Mishra Nagendra N, Bayer Arnold S, Weidenmaier Christopher, Grau Timo, Wanner Stefanie, Stefani Stefania, Cafiso Viviana, Bertuccio Taschia, Yeaman Michael R, Nast Cynthia C, Yang Soo-Jin
Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America; The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America.
Interfaculty Institute of Microbiology and Infection Medicine, University of Tübingen, Tübingen, Germany; German Center for Infection Research (DZIF), Tübingen, Germany.
PLoS One. 2014 Sep 16;9(9):e107426. doi: 10.1371/journal.pone.0107426. eCollection 2014.
Development of in vivo daptomycin resistance (DAP-R) among Staphylococcus aureus clinical isolates, in association with clinical treatment failures, has become a major therapeutic problem. This issue is especially relevant to methicillin-resistant S. aureus (MRSA) strains in the context of invasive endovascular infections. In the current study, we used three well-characterized and clinically-derived DAP-susceptible (DAP-S) vs. resistant (DAP-R) MRSA strain-pairs to elucidate potential genotypic mechanisms of the DAP-R phenotype. In comparison to the DAP-S parental strains, DAP-R isolates demonstrated (i) altered expression of two key determinants of net positive surface charge, either during exponential or stationary growth phases (i.e., dysregulation of dltA and mprF), (ii) a significant increase in the D-alanylated wall teichoic acid (WTA) content in DAP-R strains, reflecting DltA gain-in-function; (iii) heightened elaboration of lysinylated-phosphatidylglyderol (L-PG) in DAP-R strains, reflecting MprF gain-in-function; (iv) increased cell membrane (CM) fluidity, and (v) significantly reduced susceptibility to prototypic cationic host defense peptides of platelet and leukocyte origins. In the tested DAP-R strains, genes conferring positive surface charge were dysregulated, and their functionality altered. However, there were no correlations between relative surface positive charge or cell wall thickness and the observed DAP-R phenotype. Thus, charge repulsion mechanisms via altered surface charge may not be sufficient to explain the DAP-R outcome. Instead, changes in the compositional or biophysical order of the DAP CM target of such DAP-R strains (i.e., increased fluidity) may be essential to this phenotype. Taken together, DAP-R in S. aureus appears to involve multi-factorial and strain-specific adaptive mechanisms.
金黄色葡萄球菌临床分离株中体内达托霉素耐药性（DAP-R）的产生与临床治疗失败相关，已成为一个主要的治疗问题。在侵袭性血管内感染的背景下，这个问题与耐甲氧西林金黄色葡萄球菌（MRSA）菌株尤为相关。在本研究中，我们使用了三对经过充分表征且源自临床的达托霉素敏感（DAP-S）与耐药（DAP-R）的MRSA菌株对，以阐明DAP-R表型的潜在基因型机制。与DAP-S亲本菌株相比，DAP-R分离株表现出：（i）在指数生长期或稳定生长期，两个决定净正表面电荷的关键因素的表达发生改变（即dltA和mprF失调）；（ii）DAP-R菌株中D-丙氨酰化壁磷壁酸（WTA）含量显著增加，反映DltA功能增强；（iii）DAP-R菌株中赖氨酸化磷脂酰甘油（L-PG）的合成增加，反映MprF功能增强；（iv）细胞膜（CM）流动性增加；（v）对血小板和白细胞来源的原型阳离子宿主防御肽的敏感性显著降低。在测试的DAP-R菌株中，赋予正表面电荷的基因失调，其功能发生改变。然而，相对表面正电荷或细胞壁厚度与观察到的DAP-R表型之间没有相关性。因此，通过改变表面电荷的电荷排斥机制可能不足以解释DAP-R的结果。相反，此类DAP-R菌株的DAP CM靶点的组成或生物物理顺序的变化（即流动性增加）可能对此表型至关重要。综上所述，金黄色葡萄球菌中的DAP-R似乎涉及多因素和菌株特异性的适应性机制。
