Supplementary Information

<i>Pseudomonas aeruginosa</i> is an opportunistic bacterium frequently infecting the lower airways of individuals with cystic fibrosis (iwCF). This study examines colistin (CST) resistance mechanisms in <i>Psa</i>-ST3351 and their effects on bacterial virulence. <i>Psa</i>-ST3351 represents a novel sequence type, CST-resistant isolate from a child with CF. We show that <i>Psa</i>-ST3351 CST-resistance requires the addition of 4-amino-4-deoxy-L-arabinose to lipid A. Surprisingly, CST-exposure induced a non-mucoid-to-mucoid transition characterized by enhanced swarming motility, decreased aminoglycoside susceptibility, impaired ExoS secretion via the type-3 secretion system, and increased bacterial competition, all hallmarks of a chronic infection phenotype. CST-treated <i>Psa</i>-ST3351 exhibited reduced phagocytosis by macrophages, although the induction of pro-inflammatory cytokines remained intact. Moreover, CST exposure enhanced the pathogenicity of <i>Psa</i>-ST3351 in a murine pneumonia model. We conclude that CST-mediated transition from a non-mucoid-to-mucoid phenotype in <i>Psa</i>-ST3351 may have implications, particularly when CST-resistance and mucoid conversion remain undetected in iwCF treated with nebulized CST.

<i>铜绿假单胞菌</i>（Pseudomonas aeruginosa）是一种机会致病菌（opportunistic bacterium），常感染囊性纤维化患者（individuals with cystic fibrosis，iwCF）的下呼吸道。本研究探讨了<i>Psa</i>-ST3351的粘菌素（colistin，CST）耐药机制及其对细菌毒力的影响。<i>Psa</i>-ST3351是一种新型序列型（sequence type）、耐CST的分离株，来自一名囊性纤维化患儿。研究表明，<i>Psa</i>-ST3351对CST的耐药性依赖于在脂质A（lipid A）上添加4-氨基-4-脱氧-L-阿拉伯糖。令人惊讶的是，暴露于CST可诱导该菌株从非粘液型向粘液型（mucoid）转变，表现为群集运动（swarming motility）增强、对氨基糖苷类（aminoglycoside）敏感性降低、通过Ⅲ型分泌系统（type-3 secretion system）的ExoS分泌受损以及细菌竞争力增加——这些均为慢性感染表型的标志。经CST处理的<i>Psa</i>-ST3351被巨噬细胞吞噬的能力降低，尽管促炎细胞因子（pro-inflammatory cytokines）的诱导仍保持完整。此外，暴露于CST增强了<i>Psa</i>-ST3351在小鼠肺炎模型（murine pneumonia model）中的致病性。我们得出结论：<i>Psa</i>-ST3351中由CST介导的非粘液型向粘液型表型转变可能具有临床意义，尤其是当接受雾化CST治疗的囊性纤维化患者中CST耐药性和粘液型转化未被检测到时。