Selective effects of histidine-rich polypeptides on the aggregation and viability of Streptococcus mutans and Streptococcus sanguis

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Abstract
Enriched preparations of histidine-rich polypeptides (HRPs) and isolated HRP pairs (1-2, 3-4 and 5-6) degrade in the presence of fresh autologous whole saliva to a series of low-molecular-weight cationic peptides (HRPs 6a-c and 7). Analysis of the HRPs during degradation indicates that: HRP 1 is not the parent molecule of the HRPs; the HRP pairs do not convert to each other in a cascade-like sequence in saliva; and the HRPs can be separated into 2 groups consisting of HRPs 1-2 and 3-7. Preparations containing HRPs 1-7, 1-2, and 3-7 were obtained by fractionation and separation on Bio-Rex 70, and tested for aggregating and antibacterial effects against Streptococcus mutans BHT, S. mutans GS-5 and Streptococcus sanguis G9B. HRPs 1-2 had significant aggregating effects on all 3 strains but the other HRPs had little to no agglutinating ability. The HRPs did not inhibit the growth of S. sanguis, and HRPs 1-2 enhanced its growth. No growth enhancement by the HRPs was observed for the 2 S. mutans strains. However, significant bacterial inhibition of the S. mutans strains was noted after incubation with HRPs 3-7. The data suggest that the dissimilar effects of HRPs 1-2 and 3-7 may be of importance in the colonization and growth of S. mutans and S. sanguis in vivo.