Laboratory culture of M tuberculosis
When M. tuberculosis is cultured from clinical specimens (e.g. sputum, lymph node aspirate, cerebrospinal fluid) this provides the gold standard for the definitive diagnosis of TB. Tubercle bacilli that have grown in culture can also be tested in vitro for sensitivity to anti-TB drugs. The usual culture medium is Lowenstein Jensen, although liquid culture media and automated systems (e.g. Bactec) can also be used in more sophisticated laboratories.
M. tuberculosis is a slow-growing organism, and it often takes between 6 and 8 weeks before cultures become positive. Culture results may therefore not be helpful in making a rapid individual diagnosis, although they can be helpful retrospectively. There is also the need for considerable laboratory infrastructure and laboratory skills in order to sustain a mycobacterial culture facility. Most developing countries have one or two mycobacterial reference centres where cultures and drug sensitivity analysis can be performed. However, most hospitals will not have TB culture facilities readily available.
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