British Society for Microbial Technology. The laboratory diagnosis of tuberculosis 25 years of progress. D A Mitchison St George’s, University of London. With assistance from FINDdiagnostics. Diagnostic testing at different levels of health system. Sputum: 25 years ago (1985).
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The laboratory diagnosis of tuberculosis
25 years of progress
D A Mitchison
St George’s, University of London
With assistance from FINDdiagnostics
Fluorescence v. Bright field microscopy
Introduced in 1940s.
5x more rapid than Bright field
BUT: Mercury vapour bulb:
Expensive. Limited life.
LED illumination introduced during past 5 years
Solid: LJ slopes. 7H11 slopes or plates.
Liquid: Early attempts high contamination.
1971 Selective medium paper
(Mitchison et al J Med Microbiol 1971; 5: 165)
Penta used in Bactec machine
Automated liquid systems v. solid media
Contamination. NTMs v. TB.
HAINMDTBDR plusPCR & Line probe based 1. Identifies as TB complex.
2.DSTs for RIF & INH (95%)
Can be used directly on sputum avoiding culture
Genetic tests for reserve drugs not adequate yet. Therefore cultures in liquid or on solid medium necessary as well as genetic techniques.
1Rusch-Gerdes S et al. JCM 2006;44:688-92.
2Rodrigues C et al. IJTLD; 2008;12:1449-55.
3Kruuner A et al. JCM 2006;44:811-8.
Classic on LJ slopes or 7H11 plates. Takes 7 weeks +.
MGIT or other automated liquid tests.
Sensitive, time consuming, ?dangerous
Quicker. Less dangerous
7H11 thin layer plates made selective
Each plate with up to 6 strains in quadrants
Control: no drug
PNB (p-nitrobenzoate): TB inhibited.
INH 0.2 µg/ml
RIF 2.0 µg/ml
SM 2.0 µg/ml
PZA 2,000 µg/ml nicotinamide
Defined from distribution of MICs on ‘wild’ strains
define the ‘therapeutic’ margin