Comparison of the antimicrobial, anti-biofilm, and cytotoxic effects of thymol/ampicillin and thymol/cefotaxime against Escherichia coli bacteria

OBJECTIVE: Using essential oils in combination with antibiotics helps to combat antibiotic resistance. Thymol is a major phenolic compound found in many essential oils. The antimicrobial effects of thymol, ampicillin, cefotaxime, and their combinations were examined on Escherichia coli (E. coli) ATCC 25,922. Then, the antimicrobial effects of synergistic compounds were evaluated on twenty clinical strains. The chemical bonds, functional groups, and molecular interactions of the mentioned compounds were investigated with an FT-IR device. The time-killing curve, biofilm inhibition, hemolysis, and MTT methods were also conducted. RESULTS: Antimicrobial effects of thymol/ampicillin were greater than thymol/cefotaxime in both the ATCC and clinical strains. In the examination with the FT-IR device, both compounds showed a connection between components. The biofilm inhibition effect of thymol/ampicillin (62%) was greater than thymol/cefotaxime (39.28%). The bacterial killing time curve of Thymol/ampicillin was faster and more effective. The cytotoxic effects of compounds on red blood cells (RBCs) and human foreskin fibroblast (HFF) were lower than Triton X-100 (0.1%). In the treatment of diseases caused by E. coli bacteria, thymol/ampicillin had better effects than thymol/cefotaxime.