title: Macrocolonies (Granules) Formation as a Cause of False-Negative Results in the MGIT 960 System: Cause Analysis and Correlation with Mycobacterial Species.
abstract: BACKGROUND
  The viable mycobacterial bacilli can sometimes form granules in the Mycobacterium Growth Indicator Tube (MGIT) to produce instrument-negative outcomes when BACTEC MGIT 960 culture is performed. The cause of this phenomenon has never been analyzed.
  
  
  METHODS
  Thirty-one instrument-negative, granule presenting MGIT vials were collected for conducting acid-fast staining and also liquid and solid subculture. Species identification and drug susceptibility test were performed with the recovered strains. Cultivation test was done by inoculating small amount of bacilli into the MGIT vials.
  
  
  RESULTS
  Twenty-four and twenty-nine of the tested MGIT vials were smear and culture positive, respectively. In total, 18, 4, and 7 of the cultivated strains were identified as Mycobacterium tuberculosis complex, M. intracellulare, and M. xenopi, respectively. When a limited amount of bacilli was inoculated, the granule formation was observed for M. xenopi strains in the MGIT system.
  
  
  CONCLUSIONS
  The granules observed in the instrument-negative MGIT vials consisted of viable bacilli, which emphasized the need of visual inspection to increase recovery rate. Limited bacterial load and specific species might be the cause of granule forming.
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Yu
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Liping
authors.initials: L
authors.lastname: Zhao
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Guanglu
authors.initials: G
authors.lastname: Jiang
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Yifeng
authors.initials: Y
authors.lastname: Ma
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Weimin
authors.initials: W
authors.lastname: Li
authors.affiliation: National Clinical Laboratory on Tuberculosis, Beijing Key laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University, Beijing Tuberculosis and Thoracic Tumor Institute, Beijing 101149, China.
authors.forename: Hairong
authors.initials: H
authors.lastname: Huang
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D003470:Culture Media / Q000378:metabolism; D005188:False Negative Reactions; D009169:Mycobacterium tuberculosis / Q000254:growth & development*; D011933:Reagent Kits, Diagnostic
chemical_list: D003470:Culture Media; D011933:Reagent Kits, Diagnostic