Antibacterial Activity of Clove (Syzygium aromaticum) Extracts against Selected Multidrug-Resistant Clinical Bacteria

Abstract

Multidrug-resistant (MDR) bacteria are a significant health issue throughout the world that limit the possibilities of treatment and increasing the number of deaths that occur due to the infection. The necessity to find alternative antibacterial agents increases as conventional antibiotics become less effective because of their high resistance rates attributed to the presence of resistance mechanisms. Clove (Syzygium aromaticum) is a spice containing bioactive phytochemicals with promising antibacterial effects. This study aimed to evaluate the antibacterial activity of Syzygium aromaticum extracts on selected clinically relevant MDR bacteria. Dried Clove bud was purchased from the market, and authenticated by a botanist in the Department of Botany, University of Ilorin. Clove extracts were prepared in ethanol, methanol, and water, and tested against methicillin-resistant Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa collected from Department of Microbiology of University of Ilorin. Antibacterial activity was assessed using agar well diffusion at five concentrations (6.25–100 mg/mL). MIC and MBC were determined using standard microbiological technique. No activity was detected in 6.25 and 12.5 mg/mL whereas the inhibition zones were concentration-dependent and increased between 25-100 mg/mL (p< 0.05). Ethanol extracts consistently produced the largest zones, followed by methanol, with aqueous extracts showing the least activity. The most susceptible organisms were MRSA (11.5–23.1 mm) and E. faecalis (7.2–20.1 mm) and the least was P. aeruginosa (3.5–15.8 mm). MIC ranged from 25-100 mg/mL and MBC from 50-200 mg/mL and ethanol extracts tended to be the lowest required concentration. In conclusion, clove extracts exhibit concentration-dependent antibacterial activity against MDR bacteria, with higher efficacy against Gram-positive bacteria.