In vitrosusceptibility of theStreptococcus millerigroup to antimicrobial peptides

Abstract

To determine the susceptibility of strains of the Streptococcus milleri group (SMG) to commercially available antimicrobial peptides. Thirty strains of SMG from a range of sources were assessed for their susceptibility to 10 antimicrobial peptides of either human, animal or insect origin, using a double layer diffusion assay. The majority of the test strains were sensitive to the amidated peptides, mastoparan (100%; n = 30), magainin 2 amide (95%; n = 21) and indolicin (91%; n = 23). Some strains were susceptible to cecropin B (30%; n = 30) and histatin (10%; n = 30), whilst no activity was observed for the defensins HNP-1 and HNP-2, histatin 8, cecropin P1 and magainin 2. The majority of strains were resistant to the human derived peptides. The ability to resist such peptides may be a factor in the colonisation of the oral cavity and the survival and initiation of infection in the pulp and root canal environment. Interestingly, the present study indicated that amidated and alpha helical peptides exhibit antimicrobial activity against SMG. Structural modification of these peptides may allow a targeted approach for the development of these substances as preventative or therapeutic agents.