Identification of the chemical compounds and antibacterial activity of Ocimum basilicum essential oil and the effects of its interaction with tetracycline and chloramphenicol antibiotics on some pathogenic microorganisms causing infection and food poisoning

In this study, the antimicrobial effect of Ocimum basilicum essential oil with different qualitative and quantitative methods (disc diffusion, minimum inhibitory concentration and minimum bactericidal concentration) as well as the effects of its interaction with tetracycline and chloramphenicol antibiotics on Listeria innocua, Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa and Escherichia coli were evaluated. The chemical compounds, antioxidant activity and total phenolic content of Ocimum basilicum essential oil were measured. The results showed that Ocimum basilicum essential oil contained 31 compounds. Estragole was the major constituent of the essential oil with a percentage of 30.75. The antioxidant activity of Ocimum basilicum essential oil was 70% based on free radical scavenging capacity (DPPH). The total phenolic content of the essential oil was 29.05±0.50 mg GAE/g. The most sensitive and the most resistant bacteria with diameter inhibition zone 21.95 mm and 10.00 mm were Bacillus cereus and Escherichia coli respectively. The effects of interaction of Ocimum basilicum essential oil with tetracycline and chloramphenicol antibiotics on gram negative bacteria showed synergistic status. The minimum inhibitory concentration of the essential oil was equal to 12.5, 6.25, 6.25, 200 and 200 mg/ml for Listeria innocua, Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa and Escherichia coli respectively. The minimum bactericidal concentration of Ocimum basilicum essential oil was equal to 50, 12. 5, 12.5, 400 and 400 mg/ml for bacteria respectively.