The effects of histatin-derived basic antimicrobial peptides on oral biofilms

Susceptibility of bacteria to antimicrobial agents is strongly reduced by the formation of complex biofilms. We investigated whether synthetic histatin analogs with broad-spectrum antibacterial activity in vitro were also active against these complex mixtures of bacteria, as present in saliva and plaque. In a simplified model system for dental plaque, hydroxyapatite discs were placed in a continuous culture system comprised of Streptococcus mutans, S. sanguis, S. salivarius, Actinomyces naeslundii, Veillonella parvula, Fusobacterium nucleatum, and Prevotella intermedia. Ex situ treatment of the biofilms formed on these discs with 100 microg/mL of peptide dhvar4 significantly reduced facultative anaerobic, total anaerobic, and obligate anaerobic Gram-negative counts with 0.8, 0.5, and 0.5 log units, respectively. Ex vivo treatment of salivary bacteria gave reductions of 0.4, 0.7, and 1.5 log units, respectively. For ex vivo treatment of plaque bacteria, reductions of 0.4, 0.4, and 1.4 log units, respectively, were found. In both saliva and plaque samples, obligate anaerobic Gram-negative bacteria were significantly more susceptible to dhvar4 than facultatively anaerobic or anaerobic bacteria as a whole (p=0.013 and p=0.018, for salivary bacteria, and p=0.021 and p=0.020 for plaque bacteria, respectively). Although the oral bacteria are protected by biofilm formation, the synthetic histatin analog caused a significant reduction of viable counts in a model for oral biofilm as well as in isolated oral biofilms.