Reliability of cord formation in BACTEC media for presumptive identification of mycobacteria

We evaluated cord formation in BACTEC media as a criterion for presumptive identification of Mycobacterium tuberculosis complex. Auramine-rhodamine smears from 673 radiometrically positive BACTEC vials were examined. The presence of cording had a sensitivity, a specificity, and positive and negative predictive values of 22.9, 98.5, 82.9, and 80.3%, respectively. Before cord formation is used to report presumptive identification of M. tuberculosis complex, workers should determine the reliability of this finding in their own laboratories.