| China is one of the tuberculosis (TB) high burden countries reported by WHO and the incidence number of TB in China ranks the second in the world, following India. The epidemic of MDR TB is severe in China either. A recent study reported that 9.3% of all TB cases in China are MDR, almost twice higher than the world’s average MDR prevalence. MDR TB indicates longer treatment, more adverse effect and low treatment outcome. Thus, MDR TB control is important for the management of TB in China.Novel tools are urgently needed for the rapid, reliable detection of multi-drug resistant (MDR) and even extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis. To develop such tools, we need information about the frequency and distribution of the mycobacterial mutations and genotypes that are associated with phenotypic drug resistance. In a population-based study, we collected 115 MDR isolates resistant to at least rifampin, isoniazid and 22 pan-susceptible isolates from TB patients in Henan, China. The culture-based proportion method was used as drug susceptibility testing (DST) and for each isolate, four anti-tuberculosis drug susceptibility(RIF, INH, EMB, STR) were identified. We detected mutations within nine known drug resistance related genes, including:rpoB, katG, inhA, oxyR, ahpC, kasA, embB, rpsL and rrs. The full length ORFs and the partial region of promoters were amplified and sequenced for fully understanding the mutation pattern of these above genesAfter comprehensive analysis of the mutation pattern and the drug resistance spectrum of study isolates, several conclusion can be drawn:1. The priorities of frequency of main mutation locus in drug resistance related genes are not changed, e.g.:rpoB531>rpoB526> rpoB516,rpsL43> rpsL88> rrs513. And in one region, the frequencies of all mutation locus in drug resistance related genes are not changed.2. In one region, there are higher frequencies of main mutation locus reported by the studies with more MDR isolates, e.g.:rpoB531, katG315, embB306, rpsL43.3. Some drug sensitive but MDR isolates may carry mutations of some drug related genes, e.g.:embB306 and rpsL 43.In addition, based on the data of mutation pattern and drug resistance pattern, we analyzed the association between embB gene mutations and drug resistance of MDR isolates. There are the conclusions as follows:1. embB306 is not the single cause of EMB resistance, but it is a useful candidate marker for the EMB resistance analysis and the sensitivity of EMB resistance prediction can be improved to 89.6% by combining more embB sites.2. All embB specific mutations among drug resistant isolates, can be candidate markers for broad drug resistance prediction. A total of 90.2% isolates concurrent resistant to four first line drugs carry mutation at embB mutation sites.3. A 576bp fragment of embB covers four mutation sites of embB306,354,406 and 497 can detect 83.6% of these four drug resistant isolates which may leads the development of a simple and rapid molecular test to detect four first-line drugs resistance in Henan, China... |
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