rpoB gene mutation profile in rifampicin-resistant Mycobacterium tuberculosis clinical isolates from Guizhou, one of the highest incidence rate regions in China.

Sir, Tuberculosis (TB) is the leading single-agent infectious disease killer in the world, especially in Asia and Africa. Worldwide, 9.2 million new cases of TB (139 per 100000 population) and 1.7 million deaths from TB occurred in 2006. Ranked first to fifth, respectively, in terms of total numbers of TB cases in the world are India, China, Indonesia, South Africa and Nigeria; and the African region has the highest incidence rate per capita (363 per 100000 population). China is one of the high-burden countries for TB (99 per 100000 population) and Guizhou Province is one of the highest incidence rate regions in China, with 699 TB cases per 100000 population (www.gog.com.cn). A combination of four drugs, rifampicin, isoniazid, pyrazinamide and ethambutol, with or without streptomycin, is recommended for the standard or first-line treatment of TB. Resistance to these drugs has been linked to mutations in at least nine genes; katG, inhA, aphC and kasA for isoniazid resistance, rpoB for rifampicin resistance, rpsL and rrs for streptomycin resistance, embB for ethambutol resistance and pncA for pyrazinamide resistance. It is estimated that 4.3% of all new and previously treated TB cases are caused by multidrug-resistant (MDR) strains of Mycobacterium tuberculosis. China, India and the Russian Federation accounted for 62% of the estimated global burden of MDR-TB cases. China is ranked number one in terms of the total number of MDR-TB cases. Many mutations have been identified in different regions of these drug resistance genes, and resistance to rifampicin has been shown to be associated with mutations in the 81 bp rifampicin resistancedetermining region (RRDR) of the RNA polymerase b-subunit (rpoB) gene. In today’s world of global travel, infectious diseases such as MDR-TB pass into industrialized countries from the developing world. However, there are ways to combat the problems of MDR-TB, for example early recognition of MDR could lead to effective drug interventions using second-line anti-TB drugs. Recognizing the threat of MDR-TB, the WHO launched The Global Plan to Stop TB 2006–2015 in 2006 and set out how the Stop TB Strategy should be implemented over the decade 2006–2015. The US CDC has emphasized the importance of expeditious detection of drug resistance and the implementation of appropriate therapy. We report here the determination of the rpoB gene mutation profile in rifampicin-resistant M. tuberculosis clinical isolates from Guizhou Province and the comparison with mutation profiles from different regions of China and nine other countries of Asia, Europe and America in order to select region-specific mutations, which could potentially be used for the development of quick diagnostic tools for MDR-TB suitable for particular regions of the world. One hundred M. tuberculosis isolates were obtained from the Affiliated Hospital of Zunyi Medical College, Guizhou Province, China from March 2007 to September 2008. These clinical isolates were grown on Löwenstein–Jensen agar slants at 378C for 4 weeks and were examined for microscopic colony morphology. All cultures were used for rifampicin resistance testing by the absolute concentration method, and the isolates were considered resistant to rifampicin when they were resistant to at least 50 mg/L rifampicin. M. tuberculosis DNA Research letters