Beyond Resistance Genes: Pseudomonas aeruginosa as a Complex Adaptive System Driving Persistence, Evolution, and Antimicrobial Resistance.

Pseudomonas aeruginosa (P. aeruginosa) is one of the most adaptable bacterial pathogens and a major cause of difficult-to-treat infections worldwide. Although antimicrobial resistance (AMR) is commonly attributed to resistance genes and their associated mechanisms, this perspective does not fully explain the ability of P. aeruginosa to survive antimicrobial exposure, establish chronic infections, and persist across diverse environmental and host-associated habitats. In this review, we examine P. aeruginosa within a complex adaptive systems framework, integrating evidence from molecular microbiology, physiology, ecology, population biology, and evolutionary genomics. We describe how environmental sensing, regulatory integration, phenotypic plasticity, population heterogeneity, persistence, biofilm formation, collective behavior, and evolutionary diversification interact across biological scales to shape bacterial survival and long-term success. Evidence from chronic infections and environmental reservoirs indicates that resistance emerges from interconnected physiological, ecological, and evolutionary processes rather than from isolated genetic determinants alone. Building on these observations, we propose an adaptive resilience cascade framework in which environmental sensing drives physiological diversification, persistence maintains survival under stress, evolutionary selection stabilizes advantageous traits, and ecological dissemination promotes the spread of successful lineages. This framework provides a systems-level explanation for treatment failure, chronic colonization, and resistance emergence while linking cellular responses to population, ecological, and evolutionary outcomes. Emerging approaches, including single-cell analyses, spatial omics, evolution-informed interventions, engineered biological therapeutics, and artificial intelligence-assisted modeling, further support a shift toward targeting adaptive resilience rather than resistance determinants alone. Viewing P. aeruginosa as a complex adaptive system offers an integrated conceptual foundation for future surveillance, therapeutic development, and antimicrobial stewardship strategies.