Catabolism of arginine by the mixed bacteria in human salivary sediment under conditions of low and high glucose concentration

Effectiveness of perioperative oral hygiene management using a cetylpyridinium chloride-, dipotassium glycyrrhizinate, and tranexamic acid-based mouthwash as an adjunct to mechanical oral hygiene in patients with maxillomandibular fixation: A randomized controlled clinical trial

OBJECTIVES

Maxillomandibular fixation requires the jawbones to remain static. Mechanical cleaning is also carried out by brushing or with a water flosser to maintain the oral cavity in a hygienic state, but this cannot be considered sufficient. Mouthwashes are used as a substitute for mechanical cleaning or in a supplementary role after such cleaning. The aim is to evaluate the effectiveness of HABITPRO mouthwash, which contains cetylpyridinium chloride, dipotassium glycyrrhizinate, and tranexamic acid in the specific environment created by maxillomandibular fixation used as an adjunct to mechanical cleaning.

MATERIAL AND METHODS

A total of 55 patients who had undergone maxillomandibular fixation were randomly allocated to either a HABITPRO group (n = 29) or a placebo group (n = 26). To investigate their oral hygiene status, their plaque control record (PCR) was reviewed, and the caries-related bacterial counts, pH, acid buffering capacity, white blood cell count, and ammonia in saliva were measured immediately before maxillomandibular fixation, on Day 10 of fixation, and immediately after fixation was released.

RESULTS

After approximately 2-3 weeks of mouthwash use, the PCR index also increased significantly in the placebo group compared with baseline, whereas it remained almost steady in the HABITPRO group. Additionally, salivary ammonia levels decreased significantly in the HABITPRO group compared to that of the placebo group.

CONCLUSIONS

Even with maxillomandibular fixation, continued gargling with HABITPRO mouthwash in the perioperative period as an adjunct to mechanical cleaning can help maintain better oral hygiene and reduce bacterial counts.

Investigation of oral malodor prevention by dentifrices as measured by VSC reduction

The oral malodor reduction efficacy of dentifrices containing stannous fluoride (SnF₂) or zinc plus arginine (Zn/Arg) was evaluated using a halimeter to measure volatile sulfur compounds (VSCs) in two randomized, controlled, single-blind, cross-over pilot clinical trials. Study 1 (N= 16) had five 1100 ppm F dentifrices and five treatment periods: negative control (NC): 0.243% sodium fluoride (NaF); SnF₂A: 0.454% SnF₂+ pyrophosphate; SnF₂B: 0.454% SnF₂+ sodium hexametaphosphate; SnF₂C: 0.454% SnF₂+ citrate; and SnF₂D: experimental 0.454% SnF₂with increased bioavailable Sn. Study 2 (N= 16) had four 1450 ppm F dentifrices and four treatment periods: NC: 0.1% NaF + 0.76% sodium monofluorophosphate; Zn/Arg: NaF + zinc + arginine; SnF₂E: 0.454% SnF₂+ 0.078% NaF + sodium hexametaphosphate; SnF₂F: 0.454% SnF₂+ 0.078% NaF + citrate. Each period took 96 h; baseline (day 0) morning to day 4 morning. Subjects brushed 2x/day with the treatment dentifrice. VSC levels were measured in the morning, prior to morning brushing, on days 0 and 4. Changes in VSC scores from day 0 to day 4 were assessed using a mixed-model analysis of covariance for cross-over studies. In study 1, SnF₂dentifrices B, C and D showed statistically significant reductions (31.3%, 24.8%, 34%, respectively) in VSC scores versus baseline (p< 0.001); the benefits of these treatments versus NC and SnF₂dentifrice A were statistically significant (p⩽ 0.001). In study 2, SnF₂dentifrices E and F showed statistically significant reductions (31.2%, 22.1%, respectively) in VSC scores versus baseline (p⩽ 0.010); the benefits of these treatments versus NC and the Zn/Arg dentifrice were statistically significant (p⩽ 0.035). The Zn/Arg dentifrice showed a significant increase of 35.2% (p< 0.001) in VSC scores versus baseline. These studies demonstrated that SnF₂dentifrices can provide significant oral malodor reductions, but the benefit is formulation dependent. The presence of SnF₂is not sufficient to ensure efficacy. The Zn/Arg dentifrice increased VSC levels, indicating greater malodor.Clinical Trial Numbers: 20190429 and 20191028.

Accuracy of a salivary examination kit for the screening of periodontal disease in a group medical check-up (Japanese-specific health check-up)

The purpose of the present study was to investigate the accuracy of a screening method using salivary tests to screen for periodontal disease.In total, 1888 individuals older than 30 years in 2017 and 2296 in 2018 who underwent medical check-ups for metabolic syndrome agreed to participate and simultaneously underwent a dental examination by dentists and salivary tests. Salivary occult blood, protein, and ammonia levels and white blood cell counts were evaluated in salivary tests using commercially available kits. The relationship between the results of the salivary tests and dental examination was examined and classification performance was analyzed.The prevalence of periodontal disease was 69.9% in 2017 and 66.8% in 2018. Salivary ammonia showed the highest classification performance in both years (sensitivity 83.5 and 83.1%, precision 73.0 and 69.3%, F-measure 0.779 and 0.756). Occult blood, which was assessed using a monoclonal antibody to human hemoglobin, also showed good performance (sensitivity 69.5%, precision 70.6%, F-measure 0.701). Questions regarding self-reported gingival bleeding were not sufficient to screen for periodontitis. The present results suggest that screening tests using salivary samples may detect periodontal disease in approximately 70% to 80% of subjects in a large population.Conclusion: Salivary ammonia and hemoglobin have potential as salivary markers in the screening of periodontal disease.

Environment-Specific Probiotic Supernatants Modify the Metabolic Activity and Survival of Streptococcus mutans in vitro

A range of studies showed probiotics like Streptococcus oligofermentans and Limosilactobacillus reuteri to inhibit the cariogenic activity and survival of Streptococcus mutans, possibly via the production of substances like H₂O₂, reuterin, ammonia and organic acids. We aimed to assess the environment-specific mechanisms underlying this inhibition. We cultured L. reuteri and S. oligofermentans in various environments; minimal medium (MM), MM containing glucose (MM+Glu), glycerol (MM+Gly), lactic acid (MM+Lac), arginine (MM+Arg) and all four substances (MM+all) in vitro. Culture supernatants were obtained and metabolite concentrations (reuterin, ammonia, H₂O₂, lactate) measured. S. mutans was similarly cultivated in the above six different MM variation media, with glucose being additionally added to the MM+Gly, MM+Lac, and MM+Arg group, with (test groups) and without (control groups) the addition of the supernatants of the described probiotic cultures. Lactate production by S. mutans was measured and its survival (as colony-forming-units/mL) assessed. L. reuteri environment-specifically produced reuterin, H₂O₂, ammonia and lactate, as did S. oligofermentans. When cultured in S. oligofermentans supernatants, lactate production by S. mutans was significantly reduced (p < 0.01), especially in MM+Lac+Glu and MM+all, with no detectable lactate production at all (controls means ± SD: 4.46 ± 0.41 mM and 6.00 ± 0.29 mM, respectively, p < 0.001). A similar reduction in lactate production was found when S. mutans was cultured in L. reuteri supernatants (p < 0.05) for all groups except MM+Lac+Glu. Survival of S. mutans cultured in S. oligofermentans supernatants in MM+Lac+Glu and MM+all was significantly reduced by 0.6-log₁₀ and 0.5-log₁₀, respectively. Treatment with the supernatant of L. reuteri resulted in a reduction in the viability of S. mutans in MM+Gly+Glu and MM+all by 6.1-log₁₀ and 7.1-log₁₀, respectively. Probiotic effects on the metabolic activity and survival of S. mutans were environment-specific through different pathways.

