Investigation of bioactive compounds and antimicrobial properties of aqueous garlic extracts on important food-borne zoonotic bacteria for food applications

The antimicrobial effects of aqueous extracts prepared by different extraction methods on important food-borne zoonotic bacteria (Klebsiella pneumoniae (ATCC700603), Campylobacter jejuni (ATTC 33,560), Salmonella Paratyphi A (NCTC13), Staphylococcus aureus (ATCC29213), and Enterococcus faecalis (ATCC29212)) were investigated. The bioactive components of aqueous garlic extract (GE) and aqueous garlic extract with particles (GEP) were analysed with solid-phase microextraction-gas chromatography mass spectrometry (SPME/GC-MS) system. The antimicrobial effect of GE and GEP were determined using agar well diffusion method, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), and time-kill assay. The results showed there were two main components in GE and GEP, namely, diallyl disulphide (46.83% vs. 41.77%), and allyl trisulfide/trisulfide di-2-propenyl (20.81% vs. 19.74%). The data obtained from inhibition zone assay statistically indicated that GEP exhibited a higher antibacterial effect against Campylobacter jejuni and Salmonella Paratyphi A with zone diameters of 34.00 & PLUSMN; 0.82 and 34.50 & PLUSMN; 0.84, respectively (p < 0.05). GEP and GE showed more effective inhibitory effect on Gram positive E. faecalis with the MIC and MBC values of 50 mg/ml. S. aureus had high sensitivity as the lower concentration (< 50 mg/ml) of GEP was needed for its growth inhibition. All bacterial cells tested in the killing assay were reduced to remarkable levels within 3, 6, and 9 h after interacting with GEP and fully lost viability within 24 h. The study revealed that aqueous garlic extracts especially the particulate form were a very strong antimicrobial agent for overcoming food pathogens due to their bioactive substances.