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Oxford University Hospitals NHS Foundation Trust
Microbiology

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Laboratory investigation of Mycobacteria tuberculosis and other Mycobacteria species

Tuberculosis (TB) in humans is caused predominantly by Mycobacterium tuberculosis and less often by other members of the M. tuberculosis complex (MTBC) including M. bovis, M. africanum and M. canetti.

Mycobacteria other than tubercle (MOTT) bacilli are increasingly encountered as a cause of disease in humans.

Specimen requirements

Sputum specimens should be relatively fresh (less than one day old) to minimise contamination. Purulent specimens are the specimen of choice. Approximately 5 ml per sample early in the morning on three consecutive days should be collected.

Sterile Body fluids (e.g. CSF, Pleural fluid) can also be used. For CSF samples collect aseptically as much as possible into a sterile container. A minimum of 1 ml of other fluids is required. If a small volume is available after initial lumbar puncture and the findings of cell counts and protein suggest TB meningitis, a second procedure should be considered to obtain a larger volume to improve chances of achieving positive cultures.

Urine specimens should be collected in the early morning on three consecutive days in a universal container.

Skin, tissue or post mortem specimens of any type should be homogenised. Once received in the laboratory it may be necessary to select and cut out a suitable piece of tissue if a large piece is received. Specimens should be collected aseptically to a sterile container without preservatives, and add sterile distilled water to prevent desiccation.

Samples should be transported to the laboratory as soon as possible. If specimen transport will be delayed, e.g. from primary care, specimens should be stored in a refrigerator until transported to the laboratory.

Laboratory turnaround time

Ziehl-Neilson (ZN) stained microscopy for acid-alcohol fast bacilli (AAFB) are available within 24 hours of receipt of the specimen. The laboratory turnaround time for culture of these samples can be up to 63 days.

Laboratory method

Specimens submitted for mycobacterial culture fall into two categories:

  • specimens normally contaminated with resident flora
  • specimens from normally sterile sites.

Contaminated specimens require a decontamination step before culture to reduce the likelihood of overgrowth by organisms other than mycobacteria.

The system used for the detection and recovery of Mycobacteria is the BD BACTEC™ MIGT™ System; samples that flag as positive are processed in the laboratory to confirm the presence of AAFBs using a ZN stain.

Depending on the nature of the sample, Mycobacteria are either confirmed in-house or sent to the reference unit for speciation and susceptibility testing.

Where to find results of these tests

  • All results are returned electronically where possible (EPR, SunquestICE).
  • Some results may be phoned to clinicians and GPs.
  • Results are never given directly to patients by the laboratory staff.

Further information and contact details

For further information please email:

Confidential patient information should only be sent from nhs.net accounts.