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TB Methodologies

TB Methodologies. Dr. John G. Magee Regional Reference Centre for Mycobacteriology Health Protection Agency Regional Laboratory, Newcastle upon Tyne. Annual report, tuberculosis cases reported in 2000, England, Wales and Northern Ireland.

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TB Methodologies

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  1. TB Methodologies Dr. John G. Magee Regional Reference Centre for Mycobacteriology Health Protection Agency Regional Laboratory, Newcastle upon Tyne

  2. Annual report, tuberculosis cases reported in 2000, England, Wales and Northern Ireland Of 6323 cases ONLY 3350 (53%) were culture confirmed Of 3729 with pulmonary disease: ONLY 2249 (60%) were culture confirmed ONLY 2513 had a smear result! ONLY 1406 (56%) were smear positive

  3. DoH - Getting ahead of the curve - “Tuberculosis Action Plan” • The HPA will work with reference laboratories and NHS microbiologists • to improve the speed and consistency of laboratory diagnosis by: • providing high quality diagnostic services through a network of suitably • equipped and experienced laboratories • standardising methods • establishing quality assurance/performance monitoring programmes • covering • .. liquid culture for all specimens • .. molecular confirmation • .. unique typing designation

  4. DoH - Getting ahead of the curve - “Tuberculosis Action Plan” • STANDARDS EXPECTED • smear turnaround time - 1 working day • all clinical samples to have access to automated liquid culture • performed in experienced centres with large throughput and • dedicated facilities and staff • all isolates referred to regional mycobacteriology centre for • identification & susceptibility testing

  5. Diagnostic and Reference Mycobacteriology Detection Smear /Culture Molecular amplification of unique fragments Identification Phenotypic tests • “Gene probes” • PCR • Sequencing Susceptibility testing Phenotypic expression Detection of gene mutations Fingerprinting (Typing) Numerical taxonomy • RFLP … HIP • Spoligotyping • VNTR/MIRU Regional Centre for Mycobacteriology, Newcastle upon Tyne

  6. Direct detection using molecular biological tests The problems are have something to do with low organism numbers and much to do with extraction of DNA from clinical samples

  7. Direct detection using molecular biological tests • Commercial Assays: • Roche Amplicor (Cobas & “Manual”) • Abbott LCx (LCR) • GenProbe Direct (TMA) • BD ProbeTec ET (SDA) Regional Centre for Mycobacteriology, Newcastle upon Tyne

  8. Amplification control (58C) Target (62C) -dF/dT Negative control Temp (°C) Direct detection using molecular biological tests • In-House Assays: • Single PCR; Semi-Nested PCR; Nested PCR…... and now Real-Time PCR Regional Centre for Mycobacteriology, Newcastle upon Tyne

  9. Diagnostic and Reference Mycobacteriology Microscopy for AFB, if done well, remains a cheap, simple, fast and effective diagnostic technique Regional Centre for Mycobacteriology, Newcastle upon Tyne

  10. Isolation Regional Centre for Mycobacteriology, Newcastle upon Tyne

  11. UK NEQAS Distribution 1601 - Mycobacterium culture • Sample 6492 - M.tuberculosis present • of 330 laboratories 31.8% failed to isolate M.tuberculosis • of 176 UK laboratories 39.2% failed • Sample 6491 - M.tuberculosis present • of 331 laboratories 5.1% failed to isolate M.tuberculosis • of 176 UK laboratories 8.5% failed

  12. Isolation: Liquid Media circa 1983 Regional Centre for Mycobacteriology, Newcastle upon Tyne

  13. Isolation: Liquid Media circa 1993 Regional Centre for Mycobacteriology, Newcastle upon Tyne

  14. Continuous Automated Mycobacterial Liquid Culture systems Regional Centre for Mycobacteriology, Newcastle upon Tyne

  15. Cumulative weekly totals of Mtb complex isolates by CAMLiC and LJ slope culture 140 CAMLiC 120 100 80 Number of isolates 60 40 LJ 20 0 1 2 3 4 5 6 >6 Weeks after inoculation Regional Centre for Mycobacteriology, Newcastle upon Tyne

  16. Surety of Competence Detection of Acid-Fast Bacilli:  20 smears per week 1000 per year Mycobacterial Culture: 25 samples per week  1250 per year Susceptibility testing: 20 isolates per week 1000 per year Regional Centre for Mycobacteriology, Newcastle upon Tyne