Metabolic Profile of Supragingival Plaque Exposed to Arginine and Fluoride

Caries lesions develop when acid production from bacterial metabolism of dietary carbohydrates outweighs the various mechanisms that promote pH homeostasis, including bacterial alkali production. Therapies that provide arginine as a substrate for alkali production in supragingival oral biofilms have strong anticaries potential. The objective of this study was to investigate the metabolic profile of site-specific supragingival plaque in response to the use of arginine (Arg: 1.5% arginine, fluoride-free) or fluoride (F: 1,100 ppm F/NaF) toothpastes. Eighty-three adults of different caries status were recruited and assigned to treatment with Arg or F for 12 wk. Caries lesions were diagnosed using International Caries Detection and Assessment System II, and plaque samples were collected from caries-free and carious tooth surfaces. Taxonomic profiles were obtained by HOMINGS (Human Oral Microbe Identification using Next Generation Sequencing), and plaque metabolism was assessed by the levels of arginine catabolism via the arginine deiminase pathway (ADS), acidogenicity, and global metabolomics. Principal component analysis (PCA), partial least squares-discriminant analysis, analysis of variance, and random forest tests were used to distinguish metabolic profiles. Of the 509 active lesions diagnosed at baseline, 70 (14%) were inactive after 12 wk. Generalized linear model showed that enamel lesions were significantly more likely to become inactive compared to dentin lesions (P < 0.0001), but no difference was found when treatment with Arg was compared to F (P = 0.46). Arg significantly increased plaque ADS activity (P = 0.031) and plaque pH values after incubation with glucose (P = 0.001). F reduced plaque lactate production from endogenous sources (P = 0.02). PCA revealed differences between the metabolic profiles of plaque treated with Arg or F. Arg significantly affected the concentrations of 16 metabolites, including phenethylamine, agmatine, and glucosamine-6-phosphate (P < 0.05), while F affected the concentrations of 9 metabolites, including phenethylamine, N-methyl-glutamate, and agmatine (P < 0.05). The anticaries mechanisms of action of arginine and fluoride are distinct. Arginine metabolism promotes biofilm pH homeostasis, whereas fluoride is thought to enhance resistance of tooth minerals to low pH and reduce acid production by supragingival oral biofilms.

Approaches to Modulate Biofilm Ecology

Dental caries is closely related to a dysbiosis of the microbial consortia of supragingival oral biofilms driven by a sugar-frequent and acidic-pH environment. The pH is a key factor affecting the homeostasis of supragingival biofilms seen in health. There is increasing interest on the ecological dynamics of the oral microbiome and how a dysbiotic microbiota can be successfully replaced by health-beneficial flora. The concept of preventing the microbial dysbiosis related to caries through modulation of sugar intake and pH has fully emerged.

Arginine Metabolism in Supragingival Oral Biofilms as a Potential Predictor of Caries Risk

INTRODUCTION

Ammonia production via the arginine deiminase system (ADS) of oral bacteria can function to reduce the cariogenicity of oral biofilms by neutralizing glycolytic acids that cause tooth demineralization.

OBJECTIVES

This cohort study investigated the relationship between ADS activity and bacterial profile changes of supragingival biofilms with caries experience among children over time.

METHODS

A total of 79 children aged 2 to 7 y at baseline were assessed every 6 mo for a period of 18 mo. Children were grouped as caries free (CF), caries active with enamel lesions (CAE), or caries active with dentin lesions (CA). Supragingival plaque samples were collected from caries-free surfaces (PF) and from enamel (PE) and dentin (PD) lesions. Plaque ADS activity was measured by monitoring citrulline production from arginine and compared with ribosomal 16S rRNA-derived taxonomic profiles for the same samples.

RESULTS

At baseline, 37% of the children were CF, 34% CAE, and 29% CA. At 18 mo, 26% were CF, 41% CAE, 23% CA, and 10% were caries experienced (new restorations but no caries activity). Throughout the study period, ADS activity was significantly higher in the CF group than the CA group (P < 0.0001), and ADS activity in the PF samples was significantly higher than in the PE and PD samples (P < 0.0001). Distance-based redundancy analysis showed that the bacterial communities could be differentiated when plaque samples are grouped into levels of high and low ADS activity.

CONCLUSIONS

There is a positive correlation between caries activity and low arginolytic capacity of the supragingival oral biofilms of children and tooth surfaces over time. Measurements of arginine metabolism via ADS may be useful to differentiate the caries risk of individuals and tooth surfaces.

KNOWLEDGE TRANSFER STATEMENT

Findings from this study support the development of new strategies for caries risk assessment and prevention based on modulation of the virulence of the oral microbiome through arginine metabolism in supragingival biofilms.

Critical Appraisal of Oral Pre- and Probiotics for Caries Prevention and Care

In recent years, the concept of preventing caries-related microbial dysbiosis by enhancing the growth and survival of health-associated oral microbiota has emerged. In this article, the current evidence for the role of oral pre- and probiotics in caries prevention and caries management is discussed. Prebiotics are defined as "substrates that are selectively utilized by host microorganisms conferring a health benefit." With regard to caries, this would include alkali-generating substances such as urea and arginine, which are metabolized by some oral bacteria, resulting in ammonia production and increase in pH. While there is no evidence that urea added to chewing gums or mouth rinses significantly contributes to caries inhibition, multiple studies have shown that arginine in consumer products can exert an inhibitory effect on the caries process. Probiotics are "live microorganisms which when administrated in adequate amounts confer a health benefit on the host." Clinical trials have suggested that school-based programs with milk supplemented with probiotics and probiotic lozenges can reduce caries development in preschool children and in schoolchildren with high caries risk. Due to issues with research ethics (prebiotics) and risk of bias (prebiotics, probiotics), the confidence in the effect estimate is however limited. Further long-term clinical studies are needed with orally derived probiotic candidates, including the health-economic perspectives. In particular, the development and evaluation of oral synbiotic products, containing both prebiotics and a probiotic, would be of interest in the future management of dental caries.

Potential Uses of Arginine in Dentistry

Carious lesions develop in tooth surfaces where there is an imbalance of the processes of acid and alkali production by supragingival biofilms. Since low pH is the main driving factor in the development of carious lesions, most efforts to identify an effective anticaries therapy have focused on targeting the acid-producing bacteria and their mechanisms of acid production. An expanding area of oral microbiology has now been devoted to explore microbial metabolic activities that help to neutralize biofilm pH and thus inhibit the caries process. Arginine metabolism via the arginine deiminase pathway (ADS) produces alkali in the form of ammonia that counteracts the effects of biofilm acidification from bacterial glycolysis. ADS also functions as an adaptive strategy used by certain bacteria to thrive in oral biofilms. Substantial evidence accumulated from laboratory and clinical observations supports the hypotheses that measurements of arginine metabolism via ADS may serve as an important caries risk assessment criterion and that providing arginine regularly to supragingival biofilms can be an effective therapy for caries intervention. This article reviews the potential of arginine-based therapies such as the use of arginine as prebiotic, ADS+ strains as probiotics, and oral care formulations containing arginine for prevention and management of dental caries.

