Phytochemical Composition, Toxic Effects, and Antimicrobial Activity Studies of Digitaria Abyssinica (a. Rich.) Stapf (Poaceae) Rhizome Extracts Against Selected Uropathogenic Microorganisms

Abstract

Urinary tract infections (UTIs) are among the most severe public health problems that affect over one hundred and fifty million people worldwide annually. They are caused by a wide range of microorganisms where Escherichia coli is known to be the main causative pathogen. Medicinal plants are used in traditional Kenya setup for treatment and in the most recent as alternative source of treatment of UTIs due to increased cost of treatment and many challenges experienced with antibiotic therapy. The current study was designed to investigate the phytochemical composition, acute oral toxicity and antimicrobial activity of Digitaria abyssinica rhizome extracts against Staphylococcus aureus, Escherichia coli, Neisseria gonorrhoeae and Candida albicans. The rhizomes of Digitaria abyssinica were obtained, dried, ground and extracted using water and organic solvents (methanol and dichloromethane). Phytochemical assay was carried out using standard phytochemical screening methods. The Organization for Economic Co-operation and Development (OECD) guidelines for testing of chemicals document 425 for 2008 was used to assess the toxic effects on female Wistar rats. Disk diffusion method was used to obtain the zones of inhibition while microbroth dilution techniques were used to obtain the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) for the antimicrobial assay. The data that was obtained from phytochemical screening was entered into a Word sheet and presented in a table. The weights of the Wistar rats from day 0, day 7 and day 14 following oral admission of the Digitaria abyssinica rhizome extracts were entered in an Excel sheet. All experiments in the antimicrobial activity testing were performed in triplicates for verification and validation of data. GraphPad Prism software version 9.0.0 was used to compute mean ± standard error of the mean (SEM). One-way analysis of variance (ANOVA) and post hoc ANOVA at 95% confidence level and statistical significancy was taken at p <0.05. Results revealed that saponins, phenolics, alkaloids, cardiac glycosides, tannins, flavonoids, steroids, and terpenes were present in the powder, aqueous, methanol, and dichloromethane:methanol extracts. All the extracts had an LD50 of above 2,000 mg/kg of body weight and there was no observation of behavioural changes. The extracts revealed antifungal activity against the Candida albicans. However, there was no antibacterial activity at a concentration of 500 mg/ml on Staphylococcus aureus, Escherichia coli and Neisseria gonorrhoeae. The highest antifungal activity was demonstrated by aqueous extract which MIC of 31.25 mg/ml, MFC 62.5 mg/ml and a zone of inhibition of 16.33 ± 0.82 mm at a concentration of 500 mg/ml. The current study reports that Digitaria abyssinica rhizome extracts had antifungal activity, thus confirming its traditional use to treat candidiasis. This research recommends that other solvents could be used, which could lead to improved yield and biological activity. Comprehensive research of the antimicrobial efficacy of the studied plant extracts on other microbial strains of clinical significance are encouraged. It is necessary to do additional research to determine the precise mode(s) by which the plant extracts under study exert their antifungal activity. To determine the safety of long-term usage of Digitaria abyssinica rhizome extracts, extensive sub-acute and chronic investigations should be conducted.