Streptococcus mutans is a leading cariogenic pathogen of dental caries worldwide. Clinically, eliminating S. mutans from dental biofilms using antibiotics is not practical, because these agents indiscriminately kill other members of the resident flora, leading to ecological disruption and other negative clinical consequences. To develop target-specific antimicrobials, we evaluated several fusion peptides and identified a new peptide HP30 that showed a high selectivity for targeted killing of S. mutans.