Abstract

"The automated BACTEC MGIT 960 system was compared with the method of proportion (MP) for testing susceptibility of Mycobacterium tuberculosis to antituberculous drugs. 275 strains of M. tuberculosis isolated in Chile from 270 patients between 2001 and 2003 were tested. Concordance of BACTEC MGIT 960 with MP depending on the antituberculous drug tested was the following: 97.0% for streptomycin, 98,9% for rifampicin, 97,4% for isoniazid and 98,1% for ethambutol. Total resistance to antituberculous drugs of the 275 strains of M. tuberculosis tested varied from 20.4 % assessed by MP to 25.1% evaluated by BACTEC MGIT 960. These differences were not significant (p: ns; t test). BACTEC MGIT 960 yielded 17 strains as resistant. These same 17 strains were detected as sensitives by MP. Therefore, BACTED MGIT overestimates the number of resistant strains. In our study BACTEC MGIT 960 showed a very good concordance with MP and besides it allowed to get the results in a much shorter period of time than MP. Additional analysis are needed to know the factors envolved in BACTED MGIT overestimation of resistant strains"