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Helicobacter pylori has frequently been isolated from human dental plaque, and oral spread via saliva is thought to be one of its principal modes of transmission. Among other innate defence systems human saliva contains peroxidase enzymes and lysozyme. The sensitivity of H. pylori to physiological concentrations of lactoperoxidase and its salivary substrate thiocyanate, and different amounts of hydrogen peroxide (H(2)O(2)) was investigated in buffer and in human whole saliva. The effect of lysozyme was also studied in saliva. All tested H. pylori strains, ATCC 43504(T) and five clinical isolates, were efficiently inhibited by the peroxidase system with high concentrations of H(2)O(2) in buffer. The inhibition was stronger at lower pH. However, in human saliva these high concentrations of H(2)O(2) generated less hypothiocyanite, the antibacterial product of the peroxidase system and the effects of the peroxidase system were weaker. Physiological concentration of lysozyme was not bacteriocidal against H. pylori, nor did it enhance the effect of the peroxidase system in saliva. Thus, further studies are needed to enhance the efficacy of peroxidase systems in human saliva to make it more beneficial not only against dental but also against gastric pathogens.

Previous studies have shown that the peroxidase system with iodide is particularly effective against Actinobacillus actinomycetemcomitans. In the present study, the effects of iodide, chloride and thiocyanate in combinations with lactoperoxidase (LP) and myeloperoxidase (MP) on the viability of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and S. rattus were analysed. Bacteria were incubated in buffer solution containing peroxidase, substrate(s) and H2O2 (all in oral physiological concentrations), and plated after 0, 0.5 and 1 h. The oxidation product of iodide was the most bactericidal against all the bacteria tested. The effect was significantly weaker on mutans streptococci. Physiological concentrations of thiocyanate abolished the effects of LP-H2O2-iodide and MP-H2O2-iodide/chloride combinations. Thiocyanate-peroxidase systems have already been used in oral hygiene products. The incorporation of iodide into these products could make them much more potent against periodontal pathogens, and also help to prevent transmission of these pathogens from person to person via saliva.

Passive immunisation, based on bovine colostral preparations, is an area of active research. Specific bovine antibodies inhibit the virulence factors of target pathogens but the interactions between whey preparations and human immune defence cells are not well known. Bovine colostrum inhibits the phagocytic activity of bovine leucocytes and this may reflect the biological activity of immunoglobulins in it. Therefore, this study aimed to examine the effects of bovine whey protein preparations from the colostrum of Streptococcus mutans/S. sobrinus-immunised and sham-immunised cows on binding, ingestion and killing of these bacteria by human leucocytes. Binding and ingestion of FITC-labelled bacteria were estimated by flow cytometry and leukocyte activation was measured as chemiluminescence. Killing rate was estimated by plate counting and by measuring bioluminescence from S. mutans- containing the insect luciferase gene. Colostral whey protein preparation from hyperimmunised cows activated human leucocytes by opsonising specific bacteria. Neutrophils, eosinophils and monocytes weakly phagocytosed non-opsonised bacteria and bacteria opsonised with control product. On the contrary, binding and ingestion were efficient in the presence of the preparation from immunised cows. Thus, these results show that bovine colostral whey proteins are able to support the activation of human phagocytes against pathogenic microbes and that this property is related to specific antibodies in whey preparations. These whey proteins may also be clinically useful, especially in preventing the colonisation of newly erupted teeth by mutans streptococci.