Synergistic antibacterial activity of garlic extract against uropathogenic gram-negative bacilli

Garlic extract is known to have distinct antibacterial activity and synergistic effect with various antibacterial agents. This study was carried out to evaluate synergistic activity of garlic extract with antibiotics against uropathogenic gram-negative bacteria isolated from patients with symptomatic urinary tract infection. Gram negative bacterial isolates with significant bacteriuria (>10,000 CFU/ml) recovered on urine culture from patients with symptomatic UTI were included in the study. Biochemical identification antibiotic susceptibility tests were performed as per standard microbiology procedures. The synergy of garlic extract with antibiotics was determined by disc diffusion method. A total of 92 bacterial isolates, including 54 multi-drug resistant bacterial isolates, were obtained from 53 female and 39 male patients. Escherichia coli was the most common (55.4%), followed by Klebsiella pneumoniae (25%), Non-fermenter gram negative bacilli (9.8%), Citrobacter spp (7.6%), and Proteus vulgaris (2.2%). Resistance to cefotaxime, nalidixic acid, norfloxacin cotrimoxazole and nitrofurantoin was 72.8%, 64.1%, 50%, 47.8% and 45.7% respectively. A large majority of these isolates showed synergy of garlic extract with amikacin (80.4%), gentamicin (83.7%), imipenem (83.7%), meropenem (77.2%), fosfomycin (82.6%), nitrofurantoin (80.4%), cefoperazone-sulbactam (77.2%). Furthermore, addition of garlic extract effectively improved susceptibility of these gram-negative uropathogenic bacteria to amikacin, gentamicin, imipenem and nitrofurantoin. Our study demonstrated synergistic effects of garlic extract with several antibiotics against uropathogenic bacteria, suggesting its potential use as an adjunctive therapy with antibiotics. However, further studies are required before it can be introduced for clinical use.