Humoral immunity to commensal oral bacteria in human infants: salivary secretory immunoglobulin A antibodies reactive with Streptococcus mitis biovar 1, Streptococcus oralis, Streptococcus mutans, and Enterococcus faecalis during the first two years of life

Low rate of asymptomatic carriage and salivary immunoglobulin A response to Group A Streptococci in the healthy adult population in Finland

Streptococcus pyogenes, also called group A streptococcus (GAS), is a human pathogen causing a wide range of infections ranging from mild tonsillitis to severe, life threatening conditions such as bacteraemia, necrotizing fasciitis, and streptococcal toxic shock syndrome. GAS may also colonise the oropharynx without causing any signs of disease which is known as asymptomatic carriage. This study aims to investigate IgA responses against GAS and oral streptococci from saliva samples collected from healthy Finnish adults. In addition, asymptomatic throat GAS carriage was studied. The study participants consisted of healthy adult volunteers who provided one saliva sample, a throat swab, and a background questionnaire. Total salivary IgA, and GAS specific IgA were analysed from the saliva samples using enzyme-linked immunosorbent assays (ELISA) and the results were compared to oral streptococci specific IgA levels. Asymptomatic GAS throat carriers were identified by bacterial culture, and the isolates were emm typed. Samples from a total of 182 individuals were analysed. The median salivary IgA concentration was 62.9 µg/ml (range 17.3–649.9 µg/ml), and median GAS and oral streptococcal specific IgA concentrations 2.7 and 3.3 arbitrary units (AU, range 1.4–7.4 AU and 1.6–12.0 AU), respectively. Three individuals with asymptomatic GAS throat carriage were identified.

Presence of non-oral bacteria in the oral cavity

A homeostatic balance exists between the resident microbiota in the oral cavity and the host. Perturbations of the oral microbiota under particular conditions can contribute to the growth of non-oral pathogens that are hard to kill because of their higher resistance to antimicrobials, raising the probability of treatment failure and reinfection. The presence of these bacteria in the oral cavity has been proven to be associated with several oral diseases such as periodontitis, caries, and gingivitis, and systemic diseases of importance in clinical medicine such as cystic fibrosis, HIV, and rheumatoid arthritis. However, it is still controversial whether these species are merely transient members or unique to the oral cavity. Mutualistic and antagonistic interactions between the oral microbiota and non-oral pathogens can also occur, though the mechanisms used by these bacteria are not clear. Therefore, this review presents an overview of the current knowledge about the presence of non-oral bacteria in the oral cavity, their relationship with systemic and oral diseases, and their interactions with oral bacteria.

Mucosal IgA Prevents Commensal Candida albicans Dysbiosis in the Oral Cavity

The fungus Candida albicans colonizes the oral mucosal surface of 30–70% of healthy individuals. Due to local or systemic immunosuppression, this commensal fungus is able to proliferate resulting in oral disease, called oropharyngeal candidiasis (OPC). However, in healthy individuals C. albicans causes no harm. Unlike humans mice do not host C. albicans in their mycobiome. Thus, oral fungal challenge generates an acute immune response in a naive host. Therefore, we utilized C. albicans clinical isolates which are able to persist in the oral cavity without causing disease to analyze adaptive responses to oral fungal commensalism. We performed RNA sequencing to determine the transcriptional host response landscape during C. albicans colonization. Pathway analysis revealed an upregulation of adaptive host responses due to C. albicans oral persistence, including the upregulation of the immune network for IgA production. Fungal colonization increased cross-specific IgA levels in the saliva and the tongue, and IgA⁺ cells migrated to foci of fungal colonization. Binding of IgA prevented fungal epithelial adhesion and invasion resulting in a dampened proinflammatory epithelial response. Besides CD19⁺ CD138⁻ B cells, plasmablasts, and plasma cells were enriched in the tongue of mice colonized with C. albicans suggesting a potential role of B lymphocytes during oral fungal colonization. B cell deficiency increased the oral fungal load without causing severe OPC. Thus, in the oral cavity B lymphocytes contribute to control commensal C. albicans carriage by secreting IgA at foci of colonization thereby preventing fungal dysbiosis.

