Mlynek Kevin D, Callahan Mary T, Shimkevitch Anton V, Farmer Jackson T, Endres Jennifer L, Marchand Mélodie, Bayles Kenneth W, Horswill Alexander R, Kaplan Jeffrey B
Department of Biology, American University, Washington, DC, USA.
Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
Antimicrob Agents Chemother. 2016 Apr 22;60(5):2639-51. doi: 10.1128/AAC.02070-15. Print 2016 May.
Previous studies showed that sub-MIC levels of β-lactam antibiotics stimulate biofilm formation in most methicillin-resistant Staphylococcus aureus (MRSA) strains. Here, we investigated this process by measuring the effects of sub-MIC amoxicillin on biofilm formation by the epidemic community-associated MRSA strain USA300. We found that sub-MIC amoxicillin increased the ability of USA300 cells to attach to surfaces and form biofilms under both static and flow conditions. We also found that USA300 biofilms cultured in sub-MIC amoxicillin were thicker, contained more pillar and channel structures, and were less porous than biofilms cultured without antibiotic. Biofilm formation in sub-MIC amoxicillin correlated with the production of extracellular DNA (eDNA). However, eDNA released by amoxicillin-induced cell lysis alone was evidently not sufficient to stimulate biofilm. Sub-MIC levels of two other cell wall-active agents with different mechanisms of action-d-cycloserine and fosfomycin-also stimulated eDNA-dependent biofilm, suggesting that biofilm formation may be a mechanistic adaptation to cell wall stress. Screening a USA300 mariner transposon library for mutants deficient in biofilm formation in sub-MIC amoxicillin identified numerous known mediators of S. aureus β-lactam resistance and biofilm formation, as well as novel genes not previously associated with these phenotypes. Our results link cell wall stress and biofilm formation in MRSA and suggest that eDNA-dependent biofilm formation by strain USA300 in low-dose amoxicillin is an inducible phenotype that can be used to identify novel genes impacting MRSA β-lactam resistance and biofilm formation.
先前的研究表明,β-内酰胺类抗生素的亚抑菌浓度水平会刺激大多数耐甲氧西林金黄色葡萄球菌(MRSA)菌株形成生物膜。在此,我们通过测量亚抑菌浓度的阿莫西林对流行的社区相关MRSA菌株USA300形成生物膜的影响来研究这一过程。我们发现,亚抑菌浓度的阿莫西林提高了USA300细胞在静态和流动条件下附着于表面并形成生物膜的能力。我们还发现,在亚抑菌浓度阿莫西林中培养的USA300生物膜更厚,包含更多的柱状和通道结构,并且比未用抗生素培养的生物膜孔隙更少。在亚抑菌浓度阿莫西林中生物膜的形成与细胞外DNA(eDNA)的产生相关。然而,仅由阿莫西林诱导的细胞裂解释放的eDNA显然不足以刺激生物膜形成。另外两种具有不同作用机制的细胞壁活性剂——d-环丝氨酸和磷霉素的亚抑菌浓度水平也刺激了依赖eDNA的生物膜形成,这表明生物膜的形成可能是对细胞壁应激的一种机制性适应。筛选USA300水手转座子文库以寻找在亚抑菌浓度阿莫西林中生物膜形成缺陷的突变体,鉴定出许多已知的金黄色葡萄球菌β-内酰胺抗性和生物膜形成的介质,以及先前与这些表型无关的新基因。我们的结果将MRSA中的细胞壁应激与生物膜形成联系起来,并表明USA300菌株在低剂量阿莫西林中依赖eDNA的生物膜形成是一种可诱导的表型,可用于鉴定影响MRSAβ-内酰胺抗性和生物膜形成的新基因。