Identification of chemical compounds of Allium cepa essential oil and evaluation of its antimicrobial activity on Staphylococcus aureus, Listeria innocua, Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa and Candida albicans

In order to reduce the economic losses and life risks caused by microbial pathogens, the use of natural substances as antimicrobial compounds seems to be an effective way to control the presence of pathogenic bacteria. In this study, the chemical composition of onion essential oil was determined by gas chromatography–mass spectrometry (GC-MS). The methods in disk diffusion agar (DDA) and well diffusion agar (WDA) were used to investigate the inhibition zone diameter, micro-dilution broth was used to measure the minimum inhibitory concentration (MIC) and pour-plate technique was also used for minimum bactericidal/fungicidal (MBC/MFC) concentration. A total of 20 chemical volatiles (approximately 100% of onion essential oil compounds) were identified. The compounds Trisulfide dipropyl, Disulfide dipropyl, n-Decane and Furfuryl methyl sulfide with 20.67, 16.18, 13.51 and 10.23% of the main constituents of onion essential oil, respectively. The results of WDA showed that onion essential oil had the most and the least effect on Gram-positive bacteria Staphylococcus aureus with a diameter of 15 mm and Gram-negative bacteria Pseudomonas aeruginosa with a diameter of 10 mm, respectively. The results of MIC onion essential oil for Staphylococcus aureus, Listeria innocua, Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa and Candida albicans 512, 512, 512, 512, 512 and 1024 mg/mL, respectively. In general, the results of this study showed that the antimicrobial effect of onion essential oil can be somewhat different depending on the type of microorganism.