In vitro Antibacterial Evaluation of Four Selected Medicinal Plants against Staphylococcus aureus Isolated from Bovine Mastitis in Mieso District West Hararghe Zone, Oromia Regional State, Ethiopia

Abstract

Background: Bovine mastitis is a major disease mostly caused by bacterial infection and associated with losses in the global dairy industry. Since mastitis-causing bacterial developing multidrug resistance to conventional antibiotics, there is an admirable supplementary study on medicinal plants to use them as an alternative therapy. This study aimed to evaluate the antibacterial activity and phytochemical screening of four selected medicinal plants against Staphylococcus aureus. Methods: An experimental study was done to evaluate the antibacterial activity of crude methanolic extracts of four traditionally used medicinal plants against S. aureus. Standard phytochemical screening tests were conducted to detect the bioactive principle of plants. Agar well diffusion assay was used to evaluate the antimicrobial activity of crude methanolic plant extract. The broth dilution method was also used to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of plant extracts. Results: The percentage yields obtained from the root of Clerodandrum myricoides, Kalanchoe densiflora, Kalanchoe marmorata and leaf of Kalanchoe marmorata and Datura stramonium were 22.6%, 37.2%, 51.6%, 32.3% and 50.7%, respectively. Phytochemical screening tests revealed the presence of secondary metabolites such as tannins, phenols, and steroids in all plant extract, except in D. stramonium, while others like alkaloids, flavonoids, quinones, and saponins were fairly detected in all samples. The agar well diffusion results showed significant (p < 0.05) differences in the mean zone of inhibition (ZOI) between each plant at different concentrations with significant potency comparable to gentamicin. C. myricoides and D. stramonium revealed the broadest spectrum of action yielding the highest ZOI (27.0 ± 0.58 mm), whereas K. marmorata leaf showed less activity with the lowest ZOI (22.3 ± 0.33 mm). The broth dilution method indicated that the MIC value of plant extracts against S. aureus ranged between 3.90 and 7.80 mg/ml while its corresponding MBC value ranged between 7.80 and 15.6 mg/ml. According to the MIC/MBC ratio, all tested plants (except K. densiflora) against standard S. aureus while C. myricoides and D. stramonium against clinical S. aureus isolate were determined to be bactericidal. Conclusion: This finding confirmed that all tested plants had a potential anti-staphylococcal effect. Thus, further study on in vivo experiments and cytotoxicity analyses must be conducted to suggest these plants as alternative mastitis treatments.