Bayer Arnold S, Mishra Nagendra N, Sakoulas George, Nonejuie Poochit, Nast Cynthia C, Pogliano Joseph, Chen Kuan-Tsen, Ellison Steven N, Yeaman Michael R, Yang Soo-Jin
Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA The David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
University of California, San Diego School of Medicine, La Jolla, California, USA Department of Medicine, Sharp Memorial Hospital, San Diego, California, USA.
Antimicrob Agents Chemother. 2014 Dec;58(12):7462-7. doi: 10.1128/AAC.03422-14. Epub 2014 Oct 6.
Over the past several years, single-nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) have been proposed to be associated with a gain-of-function phenotype in terms of daptomycin (DAP) nonsusceptibility (referred to as daptomycin resistance [DAP-R] herein for ease of presentation) in Staphylococcus aureus. We investigated the frequencies of SNPs within the mprF ORF and the relationships of such SNPs to cross-resistance between DAP and cationic host defense peptides (HDPs). Thirty-five well-characterized, unique DAP-susceptible (DAP-S) and DAP-R methicillin-resistant S. aureus (MRSA) isolates of the clonal complex 5 genotype were used. In addition to mprF SNPs and DAP-HDP cross-resistance, several other key genotypic and phenotypic metrics often associated with DAP-R were delineated, as follows: (i) mprF expression, (ii) membrane phospholipid content, (iii) positive surface charge, (iv) DAP binding, and (v) cell wall thickness profiles. A number of DAP-S strains (MICs of ≤ 1 μg/ml) exhibited mprF SNPs, occasionally with high-level mprF sequence variation from the genotype reference strain. However, none of these SNPs were localized to well-chronicled mprF hot spot locations associated with DAP-R in S. aureus. In contrast, all 8 DAP-R isolates demonstrated SNPs within such known mprF hot spots. Moreover, only the DAP-R strains showed MprF gain-of-function phenotypes, enhanced mprF expression, higher survival against two prototypical HDPs, and reduced DAP binding. Although a heterogenous array of mprF SNPs were often found in DAP-S strains, only selected hot spot SNPs, combined with concurrent mprF dysregulation, were associated with the DAP-R phenotype.
在过去几年中，有人提出mprF开放阅读框（ORF）内的单核苷酸多态性（SNP）与金黄色葡萄球菌对达托霉素（DAP）不敏感（为便于表述，本文中称为达托霉素耐药[DAP-R]）的功能获得性表型相关。我们研究了mprF ORF内SNP的频率以及这些SNP与DAP和阳离子宿主防御肽（HDP）之间交叉耐药性的关系。使用了35株特征明确、独特的DAP敏感（DAP-S）和DAP耐药的克隆复合体5基因型耐甲氧西林金黄色葡萄球菌（MRSA）分离株。除了mprF SNP和DAP-HDP交叉耐药性外，还描述了其他一些通常与DAP-R相关的关键基因型和表型指标，如下：（i）mprF表达，（ii）膜磷脂含量，（iii）表面正电荷，（iv）DAP结合，以及（v）细胞壁厚度分布。许多DAP-S菌株（最低抑菌浓度≤1μg/ml）表现出mprF SNP，偶尔与基因型参考菌株有高水平的mprF序列变异。然而，这些SNP均未定位到金黄色葡萄球菌中与DAP-R相关的记载详尽的mprF热点位置。相比之下，所有8株DAP-R分离株在这些已知的mprF热点内均显示出SNP。此外，只有DAP-R菌株表现出MprF功能获得性表型、mprF表达增强、对两种原型HDP的存活率提高以及DAP结合减少。尽管在DAP-S菌株中经常发现一系列异质性的mprF SNP，但只有选定的热点SNP与mprF同时失调才与DAP-R表型相关。
