AFM characterization of early P. aeruginosa aggregates highlights emergent mechanical properties

Abstract

Pseudomonas aeruginosa (Pa) is a leading cause of chronic lung infections in people with cystic fibrosis (pwCF), where its ability to form resilient, multicellular communities contributes to antibiotic tolerance and long-term persistence. While much of our understanding of Pa biofilms comes from surface-attached models, recent studies have emphasized the clinical relevance of suspended bacterial aggregates - dense, three-dimensional clusters that form early during infection and exhibit key biofilm-like properties. However, the physical characteristics of these aggregates remain poorly defined. Here, we apply atomic force microscopy (AFM) to visualize and quantify the structural and mechanical properties of Pa aggregates formed in synthetic cystic fibrosis sputum medium (SCFM2). Compared to planktonic cultures grown without mucin, aggregates formed in SCFM2 exhibited complex architecture and increased resistance to deformation, as measured by force spectroscopy. These differences emerged despite the absence of mature extracellular matrix components, suggesting that environmental cues and spatial organization alone may be sufficient to enhance aggregate mechanical resilience. Our results demonstrate that AFM provides a powerful, high-resolution approach for studying early-stage bacterial aggregates under physiologically relevant conditions. By resolving structural features and quantifying localized mechanical strength, this method offers new insight into how aggregate architecture contributes to persistence during chronic infection. These findings lay the groundwork for future studies targeting the physical robustness of bacterial communities as an early vulnerability in the pathogenesis of Pa both in CF and in other infection settings.