Recalcitrance of Streptococcus mutans biofilms towards detergent-stimulated detachment

The biofilm mode of growth protects the plaque microorganisms against environmental attacks, such as from antimicrobials or detergents. Detergents have a demonstrated ability to detach initially adhering bacteria from enamel surfaces, but the ability of detergent components to detach plaque bacteria is not always obvious from in vivo experiments and reports on their clinical efficacy are inconsistent. It is likely that antimicrobials or detergents are unable to penetrate the plaque and reach the bacteria that actually link the plaque mass to the substratum surface. Attenuated total reflectance/Fourier transform infrared spectroscopy was used to measure the transport of sodium lauryl sulphate (SLS) through Streptococcus mutans HG 985 biofilms. The transport of SLS to the base of the S. mutans biofilms was not hindered, while moreover an accumulation of SLS near the base of the biofilms was found, suggesting that SLS was adsorbed to biofilm components. X-ray photoelectron spectroscopy confirmed the ability of S. mutans, grown on sucrose supplemented medium, to adsorb SLS, and simultaneously indicated that exposure of cells to SLS might lead to a loss of surface proteins. Furthermore, experiments in a parallel-plate flow chamber demonstrated that initially adhering S. mutans HG 985 could be stimulated to detach by SLS, but that, depending on the growth stage of the biofilm, only maximally 27% of biofilm bacteria could be stimulated to detach by a 4% (w/v) SLS solution.