title: Role of the ammonium group in the diffusion of quaternary ammonium compounds in Streptococcus mutans biofilms.
abstract: OBJECTIVE
  Cetylpyridinium chloride (CPC), a quaternary ammonium compound, was shown to interact irreversibly with Streptococcus mutans biofilms, leading to a slow diffusion compared with poly(ethylene glycol) (PEG) molecules of similar size. The objective of this work is to determine if the retardation of CPC diffusion and its strong binding to biofilms is caused by interactions between the ammonium group of CPC and the exopolysaccharide (EPS) matrix.
  
  
  METHODS
  First, we characterized the diffusion of two analogues of CPC in S. mutans biofilms: dodecylpyridinium chloride (DPC), carrying a shorter alkyl chain than CPC, and tetramethylene bispyridinium chloride (TMBPC), a compound carrying two positively charged ammonium groups. Second, we cultured biofilms with different densities of EPS and examined the impact of this density on the transport properties of CPC. The diffusion of these compounds was probed using infrared spectroscopy with attenuated total reflectance sampling.
  
  
  RESULTS
  The diffusion of CPC, DPC and TMBPC in S. mutans biofilm is slower than that of PEG10k. In addition, TMBPC and DPC, as PEG10k, could be readily washed out from the biofilms while CPC association was practically irreversible. The penetration of CPC through the EPS matrix was found to be not significantly affected by the increased EPS density, whereas the penetration of PEG with a molar mass of 10k was considerably reduced.
  
  
  CONCLUSIONS
  These results suggest that the interactions between the quaternary ammonium groups and the EPS matrices are not the prime contribution of the strong CPC binding, and the alkyl chain length plays a role in this association, likely through hydrophobic interactions.
authors.affiliation: Department of Chemistry, Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors.forename: Christophe
authors.initials: C
authors.lastname: Sandt
authors.forename: Jean
authors.initials: J
authors.lastname: Barbeau
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Gagnon
authors.forename: Michel
authors.initials: M
authors.lastname: Lafleur
mesh_terms: D018441:Biofilms; D002594:Cetylpyridinium / Q000737:chemistry / Q000378:metabolism*; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy; D011092:Polyethylene Glycols / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013295:Streptococcus mutans / Q000378:metabolism*
chemical_list: D011135:Polysaccharides, Bacterial; D000644:Quaternary Ammonium Compounds; C098632:exopolysaccharide, Streptococcus; D011092:Polyethylene Glycols; D002594:Cetylpyridinium