Anti-Caries Effect of Arginine-Containing Formulations in vivo: A Systematic Review and Meta-Analysis

Objective: To assess the anti-caries effect of arginine-containing formulations in vivo on caries lesions compared with fluorides or placebo. Methods: Randomized or quasi-randomized human clinical trials wherein arginine was delivered by any method were considered. The MEDLINE, Web of Science, EMBASE, Cochrane Library, and CBM databases were searched to identify relevant articles published up to December 2014. Grey literature was also searched. Two authors performed data extraction independently and in duplicate using data collection forms. Each included study was assessed using the Cochrane risk of bias assessment tool. Results: Of the 470 studies screened, 31 full articles were scrutinized and assessed for eligibility. Ten studies (n = 15,546 participants) were selected for final inclusion. The meta-analysis results (n = 7 studies) demonstrated a synergistic effect of arginine when used in conjunction with fluoride on early coronal and root caries compared with placebo or fluoride alone. No specific side effects related to arginine usage were identified. Conclusions: When used in combination with a calcium compound and fluoride, arginine potentially provides a superior anti-caries effect compared with matched formulations of fluoride alone. However, the level of evidence was downgraded because of risks of bias and potential publication bias. In the future, more high quality, non-industry-supported clinical studies in this research area are required before any definitive recommendations can be made.

Meta-omics uncover temporal regulation of pathways across oral microbiome genera during in vitro sugar metabolism

Dental caries, one of the most globally widespread infectious diseases, is intimately linked to pH dynamics. In supragingival plaque, after the addition of a carbohydrate source, bacterial metabolism decreases the pH which then subsequently recovers. Molecular mechanisms supporting this important homeostasis are poorly characterized in part due to the fact that there are hundreds of active species in dental plaque. Only a few mechanisms (for example, lactate fermentation, the arginine deiminase system) have been identified and studied in detail. Here, we conducted what is to our knowledge, the first full transcriptome and metabolome analysis of a diverse oral plaque community by using a functionally and taxonomically robust in vitro model system greater than 100 species. Differential gene expression analyses from the complete transcriptome of 14 key community members revealed highly varied regulation of both known and previously unassociated pH-neutralizing pathways as a response to the pH drop. Unique expression and metabolite signatures from 400 detected metabolites were found for each stage along the pH curve suggesting it may be possible to define healthy and diseased states of activity. Importantly, for the maintenance of healthy plaque pH, gene transcription activity of known and previously unrecognized pH-neutralizing pathways was associated with the genera Lactobacillus, Veillonella and Streptococcus during the pH recovery phase. Our in vitro study provides a baseline for defining healthy and disease-like states and highlights the power of moving beyond single and dual species applications to capture key players and their orchestrated metabolic activities within a complex human oral microbiome model.

The development and validation of a new technology, based upon 1.5% arginine, an insoluble calcium compound and fluoride, for everyday use in the prevention and treatment of dental caries

OBJECTIVE

This paper briefly discusses caries prevalence, the multi-factorial nature of caries etiology, caries risk and the role and efficacy of fluoride. The paper also highlights research on bacterial metabolism which provided understanding of the mouth's natural defenses against caries and the basis for the development of a new technology for the everyday prevention and treatment of caries. Finally, evidence that the technology complements and enhances the anti-caries efficacy of fluoride toothpaste is summarized.

CONCLUSIONS

Global data show that dental caries is a prevalent disease, despite the successful introduction of fluoride. Caries experience depends on the balance between consumption of sugars and oral hygiene and the use of fluoride. Three scientific concepts are fundamental to new measures to detect, treat and monitor caries: (1) dental caries is a dynamic process, (2) dental caries is a continuum of stages from reversible, pre-clinical to irreversible, clinically detectable lesions, and (3) the caries process is a balance of pathological and protective factors that can be modulated to manage caries. Fluoride functions as a protective factor by arresting and reversing the caries process, but fluoride does not prevent pathological factors that initiate the process. A novel technology, based upon arginine and an insoluble calcium compound, has been identified which targets dental plaque to prevent initiation of the caries process by reducing pathological factors. As the mechanisms of action of arginine and fluoride are highly complementary, a new dentifrice, which combines arginine with fluoride, has been developed and clinically proven to provide superior caries prevention.

Desarrollo y validación de una nueva tecnología, basada en arginina al 1.5%, un compuesto de calcio insoluble y fluoruro, para el uso diario en la prevención y tratamiento de la caries dental

OBJETIVO

este artículo discute brevemente la prevalencia de caries, la naturaleza multifactorial de su etiología, el riesgo de caries y el papel y eficacia del fluoruro. Resalta también la investigación sobre el metabolismo bacteriano, que ha aportado conocimientos sobre la defensa natural oral contra la caries y la base para el desarrollo de una nueva tecnología para la prevención diaria y el tratamiento de la caries. Por último, se resume la evidencia que respalda que la tecnología complementa y mejora la eficacia anti-caries de la crema dental con fluoruro.

CONCLUSIONES

los datos globales muestran que a pesar de la exitosa introducción del fluoruro, la caries dental es una enfermedad prevalente. La experiencia de caries depende del balance entre el consumo de azúcares, la higiene oral y el uso del fluoruro. Hay tres conceptos científicos que son fundamentales en las nuevas mediciones para detectar, tratar y monitorear la caries: (1) la caries dental es un proceso dinámico, (2) la caries dental es un proceso continuo de etapas que van desde reversible (pre-clínica) hasta irreversible (lesiones clínicamente detectables), y (3) el proceso de la caries es un balance de factores patológicos y protectores que pueden modularse para el manejo de la caries. El fluoruro funciona como factor protector al detener y revertir el proceso de la caries, pero el fluoruro no previene los factores patológicos que inician el proceso. Se ha identificado una tecnología novedosa, basada en arginina y un compuesto insoluble de calcio, que está dirigida a la placa dental para prevenir la iniciación del proceso de caries al reducir los factores patológicos. Como los mecanismos de acción de la arginina y el fluoruro son altamente complementarios, se ha desarrollado un nuevo dentífrico que combina la arginina y el fluoruro, y se ha probado clínicamente que brinda una prevención superior contra la caries.

Bacterial ammonia causes significant plant growth inhibition

Many and complex plant-bacteria inter-relationships are found in the rhizosphere, since plants release a variety of photosynthetic exudates from their roots and rhizobacteria produce multifaceted specialized compounds including rich mixtures of volatiles, e.g., the bouquet of Serratia odorifera 4Rx13 is composed of up to 100 volatile organic and inorganic compounds. Here we show that when growing on peptone-rich nutrient medium S. odorifera 4Rx13 and six other rhizobacteria emit high levels of ammonia, which during co-cultivation in compartmented Petri dishes caused alkalization of the neighboring plant medium and subsequently reduced the growth of A. thaliana. It is argued that in nature high-protein resource degradations (carcasses, whey, manure and compost) are also accompanied by bacterial ammonia emission which alters the pH of the rhizosphere and thereby influences organismal diversity and plant-microbe interactions. Consequently, bacterial ammonia emission may be more relevant for plant colonization and growth development than previously thought.

Probiotic Lactobacillus reuteri strains ATCC PTA 5289 and ATCC 55730 differ in their cariogenic properties in vitro

OBJECTIVE

The effects of probiotics on cariogenic biofilms remain controversial. Our aim was to characterise two probiotic Lactobacillus reuteri strains, ATCC PTA 5289 and ATCC 55730 from a cariogenic standpoint in vitro. These strains are used in commercial products designed for oral health purposes.