Salivary Factors that Maintain the Normal Oral Commensal Microflora

The oral microbiome is one of the most stable ecosystems in the body and yet the reasons for this are still unclear. As well as being stable, it is also highly diverse which can be ascribed to the variety of niches available in the mouth. Previous studies have focused on the microflora in disease-either caries or periodontitis-and only recently have they considered factors that maintain the normal microflora. This has led to the perception that the microflora proliferate in nutrient-rich periods during oral processing of foods and drinks and starves in between times. In this review, evidence is presented which shows that the normal flora are maintained on a diet of salivary factors including urea, lactate, and salivary protein degradation. These factors are actively secreted by salivary glands which suggests these factors are important in maintaining normal commensals in the mouth. In addition, the immobilization of SIgA in the mucosal pellicle indicates a mechanism to retain certain bacteria that does not rely on the bacterial-centric mechanisms such as adhesins. By examining the salivary metabolome, it is clear that protein degradation is a key nutrient and the availability of free amino acids increases resistance to environmental stresses.

PcsB Expression Diversity Influences on Streptococcus mitis Phenotypes Associated With Host Persistence and Virulence

S. mitis is an abundant member of the commensal microbiota of the oral cavity and pharynx, which has the potential to promote systemic infections. By analyzing a collection of S. mitis strains isolated from the oral cavity at commensal states or from systemic infections (blood strains), we established that S. mitis ubiquitously express the surface immunodominant protein, PcsB (also called GbpB), required for binding to sucrose-derived exopolysaccharides (EPS). Immuno dot blot assays with anti-PcsB antibodies and RT-qPCR transcription analyses revealed strain-specific profiles of PcsB production associated with diversity in pcsB transcriptional activities. Additionally, blood strains showed significantly higher levels of PcsB expression compared to commensal isolates. Because Streptococcus mutans co-colonizes S. mitis dental biofilms, and secretes glucosyltransferases (GtfB/C/D) for the synthesis of highly insoluble EPS from sucrose, profiles of S. mitis binding to EPS, biofilm formation and evasion of the complement system were assessed in sucrose-containing BHI medium supplemented or not with filter-sterilized S. mutans culture supernatants. These analyses showed significant S. mitis binding to EPS and biofilm formation in the presence of S. mutans supernatants supplemented with sucrose, compared to BHI or BHI-sucrose medium. In addition, these phenotypes were abolished if strains were grown in culture supernatants of a gtfBCD-defective S. mutans mutant. Importantly, GtfB/C/D-associated phenotypes were enhanced in high PcsB-expressing strains, compared to low PcsB producers. Increased PcsB expression was further correlated with increased resistance to deposition of C3b/iC3b of the complement system after exposure to human serum, when strains were previously grown in the presence of S. mutans supernatants. Finally, analyses of PcsB polymorphisms and bioinformatic prediction of epitopes with significant binding to MHC class II alleles revealed that blood isolates harbor PcsB polymorphisms in its functionally conserved CHAP-domain, suggesting antigenic variation. These findings reveal important roles of PcsB in S. mitis-host interactions under commensal and pathogenic states, highlighting the need for studies to elucidate mechanisms regulating PcsB expression in this species.

Prenatal and postnatal cigarette and cannabis exposure: Effects on Secretory Immunoglobulin A in early childhood

AIMS

Secretory Immunoglobulin A (SIgA) plays a critical role in immune functioning by preventing pathogens from adhering to epithelial mucosa. Most infectious agents enter the body via mucosal surfaces, thus SIgA serves in the defense against respiratory, intestinal, and urinogenitary infections, as well as periodontal disease and caries. This study examined the possibility that pre- and postnatal exposure to cigarette and cannabis is associated with individual differences in Secretory Immunoglobulin A (SIgA) levels in early childhood.

METHODS

Participants were 50 mother/infant (29 boys; 35% Caucasian) dyads recruited at their first prenatal appointment in a large northeastern community hospital in the United States. Repeated assessments of pre- and postnatal cigarette and cannabis were conducted beginning in the first trimester of pregnancy, using multiple methods (i.e., saliva, meconium, self-report). Infants were grouped into those prenatally exposed to either cigarette only (n = 19), cigarette and cannabis (n = 19), or with no prenatal substance exposure (n = 12). At age 5 years, the children's saliva was collected and assayed for SIgA.

RESULTS

There were group differences in SIgA levels as a function of prenatal exposure to cigarette and cannabis - children in the cigarette only and the cigarette and cannabis groups had higher SIgA levels compared to the non-exposed children. Children who experienced the combination of postnatal exposure to cigarette and cannabis had higher levels of SIgA, even after accounting for prenatal exposures and other covariates relevant to immune system functioning.

