Jorma Tenovuo

Antimicrobial function of human saliva - how important is it for oral health?

Human saliva contains a number of physical physicochemical, and chemical agents that protect oral tissues against noxious compounds, in particular those produced by various microorganisms. Among such protective factors, the flushing effect of saliva flow is the most important one, not only because it so effectively removes exogenous and endogenous microorganisms and their products into the gut but also because a steady supply of saliva guarantees continuous presence of both non-immune and immune factors in the mouth. A great number of studies with controversial results have been published regarding various individual agents and their possible association to oral health, particularly to dental caries. It appears that no single chemical agent is far more important than the others. For example, patients with selective IgA deficiency have normal levels of non-immune defense factors and often display a compensatory increase in the other immunoglobulin isotypes. The concerted action of all agents in whole saliva, both saliva- and serum-derived, provides a multifunctional protective network that is collapsed only if salivary flow rate is substantially reduced. In this mixture of defense factors, many show additive or even synergistic interactions against oral pathogens. Increased knowledge of the molecular functions of various agents has made it possible to prepare oral hygiene product that include host-derived antimicrobial agents instead of synthetic agents. Although the clinical efficacy of such products is still unsatisfactory and poorly described, new technologies, for example in the production of specific antibodies against oral pathogens, may considerably improve the antimicrobial power of these products.

Influence of Maternal Xylitol Consumption on Mother–Child Transmission of Mutans Streptococci: 6–Year Follow–Up

Xylitol is effective as a noncariogenic or even cariostatic sugar substitute. Habitual xylitol consumption appears to select for mutans streptococci (MS) which shed easily into saliva from plaque. We have earlier shown that habitual xylitol consumption of mothers was associated with a statistically significant reduction in the probability of mother–child transmission of MS assessed at 2 years of age. The aim of the present study was to assess the children’s MS counts 1 and 4 years after the maternal xylitol consumption had been discontinued. At baseline, during pregnancy, all mothers (n = 195) showed high salivary levels of MS. The mothers were randomly assigned to xylitol, fluoride (F) and chlorhexidine (CHX) groups. In the xylitol group, the mothers chewed xylitol–sweetened gum, for 21 months, starting 3 months after delivery. In the two control groups, the mothers received CHX or F varnish treatments at 6, 12 and 18 months after delivery. At the 2–year examination, 169 mother–child pairs participated. At the 3–year and 6–year examinations, there were 159 and 147 children in the study, respectively. For children’s MS analyses, visible plaque was collected using toothpicks at the age of 3 and paraffin–stimulated saliva at the age of 6. The persons involved in the collection and analysis of the microbiological samples were blinded as to the study design and group. Both the plaque and salivary MS were cultured on Mitis salivarius agars containing bacitracin. In all groups, the colonization percentages increased during the follow–up. At the 3–year examination, the children’s risk of having MS colonization was 2.3–fold in the F group (95% CI 1.3–4.2) compared to the xylitol group. This difference was statistically significant. Even at 6 years of age, the salivary MS levels were significantly lower in the xylitol group than in the other groups (ANOVA, p<0.001). In conclusion, the earlier demonstrated, xylitol–associated reduction in the probability of mother–child transmission of MS was still found in the children’s MS counts at the age of 3 and 6 years.

Effects of Chlorhexidine-Fluoride Gel Treatments in Mothers on the Establishment of Mutans Streptococci in Primary Teeth and the Development of Dental Caries in Children

In a longitudinal 3-year study, 151 children were followed for the colonization of the primary dentition by mutans streptococci (MS) and for the development of dental caries. At the age of 1 year, the child-mother pairs were divided into three groups on the basis of the levels of MS in maternal saliva. In the experimental group, the mothers had MS levels higher than 10(5) CFU/ml, and they were given chlorhexidine (1%)-sodium fluoride (0.2%) gel treatments twice a year for 3 years. Two control groups were formed. In control group 1, the mothers also had high levels of MS, but no gel was given. In control group 2, the mothers had low (< 10(5) CFU/ml) baseline levels of salivary MS, and no chlorhexidine-fluoride gel was used. In the total study population, 16, 42, and 54% of the children were colonized by MS by the age of 2, 3, and 4 years, respectively. Most children harbored only Streptococcus mutans, but 2 had both S. mutans and Streptococcus sobrinus, and 2 had only S. sobrinus. Twenty-eight percent of the MS-positive children developed caries by the age of 4 years, whereas 4 out of 27 children with dental caries did not have any detectable MS in their plaque samples. Both the colonization by MS and the caries incidence were highest in control group 1 and lower in the experimental group and in control group 2. These observations suggest that the reduction of maternal salivary MS at the time of tooth emergence may delay, or perhaps even prevent, the colonization of MS in the childrens primary dentition with a concomitant decline in caries incidence, even in a population with an already low prevalence of dental caries.

Fungicidal effect of human lactoferrin against Candida albicans

Human lactoferrin (LF) in its iron-free state (apo LF), killed Candida albicans in a time- and dose-dependent way. The lethal effect was stronger at pH 7.0 than at pH 5.5 and maximum inhibition at neutral pH was achieved in 25 min when the fungal cells were exposed to LF in 0.05 mM KCl at 37 degrees C. Fe(3+)-saturated LF had no fungicidal activity. Apo LF-mediated killing was also temperature-dependent with enhanced inhibition at higher temperatures (37 degrees, 42 degrees C). The presence of 1 mM D-glucose did not affect the candidacidal activity of apo LF but both phosphate and bicarbonate ions at physiological salivary concentrations completely blocked the anti-fungal effect. Therefore it seems unlikely that LF belongs to the major host defence factors against oral candidosis.

