Fungal Biofilms and Polymicrobial Diseases

Abstract

Biofilm formation is an important virulence factor for pathogenic fungi. Both yeasts and filamentous fungi can adhere to biotic and abiotic surfaces, developing into highly organized communities that are resistant to antimicrobials and environmental conditions. In recent years, new genera of fungi have been correlated with biofilm formation. However, Candida biofilms remain the most widely studied from the morphological and molecular perspectives. Biofilms formed by yeast and filamentous fungi present differences, and studies of polymicrobial communities have become increasingly important. A key feature of resistance is the extracellular matrix, which covers and protects biofilm cells from the surrounding environment. Furthermore, to achieve cell-cell communication, microorganisms secrete quorum-sensing molecules that control their biological activities and behaviors and play a role in fungal resistance and pathogenicity. Several in vitro techniques have been developed to study fungal biofilms, from colorimetric methods to omics approaches that aim to identify new therapeutic strategies by developing new compounds to combat these microbial communities as well as new diagnostic tools to identify these complex formations in vivo. In this review, recent advances related to pathogenic fungal biofilms are addressed.

Keywords: drug combination; drug discovery; fungal biofilms; in vitro techniques; in vivo techniques; omics approaches; polymicrobial biofilms; resistance.

Figure 1

Models of biofilm development in filamentous fungi (a) and C. albicans (b). The stages of development are similar, although the morphology and number of stages are different. In the first model (a), six stages were proposed by Harding et al. [12]: (I) adsorption, (II) active attachment, (III) first formation of microcolony through germination and/or monolayer development, (IV) mycelial development, (V) biofilm maturation, and (VI) dispersion of conidia and/or arthroconidia. The second model corresponds to classical C. albicans biofilm development (b) which includes five stages, such as in bacteria: (i) adsorption, (ii) adhesion, (iii) microcolony formation, (iv) mature biofilm, and (v) dispersion. Modified from Harding et al. [12]. T. rubrum mature biofilm Costa-Orlandi et al. [7]; Pires et al. [18].

Figure 2

Scheme of the mechanisms and factors that promote fungal biofilm resistance, which are common to several fungi. Adapted from Ramage et al. [189].