# Candida tropicalis culture supernatants modulate Pseudomonas aeruginosa antimicrobial resistance and biofilm formation

## TL;DR

This study explores how Candida tropicalis affects Pseudomonas aeruginosa in chronic wounds, influencing biofilm formation and antibiotic resistance.

## Contribution

The study reveals strain-specific microbial interactions and how metabolites modulate antimicrobial resistance and biofilm dynamics in polymicrobial infections.

## Key findings

- CT supernatants from high biofilm formers reduced PA biofilm and growth, while low biofilm CT enhanced PA biofilm formation.
- CT supernatants increased PA resistance to aminoglycosides and fluoroquinolones by upregulating aph(3’)-IIb and gyrA genes.
- PA supernatants sensitized CT to antifungals like amphotericin B and fluconazole.

## Abstract

Polymicrobial infections involving Pseudomonas aeruginosa (PA) and Candida tropicalis (CT) majorly contribute to persistent infections resulting in challenges to effectively treat chronic wounds, such as diabetic foot ulcers (DFUs). We investigated the interactions between PA and CT, especially on the role of microbial metabolites in modulating biofilm formation, growth dynamics, antimicrobial susceptibility, and gene expression in co-habitants. Using clinical isolates from DFUs, we examined the effects of microbial supernatants on biofilm formation, microbial growth, and resistance to antibiotics and antifungals. Additionally, we assessed the expression of resistance genes (aph(3’)-IIb and gyrA) in PA in response to treatment with cell-free CT supernatant. Our findings revealed strain-specific interactions between PA and CT. Supernatants from high biofilm forming CT significantly affected biofilm formation and growth in PA, while PA supernatants universally suppressed CT growth. Notably, low biofilm forming strain of PA exhibited enhanced biofilm formation and growth when treated with supernatant from low biofilm forming CT, suggesting a cooperative interaction. Antimicrobial susceptibility assays demonstrated that CT supernatants modulated resistance to aminoglycosides and fluoroquinolones in PA, with aph(3’)-IIb and gyrA gene expression being significantly upregulated. Conversely, PA supernatants sensitized CT to antifungals, particularly amphotericin B and fluconazole. The results underscore the importance of understanding interspecific interactions in polymicrobial infections. Our results highlight the complex interplay between PA and CT, driven by microbial metabolites that influence biofilm formation, growth, and antimicrobial resistance and provides fresh insights into the mechanisms underlying PA-CT interactions and their implications for chronic wound management.

The online version contains supplementary material available at 10.1038/s41598-025-31858-6.