Protein Expression in Streptococcus mutans virulent and avirulent isolates

Objectives: The Streptococcus mutans (S.mutans) is generally considered to be the principal aetiological agent of dental caries. Clinical isolates of S.mutans show enormous variations in their protein expression. To screen out novel proteins specific to virulent strain proteomic comparison was applied. Methods: The clinical isolates were isolated from dental plaque samples from twenty caries-active subjects [DMFS (the number of decayed, missing, and filled surfaces) =10.0±3.01]. Six to eight isolates per subject were bio-, sero-, and AP-PCR typed. One strain representative of each genotype identified was examined for its cariogenic ability. The main virulence traits associated with cariogenicity of S. mutans include adhesion, acidogenicity, aciduricity, and extracellular polysaccharide synthesis. The proteins were extracted from the S. mutans highly cariogenic isolate and low cariogenic isolate and separated by two-dimensional gel electrophoresis followed by autoradiography and image analysis. Proteins with high-expression in virulent strain were excised and digested with trypsin by using an in-gel protocol. Tryptic digests were analyzed using matrix-assisted laser desorption ionization mass spectrometry to generate peptide mass fingerprints, and these were used to assign putative functions according to their homology with the translated sequences in the S. mutans genomic database. Results: A couple of S. mutans virulent strain 9-1 and avirulent strain 9-2 which all colonized in the same oral cavity was screened according to the main virulence traits. Proteomic comparison of two-dimensional gel electrophoresis profiles from the two S.mutans isolates was carried out. Eleven individual proteins exhibited specific expression to virulent strain which included genes involved in repairing stress damage, biochemical metabolism, adhesion, signal transduction, protein synthesis. Conclusion: The identification of proteins differentially expressed provides new information regarding the virulence and has identified new target genes for mutagenesis studies to further assess their physiological significance.