The increase in resistance to synthetic drugs by many bacteria and fungi causing human infections has led to the development of new antimicrobial drugs from plant sources which are more stable, reliable and non lethal to human health at increased dosage. The antibacterial and antifungal potentials of methanol and aqueous extracts of Geophila obvallata were tested on clinical isolates (Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis, Streptococcus pyogenes, Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus) obtained from the Pharmaceutical Microbiology laboratory of the University of Benin, Nigeria using standard techniques. The zones of inhibition were shown to increase with increasing concentrations of the extracts. Inhibition was higher in Gram positive bacteria (9.10 to 31.00mm in 40mg/ml concentration) than Gram negative bacteria (3.50 to 27.00mm in 40mg/ml concentration), while the fungal isolates had the least zones of inhibition (2.83 to 25.00mm in 40mg/ml concentration). The minimum inhibitory concentrations (MIC) were lower in methanol extracts than in aqueous extracts. The lowest MIC for bacteria (Bacillus subtilis) and fungi (Aspergillus fumigatus) were 0.3 and 2.0mg/ml respectively. Methanol extracts had higher antibacterial and antifungal activities than aqueous extracts. Ciprofloxacin, used as control for bacteria had the highest inhibitory activity (33.67mm) when compared to that of the highest concentration of plant extracts administered. Also, ketoconazole gave the highest zones of inhibition (32.33mm) on the fungi isolates compared to those of the extracts. The formulated treatment of distilled water used as control had no antimicrobial potential. The performance of the methanol extract of 40mg/ml of Geophila obvallata in the inhibition of Bacillus subtilis was not significantly different from that of the synthetic drug Ciprofloxacin (P<0.05). The findings in this study therefore validate the antimicrobial properties of Geophila obvallata leaf extracts as well as its possible application in medicine.

Keywords: Geophila obvallata, Ciprofloxacin, Ketoconazole, Antimicrobial, Inhibition zone diameter, MIC