In vitro susceptibility of Streptococcus mutans to chlorhexidine and six other antimicrobial agents.

The susceptibility of Streptococcus mutans to chlorhexidine and to six commonly used, systemic antibacterial agents (amoxicillin, cefuroxime, penicillin, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin) was studied for 424 clinical isolates from 116 children and students. The MIC of chlorhexidine for all isolates was < or = 1 micrograms/ml. No resistance to the other antimicrobial agents was detected. Although widely exposed to various antimicrobial agents, S. mutans has remained susceptible to common antimicrobial agents, most importantly to chlorhexidine.

The fungicidal effect of human lactoferrin on Candida albicans and Candida krusei

Five oral isolates each of Candida albicans and Candida krusei were studied for their sensitivity to the fungicidal effect of human lactoferrin. Significant inter- and intraspecies variations were observed and with most isolates the sensitivity of C. krusei to lactoferrin was greater than that of C. albicans. Fungicidal activity of lactoferrin was dose-dependent and observable only with the iron-free form of the molecule (apo-lactoferrin). Iron-saturated lactoferrin was ineffective against all isolates. Supernatant protein assays and scanning electron microscopy indicated cell surface alterations--leakage of proteins and formation of surface blebs--only in those Candida isolates that were sensitive to apo-lactoferrin. As lactoferrin is a common, non-immune, mucosal defence protein, its varying mode of action against C. albicans and C. krusei may be related to their different oral carriage rates.

Concentration of Thiocyanate and Ionizable Iodine in Saliva of Smokers and Nonsmokers

A total of 27 smokers and 92 nonsmokers were analyzed for salivary thiocyanate and ionizable iodine concentrations. Smoking statistically increased the amount of thiocyanate and decreased that of iodine in the saliva samples significantly. Male smokers. had significantly more thiocyanate and less ionizable iodine in saliva than female smokers.

Probiotic bacteria affect the composition of salivary pellicle and streptococcal adhesion in vitro

INTRODUCTION The use of probiotic bacteria is increasing worldwide and at least some of them can transiently colonize the oral cavity. Several studies have shown that probiotic bacteria, which are often thought of in relation only to intestinal health, can also affect the oral ecology, but the mechanisms for this are largely unknown. The aim of this study was to investigate in vitro if the probiotic bacteria used in commercial products affect the protein composition of the salivary pellicle and the adherence of other oral bacteria. METHODS Salivary pellicle on hydroxyapatite and the adhesion of two oral streptococci, Streptococcus mutans and Streptococcus gordonii, were used as a model. RESULTS Probiotic bacteria that bound to saliva-coated hydroxyapatite reduced the adhesion of S. mutans but the inhibitory effect on the adherence of S. gordonii was weaker. Salivary pellicle protein composition was modified by all the strains tested. The modifications in the pellicle affected the adherence of S. mutans but not of S. gordonii. Two of the proteins missing from the pellicles made of saliva-treated with the probiotic bacteria were identified as salivary agglutinin gp340 and salivary peroxidase. All bacterial strains bound salivary agglutinin gp340. The ability of the probiotic bacteria to degrade peroxidase was demonstrated with purified bovine lactoperoxidase and two of the probiotic strains. CONCLUSION This in vitro study showed that probiotic strains used in commercial products may affect the oral ecology by specifically preventing the adherence of other bacteria and by modifying the protein composition of the salivary pellicle.

Pregnancy-related changes in human whole saliva

Flow rate, pH, buffer capacity, viscosity, sialic acid, selected proteins (amylase, lysozyme, peroxidase, lactoferrin) and anions (thiocyanate, hypothiocyanite) were analysed in paraffin-stimulated whole saliva of 16 women during the three trimesters of pregnancy and post partum. Salivary pH and buffer capacity decreased towards late pregnancy, followed by a rapid and significant (p less than 0.01) increase after delivery. The specific activity of salivary peroxidase increased significantly (p less than 0.05) during the third trimester, thus supporting the concept of oestrogen-dependency of this enzyme. None of the other parameters changed significantly during pregnancy or lactation. The results suggest that the composition of human saliva is influenced by female sex steroids during pregnancy.

Antimicrobial systems of human whole saliva in relation to dental caries, cariogenic bacteria, and gingival inflammation in young adults

The association of salivary antibody (total IgA, IgG, and IgM and antibodies reactive with Streptococcus mutans) and non-antibody (lysozyme, lactoferrin, salivary peroxidase, myeloperoxidase, hypothiocyanite, thiocyanate) defense factors with oral health (past and present dental caries, gingival bleeding, the number of salivary S. mutans and lactobacilli) were studied in 50 naval recruits. Dental caries was significantly associated with large amounts of S. mutans, lactobacilli, and total salivary immunoglobulins and with low salivary flow rate and buffer capacity. Salivary anti-S. mutans antibodies did not correlate with dental caries or S. mutans levels. Moreover, none of the salivary non-antibody factors alone had any strong relationship to dental caries or S. mutans levels. Gingival inflammation was associated with elevated levels of lysozyme in whole saliva. It is concluded that in adults the associations between single-point measurements of most salivary antimicrobial constituents and the factors describing oral health are weak.