Manual MGIT™ system for the detection of Mycobacterium tuberculosis: insights from a high TB burden setting

Evaluation of Various Diagnostic Techniques for the Diagnosis of Pulmonary and Extra Pulmonary Tuberculosis at a Tertiary Care Center in North India

INTRODUCTION

Tuberculosis (TB) is a one of the main causes of mortality and morbidity worldwide. Bactec MGIT (Mycobacteria Growth Indicator Tube) system is a rapid, reliable automated system for early diagnosis of pulmonary and extra pulmonary TB in setups where purchase of expensive instruments is not possible. The present study was thus carried out to evaluate AFB microscopy, culture on Lowenstein Jensen media and micro MGIT system for early and accurate diagnosis of Tuberculosis.

METHODS

A total of 280 samples were processed for direct AFB smear examination, and culture on micro MGIT and LJ media. The identification of Mycobacterium tuberculosis complex in positive cultures was done by MPT64 Ag card test (BD MGIT TBC Identification Test).

RESULTS

Out of the processed samples, (47.1%) 132/280 were positive for Mycobacterium spp by Micro MGIT, (35%) 98/280 on LJ medium and (25.7%) 72/280 by AFB smear. A total of (48.5%) 136 samples were positive by a combination of Micro MGIT and LJ medium. Among the total positive samples (136/280), Micro MGIT was found to be positive in 97% (132/136) of samples, LJ was positive in 72% (98/136), while 52.9% (72/136) were positive by AFB smear.

CONCLUSION

Manual MGIT System is a simple and efficient, safe to use the diagnostic system. It does not require any expensive/special instrumentation other than the UV lamp for the detection of fluorescence. In areas with limited resources where the purchase of expensive instruments such as the MGIT 960 is out of scope, the use of manual MGIT for rapid susceptibility testing for MDR-TB could be an option. We would recommend testing MGIT 960 using first and secondline drugs to determine DST.

Evaluation of a manual identification system for detection of Mycobacterium tuberculosis in a primary tuberculosis laboratory in China

OBJECTIVE

To compare the diagnostic performance of the manual BACTEC™ Mycobacteria Growth Indicator Tube (MGIT™) system (M-MGIT) with the automated BACTEC™ MGIT™ 960 system (A-MGIT) and Löwenstein-Jensen (L-J) culture method in detecting mycobacteria in sputum specimens from patients with suspected pulmonary tuberculosis (TB).

METHODS

For this cross-sectional study, sputum samples were taken from patients aged ≥18 years attending a TB clinic in Beijing, China between July 2015 and October 2016. Processed sputum samples were inoculated into the MGIT systems and L-J medium for up to 6 and 8 weeks, respectively.

RESULTS

The M-MGIT and A-MGIT methods detected significantly more Mycobacterium tuberculosis complex (MTC) isolates than L-J culture from the 565 sputum samples (39%, 40% and 32%, respectively). Using a positive result from any of the three culture systems as reference, the sensitivity of M-MGIT, A-MGIT and L-J methods were 92%, 94%, and 74%, respectively. The time-to-detection of mycobacteria was 12.9±4.2 days for M-MGIT, 11.8±5.2 days for A-MGIT and 24.2±8.7 days for L-J.

CONCLUSIONS

M-MGIT has a similar diagnostic performance to A-MGIT, and is a fast and reliable alternative to conventional culture methods in the diagnosis of pulmonary TB in a developing country.