Diagnostic Mycobacteriology Laboratory Practices

The resurgence of tuberculosis has forced clinical laboratories to improve the methods used for detection of M. tuberculosis. Current recommendations for diagnostic laboratory performance [7] include (1) daily processing of specimens (i.e., handling these specimens in the same way that all other specimens sent to the laboratory are handled); (2) inoculation of liquid media (e.g., BACTEC) for the primary culture; (3) use of nucleic acid probes or the NAP test for identifying isolates as M. tuberculosis as soon as possible; (4) determining drug susceptibility with use of liquid media; and (5) reporting results of each step to physicians in a timely manner. The immediate goals are to report identification of M. tuberculosis within 10-14 days of receipt of the specimen and to report drug susceptibilities within 15-30 days. This can be done if current technologies are fully utilized. The amplification-based systems for the identification of M. tuberculosis and the luciferase-based systems for rapid determination of drug susceptibilities should help further shorten turn-around times. The results to date demonstrate that these systems are feasible, although they must be reduced to formats that can be used routinely in clinical laboratories. The gene-amplification systems may be the most promising, and they are nearing commercial availability. If the assays function as well during routine use as they have during clinical trials, a clinical laboratory may soon be able to report confirmed M. tuberculosis infection to the physician within hours of receiving a specimen, instead of within the typical period of 2-4 weeks.