Selective Inhibition of Streptococci Biofilm Growth via a Hydroxylated Azobenzene Coating

Abstract

Strategies to engineer surfaces that can enable the selective inhibition of bacterial pathogens while preserving beneficial microbes can serve as tools to precisely edit the microbiome. In the oral microbiome, this selectivity is crucial in preventing the proliferation of cariogenic species such as Streptococcus mutans (S. mutans). In this communication, coatings consisting of a covalently tethered hydroxylated azobenzene (OH-AAZO) on glassy acrylic resins are studied and characterized for their ability to selectively prevent the attachment and growth of oral Streptococci biofilms. The coating applied on the surface of glassy resins inhibits the growth and proliferation of cariogenic S. mutans and S. oralis biofilms while A. actinomycetemcomitans, S. aureus, and E. coli biofilms are unaffected by the coating . The antibacterial effect is characterized as a function of both the OH-AAZO concentration in the coatings (≥50 mg mL^-1) and the structure of the monomer in the coating. Preliminary mechanistic results suggest that the targeted bactericidal effect against Streptococci species is caused by a disruption of membrane ion potential, inducing cell death.

Keywords: antibacterial coatings; biofilms; biomaterials; polymers.

Figure 1.

a) S. mutans biofilms growth as a function of OH-AAZO concentration within the coating formulation (all n ≥ 3). Digital microscope images (630X magnification) of S. mutans bacteria growing on both b) uncoated and c) coated substrates.

Figure 2.

a) Biofilms grown on OH-AAZO coatings and the observed selective inhibitory effect on Streptococcus biofilms. Bacterial biofilms of b) S. oralis indicate selective inhibition of Streptococci biofilms on OH-AAZO coated-substrates, whereas bacterial biofilms of c) E. coli, d) S. aureus, and e) A. actinomycetemcomitans were not inhibited. All biofilms grown on coated substrates were compared to those grown on uncoated substrates.

Figure 3.

a) Coatings generated from monomers with different functional groups to study the inhibitory effect. CFU values listed are from biofilms growing on the substrate. S. mutans biofilm growth quantified at 24 h indicates that the antibacterial properties are specific to the OH-AAZO coatings. b) Kill curve of S. mutans in media containing OH-AAZO coated substrates in comparison with an uncoated substrate over time. c) The membrane potential assay results at different concentrations of coated OH-AAZO substrates. Raw data was corrected against the fluorescence values of the corresponding substrate (all raw values n = 3).