In vitro antibacterial activity of gunnera perpensa and elephantorrhiza elephantina against human pathogenic bacteria

Abstract

INTRODUCTION: In the history of the African population, medicinal plants are a heritage that has been able to be preserved and used in modern times. The use of medicinal plants is still regarded as a treatment option in the current healthcare sector and among rural communities. Traditional medicinal plants have been used by African communities for many years as they are more affordable, easily accessible, less toxic, and more trustworthy in African cultures because the knowledge of remedies practised by traditional healers has been passed down by the ancestors through cultural practices in current and past generations. In recent years, even with the modernisation of the healthcare system, people still seek help of traditional healers. Multidrugresistant (MDR) bacteria have increased at an alarming rate over the recent decades and have caused a substantial health burden. MDR bacteria are pathogenic bacteria that are naturally harmful and cause severe infection/disease among humans. These illnesses/conditions may include abdominal pain, bladder problems, cancer, colds, earaches, endometritis, gastrointestinal parasites, gonorrhoea, heart diseases, hypertension, impotence, infertility, kidney problems, poor appetite, rheumatic pains, scabies, syphilis, and urinary infections. This study sought to assess Elephantorrhiza elephantina and Gunnera perpensa as antibacterial agents used to treat infections associated with MDR bacteria. METHODS: Medicinal plant extracts (using roots/rhizome) were prepared by maceration with methanol and water. Secondary metabolites were qualitatively and quantitatively assessed, while antibacterial activities were determined using the disk diffusion assay and the p-Iodonitrotetrazolium chloride assay on the following Grampositive bacteria: Staphylococcus aureus, S. epidermidis, S. saprophyticus, and Bacillus subtilis, and the following Gram-negative bacteria: Klebsiella pneumoniae and Escherichia coli. Further investigation of the antibacterial activity and the effects of E. elephantina methanol extract on the bacterial morphology of S. aureus was performed. This was investigated using a scanning electron microscope (SEM) and transmission electron microscope (TEM). RESULTS: The phytochemical analysis of the plants confirmed that the following phytochemical compounds were present in both the methanol extract of G. perpensa and E. elephantina: alkaloids, glycosides, flavonoids, tannins, phytosterols, and phenols. Gallic acid equivalents (GAEs) of the estimated phenolic concentrations ranged from 0.140 ± 0.0076 to 0.068 ± 0.0025 mg (GAE). The estimated flavonoid concentrations ranged from 0.905 ± 0.0190 to 0.375 ± 0.0073 mg (QE/g). The antibacterial activity results of the E. elephantina methanol extracts showed strong antibacterial activity against S. aureus, B. subtilis, and K. pneumoniae and indicated the minimum inhibitory concentration at concentrations of 60 µg/mL, 125 µg/mL, and 60 µg/mL respectively. The SEM and TEM evaluation of S. aureus showed major structural changes, including damage to cell walls, which was evident from holes in the cell surface. The loss of cellular or cytoplasmic contents resulted in shrinkage of the cell, which was seen by the wrinkled and indented surface of the cell. CONCLUSION: The antibacterial activity of G. perpensa demonstrated strong activity against Gram-positive bacteria S. aureus and B. subtilis; however, poor activity was demonstrated by the methanol extract and no activity was seen from the aqueous extract against the Gram-negative bacteria E. coli and K. pneumoniae. The effects of E. elephantina on the bacterial cell wall supported the antibacterial properties of the plant, as the results of the SEM and TEM show how the plant extract caused morphological damage and eventually inhibited S. aureus growth. E. elephantina managed to inhibit the growth of bacteria that are prone to drug resistance, which are eventually classified as MDR. The results obtained from this study indicate that the plant has potential as an antibacterial agent.