Effects of extracellular DNA and DNA-binding protein on the development of a Streptococcus intermedius biofilm

Aims The aim of this study was to clarify the effects of homologous and heterologous extracellular DNAs (eDNAs) and histone-like DNA-binding protein (HLP) on Streptococcus intermedius biofilm development and rigidity. Methods and Results Formed biofilm mass was measured with 0 center dot 1% crystal violet staining method and observed with a scanning electron microscope. The localizations of eDNA and extracellular HLP (eHLP) in formed biofilm were detected by staining with 7-hydoxyl-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) and anti-HLP antibody without fixation, respectively. DNase I treatment (200U ml-1) markedly decreased biofilm formation and cell density in biofilms. Colocalization of eHLP and eDNA in biofilm was confirmed. The addition of eDNA (up to 1g ml-1) purified from Strep.intermedius, other Gram-positive bacteria, Gram-negative bacteria, or human KB cells into the Strep.intermedius culture increased the biofilm mass of all tested strains of Strep.intermedius, wild-type, HLP-downregulated strain and control strains. In contrast, the addition of eDNA (>1g ml-1) decreased the biofilm mass of all Strep.intermedius strains. Conclusions These findings demonstrated that eDNA and eHLP play crucial roles in biofilm development and its rigidity. Significance and Impact of the Study eDNA- and HLP-targeting strategies may be applicable to novel treatments for bacterial biofilm-related infectious diseases.