Background: Candida albicans (CA) biofilms develop enhanced resistance to most antifungal agents, but remain sensitive to caspofungin (CSP), which inhibits glucan synthase (GS). GS mutant strains are resistant to CSP when grown in the planktonic form. In this study, we determined whether: (a) the ability to form extracellular matrix (ECM)-rich biofilms is affected in GS mutants, and (b) whether the resistance profile of biofilms formed by these mutants is similar to that observed in planktonic cells. Methods: The ability of heterozygous (HT) and homozygous (HM) GS mutants to form biofilm on catheter discs was determined using our in vitro model and compared to the isogenic wild type (WT) strain. Total biofilm mass was determined by dry weight assay, and ECM formation was visualized with fluorescence microscopy (FM). antifungal susceptibility was determined by tetrazolium reduction assay (biofilms), or M27-A (for planktonic cells). Results: Biofilms formed by HT and HM strains did not differ significantly in their dry weights (%DW = 0.823 and 0.860, respectively), as compared to the WT strain (%DW 0.915, P-value >0.05). FM revealed similar polysaccharide rich ECM formation by both mutants as well as WT strain. Planktonically grown GS mutants were resistant against CSP compared to WT cells (MIC = 2 µg/ml and 0.125 µg/ml, respectively), while all strains were susceptible to voriconazole (VOR) and amphotericin B (AMB). When grown as biofilm, all 3 strains were resistant to VOR (MIC = 128 µg/ml) and AMB (MIC = 16 µg/ml). Although biofilms formed by WT remained susceptible to CSP (MIC = 0.125 µg/ml), those formed by the mutant strains were resistant to this drug (HT and HM MIC = 32 µg/ml and 64 µg/ml, respectively). Interestingly, the biofilms formed by mutants were 15 - 30 fold more resistant to CSP than planktonic cells. Conclusions: These studies indicate GS-independent mechanisms may occur in CA biofilm ECM formation and development of resistance against echinocandins.
Full conference title:
43rd Interscience Conference on Antimicrobial Agents
- ICAAC 43rd