Antimicrobial, Cytotoxicity, Acute Oral Toxicity, and Qualitative Phytochemical Screening of the Aqueous and Methanolic Stem-Bark Extracts of Croton megalocarpus Hutch. (Euphorbiaceae)

Abstract

Microbial infections are feared to cause over 10 million deaths by the year 2050, whereby 50% of the global burden squarely lies in less developed countries of Africa and Asian continents. The current drugs have suffered resistance by previously susceptible strains, are associated with severe side effects, among other therapeutic and economic drawbacks, hence the need for alternatives. Despite the widespread usage of medicinal plants by over 80% of the global population to treat common ailments, including microbial infections, only a few have been empirically validated. Croton megalocarpus is used to treat microbial-associated infections like pneumonia and typhoid among the Agikuyu community of Kenya. However, its healing claims and safety have not been evaluated empirically to date, hence this study. We investigated the antimicrobial, cytotoxicity, acute oral toxicity, and qualitative phytochemical composition of the aqueous and methanolic stem bark extracts of C. megalocarpus. The disk diffusion and broth microdilution techniques described by the Clinical Laboratory Standards Institute (CLSI) were adopted for antimicrobial assays. The acute oral toxicity effects of the studied plant extracts were evaluated according to the Organisation of Economic Co-operation and Development (OECD) guideline document number 425. The brine shrimp lethality assay technique was used to appraise the cytotoxic effects of the studied plant extracts. Qualitative phytochemical screening was performed following standard procedures. The results revealed that all the studied plant extracts had varied antimicrobial effects on selected microbial strains and showed MIC values of <1000 µg/ml indicating their antimicrobial potential. Moreover, the studied plant extracts had LC50 values of >100 µg/ml and >2000 mg/Kg bw in the brine shrimp lethality and acute oral toxicity assays, respectively, demonstrating their safety. Antimicrobial- associated phytocompounds were detected in the studied plant extracts suggesting they were responsible for the reported bioactivity. Further studies to establish the specific mode(s) of antimicrobial action, toxicological, and safety should be performed. Furthermore, antimicrobial investigations of the studied plant extracts on other clinically significant microbial strains and the isolation, characterization, and optimization of antimicrobials from the studied plant extracts should be done.