infections and diseases. However, the available agents are associated with number of side effects and P. acnes show the genetic base of antibacterial resistance against erythromycin and clindamycin. Therefore, alternative natural approaches for the treatment are needed for an hour for alleviation of infection caused by P. acnes. To find out the most effective anti P. acnes extract amongst the selected four plants commonly used for anti-acne potential and to obtain the characterized fraction of the extract with highest anti P. acnes potential, in vitro antimicrobial activity was evaluated using disk diffusion method and the zone of inhibition was compared using Hi-media zone measuring ruler. Afterwards, minimum inhibitory concentration (MIC) was determined for the potent fraction and the results were compared with Clindamycin. The active fraction was characterized chemically and its thin-layer chromatography (TLC) finger printing profile was prepared in order to standardize it. The methanolic extracts of Rubia cordifolia showed maximum (14.0 and 24.0 mm) anti P. acnes activity. The petro-ether fraction showed highest potential compared to other fractions of the extract. Sub-fraction D of petro-ether fraction with maximum activity was further purified. But, the results were similar to the sub-fraction D. The MIC was found to be 3 µg/ml of sub-fraction. R. cordifolia extracts have significant anti P. acnes activity in comparison to Tephrosia purpurea, Viola tricolor and Serenoa repens. The fractionation of R. cordifolia extract enhanced the activity but only up to certain extent. The TLC finger printing profile and chemical identification tests can be used for the identification/standardization purpose of this active fraction. Key words: Rubia cordifolia, Tephrosia purpurea, Viola tricolor, Serenoa repens, antibacterial activity.