Mycobacteria testing

Specimen:

Sputum (3-5 separate samples);

bronchoscopy brushing, lavage;

tissue biopsy (eg, lymph node, lung, endometrial curettings, bone);

body fluids (eg, CSF, pleural, synovial, pericardial fluids);

pus (swabs do not provide an adequate sample);

urine (3 complete early morning collections);

blood culture collected into specialized culture medium;

bone marrow aspirate;

faeces;

tissue fluid from eg, eyebrows, ear lobes.

Method:

Acid fast staining (eg, Ziehl-Neelsen) or auramine staining for microscopy;

gene probe following PCR amplification for some specimens (eg, CSF);

culture in/on appropriate media (eg, Lowenstein-Jensen or Middlebrook).

Rapid growers (eg, M. fortuitum) may grow in 1-2 weeks, but 6-8 weeks of incubation are required before discarding negative cultures.

Identification of mycobacteria and antibiotic susceptibility testing take another 4 weeks using conventional techniques.

The use of culture systems using liquid media combined with gene probe (for identification) considerably reduces the time required for testing.

Application:

Suspected tuberculosis or atypical mycobacterial infection, including unexplained lung infection;

'sterile' pyuria;

meningitis;

diarrhoea or fever in patients who have AIDS;

chronic skin ulcers/lesions;

subacute/chronic unexplained lymph adenopathy;

infertility (endometrial curettings);

suspected leprosy (microscopy of tissue fluid from eyebrows, ear lobes, skin, or biopsy).

Biopsy of tissue has higher sensitivity than fluid samples.

Interpretation:

The presence of acid fast bacilli in sputum or in normally sterile fluids or tissues is generally sufficient to establish the diagnosis of tuberculosis in the context of a typical clinical presentation.

However, the sensitivity of microscopy in body fluids and CSF is low (<20%).

NAA allows more rapid detection and differentiation of Mycobacterium tuberculosis from other mycobacteria; culture confirms the diagnosis and allows identification of non-tuberculous mycobacteria and antibiotic susceptibility testing.

M. leprae cannot be grown in vitro and the diagnosis of leprosy is based on the presence of acid fast bacilli in a clinically suspicious lesion or NAA detection.

Reference:

Pfyffer GE et al. In: Murray PR et al eds. Manual of Clinical Microbiology. 8th Ed.2003. ASM Press.

Hale YM  et al. Clin Infect Dis. 2001; 33: 834-846.