In vitro antimicrobial properties of aqueous garlic extract against multidrug-resistant bacteria and Candida species from Nigeria

The antimicrobial effects of aqueous garlic extract (AGE) against 133 multidrug-resistant gram-positive and gram-negative bacterial isolates, including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Salmonella typhi, Pseudomonas aeruginosa, Escherichia coli, Shigella spp., and Proteus spp., and against 10 Candida spp. were studied. Antibacterial activity of AGE by well-diffusion and macrobroth dilution method was characterized by inhibition zones of 20.2-22.7 mm for gram-positives and 19.8-24.5 mm for gram-negatives and minimum inhibitory concentration (MIC) ranges of 15.6-48.3 mg/mL and 22.9-37.2 mg/mL, respectively. With the exception of P. aeruginosa, the observed disparity in MIC values at 24 and 48 hours was not significant (P >.05) in these isolates. The anticandidal effect of AGE resulted in a growth inhibition zone of 27.4 +/- 3.7 mm with no significant difference (P >.05) in MIC values at 24 and 48 hours, respectively. Minimum fungicidal concentrations were found to be 14.9 and 15.5 mg/mL, respectively, at these incubation periods. Further analysis revealed the antimicrobial efficacy of AGE to be dose and time dependent, producing five distinct time-kill profiles among the isolates tested. The results of this study support the use of garlic in health products and herbal remedies in Nigeria.