Bacteriological diagnosis of tuberculosis

Microscopic examination and culture are still today essential elements of the bacteriological diagnosis of tuberculosis. Microscopic examination of a Ziehl fuchsin or auramine stained specimen allows detection of most strains in less than an hour. Culture on L?wenstein-Jensen medium is more sensitive than the microscopic examination and is required for identification and to measure sensitivity to antibiotics. Mycobacterium colonies, generally the causal agent in tuberculosis, usually grow within 28 days and are easily recognized by their "cauliflower" aspect. The niacin test is used for formal identification. Currently, radiometric respirometry allows detection of M. tuberculosis growth and provides antibiotic sensitivity results more rapidly, usually within 10 days. Use of this technique is however limited because the culture medium contains radioactive carbon. Genetic probes are on the other hand quite easy to use and allow identification of cultured bacteria in only a few hours. After polymerization chain reaction gene amplification, M. tuberculosis strains can be detected directly in the specimen within 2 or 3 hours, but in practice, this method has not become a routine laboratory technique, particularly due to lack of sufficient specificity and sensitivity. No other serologic tests are currently reliable enough for the diagnosis of tuberculosis. For cases with low-count specimens, there still is no reliable "on-the-spot" diagnostic test.