Baldry Mara, Nielsen Anita, Bojer Martin S, Zhao Yu, Friberg Cathrine, Ifrah Dan, Glasser Heede Nina, Larsen Thomas O, Frøkiær Hanne, Frees Dorte, Zhang Lixin, Dai Huanqin, Ingmer Hanne
Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Beijing, China.
PLoS One. 2016 Dec 22;11(12):e0168305. doi: 10.1371/journal.pone.0168305. eCollection 2016.
Staphylococcus aureus is a serious human pathogen and antibiotic resistant, community-associated strains, such as the methicillin resistant S. aureus (MRSA) strain USA300, continue to spread. To avoid resistance, anti-virulence therapy has been proposed where toxicity is targeted rather than viability. Previously we have shown that norlichexanthone, a small non-reduced tricyclic polyketide produced by fungi and lichens, reduces expression of hla encoding α-hemolysin as well as the regulatory RNAIII of the agr quorum sensing system in S. aureus 8325-4. The aim of the present study was to further characterise the mode of action of norlichexanthone and its effect on biofilm formation. We find that norlichexanthone reduces expression of both hla and RNAIII also in strain USA300. Structurally, norlichexanthone resembles ω-hydroxyemodin that recently was shown to bind the agr two component response regulator, AgrA, which controls expression of RNAIII and the phenol soluble modulins responsible for human neutrophil killing. We show that norlichexanthone reduces S. aureus toxicity towards human neutrophils and interferes directly with AgrA binding to its DNA target. In contrast to ω-hydroxyemodin however, norlichexanthone reduces staphylococcal biofilm formation. Transcriptomic analysis revealed that genes regulated by the SaeRS two-component system are repressed by norlichexanthone when compared to untreated cells, an effect that was mitigated in strain Newman carrying a partially constitutive SaeRS system. Our data show that norlichexanthone treatment reduces expression of key virulence factors in CA-MRSA strain USA300 via AgrA binding and represses biofilm formation.
金黄色葡萄球菌是一种严重的人类病原体，且具有抗生素抗性，社区相关菌株，如耐甲氧西林金黄色葡萄球菌（MRSA）菌株USA300，仍在持续传播。为避免耐药性，有人提出了抗毒力疗法，该疗法针对的是毒性而非细菌的生存能力。此前我们已经表明，地衣赤星酮是一种由真菌和地衣产生的小型非还原三环聚酮化合物，它能降低金黄色葡萄球菌8325-4中编码α-溶血素的hla以及agr群体感应系统的调节RNAIII的表达。本研究的目的是进一步表征地衣赤星酮的作用模式及其对生物膜形成的影响。我们发现地衣赤星酮在USA300菌株中也能降低hla和RNAIII的表达。在结构上，地衣赤星酮类似于ω-羟基大黄素，最近有研究表明ω-羟基大黄素能结合agr双组分反应调节因子AgrA，AgrA控制RNAIII以及负责杀死人类中性粒细胞的酚溶性调节蛋白的表达。我们表明地衣赤星酮降低了金黄色葡萄球菌对人类中性粒细胞的毒性，并直接干扰AgrA与其DNA靶点的结合。然而，与ω-羟基大黄素不同的是，地衣赤星酮能减少葡萄球菌生物膜的形成。转录组分析显示，与未处理的细胞相比，受SaeRS双组分系统调控的基因在经地衣赤星酮处理后受到抑制，在携带部分组成型SaeRS系统的纽曼菌株中这种效应有所减轻。我们的数据表明，地衣赤星酮处理通过AgrA结合降低了社区获得性耐甲氧西林金黄色葡萄球菌USA300菌株中关键毒力因子的表达，并抑制了生物膜的形成。
