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

Susceptibility of bacteria to antimicrobial agents is strongly reduced by t he formation of complex biofilms. We investigated whether synthetic histati n analogs with broad-spectrum antibacterial activity in vitro were also act ive against these complex mixtures of bacteria, as present in saliva and pl aque. In a simplified model system for dental plaque, hydroxyapatite discs were placed in a continuous culture system comprised of Streptococcus mutan s, S. sanguis, S. salivarius, Actinomyces naeslundii, Veillonella parvula, Fusobacterium nucleatum, and Prevotella intermedia. Ex situ treatment of th e biofilms formed on these discs with 100 mu g/mL of peptide dhvar4 signifi cantly reduced facultative anaerobic, total anaerobic, and obligate anaerob ic Gram-negative counts with 0.8, 0.5, and 0.5 log units, respectively. El vivo treatment of salivary bacteria gave reductions of 0.4, 0.7, and 1.5 lo g 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 a nd plaque samples, obligate anaerobic Gram-negative bacteria were significa ntly more susceptible to dhvar4 than facultatively anaerobic or anaerobic b acteria 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.