Comparison of the MGIT (Mycobacteria Growth Indicator Tube) with Ogawa media for recovery of Mycobacteria

Kim, Yeong Sic; Jo, Yong Hyun; Lee, Hee Joo; Suh, Jin Tae; Lee, Young Ja

Abstract

BACKGROUND: It takes long time to cultivate Mycobacterium tuberculosis on solid media from clinical specimens. Although there is progress in the detection of tuberculosis using liquid media, Ogawa media is broadly used in Korea. In the 1990s, the BACTEC 460 system (Becton Dickinson, Sparks, MD, USA) was used in some laboratories in Korea, but at present, it is not used because of the accumulation of radioactive waste and the risk of cross-contamination. The BACTEC MGIT 960 system (Becton Dickinson, Sparks, MD, USA) is one of the new systems using liquid media. MGIT system uses oxygen-quenching fluorescence sensor technology instead of radioactive material. We evaluated MGIT for the sensitivity and specificity for the diagnosis of Mycobacterium tuberculosis by comparison with Ogawa media.
METHODS
A total of 232 sputum specimens were collected from patients admitted to the hospital. All specimens were processed by 4% NaOH and 0.5% NALC. After inoculation of MGIT with 0.5 mL and Ogawa with 0.3 mL of the processed specimen, the media were observed every 3 days until 6 weeks and 8 weeks, respectively.
RESULTS
A total of 99 isolates of mycobacteria were recovered from 232 specimens. Ninety nine isolates were detected with MGIT, as contrasted with 64 detected with Ogawa media. The mean times to detection of the Mycobacterium species were 12.6 days for MGIT, 23.7 days for Ogawa media. Contamination rates were 5.1% for MGIT, 5.6% for Ogawa media.
CONCLUSION
From our study, we conclude that MGIT is a superior method for recovery rate and time to detection of Mycobacteria to Ogawa media.