Outbreaks of fluconazole-resistant Candida parapsilosis are driven by low-biofilm-producing isolates that emerge under host selection

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Candida parapsilosis is a major human fungal pathogen, with recent global outbreaks driven by fluconazole-resistant (FLCR-Cp) isolates that are difficult to eradicate and associated with poor clinical outcomes. However, the microbial traits enabling persistence of these outbreak lineages remain poorly defined. Here, we show that FLCR-Cp isolates responsible for prolonged, multi-country outbreaks consistently exhibit a striking low-biofilm-producing (LBP) phenotype. Contrary to the prevailing view that robust biofilm formation promotes persistence, LBP strains displayed enhanced stress tolerance, increased cell wall masking, and reduced immune recognition. These traits conferred resistance to neutrophil and macrophage killing and enhanced survival in immune cell-rich organs during systemic infection. Genome-wide transcriptomic profiling revealed extensive metabolic and regulatory rewiring in LBP strains. Whole-genome sequencing (WGS) of a global isolate collection further demonstrated that the LBP phenotype has emerged independently multiple times, supporting convergent evolution under host selection. Functional genomic analyses suggest that biofilm attenuation arises through multigenic changes, and disruption of key biofilm-associated transcriptional regulators enhanced fitness during immune interactions. Together, our findings overturn the assumption that robust biofilm formation drives outbreak persistence and instead identify biofilm attenuation as an adaptive tradeoff that promotes immune evasion and long-term survival. These results redefine our understanding of C. parapsilosis adaptation during healthcare-associated outbreaks and shift attention toward host-driven evolutionary processes than environmental persistence alone.

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