Rosato A, Pierre J, Billot-Klein D, Buu-Hoi A, Gutmann L
Laboratoire de Recherche Moléculaire sur les Antibiotiques, Université Paris VI, France.
Antimicrob Agents Chemother. 1995 Apr;39(4):830-3. doi: 10.1128/AAC.39.4.830.
A clinical isolate of Enterococcus avium, Ea1, which exhibited inducible, low-level resistance to vancomycin and teicoplanin, and two mutants selected from this strain, Ea3 and Ea31, were studied. Ea3 was vancomycin dependent and derived from Ea1, while Ea31 was not vancomycin dependent, was constitutively resistant, and was derived from Ea3. Hybridization studies revealed that vanA was present in Ea1 and suggested that it was located on a high-molecular-weight plasmid. In the absence of induction, Ea1 synthesized only the natural UDP-MurNAc-pentapeptide precursor, and after induction it synthesized an additional precursor identified as UDP-MurNAc-tetrapeptide-D-lactate. The latter was the only precursor found in Ea3 and Ea31, even after precursor accumulation. From these results, we infer that (i) the low level of resistance to glycopeptides in strain Ea1 may be in part due to the residual synthesis of the normal precursor and (ii) the vancomycin dependence of mutant Ea3 could be due to the fact that this strain does not produce any peptidoglycan precursor in the absence of induction.
研究了一株禽肠球菌临床分离株Ea1，其对万古霉素和替考拉宁表现出可诱导的低水平耐药性，以及从该菌株中筛选出的两个突变体Ea3和Ea31。Ea3对万古霉素依赖，源自Ea1，而Ea31不依赖万古霉素，为组成型耐药，源自Ea3。杂交研究表明vanA存在于Ea1中，并提示其位于高分子量质粒上。在无诱导情况下，Ea1仅合成天然的UDP - 胞壁酰五肽前体，诱导后它合成了另一种被鉴定为UDP - 胞壁酰四肽 - D - 乳酸的前体。即使在前体积累后，后者也是Ea3和Ea31中发现的唯一前体。根据这些结果，我们推断：（i）Ea1菌株对糖肽类药物的低水平耐药性可能部分归因于正常前体的残留合成；（ii）突变体Ea3对万古霉素的依赖性可能是由于该菌株在无诱导时不产生任何肽聚糖前体。
