Rapid purity check method for susceptibility testing of M. tuberculosis complex with the MGIT 960 system.
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.
Huang
Tsi-Shu
TS
Section of Infectious Diseases, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan, ROC.
Liu
Yung-Ching
YC
Tu
Hui-Zin
HZ
Sy
Cheng-Len
CL
Chen
Yao-Shen
YS
Chen
Bao-Chen
BC
D000995:Antitubercular Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques; D002478:Cells, Cultured; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D011933:Reagent Kits, Diagnostic; D013997:Time Factors; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis / Q000382:microbiology*
D000995:Antitubercular Agents; D011933:Reagent Kits, Diagnostic