Antipseudomonal potential of Colophospermum mopane and Acrotome inflata, medicinal plants indigenous to Namibia

Abstract

Plants with diverse therapeutic properties are indigenous to Namibia. Concoctions of Colophospermum mopane and Acrotome inflata are widely used traditionally in the management of respiratory, gastrointestinal and wound infections. Limited studies have validated these traditional uses particularly against resistant bacteria strains such as Pseudomonas spp. This study aimed to determine the antimicrobial activity and phytochemistry of extracts of C. mopane and A. inflata, medicinal plants indigenous to Namibia. Phytochemical analysis and antimicrobial testing were done on leaves and barks of C. mopane and A. inflata whole plant. Voucher specimens were collected from Omugulugoonime village, Oshikoto region and validated at the National Botanical Research institute, Windhoek. Crude extraction of dried plants was done by maceration with ethanolic and aqueous solvents. Phytochemical screening was done using methods described by Harborne (1998) and/or Tiwari et al (2011). The antimicrobial activity against wild types of Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtillis and Candida albicans was done using the disc-agar-diffusion method. The mean diameters of the zones of inhibition (mm) for each extract were determined against each test organism. The antimicrobial activity (zones of inhibition) of ethanolic extracts (5 mg/ml) of C. mopane bark (10±0.6 mm) and leaves (10±1.2 mm) and A. inflata (8.7±0.6 mm) against P. aeruginosa is comparable to that of penicillin G (14±1.4 mm). Aqueous extracts leaves and bark of C. mopane showed activity against P. aeruginosa and S. aureus. The activity of the ethanolic extracts against B subtillis was: C. mopane leaves (7.3±0.6 mm), C. mopane bark (8.7±0.6 mm) and A. inflata (11.3±3.21 mm) and Penicillin G (26±1.4 mm). Both ethanolic and aqueous extracts did not have activity on C. albicans. Aqeous extracts of A. inflata had no activity on Pseudomonas and B. subtillis. Organic extracts of Colophospermum mopane and A. inflata exhibit antimicrobial potential against Pseudomonas and Bacillus species. The alkaloids, flavonoids and tannins should be further purified and characterized for antipseudomonal activity.

The Botanical, Chemical and Ethnobotanical Diversity of Southern African Lamiaceae

“…Other species such as Acrotome angustifolia G.Taylor is used as a medicinal tea administered to children for upset stomachs whereas A. inflata is used in Namibia as a treatment for coughs, fever and breast pain, and in the Eastern Cape of South Africa, it used as a treatment for skin ailments, including chickenpox, wounds, sores, rashes and eczema [ 17 , 324 , 325 ]. The use of A. inflata for topical use is corroborated by Iyambo, Kibuule and Ilonga (2017) [ 34 ] who tested methanolic and aqueous extracts of the plant on several bacterial strains, including Pseudomonas aeruginosa , Staphylococcus aureus and Bacillus subtilis . The results produced in the study were comparable with that of penicillin, although the extracts did not show any activity as an antifungal agent against Candida albicans .…”

“…One of the earliest accounts of phytochemical investigations of southern African Lamiaceae was in 1964 when marrubiin was isolated from Leonotis leonurus [ 29 ]. Since then, several compounds have been isolated and their chemical structures determined, primarily diterpenes [ 30 , 31 , 32 , 33 ], phenolic compounds [ 34 ], pyrones [ 35 , 36 , 37 ], and glycosides [ 38 , 39 , 40 ].…”

“…Coumarins are reported to be present in six southern African species: Acrotome inflata Benth. [ 34 ], Basilicum polystachyon [ 47 ], Cantinoa ameriacana [ 38 ], Coleus hadiensis (Forssk.) A.J.…”