Abstract: Objective  To compare the detection effects and the accordance of three drug sensitivity test (DST) methods based on bacterial culture for testing Mycobacterium tuberculosis (M.tuberculosis) sensitivity to ethambutol (EMB).  Methods One hundred and twenty-six M.tuberculosis clinical isolates sensitivity to EMB were detected with three methods, including L-J proportion method, Bactec MGIT 960 system (960 system) and microplate Alamar blue assay (MIC assay), and their results were compared interactively. The test data were analyzed using SPSS 17.0 software. The Kappa value between 0.4-0.75 represents moderately consistency, and Kappa value ≥0.75 shows excellent concordance, whereas Kappa value less than 0.4 means poor consistency.  Results The EMB sensitivity of 126 clinical M.tuberculosis isolates was tested by the three methods, the total consistency was 75.4%（95/126）. If L-J proportion method was used as the standard control, the sensitivity, specificity and consistency of 960 system and MIC assay were 62.8% (49/78), 100.0% (48/48), 77.0% (97/126) and 82.1% (64/78), 97.9% (47/48), 88.1% (111/126), respectively. MIC method showed a better consistency with L-J proportion method (Kappa=0.76), while 960 system represented a moderate concordance with L-J method (Kappa=0.56). If 960 system were taken as the standard control, the sensitivity, specificity and consistency of 960 system and MIC assay were 100.0% (49/49), 62.3% (48/77), 77.0% (97/126) and 98.0% (48/49), 77.9% (60/77), 85.7% (108/126), respectively. Both L-J proportion method and MIC assay showed high consistency with 960 system (Kappa≥0.70). If MIC assay was set as the standard control, the sensitivity, specificity and consistency of L-J proportion method and 960 system were 98.5% (64/65), 77.0% (47/61), 88.1% (111/126), and 73.8% (48/65),98.4% (60/61), 85.7% (108/126), respectively. The inconsistency among the three methods exis-ted in the MIC value of the drug concentration range 4.0 to 16.0 μg/ml.  Conclusion There were better consistency among the three detecting methods for testing M.tuberculosis sensitivity to EMB, but in which discrepancies existed on a certain extent. The results between 960 system and MIC assay were superb consistent. The MIC assay is more cost-effective, and more suitable for early diagnosis of M.tuberculosis resistance to EMB.

Key words: Mycobacterium tuberculosis, Ethambutol, Microbial sensitivity tests