Synergistic effects of plant extracts and penicillins on staphylococcus and enterococcus faecalis
Authors:   , Nsele Nhlanhla Wiseman 
Published: March 2022

Medicinal plants have been used for centuries as remedies for human diseases because they contain components of therapeutic value. Recently, the acceptance of traditional medicine as an alternative form of health care and the development of microbial resistance to the available antibiotics has led scientists to investigate the antimicrobial activity of medicinal plants. Aim The aim of this study is to evaluate the interaction between water and ethanolic extracts of Psidium guajava (ugwava) and Sutherlandia frutescens (unwele) alone and then synergy testing of these extracts with known penicillins using both disc diffusion and microdilution method on Staphylococcus aureus(S. aureus) and Enterococcus faecalis(E. faecalis). Methodology The plants used in this study Sutherlandia frutenscens (S. fruitescens) and Psidium guajava (P. guajava) were harvested from the Silverglen Nature Reserve (Chatsworth) early in the morning (8 am). The leaves of S. frutescens and P. guajava were used to prepare the extracts. All plant extracts were prepared according to modified method of the German Homeopathic Pharmacopoea. Two solvents, water and ethanol were used for extraction. The extracts were then assessed for their antibacterial activity against methicillinresistant Staphylococcus aureus (MRSA), methicillin-sensitive Staphylococcus aureus (MSSA) and Enterococcus faecalis. The effect of the plant extracts on these bacteria was determined by the disk diffusion test, which was used as the screening test. Positive results were further subjected to the minimum inhibitory concentration and minimum bactericidal concentration assays using the agar dilution method. Dilutions that showed no growth on non-selective plates were taken as minimum inhibitory concentration and minimum bactericidal concentrations. Bacterial sensitivity testing was carried out in accordance with modified Kirby-Bauer Antimicrobial Sensitivity Test. The synergy testing was conducted by combining the extracted plants with penicillins. The combinations were then tested against MRSA, MSSA and E. faecalis and the results were compared with both the individual plant and the penicillins. Results Only the water-based extracts of plants were able to inhibit MRSA, MSSA and E. faecalis. None of the test organisms were inhibited by the ethanol extracts of all plants used in this study. In the screening test, the zones of inhibition for waterbased extracts against MRSA, MSSA and E. faecalis ranged from 17 mm to 35 mm. The minimum inhibitory concentration ranged from 0 % to 100 % inhibition depending on the dilution of the extract. In the combination studies, the zones of inhibition for water-based extracts against MRSA, MSSA and E. faecalis ranged from 18 mm to 50 mm. The minimum inhibitory concentration ranged from 0 % to 100 % inhibition depending on the dilution of the extract The results obtained in this study prove that S. frutescens and P. guajava extracts contain antibacterial substances. The water-based extracts of all plants in this study inhibited the growth of MRSA, MSSA and E. faecalis. The combination studies produced zones that were greater than the individual penicillins indicating that synergistic effects do exist. Ethanol-based plant extracts did not inhibit the growth of any bacteria in this study. The results obtained in this study might be considered sufficient for further studies aimed at isolating and identifying the active compounds. The herbs should be tested in vivo by means of clinical trials and they should also be tested for their toxicity to cells. Different parts of the plants should also be tested for antibacterial activity to a wide range of bacteria.