Antimycobacterial, antibiofilm and efflux pump inhibitory activity of extracts from selected Combretum species used in traditional medicine in Zimbabwe

Non-tuberculous mycobacteria infect mostly immunocompromised people. NTM infections incidence and prevalence increase has led to a public health problem. Combretum species are used as food by humans and animals, and medicinal purposes. The aim of the study was to evaluate the antimycobacterial effects of plant extracts from selected Combretum species on Mycobacterium smegmatis and Mycobacterium aurum as well as their mode of action on the most susceptible organisms. Antimycobacterial activity of the plant extracts was screened. Mycobacterium smegmatis was more susceptible to the extracts. The potent Combretum extracts were investigated for their effects on Rhodamine 6G transport and biofilms in M. smegmatis. The amount of Rhodamine 6G accumulated in M. smegmatis in the presence of extracts were also investigated. The C. zeyheri acetone extracts were the most potent efflux pump inhibitors. Surface extracts from C. zeyheri were the most potent disrupters and inhibitors of biofilms. The ethylacetate extract of another species, C. apiculatum lacked the effect on biofilms and this may be due to the lack of penetration of the extract into the already established biofilm. The ultra-high performance liquid chromatography UPHLC-MS/MS analysis of acetone extracts from C. zeyheri indicated the presence of cirsimaritin, quinic acid, and ampelopsin glucoside and these could have contributed to the antimycobacterial activities of the extract. In conclusion, phytochemicals from C. zeyheri, C. platypetalum, C. apicultum species used in traditional medicine in Zimbabwe showed antimycobacterial and antibiofilm activity and may be used as sources of lead compounds targeting non-tuberculosis infections caused by M. smegmatis.