Interface of Candida albicans Biofilm Matrix-Associated Drug Resistance and Cell Wall Integrity Regulation

Abstract

Candida albicans frequently infects medical devices by growing as a biofilm, i.e., a community of adherent organisms entrenched in an extracellular matrix. During biofilm growth, Candida spp. acquire the ability to resist high concentrations of antifungal drugs. One recently recognized biofilm resistance mechanism involves drug sequestration by matrix ␤-1,3 glucan. Using a candidate gene approach, we investigated potential C. albicans ␤-1,3-glucan regulators, based on their homology to Saccharomyces cerevisiae, including SMI1 and protein kinase C (PKC) pathway components. We identified a role for the SMI1 in biofilm matrix glucan production and development of the associated drug resistance phenotype. This pathway appears to act through transcription factor Rlmp and glucan synthase Fks1p. The phenotypes of these mutant biofilms mimicked those of the smi1⌬/smi1⌬ biofilm, and overexpression of FKS1 in the smi1⌬/smi1⌬ mutant restored the biofilm resistant phenotype. However, control of this pathway is distinct from that of the upstream PKC pathway because the pkc1⌬/pkc1⌬, bck1⌬/bck1⌬, mkk2⌬/mkk2⌬, and mkc1⌬/mkc1⌬ biofilms retained the resistant phenotype of the parent strain. In addition, resistance to cell-perturbing agents and gene expression data do not support a significant role for the cell wall integrity pathway during the biofilm formation. Here we show that Smi1p functions in conjunction with Rlm1p and Fks1p to produce drug-sequestering biofilm ␤-glucan. Our work provides new insight into how the C. albicans biofilm matrix production and drug resistance pathways intersect with the planktonic cell wall integrity pathway. This novel connection helps explain how pathogens in a multicellular biofilm community are protected from anti-infective therapy.

Candida species: current epidemiology, pathogenicity, biofilm formation, natural antifungal products and new therapeutic options

“…The formation of biofilms causes clinical problems of concern because they increase resistance to antifungal therapies, and the mechanism of biofilm resistance to antimicrobial agents is not fully known. One hypothesis for this resistance is the presence of the matrix, which restricts the penetration of drugs by formation of a diffusion barrier (Nett et al, 2011); hence, only the most superficial layers are in contact with lethal doses of antibiotics. Planktonic cells generally rely on irreversible genetic changes to maintain a resistant phenotype, whereas biofilms are able to persist due to their physical presence and the density of the population, which provides an almost inducible resistant phenotype irrespective of defined genetic alterations (Ramage et al, 2012).…”

Plasticity of Candida albicans Biofilms

“…CV targets primarily mucopolysaccharides and amyloids (229), which may vary dramatically as a result of differences in matrix deposition. In an excellent analysis of the parameters that can affect XTT reduction methods for antifungal susceptibility studies, Nett et al (230) provided a list of problems and possible reasons for those problems. They also provided methods for optimization.…”

Clinical Implications of Oral Candidiasis: Host Tissue Damage and Disseminated Bacterial Disease

“…In fact, the majority of C. albicans infections are associated with its ability to form biofilms where adhesion of yeast cells to the substrate is followed by proliferation and hypha formation resulting in a network of cells embedded in extracellular polymeric matrix (21)(22)(23). In the oral cavity, C. albicans coexists and forms tight associations with various commensal bacterial species forming complex mucosal biofilms, a phenomenon known to play an important factor in C. albicans colonization (2,5,10,11,(24)(25)(26).…”