DESIGN

The adhesion and biofilm formation were studied on saliva-coated hydroxyapatite. The effects of glucose or sucrose on the biofilm formation were also tested. Arginine metabolism was assessed by measuring the pH in the presence of glucose and arginine. The degradation of hydroxyapatite was measured in three different growth media. Streptococcus mutans strains Ingbritt and MT 8148 were used as positive controls for bacterial adhesion and degradation of hydroxyapatite.

RESULTS

Strain ATCC PTA 5289 adhered on saliva-coated hydroxyapatite and formed detectable biofilm, but strain ATCC 55730 was poor in both adhesion and biofilm formation. Both strains were arginolytic and raised the pH in the presence of arginine. The amount of dissolved calcium from hydroxyapatite correlated with bacterial growth rate and the final pH of the growth medium.

CONCLUSION

L. reuteri strains ATCC PTA 5289 and ATCC 55730 differed in their adhesion, biofilm formation and arginine metabolism in vitro. Thus, these probiotic lactobacilli are likely to differ in their behaviour and cariogenic potential also in an oral environment.

Filifactor alocis has virulence attributes that can enhance its persistence under oxidative stress conditions and mediate invasion of epithelial cells by porphyromonas gingivalis

Filifactor alocis, a Gram-positive anaerobic rod, is one of the most abundant bacteria identified in the periodontal pockets of periodontitis patients. There is a gap in our understanding of its pathogenicity and ability to interact with other periodontal pathogens. To evaluate the virulence potential of F. alocis and its ability to interact with Porphyromonas gingivalis W83, several clinical isolates of F. alocis were characterized. F. alocis showed nongingipain protease and sialidase activities. In silico analysis revealed the molecular relatedness of several virulence factors from F. alocis and P. gingivalis. In contrast to P. gingivalis, F. alocis was relatively resistant to oxidative stress and its growth was stimulated under those conditions. Biofilm formation was significantly increased in coculture. There was an increase in adherence and invasion of epithelial cells in coculture compared with P. gingivalis or F. alocis monocultures. In those epithelial cells, endocytic vesicle-mediated internalization was observed only during coculture. The F. alocis clinical isolate had an increased invasive capacity in coculture with P. gingivalis compared to the ATCC 35896 strain. In addition, there was variation in the proteomes of the clinical isolates compared to the ATCC 35896 strain. Hypothetical proteins and those known to be important virulence factors in other bacteria were identified. These results indicate that F. alocis has virulence properties that may enhance its ability to survive and persist in the periodontal pocket and may play an important role in infection-induced periodontal disease.

Correlations of oral bacterial arginine and urea catabolism with caries experience

BACKGROUND/AIM

Alkali generation by oral bacteria plays a key role in plaque pH homeostasis and may be a major impediment to the development of dental caries. To determine if the capacity of oral samples to produce ammonia from arginine or urea was related to caries experience, the arginine deiminase system (ADS) and urease activity in saliva and dental plaque samples were measured in 45 adult subjects.

METHODS

The subjects were divided into three groups according to caries status; 13 caries-free (CF) individuals (decayed, missing, and filled teeth = 0); 21 caries-active (CA) individuals (decayed teeth >or= 4); and 11 caries-experienced (CE) individuals (decayed teeth = 0; missing and filled teeth > 0). Real-time polymerase chain reaction was used to quantify the proportion of certain acid- or alkali-producing organisms in the samples.

RESULTS

The amount of ammonia generated from the test substrates by plaque samples was generally higher than that produced by salivary samples in all groups. Significantly higher levels of salivary ADS activity and plaque urease activity were observed in CF subjects compared to CA subjects (P = 0.0004 and P = 0.014, respectively). The proportions of Streptococcus mutans from saliva and dental plaque of CA subjects were significantly higher than those from the CF group (P = 0.0153 and P = 0.0009, respectively). In the CA group, there was an inverse relationship between urease activity and the levels of S. mutans (P < 0.0001).

CONCLUSION

This study supports the theory that increased caries risk is associated with reduced alkali-generating capacity of the bacteria colonizing the oral cavity; providing compelling evidence to further our understanding of oral alkali-generation in health and disease.

Regulation and physiologic significance of the agmatine deiminase system of Streptococcus mutans UA159

We previously demonstrated that Streptococcus mutans expresses a functional agmatine deiminase system (AgDS) encoded by the agmatine-inducible aguBDAC operon (A. R. Griswold, Y. Y. Chen, and R. A. Burne, J. Bacteriol. 186:1902-1904, 2004). The AgDS yields ammonia, CO2, and ATP while converting agmatine to putrescine and is proposed to augment the acid resistance properties and pathogenic potential of S. mutans. To initiate a study of agu gene regulation, the aguB transcription initiation site was identified by primer extension and a putative sigma70-like promoter was mapped 5' to aguB. Analysis of the genome database revealed an open reading frame (SMU.261c) encoding a putative transcriptional regulator located 239 bases upstream of aguB. Inactivation of SMU.261c decreased AgD activity by sevenfold and eliminated agmatine induction. AgD was also found to be induced by certain environmental stresses, including low pH and heat, implying that the AgDS may also be a part of a general stress response pathway of this organism. Interestingly, an AgDS-deficient strain was unable to grow in the presence of 20 mM agmatine, suggesting that the AgDS converts a growth-inhibitory substance into products that can enhance acid tolerance and contribute to the competitive fitness of the organism at low pH. The capacity to detoxify and catabolize agmatine is likely to have major ramifications on oral biofilm ecology.

A mixed-bacteria ecological approach to understanding the role of the oral bacteria in dental caries causation: an alternative to Streptococcus mutans and the specific-plaque hypothesis

For more than 100 years, investigators have tried to identify the bacteria responsible for dental caries formation and to determine whether their role is one of specificity. Frequent association of Lactobacillus acidophilus and Streptococcus mutans with caries activity gave credence to their being specific cariogens. However, dental caries occurrence in their absence, and the presence of other bacteria able to produce substantial amounts of acid from fermentable carbohydrate, provided arguments for non-specificity. In the 1940s, Stephan found that the mixed bacteria in dental plaque produced a rapid drop in pH following a sugar rinse and a slow pH return toward baseline. This response became a cornerstone of plaque and mixed-bacterial involvement in dental caries causation when Stephan showed that the pH decrease was inversely and clearly related to caries activity. Detailed examination of the pH (acid-base) metabolisms of oral pure cultures, dental plaque, and salivary sediment identified the main bacteria and metabolic processes responsible for the pH metabolism of dental plaque. It was discovered that this metabolism in different individuals, in plaque in different dentition locations within individuals, and in individuals of different levels of caries activity could be described in terms of a relatively small number of acid-base metabolic processes. This led to an overall bacterial metabolic vector concept for dental plaque, and helped unravel the bacterial involvement in the degradation of the carbohydrate and nitrogenous substrates that produce the acids and alkali that affect the pH and favor and inhibit dental caries production, respectively. A central role of oral arginolytic and non-arginolytic acidogens in the production of the Stephan pH curve was discovered. The non-arginolytics could produce only the pH fall part of this curve, whereas the arginolytics could produce both the fall and the rise. The net result of the latter was a less acidic Stephan pH curve. Both kinds of bacteria are numerous in dental plaque. By varying their ratios, we were easily able to produce Stephan pH curves indicative of different levels of caries activity. This and substantial related metabolic and microbial data indicated that it is the proportions and numbers of acid-base-producing bacteria that are at the core of dental caries activity. The elimination of S. mutans, as with a vaccine, was considered to have little chance of success in preventing dental caries in humans, since, in most cases, this would simply make more room for one or more of the many acidogens remaining. An understanding of mixed-bacterial metabolism, knowledge of how to manipulate and work with mixed bacteria, and the use of a bacterial metabolic vector approach as described in this article have led to (1) a more ecological focus for dealing with dental caries, and (2) new means of developing and evaluating anti-caries agents directed toward microbial mixtures that counter excess acid accumulation and tooth demineralization.

