Modulation of attachment of oral bacteria to surfaces by tea extracts and mathematical modeling of the physicochemical process of bacterial attachment
thesisposted on 28.02.2017 by Wang, Yi
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The effects of five tea extracts (green, oolong, black, pu-erh and chrysanthemum) on five oral bacterial strains (Streptococcus mutansATCC 25175, Streptococcus mutans ATCC 35668, Streptococcus salivarius ATCC 13419, Streptococcus mitis ATCC 49456 and Actinomyces naeslundii ATCC 51655) were investigated with respect to cell surface properties (hydrophobicity, charge and auto-aggregation), attachment to, detachment from and biofilm formation on three hard surfaces (glass, stainless steel and hydroxyapatite). The effects of the tea extracts on the attachment of the oral strains to cultured human gingival fibroblasts were also determined. The influences of saliva and sucrose on the cell surface properties, attachment and biofilm formation of the bacterial strains were examined. The mechanism of the inhibition of attachment and biofilm formation by tea was studied. The extended Derjaguin-Landau-Verwey-Overbeek(XDLVO) theory was used to calculate the energy of interactions in the attachment systems and to predict attachment. A new mathematical approach consisting of an empirical model and a probability distributionmodel was developed to study the predictability and stochasticity of bacterial attachment. The results indicated that the tea extracts and tea compounds could alter cell surface properties of the strains. Oolong tea extract was found to inhibit the attachment of all strains to the hard surface most effectively by 0.2 to 2.2 log CFU/cm2 while pu-erh tea extract was found to inhibit the biofilm formation by the Streptococcal strains on all surfaces most effectively by 0.5 to 2.6 log CFU/cm2. The mechanism of the inhibitory effects of oolong tea and pu-erh tea on the attachment and biofilm formation by Streptococcus mutans was found to be the coating of cell surfaces by tea components including flavonoids, tannins and indolic compounds. Pu-erh tea and chrysanthemum tea extracts were found to remarkably inhibit the attachment of the Streptococcal strains to cultured human gingival fibroblasts by up to 4 log CFU/well. Saliva as a suspending fluid was found to reduce the attachment of the Streptococcal strains to hydroxyapatite by 1.4 to 1.7 log CFU/cm2. Sucrose was found to affect cell surface properties and the attachment of the strains (either increase or decrease) and enhance biofilm formation by four strains on all surfaces by 0.4 to 1 log CFU/cm2. Positive correlations were found between cell surface hydrophobicity of the Streptococcal strains and their attachment to all surfaces with R2s ranging from 0.37 to 0.91. The XDLVO theory indicated that hydrogen bonding energy dominated the overall interaction energy in all cases. This suggests that the coating by tea components blocked the hydrogen bonding sites on the cell surfaces, which reduced cell surface hydrophobicity and in turn inhibited attachment. XDLVO failed to predict the experimental results of the attachment assays while the new modeling approach could however effectively predict in both deterministic and probabilistic ways. The empirical model (R2=0.814) revealed that hydrophobic interaction is the most important parameter in a bacterial attachment system and established a range for each cell/substratum properties within which the resultant attachment is stochastic and unpredictable.