Comparison of rapid colorimetric method with conventional method in the isolation of Mycobacterium tuberculosis

The aim of the study was to evaluate two methods (colorimetric and conventional) for isolation of Mycobacterium tuberculosis. A total of 500 clinical specimens were processed by modified Petroff's method and then inoculated into MB/BacT-240 system bottles and on LJ medium slopes. The specimens included 242 sputum, 95 gastric aspirates, 47 pleural fluids, 45 CSF, 32 urine, 18 pus, 11 bronchoalveolar lavage, 3 tissue, 2 stool, 2 lymphnode specimens, 2 synovial fluid and 1 bronchial wash specimens. The isolation rate was 16.4% by the colorimetric method and 2.2% by the conventional method. The mean detection time was 16 days and 26 days respectively. Among 36 direct smear positive samples, 63.9%(23/36) and 30%(11/36) were positive by colorimetric and conventional methods respectively. Out of 464 direct smear negative samples 12.9%(60/464) and 0.6%(3/464) were positive by colorimetric and conventional methods respectively. Therefore, colorimetric method enables rapid detection leading to early diagnosis and drug susceptibility testing.