Impact of <i>Mycobacterium Africanum</i> on the Sensitivity and Specificity of MPT64 Antigen Immunochromatographic Assay

Abstract

Background: The MPT64 antigen is a protein predominantly secreted by Mycobacterium tuberculosis complex (MTBC) in cultures and is used for its rapid differentiation from other clinically relevant nontuberculous
mycobacteria (NTM). However, reports have shown that truncation of this protein and or presence of Mycobacterium africanum restricted within the West African region may have reduced sensitivity to MPT64 antigen as an identification tool for MTBC.
Objective: We evaluated the performance of MPT64 antigen immunochromatographic assay to detect MTBC in culture isolates grown from clinical specimen.
Methods: 149 mycobacterial isolates grown on Lowestein Jenseen (LJ) media from pulmonary TB patients, 8 reference mycobacterial and a non-mycobacterial strain were investigated for the presence of MPT64 protein using a commercial assay kit. The result was compared to growth of cultures on LJ containing para-nitrobenzoic acid (PNB) and line probe assay (LPA) characteristics of the isolates.
Results: The presence of MPT64 antigen band was observed in one hundred and twenty-one isolates but absent in 28 isolates which was concordant with results obtained for growth on PNB and LPA. The sensitivity, specificity, positive predictive and negative predictive values were 100% respectively.
Conclusion: The good sensitivity and specificity of the assay showed MPT64 antigen as an excellent identification tool for MTBC.