  17. UK NEQAS Distribution 1601 - Mycobacterium culture Sample 6490 - M.tuberculosis NOTpresent 8/331 laboratories (2.4%) isolated a mycobacterium! In the last 4 negative samples there were 11,4, 2 & 10 false positives False positivity is probably due to laboratory cross contamination. NEQAS refer us to Breese at al. Arch Pathol Lab Med 2001, 125(9): 1213 BUT see also- de Boer et al.J Clin Microbiol 2002; 40; 4004 They found that labs processing <3000 samples per annum showed a greater risk of cross-contamination

  18. Identification of mycobacteria Regional Centre for Mycobacteriology, Newcastle upon Tyne

  19. Identification of mycobacteria “Gene-Probes” can confirm M.tuberculosis complex in under 2 hours Regional Centre for Mycobacteriology, Newcastle upon Tyne

  20. Identification of mycobacteria • “Genetic probes” are NOT amplification procedures - • They can identify a limited number of common species: • M.tuberculosis complex • M.avium complex • M.avium • M.intracellulare • M.kansasii • M.gordonae Regional Centre for Mycobacteriology, Newcastle upon Tyne

  21. Identification of Mycobacteria • Characterisation of mycolic acids by HPLC • Detection of unique fragments of genomic DNA • 16S rRNA sequencing equipment database variances [ ] Regional Centre for Mycobacteriology, Newcastle upon Tyne

  22. Susceptibility testing of mycobacteria • In the U.K. susceptibility testing of mycobacteria is performed by one of two methods: • The Resistance Ratio Method comparing MICs of test and control strains • The Radiometric or Proportional Method using the Bactec 460 TB • The Resistance Ratio Method is reliable & reproducible but laborious and relatively slow • The Radiometric Method is faster but suffers from problems inherent in the Bactec 460 Regional Centre for Mycobacteriology, Newcastle upon Tyne

  23. Continuous Automated Mycobacterial Liquid Culture Systems Regional Centre for Mycobacteriology, Newcastle upon Tyne

  24. Molecular detection of drug resistance Resistant strains with mutation (%) Putative resistance gene Drug Isoniazid katG inhA ahpC kasA 22-64 20-34 10 14 Rifampicin rpoB 90-98 Pyrazinamide 72-96 pncA Ethambutol 48-62 embB Riska et al. Int J Tuberc Lung Dis 2000; 4(2):S4-10

  25. 4500 7 4000 6 3500 5 3000 4 2500 Number of isolates Percentage Resistant 2000 3 1500 2 1000 1 500 0 0 1994 1995 1996 1997 1998 1999 Year N % Isoniazid resistant % MDR N UK 1994-1999 Initial isolates showing resistance to any drug;Isoniazid & MDR resistance (%), Regional Centre for Mycobacteriology, Newcastle upon Tyne

  26. DoH - Getting ahead of the curve - “Tuberculosis Action Plan” Develop and implement protocols for DNA fingerprinting taking customers needs into account. Establish a central database … linking fingerprinting and epidemiological data

  27. MTBC Strain Typing Methods IS6110-based fingerprinting • Most discriminatory method • Slowest method (3-6 weeks) • Difficult to compare large numbers of patterns Restriction Fragment Length Polymorphism, RFLP PCR-RFLP Hemi-nested Inverse PCR (HIP) Regional Centre for Mycobacteriology, Newcastle upon Tyne

  28. 1353 603 310 HIP fingerprinting results Regional Centre for Mycobacteriology, Newcastle upon Tyne

  29. Spoligotyping Spacer Oligonucleotide Typing • Less discriminatory than IS6110 typing … BUT... • Faster turnaround time • Digital results, facilitating comparisons • Does not require viable cultures Regional Centre for Mycobacteriology, Newcastle upon Tyne

  30. VNTR - MIRU Variable Number of Tandem Repeats • Measures variability in 6 loci Mycobacterial Interspersed Repetitive Units • Measures variability in 12 loci • PCR-based = rapid turnaround • Digital results, facilitates comparisons • Highly discriminatory • Does not require viable cultures • High throughput (automated sequence analysers) Regional Centre for Mycobacteriology, Newcastle upon Tyne

  31. Future Genotyping Strategy • Primary typing will be high throughput, automated, PCR-based i.e. MIRU/VNTR • Secondary typing by IS6110 RFLP when needed for discrimination Regional Centre for Mycobacteriology, Newcastle upon Tyne

  32. Time taken for turnaround of final reports (from date sent by RCM to date final report reaching clinicians) 80 70 60 50 No of samples 40 30 20 10 0 <=1 day 2 days 3-4 days 5-6 days 7-8 days 9-10 days >10days Time Regional Centre for Mycobacteriology, Birmingham

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