UCD School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland.
PLoS Pathog. 2012;8(4):e1002626. doi: 10.1371/journal.ppat.1002626. Epub 2012 Apr 5.
Clinical isolates of Staphylococcus aureus can express biofilm phenotypes promoted by the major cell wall autolysin and the fibronectin-binding proteins or the icaADBC-encoded polysaccharide intercellular adhesin/poly-N-acetylglucosamine (PIA/PNAG). Biofilm production in methicillin-susceptible S. aureus (MSSA) strains is typically dependent on PIA/PNAG whereas methicillin-resistant isolates express an Atl/FnBP-mediated biofilm phenotype suggesting a relationship between susceptibility to β-lactam antibiotics and biofilm. By introducing the methicillin resistance gene mecA into the PNAG-producing laboratory strain 8325-4 we generated a heterogeneously resistant (HeR) strain, from which a homogeneous, high-level resistant (HoR) derivative was isolated following exposure to oxacillin. The HoR phenotype was associated with a R₆₀₂H substitution in the DHHA1 domain of GdpP, a recently identified c-di-AMP phosphodiesterase with roles in resistance/tolerance to β-lactam antibiotics and cell envelope stress. Transcription of icaADBC and PNAG production were impaired in the 8325-4 HoR derivative, which instead produced a proteinaceous biofilm that was significantly inhibited by antibodies against the mecA-encoded penicillin binding protein 2a (PBP2a). Conversely excision of the SCCmec element in the MRSA strain BH1CC resulted in oxacillin susceptibility and reduced biofilm production, both of which were complemented by mecA alone. Transcriptional activity of the accessory gene regulator locus was also repressed in the 8325-4 HoR strain, which in turn was accompanied by reduced protease production and significantly reduced virulence in a mouse model of device infection. Thus, homogeneous methicillin resistance has the potential to affect agr- and icaADBC-mediated phenotypes, including altered biofilm expression and virulence, which together are consistent with the adaptation of healthcare-associated MRSA strains to the antibiotic-rich hospital environment in which they are frequently responsible for device-related infections in immuno-compromised patients.
金黄色葡萄球菌的临床分离株可以表达由主要细胞壁自溶酶和纤连蛋白结合蛋白或 icaADBC 编码的多糖细胞间黏附物/多-N-乙酰葡糖胺（PIA/PNAG）促进的生物膜表型。在耐甲氧西林金黄色葡萄球菌（MSSA）菌株中，生物膜的产生通常依赖于 PIA/PNAG，而耐甲氧西林的分离株则表达 Atl/FnBP 介导的生物膜表型，这表明对β-内酰胺类抗生素的敏感性与生物膜有关。通过将耐甲氧西林基因 mecA 引入产生 PIA 的实验室菌株 8325-4 中，我们产生了一个异质耐药（HeR）菌株，从该菌株中分离出一种同质、高水平耐药（HoR）衍生物，该衍生物在接触苯唑西林后产生。HoR 表型与 GdpP 的 DHHA1 结构域中的 R₆₀₂H 取代有关，GdpP 是一种最近发现的 c-di-AMP 磷酸二酯酶，在对β-内酰胺类抗生素和细胞包膜应激的耐药性/耐受性中起作用。8325-4 HoR 衍生株的 icaADBC 转录和 PNAG 产生受损，而该衍生株产生的蛋白质生物膜被针对 mecA 编码青霉素结合蛋白 2a（PBP2a）的抗体显著抑制。相反，在 MRSA 菌株 BH1CC 中切除 SCCmec 元件导致苯唑西林敏感性和生物膜产生减少，而 mecA 单独就可以弥补这两点。8325-4 HoR 菌株的辅助基因调节基因座的转录活性也受到抑制，反过来又导致蛋白酶产生减少，在一种装置感染的小鼠模型中，毒力显著降低。因此，同质耐甲氧西林有可能影响 agr 和 icaADBC 介导的表型，包括改变生物膜表达和毒力，这与医疗保健相关的耐甲氧西林金黄色葡萄球菌菌株适应富含抗生素的医院环境相一致，在该环境中，它们经常负责免疫功能低下患者的装置相关感染。
