• Potentiating the Antimicrobial Effect of Ceftazidime by Thymol Against Klebsiella pneumoniae
  • Mina Shirmohammadpour,1 Sajjad Jafari,2 Bahman Mirzaei,3,*
    1. Department of Microbiology and Virology, Faculty of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran
    2. Department of Microbiology, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, West Azerbaijan, Iran
    3. Department of Microbiology and Virology, Faculty of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran


  • Introduction: This study aimed at the antimicrobial effects of thymol/ceftazidime on Klebsiella pneumoniae (K. pneumoniae) bacteria.
  • Methods: Antimicrobial effects of thymol/ceftazidime were performed first individually and then combined on K. pneumoniae ATCC 100031 by the MIC-MBC method. Therefore, the antimicrobial effects of the compounds that had a synergistic impact were performed on ten clinical strains using the MIC-MBC method. The identification of chemical bonds, functional groups, and molecular interactions of the mentioned compounds was investigated using an FTIR device. Checkered method, time killing curve, and biofilm inhibition on K. pneumoniae ATCC 100031, investigation of cytotoxicity on red blood cells (RBCs) by hemolysis method and human skin fibroblast cells (Ffk) by MTT method were performed. thymol/ceftazidime had synergistic effects.
  • Results: The study's findings demonstrated that when applied to K. pneumoniae ATCC 100031, the antimicrobial activities of thymol, ceftazidime, and thymol/ceftazidime (A1 compound) were, respectively, 256 µg/ml, 4 µg/ml, and 4/2 µg/ml (FICI: 1 µg/ml). The A1 compound exhibited antibacterial activity of 4-256/1-64 µg/ml on clinical strains of K. pneumoniae, respectively. Compared to the individual modes, the combined mode had a longer time curve for eliminating K. pneumoniae. Examination with FTIR showed that these two compounds have C=C conjugated, C≡C compound. Thymol, ceftazidime, and other chemicals have biofilm inhibition rates of 29.69%, 28.71%, and 58.44%, respectively against K. pneumoniae bacteria. The toxicity of thymol, cefotaxime, and A1 compound against human RBCs were 36.12, 8.33, and 8.38, and against human Ffk cells were 19.66, 7.08, and 9.03 respectively.
  • Conclusion: This study proved that the thymol/ceftazidime combination could become one of the new drugs for treating K. pneumoniae infections due to its high antimicrobial effects and low toxicity.
  • Keywords: Klebsiella pneumoniae, Thymol, Ceftazidime, Antimicrobial