Mycobacterial Culture

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.

Non-tuberculous mycobacteria (NTMs) are increasingly encountered as a cause of disease in humans.

Samples for Mycobacterium culture will go through a decontamination step (unless from a sterile site) before being incubated for 56 days. Microscopy for acid fast bacilli will also be carried out.

Upon request and depending on the sample quality and quantity, the laboratory can perform rapid PCR testing for M. tuberculosis using the Cephid® GeneXpert®.

Sample type and requirements

Sputum

Ideally three purulent samples should be sent 8-24 hours apart with at least one from early morning as this will have the greatest yield.

Broncho-Alveolar Lavage (BAL)

Urine

Three early morning urines should be taken on consecutive days: do not use Boric Acid containers.

Gastric washings

Taken from children when there are problems obtaining sputum. Three early morning samples should be collected on consecutive days and processed promptly to reduce the effect of the stomach acid on the organisms.

Note: positive microscopy results should be treated with caution as other acid-fast bacilli can be present in the stomach.

Sterile body fluids (e.g. CSF and pleural fluid)

Collect as much fluid as possible as organisms tend to be present in very low numbers.

Note: pleural and pericardial fluids are not very sensitive samples for the detection of M. tuberculosis; tissue biopsies from these sites are more useful.

Skin, tissue and bone

Pus and pus swabs

Pus is the sample of choice, however, if a swab is the only sample available it can be processed.

Blood and bone marrow

Send in a PST / lithium heparin tube.

Faeces

It is not recommended to process these samples for Mycobacterium species due to heavy contamination of the sample with other bacteria.

Minimum volume

1ml

Frequency of test

Daily

Turnaround time

8 weeks (for negative cultures)

What to request on EPR

Mycobacterial culture MCS