Evaluation of the BACTEC MGIT 960 system for the recovery of mycobacteria

Choi, Youn Mi; Lee, Myung Hee

Abstract

BACKGROUND: We evaluated the BACTEC MGIT 960 system(Becton Dickinson Microbiology Systems, Sparks, Md, USA), which is a fully automated, noninvasive and nonradiometric fluorescent indicator broth detection system for the growth and detection of mycobacteria with a capacity to incubate and continuously monitor 7 ml MGIT(Mycobacterium growth indicator tube) culture tube.
METHODS
We studied 1,690 specimens(1,258 respiratory and 432 non-respiratory specimens). Processed specimens with 2% NaOH-NALC(final NaOH concentration: 1%) were inoculated into MGIT and solid media(3% Ogawa, Japan). Polymerase chain reaction was performed for the discrimination of Mycobacterium tuberculosis complex from Mycobacterium other than tuberculosis(MOTT).
RESULTS
From all culture system, a total of 181 isolates of mycobacteria were recovered. The greatest number of isolates of mycobacteria was recovered with MGIT 960 system(174, 96.1%), followed by solid media(73, 40.3%). 108 isolates(59.7%) were recovered with MGIT only and 7(3.9%) recovered with solid media only( P value < 0.0001). From a total of 1,617 AFB smear negative specimens, 101(6.3%) were recovered with MGIT 960 system and 34(2.1%) recovered with solid media. The mean times to detection were average 11.1 days for MGIT 960 system and 31.6 days for solid media(P value < 0.0001). Contamination rates for each system were 14.9% for MGIT 960 and 2.6% for solid media.
CONCLUSIONS
The newly introduced MGIT 960 system is easy to use and has advantages of high detection rate and rapid recovery than solid media, but there are some problems such as high contamination rate and high cost in the management of this liquid system.