Multicenter Evaluation of the BACTEC MGIT 960 System for Recovery of Mycobacteria

Abstract

We evaluated the BACTEC MGIT 960 system, which is a fully automated, noninvasive system for the growth and detection of mycobacteria with a capacity to incubate and continuously monitor 960 7-ml culture tubes. We studied 3,330 specimens, 2,210 respiratory and 1,120 nonrespiratory specimens, collected from 2,346 patients treated at six sites. Processed specimens were inoculated into the BACTEC MGIT 960 and BACTEC 460 TB systems, as well as onto Lowenstein-Jensen slants and Middlebrook 7H11/7H11 selective plates. From all culture systems, a total of 362 isolates of mycobacteria were recovered; these were recovered from 353 specimens collected from 247 patients. The greatest number of isolates of mycobacteria (289, or 80% of the 362 isolates) was recovered with the BACTEC MGIT 960, followed by the BACTEC 460 TB (271, or 75%) and solid media (250, or 69%). From all culture systems a total of 132 isolates of Mycobacterium tuberculosiscomplex were recovered. The greatest number of isolates of M. tuberculosis complex was recovered when liquid medium was combined with conventional solid media; the number recovered with BACTEC 460 TB plus solid media was 128 (97%), that recovered with BACTEC MGIT 960 plus solid media was 121 (92%), that recovered with BACTEC 460 TB was 119 (90%) and that recovered with all solid media combined was 105 (79%). The recovery with BACTEC MGIT 960 alone was 102 (77%). The mean times to detection (TTD) for M. tuberculosis complex were 14.4 days for BACTEC MGIT, 15.2 days for BACTEC 460 TB, and 24.1 days for solid media. The numbers of isolates of Mycobacterium avium complex (MAC) recovered were 172 (100%) for all systems, 147 (85%) for BACTEC MGIT 960, 123 (72%) for BACTEC 460 TB, and 106 (62%) for all solid media combined. The TTD for MAC in each system were 10.0 days for BACTEC MGIT 960, 10.4 days for BACTEC 460 TB, and 25.9 days for solid media. Breakthrough contamination rates (percentages of isolates) for each of the systems were 8.1% for BACTEC MGIT 960, 4.9% for BACTEC 460 TB, and 21.1% for all solid media combined.

Isolation Prevalence Of Pulmonary Nontuberculous Mycobacteria, Ontario 2008

“…First, the increase in prevalence began before and continued well after the culture system was changed in June 2000. Second, the greater sensitivity of the new system is expected to increase the total number of positive cultures by less than 7%, 12 while the number of prevalent cases we observed increased by more than 30% between the year before and the year after introducing the new system. In addition, since the same microbiological systems are used to detect M tuberculosis complex and NTM organisms, the concurrent decrease in rates of tuberculosis in Ontario 15 may argue against an apparent increase in NTM isolation simply due to more sensitive microbiological techniques.…”

Impact of aMycobacterium tuberculosis-specific interferon-γ release assay in bronchoalveolar lavage fluid for a rapid diagnosis of tuberculosis

“…Detection of M. tuberculosis in liquid cultures or on solid media remains the gold standard for the diagnosis of tuberculosis. In routine clinical practice, initial treatment decisions cannot rely on this method as culture growth of M. tuberculosis takes several weeks before detection is possible [4]. In addition, approximately 20% of patients with tuberculosis are not identified by culture growth of M. tuberculosis [5].…”

Multiplex PCR assay for simultaneous detection and differentiation ofMycobacterium tuberculosis,Mycobacterium aviumcomplexes and other Mycobacterial species directly from clinical specimens

“…This method has the poorest detection rate in HIV positive patients . Some tertiary care hospital laboratories in these countries carry out speciation but only after culturing the organisms by the conventional Lowenstein-Jensen (L-J) culture, which is a cumbersome and time-consuming procedure (Hanna et al 1999). The whole exercise of isolation and speciation sometime takes too long time and by that time most often the patient has almost completed his treatment.…”

“…The whole exercise of isolation and speciation sometime takes too long time and by that time most often the patient has almost completed his treatment. With the employment of automated culture detection system, the time taken for detecting the bacilli has reduced and the sensitivity has also increased (Hanna et al 1999), but not to the desired level, especially for extrapulmonary samples like cerebrospinal fluid (CSF), pleural fluid and urine.…”