Evaluation of manual Mycobacterium growth indicator tube for isolation and susceptibility testing of Mycobacterium tuberculosis for implementation in low and medium volume laboratories

Abstract

Background: Manual Mycobacterium growth indicator tube (MGIT) was evaluated for isolation and drug susceptibility testing (DST) of Mycobacterium tuberculosis (MTB) for its implementation in laboratories with low and medium volume.

Methods: 1018 consecutive clinical specimens were processed using manual MGIT and conventional Lowenstein-Jensen (LJ) culture. Results obtained for culture positivity were analyzed taking combined reference of positivity by either solid or liquid culture. All positive cultures were identified and DST to first line drugs was performed by manual MGIT and 1% proportional method on LJ media. Performance of manual MGIT for DST was compared to conventional DST on LJ media.

Result: Of the total 220 culture positive samples 93.9% were isolated in MGIT while 75.7% in LJ taking combined reference of positivity by either solid or liquid culture. Turn around time for isolation of MTB was significantly less for MGIT as compared to LJ. There was good agreement between manual MGIT and 1% proportional method on LJ media for DST to first line drugs. Turnaround time from inoculation to DST results for smear positive and smear negative cases using manual MGIT was 20.2 and 30.1 days respectively. The total cost for isolation, identification and DST in manual MGIT for smear positive and smear negative cases was INR 2350 and INR 2700 respectively.

Conclusion: It is feasible to implement manual MGIT in low to medium volume laboratory that already has experience with culture provided adequate biosafety measures and appropriate training of laboratory staff are taken care of.

Keywords: Liquid culture; Mycobacterium growth indicator tube; Tuberculosis.

Fig. 1

BACTEC MicroMGIT fluorescence reader.

Fig. 2

Protocol for MTB culture by LJ and manual MGIT followed in the study.