Phytochemical Screening and Antimicrobial Properties of Parkia biglobosa (African Locust Bean) (Jacq) Leaf Extracts on Selected Microbial Isolates

Abstract

 Globally, antimicrobial resistance poses a significant threat to the effectiveness of existing antibiotics and remains a major public health concern. This challenge necessitates the exploration of alternative antimicrobial agents from medicinal plants. This study evaluated the phytochemical, constituents and antimicrobial activity of Parkia biglobosa (locust bean) ethanol and aqueous leaf extracts against selected bacterial and fungal isolates. Bioactive compounds were extracted using the maceration method, followed by phytochemical screening. Microbial isolates (Rhizopus stolonifer, Aspergillus niger, Escherichia coli, and Staphylococcus aureus) were obtained from the Federal Teaching Hospital, Lokoja, and cultured using standard microbiological techniques. Antimicrobial activity was assessed using the agar well diffusion method, while Minimum Inhibitory Concentration (MIC) was determined by the tube dilution technique. Data were analyzed using SPSS version 23.0. Phytochemical analysis revealed the presence of saponins, phenols, tannins, terpenoids, and flavonoids in both extracts, while alkaloids was detected only in the ethanolic extract. Antimicrobial activity increased with conentration, with the highest inhibition observed at 100 mg/mL. Aspergillus niger showed the highest inhibition (14.00 ± 1.00 mm), followed by E. coli (13.00 ± 1.00 mm), S. aureus (11.00 ± 1.00 mm), and R. stolonifer (11.50 ± 1.50 mm). Furthermore, The Minimum Bactericidal Concentration (MBC) of aqueous and ethanol extracts against S. aureus were 75 mg/mL and 50 mg/mL respectively. For E. coli, the aqueous extract’s MBC was 50 mg/mL while the ethanol extract's was 75 mg/mL. The Minimum Fungicidal Concentrations (MFC) for Rhizopus stolonifer were 75 mg/mL and 50 mg/mL, while for Aspergillus niger, values were 50 mg/mL and 75 mg/mL for aqueous and ethanolic extracts. Overall, the study demonstrates that P. biglobosa leaf extracts exhibit notable antimicrobial activity, supporting their traditional use and highlighting their potential as a source of novel antimicrobial agents against resistant pathogens, but was limited to some selected microbes.