The study looked at how different mouth bacteria react to the natural antimicrobial peptide LL‑37 and to white‑blood‑cell eating. Some bad bacteria that cause gum disease are tougher against LL‑37 and also avoid being eaten by immune cells, which may help them cause disease.

The aim of this study was to compare the susceptibility of nonperiodontopathic and periodontopathic bacteria to major defense mechanisms for bacterial clearance in gingival sulcus. Twenty strains of 13 oral bacterial species were studied for their susceptibility to phagocytosis by human neutrophils and to the antimicrobial peptides LL-37 and human beta defensin-3. The minimum inhibitory concentrations of LL-37 and human beta defensin-3 were determined by a liquid dilution assay, and susceptibility to phagocytosis was examined by a flow cytometric phagocytosis assay. The minimum inhibitory concentrations of LL-37 and human beta defensin-3 varied greatly, depending on the strain and species. Although a significant difference between the non- and periodontopathic groups was not observed, the red-complex bacteria were more resistant to LL-37 than the others (p=0.004). The susceptibility of oral bacteria to phagocytosis was quite variable, depending on the species but not on the strains. The periodontopathic bacteria, especially Actinobacillus actinomycetemcomitans and the red-complex triad, were more resistant to phagocytosis than were the nonperiodontopathic bacteria (p=0.0003). In addition, bacteria resistant both to antimicrobial peptides and to phagocytosis were more common in the periodontopathic group. Our results indicate that immune evasion may contribute to the pathogenicity of some periodontopathic bacteria.