Utility of the BACTEC MGIT 960 TB system for recovery of mycobacteria

Abstract

Background and Objectives: Pulmonary tuberculosis (PTB) remains a public health issue in Nigeria. The rapid diagnosis of PTB is essential for the early initiation of treatment and management of patients. The utility of the BACTEC MGIT 960 TB system was evaluated and compared with the Lowenstein Jensen (LJ) culture method for the recovery of Mycobacteria from sputum samples. Methods: A total of 2400 sputum samples submitted to the South East TB Zonal Reference Laboratory, Amachara Umuahia, Nigeria were tested. Samples were decontaminated using the standard N-Acetyl-L-Cysteine Sodium Hydroxide method and concentrated before processing. The processed samples were inoculated into both MGIT 960 tubes and LJ medium and incubated accordingly. Results: From all sputum samples, Mycobacteria were recovered from 201 (8.4%) sputum samples by the MGIT 960 system and 175 (7.3%) by LJ culture (p=0.014). The sensitivity for MGIT and LJ culture for mycobacteria were 95.0% and 80.1%, respectively. Among the 201 MGIT-positive cultures, 127 (63.2%) were identified as Mycobacterium tuberculosis complex and 74 (36.8%) as Mycobacteria other than tuberculosis (MOTT). The recovery rate of MTBC from LJ-positive samples was 84.0% and MOTT 16.0%. MGIT 960 identified more MOTT than LJ culture (p=0.045). The contamination rate associated with MGIT and LJ culture was 4.1% and 2.5%, respectively (p=0.037). The time to detection of mycobacteria in MGIT 960 and LJ was 14.8 days and 33.2 days, respectively. Conclusion: MGIT 960 has good diagnostic accuracy. It provided a more rapid and higher recovery of all mycobacteria than the LJ culture.