Comparing the Antimicrobial, Anti-Biofilm, and Cytotoxic Effects of Thymol/Ampicillin and Thymol/Cefotaxime against Escherichia coli Bacteria

Introduction: This study aimed to compare the antimicrobial, anti-biofilm, and cytotoxic effects of thymol/ampicillin with thymol/cefotaxime on Escherichia coli ( E. coli ). Material and Methods: Antimicrobial effects of thymol/ampicillin and thymol/cefotaxime were first individually and then combined on E. coli ATCC 25922 by MIC-MBC method. Therefore, the antimicrobial effect of compounds that had synergistic effects was performed on twenty clinical strains using the MIC-MBC method. Identification of chemical bonds, functional groups, and molecular interactions of the mentioned compounds were investigated with an FT-IR device. Checkered method, time killing curve, and biofilm inhibition on E. coli ATCC 25922 bacteria, and investigation of cytotoxicity on red blood cells (RBCs) by hemolysis method and human skin fibroblast cells (Ffk) by MTT method were performed. thymol/ampicillin and thymol/cefotaxime (A1, A3 compounds) had Synergistic effects. Finally, the results of the tests were compared between the two compounds. Results: The results of this study showed that the antimicrobial effects of the thymol/ampicillin 2/8) µg/ml) were better than the thymol/cefotaxime 16/128) µg/ml(in both ATCC and clinical strains. In the examination with the FT-IR device, both compounds had bonds of OH carbohydrates proteins, polyphenols, C=O Amide I band, C-O-C polysaccharide, C-Namide III band, but one band named C=C conjugated, C≡C in both compounds showed the connection between thymol/ampicillin and thymol/cefotaxime. The biofilm inhibition effect of thymol/ampicillin (62 %) was better than thymol/cefotaxime (39.28 %) on E. coli ATCC 25922. The bacterial killing time curve of the thymol/ampicillin at a lower concentration and time was better than the combination of thymol/cefotaxime. Cytotoxicity of synergistic compounds on RBCs and human skin fibroblasts (Ffk) was not different and was lower than that of Triton X-100. Discussion: Considering the antibiotic resistance of ampicillin and cefotaxime in the treatment of diseases caused by E. coli bacteria, the thymol/ampicillin in this study showed better antimicrobial, anti-biofilm, and bacterial killing time effects than the thymol/cefotaxime. This combination can be used as a new drug in patients after further studies.