Diagnostic performance of two commercial MPT64 assays for the identification of Mycobacterium tuberculosis complex from liquid culture

Tuberculosis (TB) is a chronic infectious disease caused by bacteria of the Mycobacterium tuberculosis complex (MTBC). Early diagnosis of TB is the most essential component to control TB. In this study, we evaluated the diagnostic performance of SD Bioline TB Ag MPT64 (SD Bioline) and BD MGIT TBc Identification (BD TBc ID) kits for the detection of MTBC from MGIT (Mycobacteria Growth Indicator Tube) 960 culture tube, positive for acid-fast bacilli (AFB).

A total of 198 AFB positive MGIT cultures [MTBC, 150 and non-tuberculous mycobacteria (NTM), 48] were collected during the study period (April 2021 to March 2023) and subjected to SD Bioline and BD TBc ID assays, respectively. All the 150 MTBC positive cultures were confirmed by multiplex PCR targeting MPB64, protein B and IS6110 genes, and the 48 NTM cultures were speciated by using line probe assays technique- Genotype Mycobacterium CM assay.

SD Bioline and BD TBc ID kits detected all 150 MTBC strains correctly from MGIT positive cultures and no false negative was observed. However, there was one false positive for M. abscessus by SD Bioline and two false positive results for M. abscessus and M. intracellulare each by BD TBc ID. Overall, the sensitivity of both SD Bioline and BD TBc ID tests was 100 % and specificity was 97.9 % and 95.8 %, respectively.

Our results highlighted that SD Bioline and BD TBc ID assays played a promising role in the earlier identification of MTBC present in liquid culture and may act as a potential alternative to biochemical and expensive molecular techniques.