Identification and pathogenesis of a biofilm-forming, facultatively anaerobic Gram-positive rod

Abstract

Although sucrose-dependent plaque formation by oral streptococci in the oral cavity has been thoroughly studied, little is known about how the biofilm-forming capacity of sucrose-independent oral bacteria impacts their pathogenesis. We found a viscous material-producing, facultatively Gram-positive anaerobic rod in a stock culture collection that was isolated from an oral abscess. The aim of this study was to identify this strain (designated as K20), to determine its ability to form biofilms, and to clarify its potential for pathogenesis.
     Strain K20 was identified as Actinomyces viscosus based upon 16S rRNA sequencing. Scanning electron microscopy revealed that strain K20 had dense mesh-like structures on the cell surface, which is typical of biofilm-forming bacteria. Moreover, it was attached to abiotic material and stained with Calcofluor, a polysaccharide-binding dye, suggesting that it produces exopolysaccharide and has the potential to form a biofilm. Additionally, strain K20 induced persistent abscesses in mice at a concentration of 10^7-8 cells, as did exopolysaccharide-producing Prevotella intermedia/nigrescens. In conclusion, the ability of this Actinomyces viscosus strain to form a biofilm may contribute to its pathogenic potential to induce abscesses.