Rapid immunochromatographic test for the identification and discrimination of Mycobacterium tuberculosis complex isolates from non-tuberculous mycobacteria

Background: A new rapid Immunochromatographic test (ICT) kit (SDBioline TB Ag MPT64RAPID®) developed by Standard Diagnostics, South Korea was evaluated for rapid differentiation of M. tuberculosis from non tuberculous mycobacteria (NTM). It detects MPT 64 antigen in M. tuberculosis isolates using mouse monoclonal MPT 64 antibody. The kit was assessed for routine identification of the Acid Fast Bacilli(AFB) isolated in our laboratory. Materials and Methods: Two hundred eight culture isolates of Mycobacteria were tested using ICT test kit for detection of MPT 64 antigen from liquid and solid culture. H₃₇Rv strain was employed as the positive reference control. Any negative result was referred for confirmation by Gen Probe Accu Probe assay for MTB Complex (Gen-Probe, San Diego, Calif.). Speciation of NTM was performed using genotypic Mycobacterium CM assay (Hain's life sciences, Germany). Results: Of the 208 culture positive isolates tested, 182 (87.5%) were found positive for Mycobacterium tuberculosis Complex and remaining 26 (12.5%) were considered as NTM. These results were further confirmed by Gen Probe Accu probe assay that served as the reference method for detection of MTBC. H₃₇Rv reference strain was taken as a control for ICT test and molecular tests. The reference strain showed the presence of MPT64 antigen band in the ICT test. Similar bands were formed in all MTBC (182) isolates tested, proving 100 per cent sensitivity and no bands were detected in 48 (100%) NTM isolates tested, proving 100 per cent specificity of the ICT kit. Conclusion: Tuberculosis is a global pandemic. Rapid identification of Mycobacteria as MTB complex or non-tuberculous Mycobacteria from culture is important for treatment of infected cases and drug susceptibility testing of the culture isolate. MPT 64 TB antgen detection using SD Bioline Immunochromatographic test is a simple and cost effective method for differentiation of Mycobacterial cultures as MTB complex from non- tuberculous Mycobacteria.