Rapid purity check method for susceptibility testing of M. tuberculosis complex with the MGIT 960 system

Tsi Shu Huang, Yung Ching Liu, Hui Zin Tu, Cheng Len Sy, Yao Shen Chen, Bao Chen Chen

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


The Bactec MGIT 960 system is a rapid and reliable automated method for drug susceptibility testing of Mycobacterium tuberculosis complex (MTBC) that yields a high percentage of agreement with the standard method. The microscopic cord morphology of M. tuberculosis in liquid medium is characteristic, and readily differentiates MTBC from nontuberculous mycobacteria (NTM). The goals of this study were to describe the microscopic and macroscopic growth morphology of MTBC in antimicrobial-containing MGIT tubes and to evaluate the usefulness of the growth appearance during purity checking. The macroscopic cotton wool-like appearance of MTBC isolates in isoniazid (INH), streptomycin (SM), rifampin (RMP), and ethambutol (EMB)-containing tubes was observed in 97, 90, 93, and 71% of the isolates, respectively. The percentage of typical cord, loose, or frayed rope microscopic features in smears prepared from MTBC-positive cultures of INH, SM, RMP, and EMB-containing tubes was 96, 86, 97, and 71%, respectively. The sensitivity of the macroscopic morphology for predicting the purity of drug-containing MGIT tubes was 93%, while the microscopic morphology predicted the purity with a sensitivity rate of 92%. We found that simply examining the macroscopic morphology of the antimicrobial-containing MGIT tubes of drug-resistant MTBC isolates is useful in preventing false resistant results of susceptibility testing by the MGIT 960 system.

Original languageEnglish
Pages (from-to)323-329
Number of pages7
JournalAnnals of Clinical and Laboratory Science
Issue number4
Publication statusPublished - Sept 2007
Externally publishedYes


  • Antimicrobial susceptibility testing
  • M. Tuberculosis complex
  • MGIT

ASJC Scopus subject areas

  • General Medicine


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