POLYMERASE CHAIN-REACTION FOR DETECTION OF MYCOBACTERIUM-TUBERCULOSISIN SPUTUM

The polymerase chain reaction (PCR) was evaluated in a trial which, wi th respect to the positive-to-negative ratio, approximated the situati on of a diagnostic laboratory in a tuberculosis-endemic area. Three hu ndred sputum samples were included in the study, of which one-third we re known to contain mycobacteria as judged by direct microscopy. The r epetitive insertion sequence IS6110/IS986 of Mycobacterium tuberculosi s was used as a target. The samples were spiked with DNA from a modifi ed IS6110/IS986 sequence, which gives rise to PCR products easily dist inguished from PCR products amplified from chromosomal Mycobacterium t uberculosis DNA. This allowed identification of samples that contained substances inhibitory to the Tag polymerase. The detection limit of t he assay was 0.05 pg to 0.5 pg of purified Mycobacterium tuberculosis DNA, corresponding to 10 to 100 organisms. The sensitivity and specifi city of the PCR was compared with that of conventional microscopy and culture. It was concluded that this method is fast and sensitive, but that culture currently is crucial for assessing viability and thus inf ectivity.