Abstract Description

Every year, infectious diseases cause millions of deaths worldwide, raising serious health concerns. The study reports on the antimicrobial, antibacterial mechanism, antibiofilm, cytotoxic and antioxidant effects of South African medicinal plants (Tetradenia riparia, Syzgium cordatum, Gymnosporia senegalensis and Carissa bispinosa). The phytochemicals were extracted with hexane, ethyl acetate and methanol. The phytochemical profile was generated using liquid chromatography-mass spectrometry and spectrophotometric methods. The broth microdilution assay was used to evaluate the antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus aureus. The 2-diphenyl-1-picrylhydrazyl (DPPH) was utilised to assess the antioxidant potential of the extracts and cytotoxicity was evaluated using the methylthiazol tetrazolium assay. The crystal violet staining assay was used to evaluate the anti-biofilm activity. The antibacterial mechanism was assessed by examining changes in relative dehydrogenase activity (RDA) and the leakage of intracellular constituents using spectrophotometry. S. cordatum methanol extract had the highest polyphenolic content (440 ± 1.51 mg GAE/g, 321.26 ± 4.06 mg QE/g, 430.18 ± 8.43 mg TAE/g). LC-MS revealed the presence of compounds with various biological activities in the bioactive extracts. A. venosum and S. cordatum methanol extracts had the best DPPH scavenging activity (IC50, 15,81 and 25.72 μg/mL) respectively. S. cordatum methanol extract inhibited all the tested pathogens with an MIC range of (0.31 to 0.63 mg/mL) while A. venosum ethyl (MIC 0.31-0.63 mg/mL) and T. riparia (MIC 0.16-0.31 mg/mL) ethyl acetate extracts inhibited the Gram-negative (P. aeruginosa and E. coli) and Gram-positive (S. aureus and E. faecalis) bacteria respectively. All the extract had a cell viability percentage of more than 50% at MIC. T. riparia ethyl acetate extract reduced the RDA of S. aureus with more than 80%. The methanol extract of S. cordatum yielded the highest leaked proteins ranging from 5 to 13 µg/mL at 2x MIC against the 4 pathogens. At least one extract had an initial cell attachment inhibition of over 50% against the all the pathogens. S. cordatum, A. venosum and T. riparia had promising antimicrobial, antibiofilm and antioxidant effects, further studies may focus on synergistic effects with conventional drugs and isolation of the bioactive constituents.