Comparison of an in-house multiplex PCR with two commercial immuno-chromatographic tests for rapid identification and differentiation of MTB from NTM isolates

Species specific diagnosis of mycobacterial infection is crucial because treatment of infections caused by Mycobacterium tuberculosis [MTB] differs from that of non-tuberculous mycobacterial [NTM] species. The species identification used to be cumbersome and non-reproducible a decade ago. Recently, some commercial tests have been made available to differentiate the MTB and NTM growths in culture media. Sensitivity and specificity of these tests was evaluated. In this double blind study 572 clinical samples were cultured in an automated BACTEC-MGIT-960 system. A total of 147 [25.7%] samples were MGIT culture positive. These cultures were subjected to an in-house m-PCR [which amplifies hsp-65, esat-6 and ITS region for MAC], two commercial immune-chromatographic tests [ICTs] and phenotypic tests. Of the 147 MGIT positive cultures, m-PCR was able to correctly identify MTB in 123 cultures and NTM in 24 which included 3 MAC isolates. m-PCR showed 100% agreement with two gold standard methods-the nitrate reductase assay and PNB tests-in correctly identifying MTB. Commercial strips were able to correctly identify MTB in 120 [97.5%] of 123 cultures, while 3 [2.5%] isolates were falsely identified as NTM. However, none of the growth negative spent medium gave false positive results in any of the tests. None of the commercial strips misidentified any of the 24 NTM as MTB; hence, specificity of these strips was 100%. Of the 2 IC test systems, both SD Bioline and BD TBc strip tests missed 2.5% of MTB isolates and misidentified these as NTM. The in-house m-PCR was found to be the most accurate and efficient tool for identifying the MTB, MAC and other NTMs

Multi drug resistant tuberculous meningitis in pediatric age group

Past decade has seen increase in cases of tuberculous meningitis [TBM] and multidrug resistance in such cases. The mortality rate for a mismanaged TBM is very high which increases manifold in presence of associated complicating factors. The present study was thus planned to evaluate the prevalence of MDR-TBM and look for associated complicating factors and carry out drug sensitivity pattern in all culture positive isolates. One hundred cerebro-spinal fluid [CSF] samples from children clinically suspected of having TBM were collected and processed for detection of Mycobacterium tuberculosis by conventional methods like Ziehl-Neelsen [ZN] staining, Lowenstein- Jensen [LJ] culture and newer method like BACTEC 460 TB culture. Antimicrobial susceptibility was performed on all culture positive isolates by BACTEC 460 TB system. Twenty two cases could be diagnosed as definitive TBM based on BACTEC culture. Of these 22 cases, six cases [27.3%] were positive by ZN staining and/or LJ culture. Of all isolates tested for drug sensitivity 18 were sensitive to all four drugs whereas 4 isolates were resistant to more than one drug. Since the prevalence of MDR-TBM is very high we conclude that all CSF samples should be subjected to sensitivity testing to diagnose it at an early time and determine its sensitivity pattern in view of its very high mortality