Comparison of the automated nonradiometric Bactec MGIT 960 system with Lowenstein-Jensen, Coletsos, and Middlebrook 7H11 solid media for recovery of mycobacteria

The aim of this study was to evaluate the sensitivity of as well as the rime to detection of mycobacteria by three procedures: solid media with traditional reading, microscopy on solid media, and liquid culture using the automated nonradiometric Bactec MGIT 960 system. A total of 2832 respiratory specimens were tested, 315 of which were positive for mycobacteria. The most frequently isolated species was Mycobacterium tuberculosis (201 isolates). One hundred twenty mycobacteria other than tuberculosis were isolated, 72 of which were Mycobacterium xenopi strains. Sensitivity of each of the different media compared to all media combined for growth of Mycobacterium tuberculosis was 93%, 76.1%, 79.6%, and 75.1% for Bactec MGIT 960, Middlebrook 7H11 plates, Lowenstein-Jensen, and Coletsos, respectively. Sensitivity of the Bactec MGIT 960 for detection of all mycobacterial isolates was 75.1%. When this automated system was supplemented with visual inspection, the sensitivity increased to 89.4%. The sensitivity of Middlebrook 7H11 plates, Lowenstein-Jensen, and Coletsos was 50.8%, 60.7%, and 52.3%, respectively. Time to detection of Mycobacterium tuberculosis using the Bactec MGIT 960 system and Middlebrook 7H11 plates with microscopic reading was 12.7 and 13 days, respectively; using the traditional Lowenstein-Jensen and Coletsos media, time to detection was 22.8 and 22.7 days, respectively.