The bactericidal effects of human salivary histatin 5 on Porphyromonas gingivalis

Abstract

Previous studies with oral bacterial and fungal pathogens have demonstrated that histatin 5 is the most potent histatin, a group of histidine-rich salivary proteins present in parotid secretions with respect to antibacterial and antifungal effects. The present study was aimed at investigating the ef feet of human parotid salivary histatin? on the viability of the periodontal pathogen Porphyromonas gingivalis (P.g.). Experimentally, the viability of P.g. was studied after exposure to incremental doses of histatin 5 at different pH values (pH 5.0, 6.0, 7.0 and 8.0). Histatin 5 from human parotid secretion was isolated by Bio-Gel P-2 chromatography and reverse-phase high-performance liquid chromatography. The purity of histatin 5 was determined by polyacrylamide gel electrophoresis and amino acid analysis. Following incubation, bacteria were washed by successive centrifugation, plated onto enriched Trypticase soy agar, and incubated anaerobically at 37 °C. After 48 hr, colony forming units were counted. Linear regression analysis was used to evaluate doseresponse. The most perfect fit for a linear regression was found for pH 6.0 and 7.0 (p<0.02) with corresponding LD50 values of 0.19 mM and 0.51 mM, respectively. The data indicate that histatin 5 is bactericidal on P.gingivalis and this effect is modulated by the pH values of the bacterial environment in contact with histatin 5. The relative bactericidal potency was higher at pH 5.0 and decreased as pH increased.