Introduction: Onion (Allium cepa L.) and garlic (Allium sativum L.) extracts are traditionally
used in many cultures as antimicrobial agents. Nonetheless, there is still a dearth of scientific validation
pertaining to the antibacterial and possible antibiotic potentiating activity of these plants.
Methods: Decoction as traditionally used and methanol, ethanol, ethyl acetate, and acetone extracts of
onion and garlic were evaluated for their antibacterial activity against 15 bacterial strains (6 ATCC
strains and 9 clinical isolates) using the broth microdilution method to establish the minimum inhibitory
concentration. The bacteriostatic and bactericidal actions were determined as compared to conventional
antibiotics (streptomycin and chloramphenicol). Fractional Inhibitory Concentration (FIC) was determined
to establish any synergistic interaction between the extracts and antibiotics using a modified
Results: The ethyl acetate extract of garlic showed bactericidal effect against 1 ATCC (E. coli) and 2
clinical isolates. Streptomycin produced only indifferent effect (FIC 1< and ≤ 4) when combined with
ethyl acetate extract of onion. Chloramphenicol showed synergism with ethyl acetate extract of onion
against ATCC S. aureus (FIC 0.27-0.30) and Micrococci species (FIC 0.27-0.32). Streptomycin showed
mostly antagonism whereas chloramphenicol showed synergism effects with the ethyl acetate extract of
garlic. The observed antibacterial activity might be justified due to the presence of high concentration of
phenolic compounds in the extracts.
Conclusion: This study has provided an opportunity to establish valuable baseline information on the
antibiotic potentiating activity of onion and garlic which can be further exploited for the treatment
and/or management of infectious diseases.
Keywords: Allium cepa, Allium sativum, Antibacterial, Bacteriostatic, Bactericidal, Phenols, Flavonoids, Phytochemicals,
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