Objectives: to identify the SAG-binding components on bacteria.
Methods: several Gram-positive bacteria (oral streptococci, Staphylococcus aureus and Lactobacillus casei) and Gram-negative bacteria (Escherichia coli, Salmonella typhimurium) were tested for SAG binding in fluid phase and adhesion assays. In addition, microplates were coated with lipopolysaccharide, lipoteichoic acid and peptidoglycan and tested for SAG binding.
Results: in general, Gram-positive bacteria bound SAG better than Gram-negative bacteria. Of the bacterial surface components tested peptidoglycan showed much better binding of SAG than lipopolysaccharide and lipoteichoic acid. This binding was inhibited in the presence of EDTA suggesting calcium-dependent binding. Trypsin treatment of peptidoglycan reduced binding of SAG, but treatment of peptidoglycan with lysozyme or periodic acid did not, suggesting the peptide moiety of peptidoglycan was recognized by SAG.
Conclusions: SAG recognizes peptidoglycan on the bacterial surface thus showing characteristics of pattern recognition receptors. This is in line with the finding that Gram-positive bacteria bind better than Gram-negative bacteria.This study was supported by the Netherlands Institute for Dental Sciences (IOT).