The Extracellular Matrix Component Psl Provides Fast-Acting Antibiotic Defense in Pseudomonas aeruginosa Biofilms

Bacteria within biofilms secrete and surround themselves with an extracellular matrix, which serves as a first line of defense against antibiotic attack. Polysaccharides constitute major elements of the biofilm matrix and are implied in surface adhesion and biofilm organization, but their contributions to the resistance properties of biofilms remain largely elusive. Using a combination of static and continuous-flow biofilm experiments we show that Psl, one major polysaccharide in the Pseudomonas aeruginosa biofilm matrix, provides a generic first line of defense toward antibiotics with diverse biochemical properties during the initial stages of biofilm development. Furthermore, we show with mixed-strain experiments that antibiotic-sensitive “non-producing” cells lacking Psl can gain tolerance by integrating into Psl-containing biofilms. However, non-producers dilute the protective capacity of the matrix and hence, excessive incorporation can result in the collapse of resistance of the entire community. Our data also reveal that Psl mediated protection is extendible to E. coli and S. aureus in co-culture biofilms. Together, our study shows that Psl represents a critical first bottleneck to the antibiotic attack of a biofilm community early in biofilm development.生物被膜（biofilm）内的细菌会分泌并自身包裹于细胞外基质（extracellular matrix）中，该基质是抵御抗生素攻击的第一道防御屏障。多糖是生物被膜基质的主要组成成分，参与表面黏附与生物被膜结构构建，但它们对生物被膜抗性特性的具体贡献在很大程度上仍未明确。本研究结合静态与连续流生物被膜实验，证实铜绿假单胞菌（Pseudomonas aeruginosa）生物被膜基质中的主要多糖之一Psl，可在生物被膜形成的初始阶段，对具有不同生化特性的抗生素提供通用的第一道防御屏障。此外，混合菌株实验表明，缺乏Psl的抗生素敏感型“非产生株”细胞，可通过整合到含有Psl的生物被膜中获得耐药耐受性。但非产生株会稀释基质的防护能力，因此过度整合会导致整个生物被膜群落的抗性崩溃。本研究数据还显示，Psl介导的防护作用在共培养生物被膜中可延伸至大肠杆菌（E. coli）与金黄色葡萄球菌（S. aureus）。综上，本研究表明，在生物被膜发育早期，Psl是生物被膜群落抵御抗生素攻击的关键第一道防御瓶颈。