Drug resistance in M. tuberculosis is caused by mutations in restricted regions of the genome (36). Mutations in katG, the upstream region of the fabG1-inhA operon (P fabG1-inhA ), and inhA are responsible for INH resistance (36). The katG gene encodes the bifunctional catalase-peroxidase enzyme that converts INH to an active form (35).Previously, we developed a DNA sequencing-based method to detect mutations in regions associated with INH resistance in M. tuberculosis, including katG and P fabG1-inhA (28). Consequently, five novel mutations in katG associated with INH resistance were found (28). In the present study, we cloned 21 katG mutants, including 15 novel mutants, and compared their INH oxidase activities. Certain katG mutations were shown to cause high-level INH resistance, which suggests the possibility of determining the degree of INH resistance, such as high-or low-level resistance, by detecting these katG mutations. Furthermore, to detect these mutations in ordinary-scale clinical laboratories without sequencing, we developed a new hybridization-based line probe assay (LiPA) for INH resistance in M. tuberculosis isolates, which can be applied easily in clinical use.
MATERIALS AND METHODSBacterial strains and plasmids. One hundred eight Inh r M. tuberculosis isolates were obtained from single patients at
We evaluated a new line probe assay (LiPA) kit to identify Mycobacterium species and to detect mutations related to drug resistance in Mycobacterium tuberculosis. A total of 554 clinical isolates of Mycobacterium tuberculosis (n ؍ 316), Mycobacterium avium (n ؍ 71), Mycobacterium intracellulare (n ؍ 51), Mycobacterium kansasii (n ؍ 54), and other Mycobacterium species (n ؍ 62) were tested with the LiPA kit in six hospitals. The LiPA kit was also used to directly test 163 sputum specimens. The results of LiPA identification of Mycobacterium species in clinical isolates were almost identical to those of conventional methods. Compared with standard drug susceptibility testing results for the clinical isolates, LiPA showed a sensitivity and specificity of 98.9% and 97.3%, respectively, for detecting rifampin (RIF)-resistant clinical isolates; 90.6% and 100%, respectively, for isoniazid (INH) resistance; 89.7% and 96.0%, respectively, for pyrazinamide (PZA) resistance; and 93.0% and 100%, respectively, for levofloxacin (LVX) resistance. The LiPA kit could detect target species directly in sputum specimens, with a sensitivity of 85.6%. Its sensitivity and specificity for detecting RIF-, PZA-, and LVX-resistant isolates in the sputum specimens were both 100%, and those for detecting INH-resistant isolates were 75.0% and 92.9%, respectively. The kit was able to identify mycobacterial bacilli at the species level, as well as drug-resistant phenotypes, with a high sensitivity and specificity.
Resistance of Mycobacterium tuberculosis to pyrazinamide (PZA) derives mainly from mutations in the pncA gene. We developed a reverse hybridization-based line probe assay with oligonucleotide probes designed to detect mutations in pncA. The detection of PZA resistance was evaluated in 258 clinical isolates of M. tuberculosis. The sensitivity and specificity of PZA resistance obtained by this new assay were both 100%, consistent with the results of conventional PZA susceptibility testing. This assay can be used with sputa from tuberculosis patients. It appears to be reliable and widely applicable and, given its simplicity and rapid performance, will be a valuable tool for diagnostic use.
Thirty-six multidrug-resistant (MDR) Mycobacterium tuberculosis isolates collected in Japan were examined for pyrazinamide susceptibility and pyrazinamidase activity, and analysed by pncA sequencing and a hybridization-based line probe assay (LiPA), which was used to detect pncA mutations for the rapid identification of pyrazinamide-resistant isolates. Pyrazinamide resistance was found in 19 (53%) of them. All pyrazinamide-resistant isolates had no pyrazinamidase activity and at least one mutation in pncA. Among the pncA mutations, 11 had not been previously reported. The results of the LiPA were fully consistent with the DNA sequencing results. A majority of MDR M. tuberculosis isolates in Japan were resistant to pyrazinamide.
The aim of this study was to establish the importance of detecting fluoroquinolone (FQ) resistance in multidrug resistant (MDR) Mycobacterium tuberculosis, and to show the usefulness of a hybridization-based line probe assay (LiPA) for detecting gyrA mutations. Thirty-three MDR M. tuberculosis isolates were collected from a total of sixty MDR isolates identified in Japan over 6 months during a national surveillance study in 2002. Seventeen MDR isolates were collected by the National Center for Global Health and Medicine in Japan over 6 years from 2003 to 2008. These 50 isolates were examined for FQ susceptibility, and analysed by LiPA and gyrA sequencing. Among them, 22 (44 %) showed FQ resistance. All FQ-resistant isolates had at least one mutation in gyrA. The results of the LiPA were fully consistent with the DNA sequencing results. Given that on the basis of our results almost half of the MDR M. tuberculosis isolates in Japan might have resistance to FQ, it is important to monitor FQ resistance in patients with MDR tuberculosis (TB), as well as with drug-susceptible TB, prior to commencing treatment. For the detection of FQ resistance, LiPA is useful and can rapidly and efficiently assess FQ resistance.
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