Acid-neutralizing activity during amino acid fermentation by Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum

Acid-neutralizing activity during amino acid fermentation by washed cells of Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum was studied. When the washed cells of these strains were anaerobically incubated in the presence of aspartylaspartic acid or glutamylglutamic acid for P. gingivalis, aspartic acid for P. intermedia and glutamic acid for F. nucleatum at an initial pH of 5.0 or 5.5, the pH of the incubation mixtures rose toward neutral. F. nucleatum had the highest acid-neutralizing activity, followed by P. intermedia and P. gingivalis. The P. intermedia and F. nucleatum cells were used to measure the amounts of base produced at a fixed pH of 5.0. These cells generated significant amounts of base at pH 5.0 along with the production of organic acids and ammonia from aspartic or glutamic acid. Acid-base balance theoretically calculated from the amounts of consumed substrate and end products implies that the acid-neutralizing activity was derived from the decrease in acidity during the fermentation of amino acid into organic acids and ammonia.

Purification, characterization, and sequence analysis of a potential virulence factor from Porphyromonas gingivalis, peptidylarginine deiminase

The initiation and progression of adult-onset periodontitis has been associated with infection of the gingival sulcus by Porphyromonas gingivalis. This organism utilizes a multitude of virulence factors to evade host defenses as it establishes itself as one of the predominant pathogens in periodontal pockets. A feature common to many other oral pathogens is the production of ammonia due to its protective effect during acidic cleansing cycles in the mouth. Additionally, ammonia production by P. gingivalis has been proposed as a virulence factor due to its negative effects on neutrophil function. In this study, we describe the first purification of a peptidylarginine deiminase (PAD) from a prokaryote. PAD exhibits biochemical characteristics and properties that suggest that it may be a virulence agent. PAD deiminates the guanidino group of carboxyl-terminal arginine residues on a variety of peptides, including the vasoregulatory peptide-hormone bradykinin, to yield ammonia and a citrulline residue. The soluble protein has an apparent mass of 46 kDa, while the DNA sequence predicts a full-length protein of 61.7 kDa. PAD is optimally active at 55 degrees C, stable at low pH, and shows the greatest activity above pH 9.0. Interestingly, in the presence of stabilizing factors, PAD is resistant to limited proteolysis and retains significant activity after short-term boiling. We propose that PAD, acting in concert with arginine-specific proteinases from P. gingivalis, promotes the growth of the pathogen in the periodontal pocket, initially by enhancing its survivability and then by assisting the organism in its circumvention of host humoral defenses.

Acid tolerance and acid-neutralizing activity of Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum

The tolerance to acid and the acid-neutralizing activity of three important periodontopathic bacteria, Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum were studied. P. gingivalis strains grew only at neutral pH and did not utilize glucose, whereas strains of P. intermedia and F. nucleatum could grow under acidic conditions and increased their growth by utilizing glucose. P. gingivalis tended to raise the culture pH during growth. P. intermedia and F. nucleatum raised the culture pH during growth in the absence of glucose, while in the presence of glucose they decreased the pH. Resting cell suspensions of all the bacteria raised the pH in the presence of tryptone and casamino acids. Acid-neutralizing activity was confirmed by measuring base production at a fixed pH with a pH-stat. During neutralization, the cells produced cytotoxic substrates, ammonia and organic acids (butyric, isobutyric and isovaleric acids by P. gingivalis; isovaleric and succinic acids by P. intermedia; propionic and butyric acids by F. nucleatum). These findings suggest that deamination of amino acids into ammonia and organic acids occurs simultaneously with base production, resulting in acid neutralization. These results could partially explain the survival of P. intermedia and F. nucleatum in both supragingival and subgingival plaque and the apparent restriction of P. gingivalis to subgingival plaque. The former bacteria may aid in creation of an environment fostering colonization of subgingival plaque by P. gingivalis.

Role of Models in Assessing New Agents for Caries Prevention-Non-Fluoride Systems: Reaction Paper

Several important issues have been raised concerning the need for consideration of alternatives to fluoride. The principle reason to do so has been the lack of comprehensive effectiveness of fluoride, which in turn reveals incomplete understanding of the caries process. Included among the topics required for clarification of caries initiation would be quantitative methods for relating plaque pH values to the formation of caries. Thus, methods for assessing the activity of anticaries agents over time would be of considerable assistance in monitoring the effects of these test compounds on bacteria. The use of recombinant oral micro-organisms containing genetic fusions, to provide information on the effects of agents on bacteria growing in model systems, is discussed as a possible means of obtaining relevant data in situ.

Anticariogenicity of calcium phosphate complexes of tryptic casein phosphopeptides in the rat

Casein phosphopeptides (CPP) stabilize calcium phosphate through the formation of casein-phosphopeptide amorphous calcium-phosphate complexes (CPP-CP). The ability of CPP-CP to reduce caries activity was investigated by use of specific-pathogen-free rats inoculated with Streptococcus sobrinus. The animals consumed a defined cariogenic diet free of dairy products. Solutions (100 microL) of the CPP-CP (0.1, 0.2, 0.5, 1.0% w/v) were applied to the animals' molar teeth twice daily. Other groups of animals received solutions containing 500 ppm F, the non-phosphorylated peptides of a casein tryptic digest (0.5% w/v), or the calcium-phosphate complex of a synthetic octapeptide, Ac-Glu-Ser(P)-Ile-Ser(P)-Ser(P)-Ser(P)-Glu-Glu-NHMe, corresponding to the common sequence in the CPP. The CPP-CP significantly reduced caries activity in a dose-response fashion, with 1.0% CPP-CP producing 55% and 46% reductions in smooth surface and fissure caries activity, respectively, being similar to that of 500 ppm F. The anticariogenic effects of CPP-CP and fluoride were additive, since animals receiving 0.5% CPP-CP plus 500 ppm F had significantly lower caries activity than those animals receiving either CPP-CP or fluoride alone. The tryptic digest of casein with the phosphopeptides selectively removed showed no anticariogenic activity. The synthetic octapeptide-calcium phosphate complex significantly reduced caries activity, confirming that this calcium-phosphate-stabilizing portion of the casein phospho-peptides is associated with anticariogenicity. The CPP-CP did not significantly affect the level of S. sobrinus in fissure plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and microbiological effects of chlorhexidine and arginine sustained-release varnishes in the mentally retarded

Local applications of sustained-released varnishes of chlorhexidine and arginine were used in a controlled pilot study of 34 mentally retarded patients, ages 18-45, assigned to one of these groups: chlorhexidine (C), arginine (A), or placebo (P). A professional scaling followed by four weeks of professional brushing to reach a Plaque Index (PII) and Gingival Index (GI) of 1.0 at baseline preceded eight weeks of daily varnish application to the buccal and labial surfaces of all teeth. Clinical parameters (PII and GI) and bacterial samples from selected teeth were collected at predetermined intervals. Four and eight weeks following the baseline, the PII was significantly different among the groups, with the lowest score in the chlorhexidine group. No significant differences among the three groups were noted for the GI. The chlorhexidine and arginine groups showed significant reductions (p < 0.05 and p < 0.01, respectively) in the number of S. mutans. The arginine group showed a nonsignificant increase in the number of S. sanguis. These results suggest that the topical antimicrobial agents may have some relevance to plaque control among patients with mental retardation.

