(1) Background: ( ) is the principal pathogen involved in the formation of dental caries. Other systemic diseases have also been associated with specific serotypes ( , , , and ). Silver nanoparticles (SNP) have been demonstrated to have good antibacterial effects against ; therefore, limited studies have evaluated the antimicrobial activity of biofunctionalized SNP on serotypes. The purpose of this work was to prepare and characterize coated SNP using two different organic components and to evaluate the antimicrobial activity of SNP in clinical isolates of strains and serotypes; (2) Methods: SNP with bovine serum albumin (BSA) or chitosan (CS) coatings were prepared and the physical, chemical and microbiological properties of SNP were evaluated; (3) Results: Both types of coated SNP showed antimicrobial activity against bacteria and serotypes. Better inhibition was associated with smaller particles and BSA coatings; however, no significant differences were found between the different serotypes, indicating a similar sensitivity to the coated SNP; (4) Conclusion: This study concludes that BSA and CS coated SNP had good antimicrobial activity against strains and the four serotypes, and this study suggest the widespread use of SNP as an antimicrobial agent for the inhibition of bacteria.