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-resistant M.tb. Previous elongated irregular treatment might favor the epidemic of RIFr M.tb.