Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen frequently isolated from chronic infections of the cystic fibrosis lung and burn wounds, and is a major cause of antimicrobial-resistant nosocomial infections. P. aeruginosa is frequently co-isolated with the opportunistic fungal pathogen Candida albicans, with the presence of C. albicans in dual-species biofilms promoting tolerance to meropenem. Here, transcription profiling of mature P. aeruginosa single- or dual-species biofilms was carried out to understand the molecular mechanism(s) by which C. albicans enhances meropenem tolerance. C. albicans appeared to have a mild impact on the transcriptome of P. aeruginosa mature biofilms, with most differentially regulated genes being involved in interkingdom interactions (i.e. quorum sensing and phenazine biosynthesis). The addition of meropenem to mature single- or dual-species biofilms resulted in a significant bacterial transcriptional response, including the induction of the beta-lactamase, ampC, genes involved in biofilm formation. P. aeruginosa elicited a similar transcriptional response to meropenem in the presence of C. albicans, but C. albicans promoted the expression of additional efflux pumps, which could play roles in increasing the tolerance of P. aeruginosa to meropenem.
Keywords: Candida albicans; Pseudomonas aeruginosa; dual-species biofilms; meropenem; transcriptional profiling.