Original Article Comparison of the Mycobacterium Growth Indicator Tube Method and the Method of Proportion for Drug Susceptibility Testing of Mycobacterium Tuberculosis

Objective: Tuberculosis is an important public health problem in developed and, especially, developing countries. The incidence of multidrug-resistant Mycobacterium tuberculosis (MDR-TB) has increased in recent years. Mycobacterial culture and susceptibility testing must be rapidly concluded for effective treatment and control of the disease. The present study evaluated the reliability of the Mycobacterium Growth Indicator Tube (MGIT) method for testing the susceptibility of M. tuberculosis to four first-line antimicrobial drugs by comparing MGIT results to those obtained by the method of proportion (MOP), which served as the reference method. Materials and Methods: A total of 60 clinical isolates (28 sputum, 7 bronchoalveolar lavage, 7 cerebrospinal fluid, 3 gastric aspirates, 5 urine, 4 pleural fluid and 6 other specimens) of M. tuberculosis were tested for susceptibility to streptomycin (SM), isoniazid (INH), ethambutol (EMB) and rifampin (RIF). MOP was carried out according to National Committe for Clinical Laboratory Standards (NCCLS) on Löwenstein-Jensen medium. MGIT susceptibility testing was performed according to the protocol provided by the manufacturer. Results: Resistance was detected in 18.3 % and 16.7 % of the isolates for INH, 13.3 % and 10.0 % for RIF, 16.7 % and 11.7 % for SM and 6.7% and 8.3 % for EMB by MOP and MGIT, respectively. Conclusion: MOP remains the method of choice, however, the correlation between MOP and MGIT suggested that MGIT can also be used routinely and that it is a reliable method for testing susceptibility of M. tuberculosis strains to first-line anti-tuberculosis drugs