Evaluation of the bactec MGIT 960 TB system for recovery and identification of Mycobacterium tuberculosis complex in a high volume tertiary care centre.

Aim: To evaluate the performance of an automated BACTEC MGIT 960, a non-radioactive, non-invasive liquid culture system for cultivation of M. tuberculosis complex in terms of recovery rate and time. Materials and Methods: From March 2005 to December 2007, 14,597 specimens were processed using the MGIT 960 system and the results were compared with conventional L.J medium. We standardised r-nitro benzoic acid (PNBA) assay on MGIT 960 TB system for identification of M. tuberculosis complex and evaluated its usefulness by comparing the results with an in-house molecular assay and sequencing. Results and Discussion: Of the total 6143 (42%) isolates positive for M. tuberculosis complex, 6015 (41%) were positive by MGIT 960 TB system. In contrast, 3526 (24%) M. tuberculosis complex isolates grew on the conventional L.J medium. The mean turn around time for mycobacterial growth in smear-positive specimens was nine days for MGIT 960, and 38 days for L.J. medium whereas in smear negative specimens it was 16 days by MGIT vs. 48 days by L.J. Conclusion: MGIT 960 system with PNBA assay for identification of M. tuberculosis complex is a rapid and useful method in laboratories processing a large number of specimens.

Dedicated decontamination: A necessity to prevent cross contamination in high throughput mycobacteriology laboratories.

Unrecognized cross-contamination has been known to occur in laboratories frequently, especially with sensitive recovery system like BACTEC 460 TB. In March 2001, we investigated a pseudo-outbreak of Mycobacterium tuberculosis isolates in three smear negative clinical specimens and would like to present our experience in this communication. METHODS: All suspected cases were confirmed by checking the drug susceptibility and DNA fingerprints using spoligotyping as well as restriction fragment length polymorphism. RESULTS: On investigation, the most likely cause was found to be the use of common decontamination reagents and phosphate buffer. CONCLUSIONS: To avoid erroneous diagnosis, we have devised a dedicated decontamination procedure, which includes separate aliquoting of phosphate buffer and decontamination reagents per patient. Timely molecular analysis and appropriate changes to specimen processing have been identified as useful measures for limiting laboratory cross contamination.

Use of bactec 460 TB system in the diagnosis of tuberculosis.

PURPOSE: To evaluate, the efficacy of BACTEC 460 TB system for the diagnosis of tuberculosis in a tertiary care hospital in Mumbai, India. METHODS: We compared 12,726 clinical specimens using BACTEC 460 TB system and conventional method for detection of Mycobacterium tuberculosis over a period of six years. Result: The overall recovery rate was 39% by BACTEC technique and 29% using Lowenstein-Jensen (LJ) medium. An average detection time for B actec0 460 TB system was found to be 13.3 days and 15.3 days as against 31.2 days and 35.3 days by LJ method for respiratory and nonrespiratory specimens respectively. The average reporting time for drug susceptibility results ranged from 6-10 days for the BACTEC 460 TB system. CONCLUSIONS: The BACTEC system is a good system for level II laboratories, especially in the diagnosis of extrapulmonary and smear negative tuberculosis.

Newer rapid diagnostic methods for tuberculosis: A preliminary experience.

Background:Present scenario of tuberculosis (TB) demands a reliable method for rapid diagnosis of TB. Several newer methodologies have been introduced over last 2 decades. However, clinical evaluation of all these methods is essential before bringing them into routine diagnostic practice. Aim: In the present study, we have evaluated 3 most promising methodologies viz. BACTEC 460 TB system (TB BACTEC), Transcription Mediated Amplification (TMA) and Phage assay for rapid detection of M. tuberculosis complex directly from respiratory and non-respiratory specimens. Material and Methods: Total 139 AFB smear positive and 41 AFB smear negative respiratory and non-respiratory specimens were tested by these methods and results were compared with conventional LJ method. Results and Conclusions: TMA is found to be most rapid and reliable method for detection of M. Tuberculosis complex from respiratory specimens with 93.8% sensitivity. However, for non-respiratory samples, TB BACTEC can be the method of choice. An average detection time for TB BACTEC is found to be 13 days and 15 days, compared to 31 days 35 days by LJ method in cases of smear positive respiratory and non-respiratory specimens respectively. Phage assay is highly specific for detecting M. tuberculosis complex and can be used as a rapid screening method for TB in cases of respiratory specimens collected from patients not receiving anti-TB therapy. As only viable TB bacilli are detected by phage assay, it can be used as a sensitive tool to monitor treatment success.

Evaluation of a new phage amplification technology for rapid diagnosis of tuberculosis.

PURPOSE: Rapid diagnosis of tuberculosis is essential to initiate timely and appropriate treatment to curb the spread of this potentially life threatening disease. The purpose of this study was to evaluate a phage amplification technology viz., FASTPlaque TB,TM for the diagnosis of tuberculosis. METHODS: We evaluated the clinical utility of this new assay by analyzing 50 respiratory and 40 non-respiratory specimens, using FASTPlaque TB TM kit (Biotec Laboratories, UK) and the performance was compared with TB Bactec 460 semi-automated liquid culture system and conventional LJ culture method. RESULTS: In case of respiratory specimens phage assay gave good specificity (100%) compared with TB Bactec whereas with respect to LJ method the sensitivity and specificity were 93.1% and 88.2% respectively. In case of non-respiratory specimens comparison of results obtained by phage assay showed sensitivity of 90.9% and specificity of 88.8% with respect to TB Bactec and 87.5% and 93.8% with respect to LJ method. CONCLUSIONS: We believe that this new low cost assay may have widespread applicability, especially in developing countries, due to its manual format and rapid reporting of results.