Streptococcus mutans Esterase Activity Increases During Biofilm Verses Planktonic Growth

Objectives: To compare esterase activity of Streptococcus mutans growing as a biofilm and as planktonic cells.
Methods: S. mutans UA159 was cultured in 96-well plates in a semi-defined medium containing sucrose as a carbon source for 48hrs at 37°C and 5% CO₂. Planktonic cells from 4-wells were combined in a plastic microcentrifuge tube then the biofilms were washed 3-times with phosphate-buffered-saline (PBS). Esterase buffer, containing the esterase substrate p-nitrophenyl butyrate, was added to biofilm wells. Planktonic cells were pelleted by centrifugation then re suspended in esterase buffer. Enzyme activity was monitored at 405 nm after samples had been incubated for 10hrs at 37°C. Planktonic cells and biofilm cells, from 4 other wells, were used to determine colony-forming-units (CFU’s). Biofilm cells were scraped from the surface, suspended in 1ml of PBS, passed 10-times through a 28G needle syringe, diluted and plated on Todd-Hewitt agar. Planktonic cells were made to a volume of 1ml then processed identically to determine CFU’s.
Results: S. mutans UA159 cells growing as a biofilm produced 2.75-fold more esterase activity than the same number of cells growing planktonically.
Conclusions: On an equivalent CFU basis, S. mutans UA159 growing as a biofilm produce more enzyme activity against p-nitrophenyl butyrate than when growing planktonically. Others have determined that S. mutants esterase(s) may degrade dental resin composites and adhesives contributing to the causation of secondary caries.