Costerton Biofilm Center, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark.
Department of Microbiology, Faculty of Agriculture, Cairo University, Giza, Egypt.
Antimicrob Agents Chemother. 2018 Jul 27;62(8). doi: 10.1128/AAC.00320-18. Print 2018 Aug.
The opportunistic Gram-negative pathogen , known for its intrinsic and acquired antibiotic resistance, has a notorious ability to form biofilms, which often facilitate chronic infections. The evolutionary paths to antibiotic resistance have mainly been investigated in planktonic cultures and are less studied in biofilms. We experimentally evolved PAO1 colony biofilms and stationary-phase planktonic cultures for seven passages in the presence of subinhibitory levels (0.1 mg/liter) of ciprofloxacin (CIP) and performed a genotypic (whole-bacterial population sequencing) and phenotypic assessment of the populations. We observed a higher proportion of CIP resistance in the CIP-evolved biofilm populations than in planktonic populations exposed to the same drug concentrations. However, the MICs of ciprofloxacin were lower in CIP-resistant isolates selected from the biofilm population than the MICs of CIP-resistant isolates from the planktonic cultures. We found common evolutionary trajectories between the different lineages, with mutations in known CIP resistance determinants as well as growth condition-dependent adaptations. We observed a general trend toward a reduction in type IV-pilus-dependent motility (twitching) in CIP-evolved populations and a loss of virulence-associated traits in the populations evolved in the absence of antibiotic. In conclusion, our data indicate that biofilms facilitate the development of low-level mutational resistance, probably due to the lower effective drug exposure than in planktonic cultures. These results provide a framework for the selection process of resistant variants and the evolutionary mechanisms involved under the two different growth conditions.
这种机会性病原体革兰氏阴性菌以其固有和获得性抗生素耐药性而闻名，具有形成生物膜的恶名昭彰的能力，这常常导致慢性感染。抗生素耐药性的进化途径主要在浮游培养物中进行了研究，而在生物膜中研究较少。我们在亚抑制水平（0.1 毫克/升）环丙沙星（CIP）存在下对 PAO1 集落生物膜和静止期浮游培养物进行了七次传代实验，并对种群进行了基因型（全细菌群体测序）和表型评估。我们观察到在暴露于相同药物浓度的浮游培养物中，CIP 进化的生物膜种群中的 CIP 耐药性比例高于 CIP 耐药性分离株的 MICs 在生物膜种群中选择的比在浮游培养物中选择的 CIP 耐药性分离株的 MIC 低。我们在不同谱系之间发现了共同的进化轨迹，包括已知 CIP 耐药决定因素的突变以及与生长条件相关的适应。我们观察到在 CIP 进化的种群中，依赖 IV 型菌毛的运动（抽动）普遍减少，以及在没有抗生素的情况下进化的种群中丧失与毒力相关的特征的一般趋势。总之，我们的数据表明生物膜促进了低水平突变耐药性的发展，这可能是由于与浮游培养物相比，药物暴露量较低所致。这些结果为在两种不同生长条件下耐药变体的选择过程和涉及的进化机制提供了框架。
