DETECTION AND IDENTIFICATION OF MYCOBACTERIUM DIRECTLY FROM BACTEC BOTTLES BY USING A DNA-RIBOSOMAL-RNA PROBE

Detection and identification of mycobacterial species using DNA-rRNA probes from colonies has been used for same time. Guidelines for probe use with a specific minimum growth index (GI) cutoff from BACTEC 12B bottles or its use with 7H9 broth has not been defined. This study defined this minimum GI guideline. Clinical specimens received during the study period were decontaminated and directly inoculated into BACTEC 12B bottles and appropriate solid media. An initial probe test was performed at a GI reading of greater than or equal to 100. An additional probe test was made at GI of greater than or equal to 300. A total of 1377 specimens were processed with 98 specimens containing 99 isolates of Mycobacterium. Of these, 82 were M. avium complex (MAC), six were M. tuberculosis (Mtb), and 11 were other species. At a GI of greater than or equal to 100, 82% of MAC were detected; at a GI of greater than or equal to 300, 89% were detected. All Mtb were detected at a GI of greater than or equal to 100. The probes correctly identified all isolates from backup 7H9 broths. There were no false-positive probe results for any of the isolates from either BACTEC 12B or 7H9 media. Therefore, the DNA-rRNA probe test at a GI of greater than or equal to 300 saves considerable time (on average, 21 days saved) for the detection and identification of Mtb and MAC, This time saving compares with waiting for the production of colonies while retaining acceptable sensitivity and excellent specificity.