Use of BACTEC MGIT 960 for recovery of mycobacteria from clinical specimens: Multicenter study

The BACTEC MGIT 960 instrument is a fully automated system that exploits th e fluorescence of an oxygen sensor to detect growth of mycobacteria in cult ure. Its performance was compared to those of the radiometric BACTEC 460 in strument and egg-based Lowenstein-Jensen medium. An identical volume of sam ple was inoculated in different media, and incubation was carried out for 6 weeks with the automatic systems and for 8 weeks on solid media. A total o f 2,567 specimens obtained from 1,631 patients were cultured in parallel. M ycobacteria belonging to nine different taxa were isolated by at least one of the culture systems, with 75% of them being represented by Mycobacterium tuberculosis complex. The best yield was obtained with the BACTEC 460 syst em, with 201 isolates, in comparison with 190 isolates with the BACTEC MGIT 960 system and 168 isolates with Lowenstein-Jensen medium. A similar but n ot significant difference was obtained when the most-represented organisms, the M. tuberculosis complex, Mycobacterium xenopi, and the Mycobacterium a vium complex, were analyzed separately and when combinations of a solid med ium with the BACTEC MGIT 960 system and with the BACTEC 460 system were con sidered. The shortest times to detection were obtained with the BACTEC MGIT 960 system (13.3 days); 1.5 days earlier than that with the BACTEC 460 sys tem (14.8 days) and 12 days earlier than that with Lowenstein-Jensen medium (25.6 days). The BACTEC MGIT 960 system had a contamination rate of 10.0%, intermediate between those of the radiometric system (3.7%) and the egg-ba sed medium (17.0%), We conclude, therefore, that the BACTEC MGIT 960 system is a fully automated, nonradiometric instrument that is suitable for the d etection of growth of tuberculous and other mycobacterial species and that is characterized by detection times that are even shorter than that of the "gold standard," the BACTEC 460 system. The contamination rate was higher t han that for the radiometric BACTEC 460 system and needs to be improved.