Urease activity in Streptococcus salivarius at low pH

Arginine metabolism to alkali by the arginine deiminase system in oral bacteria increases their acid tolerance. The potential of urease activity in Streptococcus salivarius to fulfil a similar role was examined. In cell extracts between pH 5.0 and 8.0, urease activity was over 80% the maximal rate. The urease rate was zero at pH 4.3, and at pH 3.6 the enzyme was rapidly inactivated (t 1/2 of 0.6 min). The pH range of intact cells was broader. In Strep. salivarius cells acidified to pH 2.6 for 5 min, urease was completely retained and the ureolytic pH rise was rapid. There was no urease activity after acidification to pH 2. In cells acidified to maintain the pH between 3.3 and 4, viability was maintained for a short period (extrapolation indicated 20 min) and then decreased. This acidification induced alkali generation or acid removal that decreased in parallel to loss of viability. A small fraction (10%) of the urease was rapidly inactivated, after which both the remaining urease and pH response decreased at a similar rate to cell viability (t 1/2 of 15-20 min), but for at least 1 h following acidification, a rapid ureolysis induced rise in pH to above 7. In cells held at pH 3.6 and treated to compromise their membranes by freeze-thawing or transient acidification to pH 2.3, 70-80% of the urease was lost rapidly and the remainder inactivated at a rate similar to that in intact cells. Therefore, although at pH below 4, S. salivarius urease is outside its pH activity range and the free enzyme is rapidly inactivated, intact cells the urease is protected and ureolytic generation of ammonia is capable of substantially raising the pH for at least 1 h while the cell population is being progressively killed by acid.

Comparison of the effects of galactose and glucose on the pH responses of human dental plaque, salivary sediment and pure cultures of oral bacteria

Comparisons made in dental plaque in vivo demonstrated that galactose produces a significantly smaller decrease in pH than does glucose. In vitro studies with plaque, salivary sediment and pure cultures of oral bacteria done in the absence of intraoral factors such as flowing saliva confirmed this lesser acidogenicity of galactose. Pure culture showed that most of the bacteria tested produce a moderate to large decrease with glucose but only a few do so with galactose; most produced a moderate to little or no pH response with this sugar. This suggested that the smaller decreases in pH seen in plaque in vivo with galactose were largely due to bacterial differences, basically that resident micro-organisms individually have less galactolytic than glucolytic capability. Variance in capability was attributed to differences in membrane transport processes and metabolic pathways normally available to bacteria for galactose and glucose catabolism. In the in vitro experiments, because plaque and sediment can produce base as readily as they can produce acid, the nitrogenous substrates identified earlier as major stimulants of base formation, urea and arginine, were concurrently examined for their attenuating effects on the galactose and glucose pH responses. These showed, consistent with its lesser acidogenicity, that galactose could be countered more readily in its ability to reduce the pH by either of these two base-forming substrates than could glucose. The effects were different with urea and with arginine, urea attenuation occurred sooner and arginine attenuation later in both plaque and sediment. The corresponding acid-base pH profiles for pure cultures were different.(ABSTRACT TRUNCATED AT 250 WORDS)

Salivary and metabolic factors involved in oral malodor formation

Saliva plays a central role in the formation of oral malodor. Such formation has as its basis bacterial putrefaction, the degradation of proteins, and the resulting amino acids by microorganisms. Saliva provides substrates that are readily oxidized and in the process facilitates oxygen depletion. This favors the reduced conditions conducive to production of odoriferous volatiles. At the same time, saliva is a major source of oxygen for the oral bacteria which generally is inhibitory of their formation. The pH is also critical to malodor development; acidity inhibits, whereas neutrality and alkalinity favor malodor production. Since the pH on oral mucosal surfaces where odor formation occurs is largely determined by the fermentative and putrefactive activities of the adhering bacteria, these acid-base processes are necessarily of major regulatory importance. Because oral malodor and periodontitis both involve excessive oral putrefaction, a better understanding of putrefaction could lead to more substantive methods of oral malodor treatment than exists today, as well as identifying new approaches to amelioration of the bacterial attack on the soft tissues leading to the destruction associated with periodontal disease.

Utilization of nitrogenous compounds by oral bacteria

In terms of the crucial acid-base balance in dental plaque, the bacterial catabolism of nitrogenous compounds, such as peptides and amino acids, is of importance because the end-products can raise plaque pH. Of particular significance is the fermentation of arginine by bacteria such as Streptococcus sanguis, a numerically important plaque organism. Aspects of the uptake of this amino acid were studied and it was also shown the organism can obtain arginine from small peptides, since it possesses cell-associated exo-peptidases. Furthermore, it could grow in media containing whole protein (casein), or one of its fractions, as the sole source of organic nitrogen. The studies thus showed that S. sanguis is well equipped, in terms of endo- and exo-peptidase activities, to obtain the metabolically important arginine from whole protein. It is suggested that knowledge of this type should lead to a better understanding of overall plaque metabolism--of relevance to both cariogenic and periodontopathic plaques.

Constituents of salivary supernatant responsible for stimulation of oxygen uptake by the bacteria in human salivary sediment

The 10,000 g supernatant of wax-stimulated whole saliva was fractionated by gel filtration and its components were tested along with amino acids, small peptides and urea for their ability to stimulate this oxygen uptake, and for their effects on pH. Fractions containing the larger components, the proteins and large peptides, stimulated much less oxygen uptake than unfractionated supernatant, and caused a small decrease in pH. Analysis with anthrone indicated that both these effects were due mainly to the carbohydrate associated with these constituents. In contrast, fractions containing the remaining lower molecular-weight components stimulated substantial oxygen uptake and a rise in pH; both effects were like those seen with whole saliva supernatant. The oxygen effects were attributed mainly to certain amino acids and small peptides in the small molecular-weight fractions. Ornithine, arginine, proline and glutamic acid consistently stimulated oxygen uptake by the oral microflora in a test of 23 amino acids with the sediments of 13 subjects. Ornithine and arginine at the same time stimulated a significant rise in pH, whereas the other two amino acids showed no such effect. Variable and sometimes significant oxygen uptake was seen with alanine, aspartic acid, asparagine, glutamine and cysteine in 4-7 of the subjects; infrequent or no effects were seen with the remainder of the amino acids tested. There was some evidence to suggest that amino acid stimulation of oxygen uptake may be inducible. Urea had no effect on uptake but did contribute significantly to the pH rise. Small peptides containing those amino acids that could stimulate oxygen uptake also stimulated such uptake; peptides without such acids did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein dissimilation by human salivary-sediment bacteria

Proteins of known composition and structural characteristics were incubated (1.0 mg/mL) with re-suspended salivary sediment (2.5% v/v) in a lactate-salt medium with an initial pH of 5.2 for two hr at 37 degrees C. Hydrolysis of the proteins was monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Hydrogen ion, amines, and ammonia were measured by use of a combined pH electrode, high-performance liquid chromatography, and glutamate dehydrogenase, respectively. Of the proteins studied, the caseins alpha s1, beta, and kappa and the histones H1 and H3 were extensively hydrolyzed by the salivary-sediment bacteria. The hydrolysis of these proteins was attributed to their relative lack of tertiary (folded) structure. The only amine detected was the polyamine putrescine arising from the catabolism of arginine following the hydrolysis of the arginine-rich histone H3. None of the other proteins extensively hydrolyzed by salivary sediment, although containing arginyl and lysyl residues, served as substrates for putrescine or cadaverine production. Pre-hydrolysis of the arginine-rich histone H3 and poly-L-arginine with trypsin resulted in a marked increase in putrescine produced, suggesting that the salivary-sediment proteolytic activity was not "trypsin-like". Incubation of salivary-sediment bacteria with the caseins and the histone H3 resulted in an increase in ammonium ion concentration and an associated decrease in hydrogen ion concentration. The increase in ammonium ion concentration not attributed to arginine hydrolysis was correlated with the content of glutaminyl plus asparaginyl residues of the proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-base pH curves in vitro with mixtures of pure cultures of human oral microorganisms

