Performance of the microscopic observation drug susceptibility assay in pyrazinamide susceptibility testing for Mycobacterium tuberculosis.
BACKGROUND
Drug susceptibility assay is very important in tuberculosis therapy. Pyrazinamide is a first line antituberculosis drug and diagnosis of its resistance in Mycobacterium tuberculosis (M. tuberculosis) is difficult and time consuming by conventional methods. In this study, we aimed to evaluate the performance of the microscopic observation drug susceptibility (MODS) assay in the detection of pyrazinamide resistance in M. tuberculosis relative to the conventional Wayne assay and Lowenstein-Jensen (LJ) proportion method.


METHODS
M. tuberculosis clinical isolates (n = 132) were tested by the MODS and the Wayne assay: the results were compared with those obtained by the LJ proportion method. Mutations in the gene were identified by direct sequencing of the pncA genes of all isolates in which pyrazinamide resistance was detected by any of the three methods.


RESULTS
Compared to the LJ results, the sensitivity and specificity of the MODS assay were 97.8% and 96.5% respectively; the sensitivity and specificity of the Wayne assay were 87.0% and 97.7% respectively. Mutations in the pncA gene were found in 41 of 46 strains that were pyrazinamide resistant (3 tests), in 1 of the 4 strains (LJ only), in 42 of 48 strains (at least 1 test), but no mutations in 1 strain sensitive according to the MODS assay only. The MODS assay, Wayne assay and LJ proportion method provided results in a median time of 6, 7 and 26 days respectively.


CONCLUSIONS
MODS assay offers a rapid, simple and reliable method for the detection of pyrazinamide resistance in M. tuberculosis and is an optimal alternative method in resource limited countries.
Department of Clinical Laboratory, First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, China.
Zi-Kun
ZK
Huang
Qing
Q
Luo
Bi-Xia
BX
Jiang
Wei-Ting
WT
Li
Xiao-Meng
XM
Xu
Guo-Liang
GL
Xiong
Jun-Ming
JM
Li
D000995:Antitubercular Agents / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D008853:Microscopy / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D011718:Pyrazinamide / Q000494:pharmacology*
D000995:Antitubercular Agents; D011718:Pyrazinamide