CONCLUSIONS

Prenatal and postnatal exposure to cigarette and cannabis may be associated with hyperactivity of mucosal immunity in early childhood. Links between cigarette and cannabis exposure and health problems in early childhood may be partially explained by prenatal and postnatal exposure-related changes in mucosal immunity.

The Application of Magnetic Bead Selection to Investigate Interactions between the Oral Microbiota and Salivary Immunoglobulins

The effect of humoral immunity on the composition of the oral microbiota is less intensively investigated than hygiene and diet, in part due to a lack of simple and robust systems for investigating interactions between salivary immunoglobulins and oral bacteria. Here we report the application of an ex situ method to investigate the specificity of salivary immunoglobulins for salivary bacteria. Saliva collected from six volunteers was separated into immunoglobulin and microbial fractions, and the microbial fractions were then directly exposed to salivary immunoglobulins of "self" and "non-self" origin. Antibody-selected bacteria were separated from their congeners using a magnetic bead system, selective for IgA or IgG isotypes. The positively selected fractions were then characterized using gel-based eubacterial-specific DNA profiling. The eubacterial profiles of positively selected fractions diverged significantly from profiles of whole salivary consortia based on volunteer (P≤ 0.001%) and immunoglobulin origin (P≤ 0.001%), but not immunoglobulin isotype (P = 0.2). DNA profiles of separated microbial fractions were significantly (p≤ 0.05) less diverse than whole salivary consortia and included oral and environmental bacteria. Consortia selected using self immunoglobulins were generally less diverse than those selected with immunoglobulins of non-self origin. Magnetic bead separation facilitated the testing of interactions between salivary antibodies and oral bacteria, showing that these interactions are specific and may reflect differences in recognition by self and non-self immunoglobulins. Further development of this system could improve understanding of the relationship between the oral microbiota and the host immune system and of mechanisms underlying the compositional stability of the oral microbiota.

Secretory IgA reactivity to social threat in youth: Relations with HPA, ANS, and behavior

Although the role of immune marker secretory immunoglobulin A (SIgA) in stress-related health outcomes is gaining recognition, SIgA responsiveness to acute stress has rarely been assessed in adults, and not at all in children. This study was designed to clarify developmental origins of differential immune function-related health risks by investigating youth SIgA responses to psychosocial stressors, including both normative responses and variability related to behavioral problems. Children and adolescents from a larger study (n=82) gave 6 saliva samples during a laboratory session in which they were exposed to a series of performance or interpersonal stressors. Samples were assayed for SIgA, as well as cortisol (representing hypothalamic-pituitary-adrenal axis activity) and alpha-amylase (sAA; representing autonomic nervous system activity). Behavioral problems were assessed with parent-report measures of youth internalizing and externalizing. Youth SIgA trajectories followed a normative pattern of reactivity and recovery around the stressors; however, these responses were blunted in youth with higher externalizing scores. SIgA showed differential associations with cortisol and sAA, and with positive and negative affect; whereas overall levels of SIgA related to cortisol output and positive affect, changes in SIgA over time synchronized with changes in sAA and negative affect. In contrast to SIgA, neither cortisol nor sAA related significantly to behavioral problems. Implications for the role of SIgA during psychosocial stress in the development of immune function-related health risks are discussed.

Commensal streptococci serve as a reservoir for β-lactam resistance genes in Streptococcus pneumoniae

Streptococcus pneumoniae is a leading cause of pneumonia, meningitis, septicemia, and middle ear infections. The incidence of S. pneumoniae isolates that are not susceptible to penicillin has risen worldwide and may be above 20% in some countries. Beta-lactam antibiotic resistance in pneumococci is associated with significant sequence polymorphism in penicillin-binding proteins (PBPs). Commensal streptococci, especially S. mitis and S. oralis, have been identified as putative donors of mutated gene fragments. However, no studies have compared sequences of the involved pbp genes in large collections of commensal streptococci with those of S. pneumoniae. We therefore investigated the sequence diversity of the transpeptidase region of the three pbp genes, pbp2x, pbp2b, and pbp1a in 107, 96, and 88 susceptible and nonsusceptible strains of commensal streptococci, respectively, at the nucleotide and amino acid levels to determine to what extent homologous recombination between commensal streptococci and S. pneumoniae plays a role in the development of beta-lactam resistance in S. pneumoniae. In contrast to pneumococci, extensive sequence variation in the transpeptidase region of pbp2x, pbp2b, and pbp1a was observed in both susceptible and nonsusceptible strains of commensal streptococci, conceivably reflecting the genetic diversity of the many evolutionary lineages of commensal streptococci combined with the recombination events occurring with intra- and interspecies homologues. Our data support the notion that resistance to beta-lactam antibiotics in pneumococci is due to sequences acquired from commensal Mitis group streptococci, especially S. mitis. However, several amino acid alterations previously linked to beta-lactam resistance in pneumococci appear to represent species signatures of the donor strain rather than being causal of resistance.

