Nisin-Producing Lactococcus lactis Decreases Biofilm Formation and Disrupts Preformed Biofilms

Objectives: Oral biofilms present complex microenvironments that contribute to multitudes of oral maladies, including caries, periodontitis and endodontic infections. Biofilms exhibit resistance to antibiotics and antimicrobials; however, recent work has shown treatment with probiotics can lead to decreased oral biofilm density. Though this research is promising, discovery of probiotic organisms falls well short of the medical community’s need for ways to eliminate pathogenic biofilms. The aim of this study is to see if nisin, a dynamic antimicrobial, and nisin-producing probiotic Lactococcus lactis, reduce oral biofilm biomass in vitro.
Methods: Salivary samples were collected from healthy individuals, pooled, and static biofilms were cultured at 37C using cell-free saliva (CFS) as culture media. Static biofilm formation was examined by adding cell-containing saliva to CFS, challenging the samples with varying concentrations of nisin and different cell densities of L. lactis at t=0. Additionally, 24h and 48h pre-formed biofilms were challenged with nisin and L. lactis. Biofilm biomass and DNA content were analyzed using gram-staining techniques and CyQUANT cell proliferation assays. Confocal microscopy was used to determine bacterial viability using BacLight LIVE/DEAD bacterial staining.
Results: Nisin significantly decreased biofilm formation at low concentrations (0.1-2ug/ml) in a dose dependent manner, yet did not decrease the total biomass of the 24h or 48h pre-formed biofilm at these same concentrations. Similarly, L. lactis significantly decreased biofilm formation in a CFU/mL dependent manner; however, it did significantly decrease 24h and 48h pre-formed biofilm biomass in a CFU/mL independent manner.
Conclusions: Though nisin was more effective at preventing biofilm formation than at decreasing the biomass of preformed biofilms at low concentrations, nisin-producing L. lactis was able to significantly decrease biofilm formation and disrupt biofilms. This work highlights the significant role Lactococcus lactis might have as a probiotic and its potential therapeutic use in the treatment of biofilm-associated oral diseases.