Antimicrobial Effect of Geophila obvallata (Schumach) Didr. Leaf Ectracts Against Pathogenic Microbes

Antimicrobial effect of plant extract against selected microbes

Abstract

The increase in synthetic drug resistance by pathogenic microbes has led to the development of plant-based
antimicrobial drugs that are more reliable and non-lethal to human health at increased dosage. The
antibacterial and antifungal potential of Geophila obvallata extracts were tested on clinical isolates
(Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis,
Streptococcus pyogenes, Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus) 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 lowest in the methanol extract than aqueous extract. Simillarly, MIC for bacteria
(Bacillus subtilis) and fungi (Aspergillus fumigatus) were 0.3 and 2.0mg/mL respectively. Methanol extract
had higher antibacterial and antifungal effect than aqueous extract. 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 performance of the methanol extract of 40mg/mL of
Geophila obvallata in the inhibition of Bacillus subtilis was not significantly different from that of
Ciprofloxacin. The findings in this study therefore validate the antimicrobial effect of Geophila obvallata leaf extracts as well as its possible application in medicine.