Salivary IgA antibody responses to Streptococcus mitis and Streptococcus mutans in preterm and fullterm newborn children

OBJECTIVES

The intensities and specificities of salivary IgA antibody responses to antigens of Streptococcus mutans, the main pathogen of dental caries, may influence colonization by these organisms during the first 1.5 year of life. Thus, the ontogeny of salivary IgA responses to oral colonizers continues to warrant investigation, especially with regard to the influence of birth conditions, e.g. prematurity, on the ability of children to efficiently respond to oral microorganisms. In this study, we characterised the salivary antibody responses to two bacterial species which are prototypes of pioneer and pathogenic microorganisms of the oral cavity (Streptococcus mitis and Streptococcus mutans, respectively) in fullterm (FT) and preterm (PT) newborn children.

METHODS

Salivas from 123 infants (70 FT and 53 PT) were collected during the first 10h after birth and levels of IgA and IgM antibodies and the presence of S. mutans and S. mitis were analysed respectively by ELISA and by chequerboard DNA-DNA hybridization. Two subgroups of 24 FT and 24 PT children were compared with respect to patterns of antibody specificities against S. mutans and S. mitis antigens, using Western blot assays. Cross-adsorption of 10 infant's saliva was tested to S. mitis, S. mutans and Enterococcus faecalis antigens.

RESULTS

Salivary levels of IgA at birth were 2.5-fold higher in FT than in PT children (Mann-Whitney; P<0.05). Salivary IgA antibodies reactive with several antigens of S. mitis and S. mutans were detected at birth in children with undetectable levels of those bacteria. Adsorption of infant saliva with cells of S. mutans produced a reduction of antibodies recognizing S. mitis antigens in half of the neonates. The diversity and intensity of IgA responses were lower in PT compared to FT children, although those differences were not significant.

CONCLUSION

These data provide evidence that children have salivary IgA antibodies shortly after birth, which might influence the establishment of the oral microbiota, and that the levels of salivary antibody might be related to prematurity.

Prevalence, phenotype, and genotype of Enterococcus faecalis isolated from saliva and root canals in patients with persistent apical periodontitis

INTRODUCTION

The aim of this study was to investigate the prevalence, phenotype, and genotype of Enterococcus faecalis isolated from saliva and root canals in patients with endodontic treatment failure.

METHODS

Samples were collected from 32 adults undergoing retreatment for periapical lesions after endodontic treatment performed at least 2 years previously. Isolates that were presumed to be E. faecalis were identified by both API20 Strep kits and 16S rRNA sequencing. Phenotypic tests for hemolysin and gelatinase production and antibiotic susceptibility were performed. Genotype analysis comprised virulence gene detection and pulsed field gel electrophoresis (PFGE).

RESULTS

The prevalence of E. faecalis was 18.8% in saliva and 40.6% in root canals (P = .666, Fisher exact test). Of the 19 isolates of E. faecalis, 6 were from saliva and 13 were from root canals. In 3 patients, E. faecalis isolates from saliva were more resistant to gentamicin than those from root canals. The genes ace, asa, gelE, cylA, and efaA were detected from all isolates. PFGE after SmaI digestion showed a genetic correlation among all isolates of 62%-100%.

CONCLUSIONS

Phenotype and genotype evidence of potential virulence factors was identified in E. faecalis from both saliva and root canals. A single patient might carry different E. faecalis strains in saliva and root canals.

Detection and quantitation of antifungal SIgA antibodies in body fluids

The measurement of antibodies in the external secretions that bathe mucosal surfaces is important in understanding the host response to the opportunistic pathogen, Candida albicans and its determinants of pathogenesis at these sites. The principal immunoglobulin isotype in mucosal secretions is secretory immunoglobulin A (SIgA). Unlike the circulatory system, mucosal surfaces are open systems in which the concentrations of immune factors are affected by diurnal variation, changes in flow rate, complex formation with mucins, and other variables. Thus, it is necessary to control these factors if meaningful data are to be obtained. This chapter outlines methods for the measurement of anti-Candida SIgA antibodies in primary units and shows how to control the factors that influence antibody measurement in external secretions.

