Growth kinetics of candida biofilm on medical polymers: a long-term in vitro study

Objectives/hypothesis: Recent in vitro models simulating biofilm formation on medical polymers are restricted to only short-term observation periods of 2 hours to 12 days.

Study design: The goal of this study was to develop an in vitro model to generate a long-term polymicrobial biofilm with Candida albicans (C albicans) and Streptococcus salivarius (S salivarius) on thermoplastic medical grade silicone (TPS) and polyurethane (TPU) and continuous documentation of growth kinetics.

Methods: Test platelets of TPS and TPU were incubated in well plates in RPMI agar at 37°C. Both microbial specimen were isolated from explanted voice prostheses and added every second day for 28 days. Afterward, only the nutrition solution has been changed regularly. Biofilm kinetics were monitored using a specially designed image analysis software to calculate the percentual surface covering of each platelet. Biofilm architecture was investigated by scanning electron microscopy (SEM). Microbial infiltration was examined by crystal violet staining and thin section microscopy.

Results: On both materials tested, a cover of living candida biofilm could be generated over 140 days. Colonization was permanent with at least 10% surface coverage. Initially, both materials showed coverage of up to 80% followed by biofilm detachment, which could be reduced by adding planktonic microbes. SEM confirmed three-dimensional biofilm architecture with dimorphic candida growth. Microbial material infiltration of nonhypheal types was proved in 2 TPU platelets, but not in TPS.

Conclusions: The in vitro model presented in this study mimics in vivo events of biofilm formation on medical polymers with continuous monitoring of living biofilm kinetics.