Biofilm adaptation and mucosal immune dysregulation in recalcitrant chronic rhinosinusitis: from pathogenesis to a therapeutic roadmap

The management of chronic rhinosinusitis (CRS) is frequently complicated by treatment recalcitrance, a phenomenon primarily driven by the persistence of microbial biofilms. Beyond their traditional role as a physical barrier against antibiotics, recent evidence positions biofilms as sophisticated immune modulators that actively perpetuate mucosal dysbiosis. This review synthesizes the pathological continuum of biofilm-associated CRS, elucidating how biofilm derived pathogen associated molecular patterns (PAMPs) trigger the release of epithelial alarmins (TSLP, IL-33, IL-25), thereby fueling a maladaptive Type 2 inflammatory loop. We further examine bacterial survival strategies, such as the formation of small colony variants (SCVs) and intracellular "Trojan Horse" reservoirs, which render conventional functional endoscopic sinus surgery (FESS) and antimicrobial monotherapies insufficient for complete eradication. Crucially, we discuss the current diagnostic disconnect where standard cultures fail to detect biofilm burdens. Finally, we propose a therapeutic paradigm shift from a purely bactericidal approach to one of ecological restoration. By integrating cutting-edge strategies, including matrix-degrading enzymes, bacteriophage cocktails, and Nasal Microbiota Transplantation (NMT), we construct a multi-dimensional framework aiming to restore sinonasal homeostasis. Together, these emerging strategies support a shift from pathogen suppression alone toward ecological and immunologic rebalancing of the sinonasal mucosa, offering a more durable conceptual framework for overcoming treatment recalcitrance.