WHO Recommended Tools to Improve Diagnosis of Active and Drug Resistant Tuberculosis.

The successful arrest or cure of tuberculosis (TB) depends largely on early case detection and proper treatment. Currently, several promising diagnostic tools with improved sensitivity and speed are available. Old microscopic and culture based technologies have been revisited and new molecular technologies have been developed. In recent years, World Health Organization (WHO) evaluated and endorsed different TB diagnostic tools and published various policy statements. These policy statements address improvements in smear microscopy, use of commercial and non-commercial culture based techniques and rapid molecular assays. This is the first comprehensive review compiling pros and cons of WHO recommended TB diagnostic tools for effective implementation in TB endemic regions.

Comparison of Mycobacterium tuberculosis culture using liquid culture medium and Lowenstein Jensen medium in abdominal tuberculosis.

Background Traditionally, the Lowenstein Jensen (LJ) medium has been used for culturing Mycobacterium tuberculosis. In abdominal tuberculosis (TB), the reported yield from tissue culture is between 20% and 60%. Liquid cultures are reported to give a higher yield but there is little data available in abdominal TB. Aim To compare the yield of TB culture with BACTEC 460TB liquid medium and LJ medium for patients with suspected abdominal TB and determine cost effectiveness. Methods This prospective study was done in consecutive cases with clinical, radiological, endoscopic/surgical, and histological suspicion of abdominal TB. Tissue biopsies obtained at colonoscopy or surgery were processed and plated on LJ medium as well as the BACTEC 460TB system. NAP (ρ-nitro-α-acetylamino-β-hydroxy-propiophenone) differentiation was carried out to determine species. The cost of each method and cost per yield were calculated. Results Of the 29 cases, 22 cases (76%) were positive on BACTEC 460TB culture while 14 (48%) were positive on LJ medium giving a 64% increment in yield. However, the culture of one patient grew on LJ medium, where the BACTEC 460TB was negative. The additional cost of BACTEC 460TB is Rs. 460 and LJ is Rs. 40. Conclusions Samples from patients with abdominal TB should be processed on both liquid and LJ medium. For high yield, the use of a liquid culture medium system is essential.

Can cord formation in BACTEC MGIT 960 medium beused as a presumptive method for identification of M tuberculosis complex.

Background: Serpentine cord formation in BACTEC MGIT 960 medium was evaluated as a rapid method for the presumptive identification of M. tuberculosis complex (MTBC). Material & Methods: Total 2527 samples were processed for AFB culture using MGIT 960 TB system over a period of three months. AFB smears were prepared from 1000 MGIT tubes flagged positive by the MGIT instrument and stained by ZN method to examine presence or absence of serpentine cording. The cord formation was compared with PNBA [pnitro benzoic acid] test on MGIT system and all controversial cases were further evaluated by NAP [p-nitro-a-acetylaminophydroxypropiophenone] test on BACTEC 460 TB system. Results & Discussion: Of the 1000 culture positives, 904 (90.4%) were identified as mycobacteria, of which 869 (96%) showed cording by smear microscopy. One (0.1%) was identified as nocardia. In the remaining 95 (9.5%) cases, primary smear made from MGIT vial was negative. Of 869 cultures showing serpentine cord formation, 842 were confirmed as MTBC and 27 as NTM by PNBA assay on MGIT 960 TB system. The sensitivity, specificity, positive and negative predictive values are found to be 99.6%, 54%, 96% and 91% respectively. An average detection time for PNBA assay was found to be eight days whereas cording results were available on the same day of culture positivity. Conclusion: Though highly sensitive it is not very specific and hence cannot be the only test for presumptive diagnosis of MTBC.

Comparison of Phenotypic and Genotypic methods for Pyrazinamide susceptibility testing.

Objectives: To evaluate Pyrazinamide (PZA) susceptibility results obtained by phenotypic MGIT 960 TB system against enzymatic Pyrazinamidase assay and genotypic pncA gene sequencing. To find the prevalence of infections caused by M. bovis in PZA resistant M. tuberculosis complex isolates. Methods: 33 consecutive PZA resistant and 30 consecutive PZA susceptible isolates reported for PZA susceptibility testing by MGIT 960 TB system were included in this study. Presence of active pyrazinamidase enzyme was sought by using the Wayne assay. The pncA gene was amplified by PCR and then sequenced to screen mutations. All the PZA resistant isolates were further spoligotyped to identify M. bovis, if present. Results: Of 33 PZA resistant strains by MGIT 960, 31 were Wayne assay negative and two were positive. Of the 30 susceptible PZA strains six were Wayne assay negative reporting false resistance. PncA gene sequencing revealed that 32 of the 33 MGIT PZA resistant isolates had diverse nucleotide changes scattered throughout the pncA gene (one isolate did not show any mutation). Of the 30 phenotypically susceptible isolates, 21 were wild types whilst nine isolates showed the presence of a silent mutation C-T at codon 195. Fifteen mutations found in this study has not been described earlier. Not a single isolate of M. bovis was detected among PZA resistant M. tuberculosis complex isolates. Conclusion: MGIT 960 showed better concordance with sequencing results in comparison with Wayne assay. In present study, a high proportion (85%) of MDR-TB isolates from patients receiving anti-TB treatment were found to be resistant to PZA.