[BACTEC MGIT 960 system for drug susceptibility testing of Mycobacterium tuberculosis: a study using external quality assessment strains].

OBJECTIVE

To evaluate the performance of the BACTEC MGIT 960 system for drug susceptibility testing (MGIT AST) of Mycobacterium tuberculosis to isoniazid, rifampin, streptomycin and ethambutol.

DESIGN

Fifty external quality assessment strains of M. tuberculosis provided by the Coordinating Centers of WHO/ IUATLD were tested by BACTEC MGIT 960 system, and the results were compared with the referee results of the WHO/IUATLD Supranational Reference Laboratory Network (SRLN).

RESULTS AND CONCLUSION

Overall concordance rates of the results obtained by MGIT AST and the referee results of the SRLN were 97.3% for four first-line drugs. Agreement rates were particularly high for isoniazid, rifampin, and streptomycin (agreement rate of over 97%), but somewhat lower for ethambutol, which relates to a lower sensitivity of MGIT AST. Turnaround times from inoculation to drug susceptibility results ranged from 6 to 13 days for the MGIT AST system with a median time of 7 days; this contrasted with three weeks for the proportion method using Middlebrook 7H10 agar, indicating that MGIT AST system has the potential to consistently meet with the turnaround time guidelines suggested by the Centers for Disease Control and Prevention of the United States. These results demonstrate that the fully automated BACTEC MGIT 960 AST system is useful for the rapid diagnosis of drug resistant tuberculosis.