Differential Effects of Amylase-binding protein A (AbpA) and B (AbpB) in Colonization of Teeth by S. gordonii.

Objectives: We sought to study the role of two amylase-binding proteins on the surface of Streptococcus gordonii in the oral colonization of the rat. Methods: Mutants of S. gordonii defective either in amylase-binding protein A (AbpA-) or amylase-binding protein B (AbpB-) were studied as to their oral colonization of specific pathogen free Osborne-Mendel rats. The rats ate either diet 2000, which contains 56% confectioner’s sugar (97% sucrose/3% cornstarch), or diet 2000CS, which contains 56% cornstarch. Inoculants were recovered unambiguously by virtue of their antibiotic resistance markers from swabs of the teeth and from sonified molar teeth at the time of sacrifice, using appropriate agar media. Results: Nine experiments demonstrated that abpA- mutants (termed FAS4ST and ChallisST) often colonized rats’ teeth better than their respective wild types (FAS4S and ChallisS). This was detected even though the wild types generally colonized very well (20-70% of total recoverable flora in various experiments). A second amylase-binding protein has been identified (AbpB). Knockout of abpB from ChallisS (strain ChallisSE) resulted in virtually complete loss of colonization ability, while knockout of abpA (ChallisST) again resulted in its superior colonization by comparison to wild type ChallisS. These phenomena were seen especially clearly when rats were fed the cornstarch diet, but the effects of the two amylase-binding determinants were still statistically evident when fed the high sucrose diet (with low cornstarch), which enables colonization due to other mechanisms as well. Conclusions: At least two amylase-binding proteins of S. gordonii affect its colonization of teeth in the rat. AbpB is required for S. gordonii colonization, while AbpA is associated usually with a net ecological decline in colonization of the teeth and persistence in the mouth. Supported by NIH DE-09838.