MYCOBACTERIAL GROWTH AND BACTERIAL-CONTAMINATION IN THE MYCOBACTERIA GROWTH INDICATOR TUBE AND BACTEC-460 CULTURE SYSTEMS

The BACTEC 460 system currently provides the most rapid detection of m ycobacterial growth, but the system is radiometric and requires needle s to inoculate specimens through the bottle's septum. The Mycobacteria Growth Indicator Tube (MGIT) system has a liquid medium, like the BAC TEC system, and does noe require needles when inoculating specimens. W e compared mycobacterium growth from 510 specimens in the two systems, Average time to acid-fast bacillus (AFB) detection and identification to the species level was less with the BACTEC system, but this result was statistically significant only for AFB detection in specimens con taining Mycobacterium avium-M. intracellulare complex, The contaminati on rate with MGIT was 29%; the BACTEC rate was 5%. To investigate MGIT contamination, we initiated a second study with changes in specimen p rocessing, The MGIT contamination rate was reduced to 12%; the BACTEC rate was mot significantly affected (5.5%), The most likely explanatio n for the contamination in MGIT is the richness of its medium compared to the BACTEC medium, Cost analysis for the two systems in a laborato ry that processes 4,500 specimens a year is presented, The data sugges t that the BACTEC 460 and the MGIT systems are approximately equivalen t in cost and ability to support the growth of AFB. The MGIT system ap pears safer and easier to use and was preferred by laboratory personne l, but it cannot currently be used for blood specimens or antitubercul osis susceptibility testing.