Department of Biological Sciences, University of Texas at Dallas, Richardson, Texas, United States of America.
PLoS One. 2021 Apr 8;16(4):e0249631. doi: 10.1371/journal.pone.0249631. eCollection 2021.
Vancomycin-resistant enterococci (VRE) are important nosocomial pathogens that cause life-threatening infections. To control hospital-associated infections, skin antisepsis and bathing utilizing chlorhexidine is recommended for VRE patients in acute care hospitals. Previously, we reported that exposure to inhibitory chlorhexidine levels induced the expression of vancomycin resistance genes in VanA-type Enterococcus faecium. However, vancomycin susceptibility actually increased for VanA-type E. faecium in the presence of chlorhexidine. Hence, a synergistic effect of the two antimicrobials was observed. In this study, we used multiple approaches to investigate the mechanism of synergism between chlorhexidine and vancomycin in the VanA-type VRE strain E. faecium 1,231,410. We generated clean deletions of 7 of 11 pbp, transpeptidase, and carboxypeptidase genes in this strain (ponA, pbpF, pbpZ, pbpA, ddcP, ldtfm, and vanY). Deletion of ddcP, encoding a membrane-bound carboxypeptidase, altered the synergism phenotype. Furthermore, using in vitro evolution, we isolated a spontaneous synergy escaper mutant and utilized whole genome sequencing to determine that a mutation in pstB, encoding an ATPase of phosphate-specific transporters, also altered synergism. Finally, addition of excess D-lactate, but not D-alanine, enhanced synergism to reduce vancomycin MIC levels. Overall, our work identified factors that alter chlorhexidine and vancomycin synergism in a model VanA-type VRE strain.
耐万古霉素肠球菌（VRE）是一种重要的医院内病原体，可引起危及生命的感染。为了控制医院相关性感染，建议急性护理医院的 VRE 患者进行皮肤消毒和使用洗必泰沐浴。此前，我们报道过，暴露于抑制性洗必泰水平会诱导 VanA 型粪肠球菌中万古霉素耐药基因的表达。然而，在洗必泰存在的情况下，VanA 型粪肠球菌对万古霉素的敏感性实际上增加了。因此，观察到这两种抗菌药物之间存在协同作用。在这项研究中，我们使用多种方法研究了 1,231,410 型 VanA 型 VRE 菌株粪肠球菌中洗必泰和万古霉素协同作用的机制。我们在该菌株中生成了 7 个转肽酶和羧肽酶基因（ponA、pbpF、pbpZ、pbpA、ddcP、ldtfm 和 vanY）的 11 个 pbp 基因的清洁缺失。缺失编码膜结合羧肽酶的 ddcP 基因改变了协同作用表型。此外，通过体外进化，我们分离出一个自发协同逃避突变体，并利用全基因组测序确定编码磷酸特异性转运体 ATP 酶的 pstB 突变也改变了协同作用。最后，添加过量的 D-乳酸而不是 D-丙氨酸增强了协同作用，降低了万古霉素 MIC 水平。总的来说，我们的工作确定了改变模型 VanA 型 VRE 菌株中洗必泰和万古霉素协同作用的因素。
