Evaluation of the Activity of Amoxicillin/Clavulanate, Ceftazidime/Avibactam and Colistin Against Drug-Resistant <i>Mycobacterium tuberculosis</i> Isolates by the E-test Method

Background: Tuberculosis (TB), a global public health problem, will always require new drug candidates unless it can be eradicated due to its ability to rapidly acquire antimicrobial resistance. In addition to developing new drug candidates, creating new areas of use for currently used and approved drugs is seen as a more advantageous strategy. Objectives: This study aimed to determine the anti-TB activity of ceftazidime/avibactam (CAV), amoxicillin/clavulanic acid (AMO/CLAV), and colistin (CS). Methods: Minimum inhibitory concentrations (MICs) of 5 ATCC strains and 36 Mycobacterium tuberculosis isolates for CAV, AMO/CLAV, and CS were determined by the E-test method (gradient diffusion method). Testing was performed on Middlebrook 7H11 agar plates using E-test strips in the concentration range of 256 - 0.01 µg/mL. Results: For CAV, MIC values were found to be in the range of 0.016 - 0.023 µg/mL in 65.71% of the tested isolates and were found to be quite effective. The MIC for all other isolates was > 256 µg/mL. For AMO/CLAV, MIC values were found to be > 256 µg/mL in 23 isolates, ≤ 0.016 in 4 isolates, and 0.064 - 128 µg/mL in 14 isolates. For CS, MIC values were found to be > 256 µg/mL in 6 isolates, 0.047 - 0.5 µg/mL in 9 isolates, and 48 - 128 µg/mL in the remaining 5 isolates. Conclusions: In our study, the CAV combination was found to be more effective than the AMO/CLAV combination. Current studies suggest that the inclusion of CAV in the TB treatment regimen will have significant contributions when used together with other antibiotics due to its sterilizing effect.