Pseudomonas aeruginosaincreases the susceptibility ofCandida albicansto amphotericin B in dual species biofilms

Abstract

AbstractBiofilms are the leading cause of nosocomial infections, and are hard to eradicate due to their inherent antimicrobial resistance.Candida albicansis the leading cause of nosocomial fungal infections, and is frequently co-isolated with the bacteriumPseudomonas aeruginosafrom biofilms in the Cystic Fibrosis lung and severe burn wounds. The presence ofC. albicansin multi-species biofilms is associated with enhanced antibacterial resistance, which is largely mediated through fungal extracellular carbohydrates sequestering the antibiotics. However, significantly less is known regarding the impact of polymicrobial biofilms on antifungal resistance. Here we show that, in dual species biofilms,P. aeruginosaenhances the sensitivity ofC. albicansto amphotericin B, an effect that was biofilm specific. Transcriptional analysis combined with gene ontology enrichment analysis identified severalC. albicansprocesses associated with oxidative stress to be differentially regulated in dual species biofilms, suggesting thatP. aeruginosaexerts oxidative stress onC. albicans, likely through the actions of secreted phenazines. However, the mitochondrial superoxide dismutaseSOD2was significantly downregulated in the presence ofP. aeruginosa.Monospecies biofilms of thesod2Δ mutant were more susceptible to amphotericin B, and the susceptibility of these biofilms was further enhanced by the addition of exogenous phenazines. Therefore, we propose that in dual species biofilms,P. aeruginosasimultaneously induces mitochondrial oxidative stress, whilst downregulating key detoxification enzymes, which preventC. albicansmounting an appropriate oxidative stress response to amphotericin B, leading to fungal cell death. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.ImportanceBiofilms are aggregates of cells encased in an extracellular matrix, and are responsible for the majority of infections in hospitals. The Gram-negative bacteriumPseudomonas aeruginosa, and the fungal pathogenCandida albicansare frequently co-isolated from biofilms in the Cystic Fibrosis lung, and in burn wounds. Here we show that in these biofilms,P. aeruginosasecreted phenazines induce mitochondrial reactive oxygen species stress, which enhances the sensitivity ofC. albicansto the antifungal amphotericin B. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.