M.tuberculosis and related species may be identified by traditional criteria, such as niacin production, nitrate reduction, cord formation, lack of growth at room temperature, drug susceptibility. Commercial DNA probes are now an acceptable alternative. These provide rapid results but will not provide speciation within the M.tuberculosis complex. All isolates likely to be pathogens should be identified, ie. Adequate clinical data is essential for determining the pathogenic role of such isolates.
Authoritative texts provide adequate reference sources for procedures and identification strategies.
Susceptibility Testing Susceptibility testing should be performed only in Level 3 facilities. Mycobacterium tuberculosis complex All initial isolates, as well as repeat isolates from relapse cases or 'treatment failures' should be tested for susceptibility to at least isoniazid, ethambutol, rifampicin and pyrazinamide. Additional drugs will be tested when resistance to first line agents is found. The value of susceptibility tests on slow-growing atypical mycobacteria remains controversial. Rapidly growing species such as M.fortuitum should be tested by disc diffusion or disc elution against a range of drugs which includes tetracyclines, amino-glycosides and sulphonamides.