[Antibacterial activity of histidine-rich polypeptides in human parotid saliva]

Two ultrasensitive antibacterial assays were applied to determine the antibacterial activity of histidine-rich polypeptides (HRPs) in human parotid saliva. The results not only confirmed the potent antibacterial activity of HRPs against Streptococcus mutans MT6R, but also showed for the first time that HRPs were effectively antibacterial to Staphylococcus aureus ATCC 25923, Escherichia coli ML-35p and Pseudomonas aeruginosa ATCC 27853. Among HRPs, HRP3, HRP5 and HRP6 were the major antibacterial components which were active against S. mutans, S. aureus, E. coli and P. aeruginosa, whereas HRP1 was only effective against E. coli. S. sanguis was resistant to the action of HRPs. These results suggest that HRPs are actually a family of endogenous antibiotic peptides with broad antimicrobial spectrum including fungi, Gram-positive and Gram-negative bacteria and may play an important role in the prevention of various infection diseases in the oral cavity as well as in the resistance to caries.