Antibacterial Activity of Different Solvent Extracts of Clove (Syzygium aromaticum) against Staphylococcus aureus and Escherichia coli Isolated from Raw Vegetables

Background: Raw vegetables have been a source of foodborne bacteria, and the spread of antibiotic-resistant strains has increased interest in natural antimicrobials that could support food safety. Aim: To isolate Staphylococcus aureus and Escherichia coli from raw vegetables and to compare the antibacterial activity of methanol, ethyl acetate and n-hexane extracts of clove against them. Study Design: Experimental laboratory study. Place and Duration of Study: The study was carried out in Bauchi metropolis, Bauchi State, Nigeria. The clove and vegetable samples were purchased from Yelwa Market and laboratory analyses were conducted at the Microbiology Laboratory, Department of Microbiology, Abubakar Tafawa Balewa University, Bauchi, Nigeria; the study was conducted during the active trading period within the study timeframe. Methodology: Dried clove buds were macerated sequentially in methanol, ethyl acetate and n-hexane. S. aureus (carrot) and E. coli (lettuce) were isolated on Mannitol Salt and MacConkey agar and identified by colony morphology, Gram staining and biochemical tests. Activity was assessed by agar well diffusion (2–10 mg/ml), minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The methanol extract was screened for phytochemicals. Results: The methanol extract gave the highest yield (18.78%, compared with 1.90% and 0.50%) and the largest inhibition zones at 10 mg/ml (19 mm for S. aureus, 18 mm for E. coli), compared with 17 mm for chloramphenicol. The MIC/MBC values for the methanol extract were 2/4 mg/ml for S. aureus and 4/6 mg/ml for E. coli. Ethyl acetate was weaker (MIC 8 and 10 mg/ml), and n- hexane was not bactericidal against either organism at 10 mg/ml. The methanol extract contained saponins, carbohydrates, tannins, flavonoids, alkaloids, glycosides, anthraquinones and terpenoids. Conclusion: The methanol extract of clove was the most active and was bactericidal against a Gram-positive and a Gram-negative foodborne isolate at low concentrations. It is a candidate natural antimicrobial for fresh-produce safety, but testing in food matrices, testing against reference strains and safety assessments are needed before any application.