Pure cultures of microorganisms commonly found in supragingival plaque were incubated alone and in combinations to determine the bacterial contribution to the pH-fall-pH-rise that is the central characteristic of the Stephan-curve pH change seen in plaque in vivo after brief exposure to a sugar solution. To avoid the complicating conditions of saliva flow and plaque diffusion, experiments were done with bacterial suspensions in incubations in vitro. In an initial experimental series where each microorganism was incubated only with glucose, all but a few produced the initial pH fall. Some also showed a subsequent small, sharp rise in the pH which then quickly levelled off; this was due to metabolism of endogenous substrate accumulated by most microorganisms during their growth in culture. When arginolytic and non-arginolytic bacteria were each then incubated with both glucose and arginine present (the glucose substrate to stimulate a pH fall and the arginine to stimulate a pH rise), the non-arginolytic gave a progressively more acidic pH response with progressive increase in the cell concentration, whereas the arginolytic bacteria produced a much smaller and variable pH decrease with similar cell concentration increase. Mixing pure cultures of either arginolytic or non-arginolytic bacteria gave acid-base pH responses similar to those of their respective pure cultures, whereas mixing arginolytic with non-arginolytic bacteria resulted in an approximate averaging of their different curves. The organisms present in highest proportion in a mixture had the greatest effects. The outcome of mixing the most numerous streptococcal and actinomyces species found normally in supragingival plaque indicated that the well-established difference in the acidity level of the Stephan pH response of caries-active and caries-inactive plaques could be due to differences in the proportions of their arginolytic and non-arginolytic members.

Arginolytic and ureolytic activities of pure cultures of human oral bacteria and their effects on the pH response of salivary sediment and dental plaque in vitro

Thirty-nine different microorganisms commonly found in supragingival plaque and salivary sediment were screened for their ability to raise the pH by producing base from arginine, lysylarginine and urea. Only Actinomyces naeslundii and Staphylococcus epidermidis showed significant pH-rise activity with all three compounds. Eleven bacteria demonstrated such activity with arginine and lysylarginine but not with urea. Only one, Actinomyces viscosus, produced a pH-rise with urea but not with the two arginine compounds. The remaining 26 bacteria showed little or no base-forming activity with any of the three test substrates. The ability of the different oral bacteria to produce base (especially from urea) was a less universal function than their ability to produce acid from fermentable carbohydrate. Substituting pure cultures of arginolytic or non-arginolytic bacteria for portions of the mixed bacterial populations of plaque or sediment in test incubations containing glucose and arginine altered their ability to produce pH-fall-pH-rise responses shaped like those of the Stephen curve in vivo. In general, addition of arginolytic bacteria made these in vitro pH responses less acidic, whereas addition of non-arginolytic bacteria made the responses more acidic. Because of the relatively high arginolytic activity of the plaque harvested in this study, the effect of adding non-arginolytic bacteria was more readily seen than the converse. Similar changes in levels of ureolytic microorganisms and incubation with glucose and urea had little effect on sediment or plaque being able to produce a pH-fall-pH-rise type of response. When increasing proportions of the mixed bacteria in salivary sediment were replaced with the highly cariogenic Lactobacillus casei or Streptococcus mutans, the pH minimum became slightly more acidic and then slightly more alkaline, whereas the pH-rise became progressively and significantly less. Thus arginolytic bacteria have a different and greater effect on shaping the pH response of plaque or sediment than ureolytic bacteria. A large change in the proportions of arginolytic or non-arginolytic microorganisms may be needed to make a plaque microflora potentially non-cariogenic or cariogenic, respectively.

Role of the arginine deiminase system in protecting oral bacteria and an enzymatic basis for acid tolerance

The arginine deiminase system was found to function in protecting bacterial cells against the damaging effects of acid environments. For example, as little as 2.9 mM arginine added to acidified suspensions of Streptococcus sanguis at a pH of 4.0 resulted in ammonia production and protection against killing. The arginine deiminase system was found to have unusual acid tolerance in a variety of lactic acid bacteria. For example, for Streptococcus rattus FA-1, the pH at which arginolysis was reduced to 10% of the maximum was between 2.1 and 2.6, or more than 1 full pH unit below the minimum for glycolysis (pH 3.7), and more than 2 units below the minimum for growth in complex medium (pH 4.7). The acid tolerance of the arginine deiminase system appeared to be primarily molecular and to depend on the tolerance of individual enzymes rather than on the membrane physiology of the bacteria; pH profiles for the activities of arginine deiminase, ornithine carbamoyltransferase, and carbamate kinase in permeabilized cells showed that the enzymes were active at pHs of 3.1 or somewhat lower. Overall, it appeared that ammonia could be produced from arginine at low pH values, even by cells with damaged membranes, and that the ammonia could then protect the cells against acid damage until the environmental pH value rose sufficiently to allow for the reestablishment of a difference in pH (delta pH) across the cell membrane.

Influence of arginine on the coexistence ofStreptococcus mutans andS. milleri in glucose-limited mixed continuous culture

Dental plaque is a complex community of bacteria coexisting in an environment frequently limited by carbon and energy sources. UnlikeStreptococcus mutans, other oral streptococci such asS. milleri andS. sanguis have an absolute requirement for and actually consume all available arginine when grown glucose limited in a chemically defined medium. The conditions, particularly in terms of arginine concentration, under which the dental plaque bacteriaS. mutans andS. milleri would coexist under glucose-limiting conditions were investigated. The minimum level of arginine supporting optimal growth ofS. milleri was found to be ca. 50μM, and above this level these strains outcompetedS. mutans. However, coexistence withS. mutans could be achieved at arginine levels of 14-40μM, depending upon theS. milleri andS. mutans strains used. Under such dual limitation,S. milleri was unable to respond to glucose pulses but did respond to pulses of arginine and arginine plus glucose. One of the twoS. milleri strains did not tolerate low pH. In contrast,S. mutans did not tolerate high pH whereasS. milleri was unaffected. This is relevant to dental plaque where arginine catabolism produces a pH rise. Additionally, arginine is an important nutrient since it can be used as an energy source by some oral streptococci.

