Djorić Dušanka, Kristich Christopher J
Department of Microbiology and Immunology, Center for Infectious Disease Research, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Department of Microbiology and Immunology, Center for Infectious Disease Research, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
J Bacteriol. 2017 Oct 31;199(23). doi: 10.1128/JB.00392-17. Print 2017 Dec 1.
Enterococci are major causes of hospital-acquired infections. Intrinsic resistance to cephalosporins is a universal trait among clinically relevant enterococci. Cephalosporin resistance enables enterococci to proliferate to high densities in the intestines of patients undergoing cephalosporin treatment, a precursor to the emergence of infection. However, the genetic and biochemical mechanisms of intrinsic cephalosporin resistance in enterococci are not well understood. A two-component signal transduction system, CroR/S, is required for cephalosporin resistance in enterococci. Although the CroR/S regulon is not well defined, one gene reported to be CroR dependent in JH2-2 encodes an extracellular putative peptidoglycan hydrolase, SalB. To test the hypothesis that SalB is responsible for CroR-dependent cephalosporin resistance, we examined Δ mutants in multiple genetic lineages of , revealing that SalB is required not only for intrinsic cephalosporin resistance but also for maintenance of cell envelope integrity in the absence of antibiotic stress. The N-terminal signal sequence is necessary for SalB secretion, and secretion is required for SalB to promote cephalosporin resistance. Functional dissection revealed that the C-terminal SCP domain of SalB is essential for biological activity and identified three residues within the SCP domain that are required for the stability and function of SalB. Additionally, we found that in contrast to what is seen in JH2-2, SalB is not regulated by the CroR/S two-component system in OG1, suggesting diversity in the CroR/S regulon among distinct lineages of Resistance to cephalosporins is universal among clinically relevant enterococci, enabling enterococcal proliferation to high densities in the intestines of patients undergoing cephalosporin treatment, a precursor to the emergence of infection. Disabling cephalosporin resistance could therefore reduce the incidence of enterococcal infections. However, the genetic and biochemical mechanisms of cephalosporin resistance are not well understood. The significance of this work is the identification of a novel extracellular factor (SalB) that promotes cephalosporin resistance in , which could potentially serve as a target for therapeutics that impair enterococcal cephalosporin resistance. Additionally, our work highlights the importance of the C-terminal SCP domain of SalB, including several conserved residues within the SCP domain, for the ability of SalB to promote cephalosporin resistance.
肠球菌是医院获得性感染的主要原因。对头孢菌素的固有耐药性是临床相关肠球菌的普遍特征。头孢菌素耐药性使肠球菌能够在接受头孢菌素治疗的患者肠道中大量增殖，这是感染出现的先兆。然而，肠球菌中固有头孢菌素耐药性的遗传和生化机制尚未完全明确。一种双组分信号转导系统CroR/S是肠球菌对头孢菌素耐药所必需的。尽管CroR/S调控子尚未明确界定，但在JH2-2中一个据报道依赖CroR的基因编码一种细胞外假定的肽聚糖水解酶SalB。为了验证SalB负责依赖CroR的头孢菌素耐药性这一假说，我们检测了多个基因谱系中的Δ突变体，发现SalB不仅是固有头孢菌素耐药性所必需的，而且在没有抗生素压力的情况下对于维持细胞包膜完整性也是必需的。SalB分泌需要N端信号序列，而SalB促进头孢菌素耐药性需要分泌。功能剖析表明，SalB的C端SCP结构域对于生物学活性至关重要，并确定了SCP结构域内三个对SalB的稳定性和功能必需的残基。此外，我们发现与JH2-2不同，在OG1中SalB不受CroR/S双组分系统调控，这表明不同谱系的肠球菌中CroR/S调控子存在差异。对头孢菌素的耐药性在临床相关肠球菌中普遍存在，使肠球菌能够在接受头孢菌素治疗的患者肠道中大量增殖，这是感染出现的先兆。因此，消除头孢菌素耐药性可能会降低肠球菌感染的发生率。然而，头孢菌素耐药性的遗传和生化机制尚未完全明确。这项工作的意义在于鉴定出一种促进肠球菌对头孢菌素耐药的新型细胞外因子（SalB），它有可能成为损害肠球菌头孢菌素耐药性的治疗靶点。此外，我们的工作突出了SalB的C端SCP结构域的重要性，包括SCP结构域内的几个保守残基，对于SalB促进头孢菌素耐药性的能力而言。
