Population-based molecular epidemiologic study of rifampicin-resistant tuberculosis in rural area of eastern China / 中华流行病学杂志

Objective To describe the drug resistance-related molecular characterization and clustering feature of rifampicin-resistant (RIFr) M.tuberculosis (M.tb) in rural area of eastern China. Methods All patients diagnosed as RIFr M.tb in Deqing and Guanyun county during one year period from 2004 to 2005 were included in the study. By proportion method of drug susceptibility test, 65 isolates were identified resistant to rifampicin and regarded as the studied strains. Hotspots of rpoB gene and katG gene were detected by direct DNA sequencing. Beijing genotype M.tb strains were identified by spoligotyping. IS6110-RFLP (IS6110 restriction fragment length polymorphism) and clustering analysis were performed on all RIFr M.tb isolates available. Results The mutations in 81 bp rifampicin-resistance determination region (RRDR) of the rpoB gene were observed among 60 (92%) RIFr M.tb isolates, with mutation in locus 531 observed in the majority of RIFr isolates (37/65). 49(82%) of the 60 isolates were multidrug resistant TB (MDR-TB), which were referred to as resistant to both RIF and isoniazid (INH). Through spoligotyping, 54(83%) isolates were identified as Beijing genotype strains. In clustering analysis of IS6110-RFLP, 24 isolates were grouped into 11 clusters, suggesting that the recent transmission of M.tb did exist among patients. Regarding the drug resistance profile in clusters, all the isolates in clusters were also MDR-TB. 7 clusters contained isolates carrying different mutations were related to RIF-resistance. Multivariate analysis showed the proportion of new cases in clustered patients is higher than that in the un-clustered patients (new/previously treated: OR=3.342; 95% CI: 1.081-10.32). Conclusion The acquisition of rifampicin resistance in M.tb was more likely to be resulted from the selective growth of RIFr M.tb in the specific drug resistant M.tb such as isoniazid-reisistant M.tb. Previous elongated irregular treatment might favor the epidemic of RIFr M.tb.

Cross-resistance Between Rifampicin and Rifabutin and Its Relationship with rpoB Gene Mutations in Clinically Isolated MDR-TB Strains / 결핵및호흡기질환

BACKGROUND: Despite the emerging danger of MDR-TB to human beings, there have only been a limited number of drugs developed to treat MDR-TB since 1970. This study investigated the cross-resistance rate between rifampicin (RFP) and rifabutin (RBU) in order to determine the efficacy of rifabutin in treating MDR-TB. In addition, the results of rifabutin were correlated with the rpoB mutations, which are believed to be markers for MDR-TB and RFP resistance. METHODS: The MICs of RBU were tested against 126 clinical isolates of MDR-TB submitted to the clinical laboratory of National Masan TB Hospital in 2004. Five different concentrations (10-160 microgram/ml) were used for the MICs. The detection of the rpoB mutations was performed using a RFP resistance detection kit with a line probe assay(LiPA), which contains the oligonucleotide probes for 5 wide type and 3 specific mutations (513CCA, 516GTC, and 531TTG). The rpoB mutation was determined by direct sequencing. RESULTS: The rate of cross-resistance between RFP and RBU was 70.5%(74/105) at 20 microgram/ml RBU(ed note: How much RFP?) Most mutations (86.3%) occurred in the 524~534 codons. The His526Gln, His526Leu, Leu533Pro, Gln513Glu, and Leu511Pro mutations(Ed note: Is this correct?) were associated with the susceptibilty to RBU. CONCLUSION: Based on the cross-resistance rate between RFP and RBU, RBU may be used effectively in some MDR-TB patients. Therefore, a conventional drug susceptibility test for RBU and a determination of the critical concentration are needed. However, rpoB gene mutation test may be have limited clinical applications in detecting RBU resistance.

The Proportion of Rifabutin-susceptible Strains among Rifampicin- resistant Isolates and Its Specific rpoB Mutations / 결핵및호흡기질환

BACKGROUND: Rifabutin (ansamycin) is a spiro-piperidyl rifamycin, which is highly active against Mycobacterium tuberculosis. It has been found that some clinical isolates of tubercle bacilli that are resistant to rifampicin are susceptible to rifabutin, with some patients with multi-drug resistant pulmonary tuberculosis having shown favorable clinical and bacteriological responses to the rifabutin. This study was conducted to find the proportion of rifabutin- susceptible strains among rifampicin-resistant isolates from Korean MDR-TB patients, and investigate the presence of specific rpoB mutations, which may confer resistance to rifampicin, but not to rifabutin. METHODS: 201 rifampicin-resistant and 50 pan-susceptible M. tuberculosis isolates were randomly selected for this study. The isolates were retested at rifampicin and rifabutin concentrations of 0, 20, 40 and 80 microgram/ml, respectively. The isolates that grew at and/or over a rifabutin concentration of 20 microgram/ml were judged rifabutin-resistant. The rpoB gene was extracted from the isolates, and then amplified for direct sequencing to investigate specific rpoB mutations that conferred rifabutin- susceptibility but rifampicin-resistance. RESULTS: Out of the 201 rifampicin-resistant M. tuberculosis, 41 strains (20.4%) were susceptible to rifabutin using the absolute concentration method on Lowenstein-Jensen media. The rpoB mutation types that showed susceptibility to rifabutin were Leu511Pro, Ser512Arg, Gln513Glu, Asp516Ala, Asp516Gly, Asp516Val, Asp516Tyr, Ser522Leu, His526Asn, His526Leu, His526Cys, Arg529Pro and Leu533Pro. A reverse hybridization technique was able to detect 92.5% of the rifabutin-susceptible isolates, with a specificity of 96.1% among 195 M. tuberculosis isolates with the rpoB mutation. CONCLUSIONS: Around 20% of the rifampicin-resistant isolates in Korea showed susceptibility to rifabutin, which was associated with some specific mutations of rpoB. Rifabutin could be used for the treatment of MDR-TB patients, especially when drug susceptibility testing reveals susceptibility to rifabutin.