Mutans streptococcal infection induces salivary antibody to virulence proteins and associated functional domains

The interplay between mucosal immune responses to natural exposure to mutans streptococci and the incorporation and accumulation of these cariogenic microorganisms in oral biofilms is unclear. An initial approach to explore this question would be to assess the native secretory immunity emerging as a consequence of Streptococcus mutans infection. To this end, we analyzed salivary immunoglobulin A (IgA) antibody to mutans streptococcal glucosyltransferase (Gtf) and glucan binding protein B (GbpB) and to domains associated with enzyme function and major histocompatibility complex (MHC) class II binding in two experiments. Salivas were collected from approximately 45-day-old Sprague-Dawley rats, which were then infected with S. mutans SJ32. Infection was verified and allowed to continue for 2 to 2.5 months. Salivas were again collected following the infection period. Pre- and postinfection salivas were then analyzed for IgA antibody activity using peptide- or protein-coated microsphere Luminex technology. S. mutans infection induced significant levels of salivary IgA antibody to Gtf (P < 0.002) and GbpB (P < 0.001) in both experiments, although the levels were usually far lower than the levels achieved when mucosal immunization is used. Significantly (P < 0.035 to P < 0.001) elevated levels of postinfection salivary IgA antibody to 6/10 Gtf peptides associated with either enzyme function or MHC binding were detected. The postinfection levels of antibody to two GbpB peptides in the N-terminal region of the six GbpB peptides assayed were also elevated (P < 0.031 and P < 0.001). Interestingly, the patterns of the rodent response to GbpB peptides were similar to the patterns seen in salivas from young children during their initial exposure to S. mutans. Thus, the presence of a detectable postinfection salivary IgA response to mutans streptococcal virulence-associated components, coupled with the correspondence between rat and human mucosal immune responsiveness to naturally presented Gtf and GbpB epitopes, suggests that the rat may be a useful model for defining mucosal responses that could be expected in humans. Under controlled infection conditions, such a model could prove to be helpful for unraveling relationships between the host response and oral biofilm development.

Antibody binding to Streptococcus mitis and Streptococcus oralis cell fractions

OBJECTIVE

To determine which cell fraction(s) of Streptococcus mitis biovar 1 serve as the best source of antigens recognized by salivary SIgA antibodies in infants.

DESIGN

Whole cells of 38 reference and wild-type isolates of S. mitis, Streptococcus oralis, Streptococcus gordonii, Enterococcus casseliflavus, and Enterococcus faecalis were fractionated into cell walls (CW), protease-treated cell walls (PTCW), cell membranes (CM) and cell protein (CP). Whole cells and these fractions were tested for binding by rabbit anti-S. mitis SK145 and anti-S. oralis SK100 sera, and also by salivary SIgA antibodies from infants and adults.

RESULTS

Anti-SK145 and anti-SK100 sera bound whole cells and fractions of all strains of S. mitis and S. oralis variably. Cluster analysis of antibody binding data placed the strains into S. mitis, S. oralis and 'non-S. mitis/non-S. oralis' clusters. Antigens from CW and CM best discriminated S. mitis from S. oralis. CM bound the most infant salivary SIgA antibody and PTCW bound the least. In contrast, adult salivary SIgA antibody bound all of the cell fractions and at higher levels.

CONCLUSIONS

Presumably the relatively short period of immune stimulation and immunological immaturity in infants, in contrast to adults, result in low levels of salivary SIgA antibody that preferentially bind CM of S. mitis but not PTCW. By utilizing isolated cell walls and membranes as sources of antigens for proteomics it may be possible to identify antigens common to oral streptococci and dissect the fine specificity of salivary SIgA antibodies induced by oral colonization by S. mitis.

Recovery of Enterococcus faecalis from cheese in the oral cavity of healthy subjects

INTRODUCTION

Enterococci are rarely found in the healthy human oral cavity, yet they are strongly associated with filled root canals. The origin of these enterococci remains unknown. Our hypothesis is that they are transient food-born colonizers under healthy conditions. This pilot study reinvestigated the prevalence of enterococci in the oral cavity of healthy volunteers, screened cheese samples for enterococci and investigated colonization of the oral cavity after ingestion of an enterocci-positive cheese.

METHOD

Concentrated oral rinse samples were collected from a cohort of 50 dental students and proved negative for viable enterococci. Twenty cheese samples were obtained from local supermarkets. Enterococci were cultured and identified using standard methods.

