Antimicrobial, Cytotoxicity, Acute Oral Toxicity Effects and Phytochemical Composition of Aqueous and Methanolic Extracts of Physalis Peruviana, Bridellia Micrantha, and Croton Megalocarpus

Abstract

Microbial infections are the major causes of high morbidity and mortality in vulnerable persons globally. The emergence of antibiotic-resistant microbes has further complicated the management of pathogenic infections. The most considerable burden of microbial infections lies in the low- and middle-income countries, especially those in the African continent. The current antimicrobial drugs are inaccessible, unaffordable and cause undesirable effects. This has prompted the search for alternative and complementary therapies to cub microbial infections. Medicinal plants present a promising alternative source of potent antimicrobials due to their wide range of phytocompounds they contain. Medicinal plants have been used for a long time in traditional medicine to manage various diseases especially those of bacterial and fungal origin; however, their pharmacologic efficacy, toxicity, and safety profiles have not been fully validated scientifically. The World Health Organization (WHO) has recognized that over 80 % of the world population, especially in low-income nations, depend on traditional medicines for primary healthcare. As a result, the WHO has recommended the evaluation of herbal remedies as potential sources of pharmacologically active molecules for drug development. Considering the inefficiencies of synthetic antibiotics and the burden of microbial infections, this study was designed to investigate the antimicrobial, cytotoxicity, acute oral toxicity effects and phytochemical composition of the aqueous and methanolic extracts of Physalis peruviana, Bridellia micrantha and Croton megalocarpus, which are utilized in the Kenyan traditional medicine to treat microbial infections, on select microbial strains. The stem barks of Physalis peruviana, Bridellia micrantha and Croton megalocarpus were collected based on their traditional usage from Murang’a County, in Kenya. They were primarily identified by their local names and then authenticated by a taxonomist at the East Africa Herbaria at the National Museums of Kenya. Voucher specimens were prepared, and duplicates were deposited at the Department of Biological Sciences, Chiromo campus for future reference. The collected stem barks were naturally dried in the laboratory for two weeks, ground into powder form before extraction. The respective powders were extracted using water and methanol following standard methods.The antimicrobial activity of Physalis peruviana, Bridellia micrantha and Croton megalocarpus extracts on Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and Candida albicans were evaluated using the disk diffusion and Broth microdilution techniques described by the Clinical and Laboratory Standards Institute (CLSI). The bacterial and fungal strains were selected based on their availability and clinical significance. The brine shrimp lethality test was used to evaluate the cytotoxicity effects while the acute oral toxicity effects were evaluated according to the Organization for Economic Development and Cooperation (OECD; Document 425). Qualitative phytochemical screening was done following the standard phytochemical screening procedures. The aqueous extract of P. peruviana exhibited slight activity at concentrations of 50 μg/ml and 100 μg/ml on S. typhimurium; slight to moderate activity on E. coli and S. aureus; and moderate to high activity on C. albicans, demonstrating its antibacterial and antifungal effects. The methanolic bark extract of P. peruviana demonstrated slight to moderate antimicrobial effects against E. coli, S. aureus and C. albicans; however, a slight antimicrobial effect by this extract was observed on the S. typhimurium. The aqueous extract of B. micrantha produced slight activity on E. coli strain; slight to moderate activities on S. typhimurium strain, and moderate to high activities S. aureus bacterial strain and C. albicans fungal strain. The methanolic extract of B. micrantha showed moderate to high activities on E. coli, slight to moderate activities on S. typhimurium, slight to high activities on S. aureus, and slight to very high activities on C. albicans strains. The aqueous extract of C. megalocarpus demonstrated slight to moderate activities on E. coli and S. aureus, and moderate activities on S. typhimurium and C. albicans strains. Only the.........................................................................................................