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BioMed Research International
Volume 2015 (2015), Article ID 651980, 7 pages
Research Article

Discrepancies in Drug Susceptibility Test for Tuberculosis Patients Resulted from the Mixed Infection and the Testing System

1Department of Tuberculosis, Tianjin Haihe Hospital, Tianjin 300350, China
2Tianjin Respiratory Disease Research Institute, Tianjin 300350, China
3National Tuberculosis Clinical Laboratory, Beijing Chest Hospital, Capital Medical University, Beijing 101149, China
4Beijing Key Laboratory in Drug Resistant Tuberculosis Research, Beijing Tuberculosis & Thoratic Tumor Research Institute, Beijing 101149, China

Received 5 June 2014; Revised 29 October 2014; Accepted 3 November 2014

Academic Editor: Madhab K. Chattopadhyay

Copyright © 2015 Zaoxian Mei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


To find the potential reasons for the discrepancies in the drug susceptibility test (DST) of M. tuberculosis isolates, twenty paired isolates with disputed drug susceptibilities to isoniazid (INH) were selected according to the MGIT960 testing and Löwenstein-Jensen (L-J) proportion methods. Their MICs were confirmed again by broth microdilution method and by L-J proportion method. The spoligotyping results showed that, of all the 20 paired strains, 11 paired isolates belonged to the Beijing genotype and 6 paired isolates belonged to SIT1634, and that each of the remaining 3 paired isolates had two genotypes, namely, SIT1 and SIT1634. Those 3 paired isolates with different intrapair spoligotypes were further confirmed as mixed infection by the results that those three pairs of isolates with different 12 locus MIRU intrapair types and one pair carried different base pair at codon 315 (AGC versus AAC). Totally mutations in the katG gene were identified in 13 paired isolates. No mutations were found in the regulatory sequences and open reading frames (ORF) of the inhA and ahpC genes in any of the tested isolates. Those results showed that the different test systems and the mixed infection with particular genotypes of M. tuberculosis strains contributed to the drug susceptibility discrepancies.