RESULTS

Viable enterococci were detected in one of five specimens of Swiss Tilsiter, three of five samples of French soft cheese, one of five Mozzarella samples and one of five Feta samples. Eight volunteers from the cohort consumed 10 g of a cheese with high Enterococcus faecalis load. Oral rinse samples were collected before and 1, 10 and 100 min after cheese ingestion. One minute after ingestion, a median of 5,480 E. faecalis colony-forming units was recovered from the oral rinse samples. Bacterial counts were reduced after 10 min, had dropped after 100 min to levels that were significantly (P < 0.005) different from the 1-min and 10-min scores and were below the detection limit after 1 week.

CONCLUSIONS

These findings suggest that colonization of the healthy oral cavity by enterococci is transitional, but at the same time add weight to our hypothesis that enterococcal root canal infections could be food-borne.

Age-specific salivary immunoglobulin A response to Streptococcus mutans GbpB

In a follow-up study of children infected with Streptococcus mutans at an early age (children previously shown to respond poorly to S. mutans GbpB), there was a delay in their immune response, rather than a complete inability to respond to this antigen. Epitopes in the N-terminal third of GbpB were identified as targets for naturally induced immunoglobulin A antibody in children at an early age.

Physiological and serological variation in Streptococcus mitis biovar 1 from the human oral cavity during the first year of life

OBJECTIVE

The purpose of the study was to explore the physiological and antigenic diversity of a large number of Streptococcus mitis biovar 1 isolates in order to begin to determine whether these properties contribute to species persistence.

DESIGN

S. mitis biovar 1 was collected from four infants from birth to the first year of age. At each of eight to nine visits, 60 isolates each were obtained from the cheeks, tongue and incisors (once erupted) yielding 4440 in total. These were tested for production of neuraminidase, beta1-N-acetylglucosaminidase, beta1-N-acetylgalactosaminidase, IgA1 protease and amylase-binding. Antigenic diversity was examined by ELISA and Western immunoblotting using antisera raised against S. mitis biovar 1 NCTC 12261(T) and SK145.

RESULTS

Three thousand three hundred and thirty (75%) of the isolates were identified as S. mitis biovar 1 and 3144 (94.4%) could be divided into four large phenotypic groups based on glycosidase production. Fifty-four percent of the isolates produced IgA1 protease, but production was disproportionate among the phenotypes. Between one-third and one-half of the strains of each phenotype bound salivary alpha-amylase. Antisera against strains NCTC 12261(T) and SK145 displayed different patterns of reactivity with randomly selected representatives of the four phenotypes.

CONCLUSIONS

S. mitis biovar 1 is physiologically and antigenically diverse, properties which could aid strains in avoiding host immunity and promote re-colonization of a habitat or transfer to a new habitat.

Salivary sIgA and cortisol: markers for functional dependence in older adults

Elderly persons with health problems and physical limitations have reduced independence. Since poor functional ability is a known risk factor for disease among older populations, including oral disease, this study was undertaken to assess whether salivary defense factors and the stress hormone cortisol are significant markers for functional dependence. Oral examinations; salivary and microbial analyses; and interviews using the Activities of Daily Living (ADD index, the Mini Nutritional Assessment (MNA) and the Perceived Life Stress Questionnaire (PLSQ) were conducted for 123 dentate subjects. Of the subjects, 80 lived independently in the community or in apartments at the Baycrest Centre for Geriatric Care in Toronto, Canada, and 43 resided in the Baycrest nursing home or the Baycrest Hospital. Whole saliva samples were assayed for total secretory immunoglobulin A (sIgA), sIgA1, sIgA2, total protein and cortisol using ELISA. Dependent residents in the nursing home/hospital scored significantly lower in the nutritional assessment, had higher mean PLSQ scores, increased total protein and cortisol concentrations, and reduced salivary flow rates in comparison to ambulatory residents in the community/apartments. In multivariable logistic regression, factors associated with functional dependence were: being male, perceiving income as inadequate, having low salivary flow rate and drinking less than 5 cups of water per day. These results indicate that salivary flow and cortisol may be useful markers of functional dependence; however, the ability of these markers to predict functional decline cannot be confirmed until longitudinal studies are conducted.

