South African medicinal plants screened against Pseudomonas aeruginosa

Background: Pseudomonas aeruginosa is amongst the three high-ranking pathogens on the World Health Organization’s global priority list of antibiotic-resistant bacteria. The list highlights research priorities in drug discovery and development. Aim: This study aimed to provide a detailed account of efforts by researchers to find anti-P. aeruginosa compounds from South African medicinal plant species during the period 2000–2020. Method: Various online research and journal databases were used to obtain information relating to South African medicinal plants and P. aeruginosa. Results: During the study period (2000–2020), only 31 studies reported on the antibacterial properties of South African medicinal plants against the pathogen. Given that P. aeruginosa is a serious cause of morbidity and mortality worldwide, it was interesting to note that none of the published reports were dedicated solely to the pathogen. Furthermore, only one study included the antibiotic-resistant mutants of the pathogen as a test organism. Over 150 plant species belonging to 78 families were screened against the bacterium. Barringtonia racemosa, Croton megalobotrys, Erythrina caffra, Leucosidea sericea, Maesa lanceolata, Morella serrata and Trichilia emetica exhibited potent anti-P. aeruginosa properties (minimum inhibitory concentration [MIC] ˂ 0.1 mg/mL). Plumbagin, a compound isolated from the leaves of Aristea ecklonii demonstrated promising activities (MIC = 0.008 mg/mL) against the bacterium. Essential oils extracted from some plants demonstrated noteworthy antibacterial synergistic effects (fractional inhibitory concentration index [FICI] ˂ 0.5) when used in pairwise combinations with conventional antibiotics. Conclusion: Overall, empirical evidence presented in the scantly available literature suggests that novel anti-P. aeruginosa agents could be developed from South African herbal extracts.