Introduction: Candida species are important commensal microorganisms mostly colonize vagina, GIT and the oral cavity. Biofilms are microbial communities of surface attached cells encased in a self-produced matrix of extracellular polymeric substance. Candida has been shown to easily form biofilms and these have been increasingly recognized as a major virulent attribute for this yeast.
Objectives: To develop in vitro model to assess yeast biofilms and, using 3 different initial concentrations, to compare the biofilm forming ability of different Candida species and strains.
Methods: 22 Candida species and strains were used in the study, 9 clinical isolates and 13 from American Type Culture Collection. Biofilms formed by growing the yeast in 96 microtiter well plates. Crystal violet (CV), XTT tetrazolium reduction and colony forming unit (CFU) assays were used to assess the formed biofilms. Further, two assays were developed, the automated cell counter (ACC) and NanoDrop, to assess biofilm biomass and for correlation to CFU.
Results: All species and strains assessed were shown to have higher biofilm growth at 10
7 initial concentration than 10
4 and 10
3 cell / ml. Automated cell counter and Nanodrop assays are well correlated with CFU and CV assays. Large variation was observed amongst different species and strains, however in general Candida albicans formed more active biofilm than non-albicans Candida.
Conclusions: Biofilm biomass and bioactivity is species and strain dependent. The growth of Candida in-vitro is directly proportional to the amount of yeast present at the initiation of biofilm growth. This study utilized three methods (ACC, CV and Nanodrop) for comparison of biofilm biomass and for correlation with number of colony forming units and found that all correlate well. Yeast biofilm bioactivity does not always positively correlate with the biofilm mass. Overall, isolates of Candida albicans generally produce more active biofilm than isolates from non-albicans Candida species.