Clonal diversity and turnover of Streptococcus mitis bv. 1 on shedding and nonshedding oral surfaces of human infants during the first year of life

Streptococcus mitis bv. 1 is a pioneer colonizer of the human oral cavity. Studies of its population dynamics within parents and their infants and within neonates have shown extensive diversity within and between subjects. We examined the genetic diversity and clonal turnover of S. mitis bv. 1 isolated from the cheeks, tongue, and primary incisors of four infants from birth to 1 year of age. In addition, we compared the clonotypes of S. mitis bv. 1 isolated from their mothers' saliva collected in parallel to determine whether the mother was the origin of the clones colonizing her infant. Of 859 isolates obtained from the infants, 568 were unique clones. Each of the surfaces examined, whether shedding or nonshedding, displayed the same degree of diversity. Among the four infants it was rare to detect the same clone colonizing more than one surface at a given visit. There was little evidence for persistence of clones, but when clones were isolated on multiple visits they were not always found on the same surface. A similar degree of clonal diversity of S. mitis bv. 1 was observed in the mothers' saliva as in their infants' mouths. Clones common to both infant and mothers' saliva were found infrequently suggesting that this is not the origin of the infants' clones. It is unclear whether mucosal immunity exerts the environmental pressure driving the genetic diversity and clonal turnover of S. mitis bv. 1, which may be mechanisms employed by this bacterium to evade immune elimination.

Naturally acquired antibodies against four Enterococcus faecalis capsular polysaccharides in healthy human sera

Healthy human sera (HHS) contain naturally acquired enterococcal antibodies which promote neutrophil-mediated killing. The target antigens remain unknown. The present study used a capsular polysaccharide (CPS)-enzyme-linked immunosorbent assay (ELISA) to investigate whether the HHS antibodies of 12 healthy donors bound to the CPS of four E. faecalis serotypes (CPS-A to CPS-D) and then employed an opsonic-killing assay to determine if these antibodies mediated phagocyte-dependent killing. All HHS contained immunoglobulin G (IgG) and IgM antibodies directed against capsular polysaccharides of the four serotypes. Absorption of the sera with homologous and heterologous strains showed a majority of antibodies to be cross-reactive among the prototype strains. The susceptibility of the four prototype strains to opsonic killing varied. Opsonic killing of CPS-A and CPS-B strains was significantly higher than killing of CPS-C and CPS-D strains. Absorption studies revealed that the opsonic killing of HHS was only partially type specific, with cross-reactivity between CPS-A and CPS-B strains and between CPS-C and CPS-D strains. These data indicate that healthy individuals possess opsonic antibodies specific for CPS-A and CPS-B but only low titers of opsonic antibodies against CPS-C and CPS-D. Titers of opsonic antibodies did not correlate with antibody titers measured by ELISA. Whether this lack of correlation is due to the low frequency of opsonic antibodies or to increased resistance to the opsonophagocytic killing of some serotypes remains to be determined.

Study of humoral immunity to commensal oral bacteria in human infants demonstrates the presence of secretory immunoglobulin A antibodies reactive with Actinomyces naeslundii genospecies 1 and 2 ribotypes

The mouths of three human infants were examined from birth to age 2 years to detect colonization of Actinomyces naeslundii genospecies 1 and 2. These bacteria did not colonize until after tooth eruption. The diversity of posteruption isolates was determined by ribotyping. Using immunoblotting and enzyme-linked immunosorbent assay, we determined the reactivity of secretory immunoglobulin A (SIgA) antibodies in saliva samples collected from each infant before and after colonization against cell wall proteins from their own A. naeslundii strains and carbohydrates from standard A. naeslundii genospecies 1 and 2 strains. A. naeslundii genospecies 1 and 2 carbohydrate-reactive SIgA antibodies were not detected in any saliva sample. However, SIgA antibodies reactive with cell wall proteins were present in saliva before these bacteria colonized the mouth. These antibodies could be almost completely removed by absorption with A. odontolyticus, a species known to colonize the human mouth shortly after birth. However, after colonization by A. naeslundii genospecies 1 and 2, specific antibodies were induced that could not be removed by absorption with A. odontolyticus. Cluster analysis of the patterns of reactivity of postcolonization salivary antibodies from each infant with antigens from their own strains showed that not only could these antibodies discriminate among strains but antibodies in saliva samples collected at different times showed different reactivity patterns. Overall, these data suggest that, although much of the salivary SIgA antibodies reactive with A. naeslundii genospecies 1 and 2 are directed against genus-specific or more broadly cross-reactive antigens, species, genospecies, and possibly strain-specific antibodies are induced in response to colonization.

