Bioactivity of selected South African medicinal plants used traditionally for the treatment and management of Neisseria gonorrhoeae

Abstract

Backround: Sexually transmitted diseases (STDs) are of a great global health concern, with an estimated one million infections acquired daily. The aim of this study was to investigate the bioactivities of eight selected South African medicinal plants used traditionally in the treatment and management of sexually transmitted diseases. Methods: The powdered dried plant material were extracted in four different solvents i.e. ethanol, ethyl acetate, dichloromethane and water, to yield forty plant extracts. The antibacterial and anti-biofilm effect of the extracts were tested against Neisseria gonorrhoeae using the MIC and crystal violet assays, respectively. All the extracts were investigated for their anti-inflammatory activity against 15-lipoxygenase enzyme. Extracts that showed good antibacterial activity were further evaluated for their anti-quorum sensing potential by investigating their ability to inhibit violacein. Phytochemicals of the most potent extracts were analysed by GCMS and the in vitro AQS potential of some of the compounds was validated using in silico molecular docking. Results: Eleven of the forty extracts tested showed good antimicrobial activity (MIC values <1 mg/ml) against N. gonorrhoeae, with the best being 0.19 mg/ml by the methanolic root extract of Pseudolachnostylis maprouneifolia. The methanolic leaf extract of P. maprouneifolia exhibited a noteworthy anti-inflammatory with an IC50 value of 20.42 μg/ml as compared to the positive control quercetin (29 μg/ml). The extracts tested for quorum sensing all showed a positive violacein inhibition with the ethanolic root extract of P. maprouneifolia having the highest inhibition (55%) at a concentration of 6.25 mg/ml. All the extracts except for P. maprouneifolia dichloromethane root extract, inhibited the initial biofilm attachment by 1%-62%; with the leaf ethanolic extract being the best showing 62% inhibition. N. gonorrhoeae preformed biofilm were more resistant to treatment, instead bacterial growth enhancement was exhibited. CLSM was then used to confirm the enhancement of growth of the bacterium. Due to the positive potential of the ethanolic and aqueous leaf extracts of P. maprouneifolia in the assays conducted, these extracts were analyzed by GC-MS: 85 known compounds and 11 unknown compounds were identified. The common compounds found in both these extracts were then subjected to in silico molecular docking to investigate their binding affinities to the CviR protein (3QP1) of C. violaceum 12472. The compound 1, 2-Benzenedicarboxylic acid, bis (2-methylpropyl) ester showed the best docking score (-6.894), significantly binding to the active site of the CviR protein better than the positive control vanillin (-4.880) but lower than quercetin (-10.613). Conclusion: The observed biological activities of the medicinal plants investigated have potential, and also support their traditional use in the treatment and management of sexually transmitted diseases.