Selective utilization of DNA probes for identification of Mycobacterium species on the basis of cord formation in primary BACTEC 12B cultures.

Primary BACTEC 12B cultures with serpentine cords observed in Kinyoun-stained smears were tested with a probe for Mycobacterium tuberculosis complex, while cultures without cords were tested with a probe for M. avium complex. The sensitivity, specificity, and positive and negative predictive values of cording for the presumptive identification of M. tuberculosis were 95, 95, 90, and 98%, respectively. With experience, the selection of a probe for testing of primary BACTEC 12B cultures on the basis of cord formation and history of tuberculosis can provide a rapid and reliable approach to the laboratory diagnosis of tuberculosis.