Membrane ATPases and acid tolerance of Actinomyces viscosus and Lactobacillus casei

Lactobacillus casei ATCC 4646 and Actinomyces viscosus OMZ105E were found to differ markedly in acid tolerance. For example, pH profiles for glycolysis of intact cells in dense suspensions indicated that glycolysis by L. casei had an optimal pH of about 6.0 and that glucose degradation was reduced by 50% at a pH of 4.2. Comparable values for A. viscosus cells were at pHs of about 7.0 and 5.6. The difference in acid tolerance appeared to depend mainly on membrane physiology, and the addition of 40 microM gramicidin to cell suspensions increased the sensitivity of the glycolytic system by as much as 1.5 pH units for L. casei and up to 0.5 pH unit for A. viscosus. L. casei cells were inherently somewhat more resistant to severe acid damage than were A. viscosus cells, in that Mg release from L. casei cells in medium with a pH of 3.0 occurred only after a lag of some 4 h, compared with rapid release from A. viscosus cells. However, the major differences pertinent to the physiology of the organisms appeared to be related to proton-translocating ATPases. Isolated membranes of L. casei had about 3.29 U of ATPase per mg of protein, compared with only about 0.06 U per mg of protein for those of A. viscosus. Moreover, the ATPase of L. casei had a pH optimum for hydrolytic activity of about 5, compared with an optimal pH of about 7 for that of A. viscosus.(ABSTRACT TRUNCATED AT 250 WORDS)

The prevention of sub-surface demineralization of bovine enamel and change in plaque composition by casein in an intra-oral model

The ability of bovine milk phosphoprotein (casein) to be incorporated into plaque, prevent enamel sub-surface demineralization, and affect bacterial composition was determined using a modified intra-oral caries model. The intra-oral model consisted of a removable appliance containing a left and right pair of bovine enamel slabs placed to simulate an approximal area. Supragingival plaque was collected and impacted into the left and right inter-enamel spaces. The left side of the appliance was exposed to various sugar and salt solutions, while the right side was exposed to sugar and casein solutions. Sodium caseinate, the major fraction alpha s1-casein, and a tryptic digest of alpha s1-casein (TD-casein) were studied. Sodium caseinate at a level of 2% w/v in a 3% sucrose-3% glucose-salt solution (pH 7.0) prevented sub-surface enamel demineralization over a ten-day period as shown by microradiography and microhardness. Two exposures of a 2% w/v sodium caseinate, alpha s1-casein, or TD-casein solution (pH 7.0) per day prevented sub-surface enamel demineralization caused by six exposures of a 3% sucrose-3% glucose-salt solution per day over a ten-day period. Intact alpha s1-casein and tryptic peptides were shown immunochemically to be incorporated into the inter-enamel plaque. The incorporation of casein and its breakdown in plaque did not produce a significant change in the amount or composition of plaque bacteria. The ability of casein and tryptic peptides to prevent enamel demineralization was related to their incorporation into plaque, thereby increasing plaque calcium phosphate and acid-buffering capacity by the phosphoseryl, histidyl, glutamyl, and aspartyl residues and indirectly through catabolism by plaque bacteria.

Arginine deiminase system and bacterial adaptation to acid environments

The arginine deiminase system in a variety of streptococci and in Pseudomonas aeruginosa was found to be unusually acid tolerant in that arginolysis occurred at pH values well below the minima for growth and glycolysis. The acid tolerance of the system allowed bacteria to survive potentially lethal acidification through production of ammonia to raise the environmental pH value.

Metabolic differences between saliva from caries-active and caries- and restoration-free children

Sucrose consumption and lactic-acid production by saliva, and the effects of pH, were first evaluated by radio-isotope techniques in populations of caries- and restoration-free (CF), and caries-active from sucrose than saliva from CA subjects. Sucrose consumption also was significantly greater in saliva of CF subjects. These results occurred at pH 7.2 but not at pH 6.0 and 5.0. Lactic acid, total volatile products and carbon-dioxide (CO2) production by saliva were then evaluated in different CF and CA populations of children. Metabolic parameters in the presence and absence of salivary supernatant (SS) also were determined. Saliva of these CF subjects also formed significantly more lactic acid from sucrose than did CA subjects. The presence of SS increased lactic-acid formation in this saliva; the increase was significant in CF subjects. Total volatile products and CO2 were greater in saliva of CF subjects but were not affected by SS. Partial microbial characterization of each salivary specimen was conducted in both series of experiments. CF subjects harboured less Streptococcus mutans (parts I and II), total lactobacilli (parts I and II) and Actinomyces species (part II) than CA subjects. Differences for lactobacilli in the first population and Actinomyces species in the second were significant.

Kinetics and product stoichiometry of ureolysis by human salivary bacteria and artificial mouth plaques

Ureolysis was investigated in salivary bacteria from persons with widely-differing oral ureolytic activities. Rate curves and product stoichiometry were established for urea disappearance, ammonia appearance and conversion of [14C]-urea to 14CO2. Ammonia, released stoichiometrically from urea, was best measured by a direct phenate-hypochlorite reaction. About 80 per cent of the urea-C was liberated as free CO2. Slight deviations from ammonia stoichiometry and most of the CO2 loss occurred in the first 5-10 min of reaction, when the rate of urea disappearance was constant and up to 2-fold higher than subsequently. This rate-change suggests that flux in the ureolysis pathway may be under feedback control. Ureolysis by salivary-sediment bacteria followed Michaelis-Menten kinetics with a Km of 2.5 mM; rates of end-product formation were independent of urea concentration between 25 and 500 mM. Ureolysis was inhibited 98 per cent by 5 mM acetohydroxamic acid, a urease inhibitor, and could be partly solubilized by sonication to give an enzyme preparation which, without cofactor supplementation, quantitatively hydrolysed urea. Thus urea metabolism by oral bacteria may principally involve urease-catalysed hydrolysis, rather than non-urease pathways.

Clearance of glucose and sucrose from the saliva of human subjects

The ability of 20 healthy people to clear test solutions of sucrose (0.73 M) and glucose (1.4 M) from the mouth was examined. Both sugars were cleared within 20 min in a two-step manner. Rapid clearance occurred between 0 and 6 min; much slower clearance occurred thereafter. It took 7.2 min with glucose and 6.3 min with sucrose for the saliva-sugar concentration to fall to 1 mg/ml. Salivary flow, stimulated during sugar exposure, decreased in a two-step pattern similar to sugar clearance. Evidently, clearance was dependent on the rate of flow of saliva which took about 1 h to return to its resting flow level. Comparison of the pattern of sugar clearance to the Stephan curve (the rapid pH fall followed by a slow pH rise seen after rinsing with sugar solutions) indicated that the pH-fall phase of the curve occurs during the initial period of rapid sugar clearance and salivary flow, and the pH-rise phase occurs during the subsequent period of slower clearance and slow saliva flow. Comparison with the data of Swenander-Lanke (1957) [Acta odont. scand. 15, 3-156], indicated that the clearance of sugar solutions also reflects the clearance of sugar-containing solid foods from the mouth.

A conceptual model for the co-existence of Streptococcus spp. and Actinomyces spp. in dental plaque

One of the most important questions in ecology is how to explain the co-existence of the variety of physiologically related organisms in the same habitat. A model is presented for the co-existence of Streptococcus species and Actinomyces species in dental plaque. The hypothesis is that these organisms co-exist because they simultaneously utilize several carbon and energy substrates. The hypothesis follows from the observation that the growth yield of oral streptococci and actinomyces in saliva is limited by carbohydrate. Preliminary experiments were undertaken to test the hypothesis using mixed chemostat cultures and gnotobiotic rats. Competition between S. mutans K1R and A. viscosus Ut2 in mixed chemostat cultures on glucose and asparagine was hampered by the early appearance of high-glucose-affinity variants of A. viscosus. From the physiological characteristics of S. sanguis and S. milleri, it might be predicted that simultaneous utilization of carbohydrate and arginine would enable these organisms to co-exist with S. mutans in an ecosystem. To test this mechanism under natural conditions, germ-free rats were inoculated with a combination of S. mutans K1R and S. sanguis P4A7 or the combination S. mutans K1R and S. milleri B448. The rats were fed on three different diets: (1) 58% cornstarch; (2) 48% cornstarch and 10% sucrose; and (3) 53% cornstarch and 5% arginine. The results of this experiment demonstrated that dietary arginine caused a significant decrease of the ratios K1R/P4A7 and K1R/B448 in dental plaque.(ABSTRACT TRUNCATED AT 250 WORDS)