Identification of Mycobacterium species following growth detection with the BACTEC MGIT 960 system by DNA line probe assay

The tuberculosis and infections caused by nontuberculous mycobacterial (NTM) species are increasing in patients presented with respiratory illness, and it is crucial to document the epidemiology of these infections.

To study the mycobacterial species and in vitro drug susceptibility trends of Mycobacterium tuberculosis found in the respiratory specimens.

A prospective descriptive study from July 2009 to December 2012. The BACTEC MGIT system tubes with growth were used in the study. GenoType Mycobacterium (Hain Diagnostika, Nehren, Germany) assays were used to identify the mycobacteria. The drug susceptibility testing was performed by the MGIT 960 system.

A total of 1745 MGIT 960 system positive tubes were included. M. tuberculosis complex (MTC) constituted 67.45% of the yield isolated, 30.83% were nontuberculous mycobacterial species, 0.17% were Mycobacterium bovis BCG and 1.55% were not interpretable to species levels. Mycobacterium fortuitum (45.71%), Mycobacterium abscessus (26.21%) and Mycobacterium intracellulare (10.41%) were major NTM identified. The drug susceptibility study showed that 6.88% (81/1177) of MTC were drug-resistant TB, 56 isolates were resistant to one of the first-line anti-TB drugs, 25 isolates were found to be resistant to 2 or more first-line anti-TB drugs, of which 19 (20.46%) were MDR-TB and one of the isolates in the year 2011 was confirmed XDR-TB.

M. tuberculosis, M. fortuitum, M. abscessus and M. intracellulare were major mycobacterial species detected in the respiratory samples. The drug susceptibility testing showed that the majority of MTC were sensitive to first-line anti-TB drugs.