Rifampicin resistance and its fitness cost in Enterococcus faecium
Rifampicin resistance and its fitness cost in Enterococcus faecium
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DOI：
10.1093/jac/dkh044
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发表时间：
2004-02-01
影响因子：
5.2
通讯作者：
Bennett, PM
中科院分区：
文献类型：
--
作者：
Enne, VI;Delsol, AA;Bennett, PM
目的：对屎肠球菌利福平耐药的遗传基础和适应度成本进行了研究。从最近从猪粪便材料中分离的四个亲本菌株中选择粪菌突变体。从PCR扩增子中确定亲本菌株的完整rpoB基因和突变体的核苷酸-189至+1785的DNA序列。通过测定生长速率、直接生长竞争和某些突变体在猪肠中存活的能力来评估突变体的适应性。结果：亲本菌株的rpoB基因彼此偏离1-10%，每个基因编码1208个氨基酸长度的蛋白质。所有突变体在其他生物体中与利福平耐药性有关的区域中具有单个氨基酸取代。6个突变体携带取代H489 Y/Q，2个突变体携带取代R492 H，1个突变体携带取代Q480 H，2个突变体携带取代S494 L和V224 I，1个突变体携带取代G485 D和V224 I。每一代的突变体的健身成本范围从2.5%的增益到10%的成本。具有H489 Y/Q取代的突变体是最适合的，而双突变体是最不适合的。突变体H489 Q在猪肠道中存活12天。利福平MIC与适应性成本之间存在一定的相关性，MIC越高，适应性成本越高。屎室抗性的适应性成本是可变的，有时可能不存在。
Objectives: The genetic basis of rifampicin resistance and the associated fitness cost in Enterococcus faecium were investigated.Methods: Twelve spontaneous rifampicin-resistant E. faecium mutants were selected from four parent strains recently isolated from porcine faecal material. The DNA sequence of the complete rpoB gene from the parent strains and of nucleotides -189 to +1785 from the mutants was determined from PCR amplicons. The fitness of the mutants was assessed by determining growth rate, by direct growth competition and by the ability of some of the mutants to survive in the pig intestine.Results: The rpoB genes of the parent strains diverged from each other by 1-10% and each encoded proteins that were 1208 amino acids in length. All mutants had a single amino acid substitution in the region implicated in rifampicin resistance in other organisms. Six mutants carried the substitution H489Y/Q, two mutants carried the substitution R492H, one mutant carried the substitution Q480H, two mutants carried the substitutions S494L and V224I, and one mutant carried the substitutions G485D and V224I. Per generation fitness costs of the mutants ranged from a gain of 2.5% to a cost of 10%. Mutants with the substitution H489Y/Q were the most fit, whereas the double mutants were the least fit. The mutant with the substitution H489Q was able to survive in the pig gut for 12 days. There was some correlation between the rifampicin MIC and fitness cost, with higher MICs being associated with higher fitness costs.Conclusions: Substitutions in RpoB are associated with rifampicin resistance in E. faecium. The fitness cost of resistance is variable and can sometimes be absent.