Performance evaluation of MPT64 Antigen detection for rapid confirmation of Mycobacterium Tuberculosis complex (MTBC) from solid culture isolates

Abstract

Background: Tuberculosis remains one of the most common infectious diseases in impoverished nations and increasing resistance to anti- tubercular drugs makes treatment difficult and early diagnosis imperative. Although molecular tests are increasingly being relied upon, culture remains the gold standard and a positive culture still needs to be confirmed as MTB Complex. The purpose of this study was to assess the MPT64 antigen detection assay's diagnostic performance in confirming MTB complex from solid culture isolates. Objective: To evaluate the MPT64 antigen detection assay's diagnostic performance for confirming Mycobacterium tuberculosis complex from positive LJ culture isolates. Materials & Methods: Clinical samples were obtained from patients suspected of having pulmonary or extra pulmonary tuberculosis. GeneXpert was conducted on all samples and GeneXpert positive samples were cultured on Lowenstein-Jensen (LJ) medium. Culture positive isolates were subjected to MPT64 antigen detection test. Results: On GeneXpert, 63 of the 1050 samples were positive for MTB complex. Out of the 63 GeneXpert positive samples that were subjected to culture on LJ medium, 42/63 (66.6%) yielded growth.  Culture positivity was higher (39.6%) in pulmonary than extra pulmonary samples (26.9%). Contrary to this, culture negativity was higher in extra pulmonary (30.1%) than (3.1%) in pulmonary specimens. MPT64 antigen detected all 42/42 (100%) of culture positive isolates as MTBC that were confirmed by conventional biochemical testing. Conclusion: MPT64 antigen detection assay is a reliable, quick and economical test for verifying MTBC from positive cultures and easy to incorporate in the Mycobacteriology culture diagnostic workflow.

Keywords: GeneXpert, Mycobacterium tuberculosis complex, MPT64 and Tuberculosis.