Two liquid medium systems, Mycobacteria Growth Indicator Tube and MB Redoxtube, for Mycobacterium tuberculosis isolation from sputum specimens

Two manual liquid medium systems, the Mycobacteria Growth Indicator Tube (M GIT) and MB Redox tube systems, were evaluated in comparison to the radiome tric BACTEC-460 semiautomated system for recovery of Mycobacterium tubercul osis from sputum specimens. The highest level of recovery, from a total of 77 culture-positive specimens, occurred with the BACTEC-460 system (92.2%), followed by the MB Redox tube (80.5%) and the MGIT (63.6%) systems. The sh ortest time to detection was observed also among the cultures in BACTEC-460 : a mean of 12 days to a growth index (GI) of 10 and 15 days to a GI of 500 . The mean times for the other systems were 16 days for the MB Redox tube s ystem and 17.4 days for the MGIT system. The proportion of cultures grown a fter more than 3 weeks of incubation was only 2.8 or 8.4% in BACTEC-460 (fo r a GI of 10 or 500) but 17.7% in MB Redox and 22.5% in MGIT. Despite these differences in comparison to the BACTEC-460 system and some differences be tween the MGIT and MB Redox tube systems, either of the two manual liquid m edium systems presents a reasonable alternative to the BACTEC-460 system, e specially for laboratories with a limited workload, and a valuable element in the laboratory protocol, in conjunction with solid media, for obtaining rapid detection of growth from about 80% of culture-positive specimens and for better overall recovery of M. tuberculosis.