Therapeutic implications of C. albicans-S. aureus mixed biofilm in a murine subcutaneous catheter model of polymicrobial infection

Abstract

Biofilm-associated polymicrobial infections tend to be challenging to treat. Candida albicans and Staphylococcus aureus are leading pathogens due to their ability to form biofilms on medical devices. However, the therapeutic implications of their interactions in a host is largely unexplored. In this study, we used a mouse subcutaneous catheter model for in vivo-grown polymicrobial biofilms to validate our in vitro findings on C. albicans-mediated enhanced S. aureus tolerance to vancomycin in vivo. Comparative assessment of S. aureus recovery from catheters with single-or mixed-species infection demonstrated failure of vancomycin against S. aureus in mice with coinfected catheters. To provide some mechanistic insights, RNA-seq analysis was performed on catheter biofilms to delineate transcriptional modulations during polymicrobial infections. C. albicans induced the activation of the S. aureus biofilm formation network via down-regulation of the lrg operon, repressor of autolysis, and up-regulation of the ica operon and production of polysaccharide intercellular adhesin (PIA), indicating an increase in eDNA production, and extracellular polysaccharide matrix, respectively. Interestingly, virulence factors important for disseminated infections, and superantigen-like proteins were down-regulated during mixed-species infection, whereas capsular polysaccharide genes were up-regulated, signifying a strategy favoring survival, persistence and host immune evasion. In vitro follow-up experiments using DNA enzymatic digestion, lrg operon mutant strains, and confocal scanning microscopy confirmed the role of C. albicans-mediated enhanced eDNA production in mixed-biofilms on S. aureus tolerance to vancomycin. Combined, these findings provide mechanistic insights into the therapeutic implications of interspecies interactions, underscoring the need for novel strategies to overcome limitations of current therapies.

Presence of Candida tropicalis on Staphylococcus epidermidis Biofilms Facilitated Biofilm Production and Candida Dissemination: An Impact of Fungi on Bacterial Biofilms

“…is common (Bouza et al, 2013;Kim et al, 2013). Additionally, the combination of both organisms might produce some microbial benefits, as the diffusion of antimicrobial agents through polymicrobial biofilms of Candida and S. epidermidis is slower than the biofilms from each organism resulting an increased drug resistance (Adam et al, 2002;Hall and Mah, 2017;Bernard et al, 2020;Vila et al, 2021). Notably, the antibiotic diffusion through C. tropicalis biofilms is the slowest among all Candida species, indicating a possibility of the unique biofilm structures (AI-Fattani and Douglas, 2006).…”

Spatially structured yeast communities: Understanding structure formation and regulation with omics tools

“…The second option is in vivo biofilms formed in the host - e.g. mouse and rat catheter models or prosthesis models [48] , [49] , [50] . Various techniques have been used to determine the structure and activity of in vitro biofilms, including microscopic analysis of cell viability, methods to determine biofilm biomass (including the effect of antifungal drugs), often in combination with analysis of specific mutants [15] .…”

“…C. albicans often forms biofilms in host organisms, along with bacteria such as Klebsiella pneumoniae , Staphylococcus aureus , Streptococcus gordonii , Streptococcus mutans and others, and the coexistence of both organisms often results in the formation of a stronger and more resistant biofilm, compared to single species biofilms [15] , [67] . Omics (especially transcriptomics and proteomics) play an irreplaceable role in revealing the mutual metabolic relationships of microbial species in biofilm and identifying their specific markers ( Table 1 , Table S1) [50] . For example, a recent transcriptomic study revealed the effect of C. albicans on another pathogen, S. aureus , in a mixed-species biofilm formed on a catheter [50] .…”

“…Omics (especially transcriptomics and proteomics) play an irreplaceable role in revealing the mutual metabolic relationships of microbial species in biofilm and identifying their specific markers ( Table 1 , Table S1) [50] . For example, a recent transcriptomic study revealed the effect of C. albicans on another pathogen, S. aureus , in a mixed-species biofilm formed on a catheter [50] . There, the presence of C. albicans stimulates the biofilm formation network in S. aureus by down-regulating the lrg operon, the autolysis repressor, and up-regulating the ica operon to produce intercellular adhesin PIA, which together leads to increased production of eDNA and ECM essential for bacterial biofilm formation and stability.…”

“…; only 3 master TFs (Bcr1p, Efg1p, Ndt80p) required for biofilms in all 4 species. whole [28] Mixed species biofilm C. albicans, S. mutans Transcriptomics Proteomics polystyrene/ UFTYE, 1% sucrose single × mixed species biofilms S. mutans provides sugars to C. albicans ; C. albicans lowers biofilm pH and helps S. mutans survive whole [68] Mixed species biofilm C. albicans, S. aureus Transcriptomics mouse catheter model single × mixed species biofilms C. albicans modulates transcription of S. aureus to increase eDNA and extracellular polysaccharides whole [50] …”