The metabolic trap: Candida parapsilosis inhibits Staphylococcus aureus biofilm maturation by disrupting pH homeostasis and inducing premature exodus.

Introduction. Hospital-acquired infections (HAIs) frequently manifest as device-related biofilms that exhibit enhanced tolerance to conventional therapies contributing to antimicrobial resistance. Polymicrobial biofilms involving Candida and Staphylococcus species are a major cause of persistent nosocomial infections. However, while the synergism between Candida albicans and Staphylococcus aureus is well-characterized, the interactions involving non-albicans Candida remain poorly understood.Hypothesis/Gap Statement. The specific interactions between Candida parapsilosis and S. aureus were entirely unknown, although it was broadly assumed they would be synergistic in nature, mirroring known Candida-Staphylococcus models.Aim. This study investigated the interspecies dynamics between C. parapsilosis and S. aureus within a mixed biofilm context.Methodology. C. parapsilosis secretome fractions were isolated and screened against methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus strains. Their effects on biofilm formation, primary attachment, planktonic growth and eradication were evaluated under varying glucose concentrations, followed by transcriptomic analysis of treated staphylococcal cells.Results. We report the discovery of a small (<10 kDa), heat-stable fungal-secreted factor that significantly inhibits the maturation of MSSA biofilms and disperses preformed biomass without affecting primary attachment or planktonic growth, although MRSA strains remained recalcitrant. This antagonism is strictly glucose-dependent; the inhibitory effect is potent in 0.2% glucose but is abolished in both 0.5 and 1.0% glucose. Transcriptome analysis revealed that the fungal secretome triggers a pleiotropic 'Metabolic Trap' in S. aureus, characterized by the downregulation of the glycolytic pathway (e.g. tpiA, gapA) and a failure to induce critical-acid-tolerance systems, including the arginine deiminase and urease operons. This metabolic reprogramming maintains a near-neutral local pH (5.8-6), which in turn provides an optimal environment for the observed upregulation of staphylococcal nuclease (nuc) ultimately degrading the extracellular matrix and preventing the development of a mature biofilm architecture.Conclusion. We propose that the C. parapsilosis secretome effectively tricks S. aureus into a premature exodus phase, where nuclease-mediated matrix degradation prevents the establishment of a stable biofilm architecture. These findings underscore the highly species-specific nature of fungal-bacterial interactions and identify a specific metabolic vulnerability in S. aureus that may be exploited to develop novel anti-biofilm strategies against polymicrobial communities.