Salivary IgA reactions to cell-surface antigens of oral streptococci

BACKGROUND

In the immunoblot technique, using whole bacteria cell extracts as antigens, both intra- and extracellular antigens are detected, which gives a large number of immunoglobulin A (IgA) reactions (immunoblot bands) when incubated with saliva. It is important to distinguish which immunoblot bands represent bacterial cell-surface antigens, since these antigens could be involved in adhesion mechanisms and be available for blocking in vivo.

METHODS

Bacterial extracts of Streptococcus mutans, Streptococcus sobrinus, Streptococcus parasanguis and the streptococcal antigen I/II were separated using SDS-PAGE. The antigens were detected with saliva in Western blot. Untreated saliva and saliva in which cell-surface reactive IgA had been absorbed with whole bacteria cells were analyzed.

RESULTS

Approximately half the number of the bands were absent for saliva absorbed with homologous cells, compared to untreated saliva. The absorption pattern was almost identical for S. mutans and S. sobrinus but not for S. parasanguis. Salivary IgA reactive against streptococcal antigen I/II was absorbed by S. mutans cells, to a lesser extent by S. sobrinus cells, and not at all by S. parasanguis cells.

CONCLUSION

It is likely that the bands that were absent after absorption represented cell-surface antigens. For S. mutans and S. sobrinus, these bands were probably the streptococcal antigen I/II.

Characterization of maternal mutans streptococci transmission in an African American population

In the current literature database, information on microbiological attributes to caries outcomes in African American populations is limited and scattered. Few reports have discussed MS infection and transmission from African American mothers to their children. During the past few years, the research group at the University of Alabama at Birmingham and the Jefferson County Pubic Health Department have done a series of extensive studies to systematically investigate the prevalence of MS colonization, the time of initial MS infection as defined as "the window of infectivity," the source of MS transmission as defined as "the fidelity of transmission, and the chemotherapeutic management of MS transmission and caries prevention. The objective of this report was to summarize the main significant findings generated during a period of 15 years of study. One limitation of the studies outlined in this article is that the research populations were predominately African American families. The inclusion of white and other minorities would make the conclusions more generalizable to the US population as a whole. Nevertheless, the information presented in this report can serve as baseline knowledge for future studies of caries etiology in African American and other ethnic populations.

Characterization of humoral and cellular immune responses elicited by meningococcal carriage

In order to study the immune response elicited by asymptomatic carriage of Neisseria meningitidis, samples of serum, peripheral blood mononuclear cells (PBMCs), and saliva were collected from a cohort of more than 200 undergraduate students in Nottingham, United Kingdom, who were subject to high rates of acquisition and carriage of meningococci. Serum immunoglobulin G levels were elevated following increases in the rate of carriage, and these responses were specific for the colonizing strains. In order to investigate T-cell responses, PBMCs from 15 individuals were stimulated with a whole-cell lysate of the H44/76 meningococcal strain (B:15:P1.7,16), stained to detect cell surface markers and intracellular cytokines, and examined by flow cytometry. The cells were analyzed for expression of CD69 (to indicate activation), gamma interferon (IFN-gamma) (a representative T-helper 1 subset [Th1]-associated cytokine), and interleukin-5 (IL-5) (a Th2-associated cytokine). Following a brief meningococcal stimulation, the numbers of CD69(+) IFN-gamma(+) CD56/16(+) NK cells were much higher than cytokine-positive CD4(+) events. Both IFN-gamma(+) and IL-5(+) events were detected among the CD69(+) CD4(+) population, leading to the conclusion that an unbiased T-helper subset response was elicited by meningococcal carriage.

Human T-cell responses to the glucosyltransferases of Streptococcus mutans

We previously reported differential humoral responses to glucosyltransferases (GTFs), with significantly higher saliva and serum antibody levels to GtfD than to GtfB or GtfC. To test the hypothesis that cellular immune responses to these molecules also may differ, peripheral blood mononuclear cell (PBMC) and T-cell proliferative responses in young adults and children with distinct genetic backgrounds were determined using purified recombinant GtfC and GtfD. PBMCs from all of the volunteers responded to GtfC and -D, but responses were directed predominantly towards GtfD and were major histocompatibility class II antigen dependent. A predominant T-cell response to GtfD, over GtfC, was detectable at various antigen concentrations ranging from 1 to 20 microg/ml and correlated with the differential serum immunoglobulin G (IgG) and salivary IgA antibody responses to the GTFs. Therefore, in naturally sensitized humans, Streptococcus mutans GTFs stimulate differential humoral and cellular immune responses, with the secreted form of GtfD eliciting a stronger response than the cell wall-associated form of GtfC.