South Asian Journal of Research in Microbiology

Aim: This study was aimed at investigating the antibacterial activities of extracts of Allium cepa and Allium sativum, as well as their synergistic activities with some selected antibiotics against the bacterial pathogens Escherichia coli and Staphylococcus aureus. 

Study Design: Onions (Allium cepa), garlic (Allium sativum) were used in this study. The study assessed how extracts of the plants alone or in combination with some commonly used antibiotics inhibited the growth of some bacterial pathogens using agar well diffusion method. 

Place and Duration of Study: The research was carried out in the Department of Microbiology, University of Nigeria, Nsukka over a period of 6 months.

Methodology: Extracts of Allium cepa and Allium sativum were obtained using ethanol, methanol and water (aqueous). Antimicrobial susceptibility tests were carried out by agar well diffusion technique.

Results: All extracts obtained showed evidence of antimicrobial property measured as the Inhibition Zone Diameter (IZD) on the test microorganisms. Values of these IZDs showed remarkable increases when used synergistically with antibiotics. For instance, aqueous extract of Allium sativum increased from a mean value of 16.5mm at 1.0mg/ml to values of 30.0mm and 38.0mm when used with tetracycline and ampicloxacillin respectively against Escherichia coli. The MIC and MBC values also dropped progressively, indicating that fewer synergistic mixtures were required to exert the same effects on the tested organisms. The phytochemical analysis strongly indicated the presence of flavonoids, glycosides and alkaloids, among other plant metabolites.

Conclusion: This result indicates that Allium cepa and Allium sativum showed strong antibacterial activity against the bacterial pathogens E. coli and S. aureus; and that synergism of the extracts with some antibiotics improved those activities. The potential of developing antimicrobials from these plants appears promising.