Evaluation of BACTEC MGIT 960 system for recovery of Mycobacterium tuberculosis complex in Pakistan

Abstract

We evaluated the performance of MGIT 960 system in terms of recover rate, detection time of mycobacteria and contamination rate from various human clinical specimens and compared it with already in use BACTEC 460 TB system and conventional LJ medium. This is the first reported study on MGIT 960 and its comparison with BACTEC 460 system in Pakistan. A total of 260 different clinical specimens received for the culture of mycobacteria were dealt during the six months study period. All the specimens were digested and decontaminated according to the standard N-acetyl-Lcysteine NaOH method. All the processed specimens were inoculated on both the liquid systems and solid medium and incubated for six weeks and eight weeks consecutively. A total of 44 mycobacterial isolates (Mycobacterium tuberculosis, n=43; Mycobacteria other than tuberculosis, n=1) were recovered from 260 clinical specimens. The recovery rate of M. tuberculosis complex was 97.6% on BACTEC MGIT 960 system and 93.0% on BACTEC 460 system and 83.7% on LJ medium. The mean detection time of mycobacteria on BACTEC MGIT 960 system was 11.2 days in smear positive cases, 14.2 days in smear negative cases and 14.8 days in smear positive cases on BACTEC 460 system. Contamination rates were 9.6% and 5.6% and 3.4% for BACTEC MGIT 960, BACTEC 460 system and LJ medium respectively. The non-radiometric, fully automated BACTEC MGIT 960 system has better diagnostic ability as compared with radiometric, semi-automated BACTEC 460 system and LJ medium, so it can be used as a reliable alternative in over burden laboratories.