Effect of conditioning films on oral microbial biofilm development

The aim of the study was to evaluate the influence of either host-or microbially-derived conditioning films on biofilm formation. Hydroxyapatite (HA) discs were pre-treated either with parotid saliva (2 h incubation), or with crude glucosyltransferase (GTF) preparations (3 h incubation in culture supernatant of Streptococcus sanguis or Streptococcus mutans, with sucrose), and then immersed in a mixed culture of oral bacteria grown in continuous culture. Discs were removed from the culture after 4 d, and biofilms were detached with a sterile probe. Numbers of bacteria in the biofilms on pre-treated discs were determined by differential viable counts, and results were compared with untreated discs. Pre-treatment with GTF from S. sanguis or S. mutans increased the total CFU on discs immersed in the culture for 4 d by 29% and 95% respectively, although these differences were not statistically significant. The two GTF preparations had differential effects, with the S. sanguis preparation increasing the numbers of S. sanguis, Streptococcus or oralis and S. mutans, whereas the S. mutans preparation increased numbers of S. sanguis, Veillonella dispar, Fusobacterium nucleatum, S. mutans and Porphyromonas gingivalis. It was also notable that each GTF preparation markedly enhanced colonisation of the species from which it was derived. Parotid saliva treatment produced no differences in biofilm counts after 4 d; in a further experiment, parotid saliva-treated discs immersed in the culture for only Ih showed a highly significant increase (p < 0.002) of 2.6-fold in CFU compared with untreated controls, with the greatest effect seen on counts of F. nucleatum. Bacterial products can form a conditioning film, and may have as important a role in the degree and pattern of oral biofilm development as do host molecules.