Normal Oral Microflora Research Articles

Vaginal and oral microbes, host genotype and preterm birth

Preterm birth (PTB) is a leading cause of infant mortality and morbidity in the US and across the globe. Infection and associated inflammation are important initiators for PTB pathways; an estimated 40% of PTBs are attributed to amniochorionic-decidual or systemic inflammation. Historically, intrauterine infections have been implicated in PTB; recent evidence suggests that infections remote from the fetal site may also be causative. There is strong epidemiological evidence that bacterial vaginosis and periodontitis--two syndromes characterized by perturbations in the normal vaginal and oral bacterial microflora, respectively--are linked to infection-associated PTB. Oral and vaginal environments are similar in their bacterial microbiology; identical bacterial species have been independently isolated in periodontitis and bacterial vaginosis. Periodontitis and bacterial vaginosis also share many behavioral and sociodemographic risk factors suggesting a possible common pathophysiology. Genetic polymorphisms in host inflammatory responses to infection are shared between bacterial vaginosis, periodontitis and PTB, suggesting common mechanisms through which host genotype modify the effect of abnormal bacterial colonization on preterm birth. We review the state of knowledge regarding the risk of PTB attributable to perturbations in bacterial flora in oral and vaginal sites and the role of host genetics in modifying the risk of infection-related PTB. We posit that bacterial species that are common in perturbed vaginal and oral sites are associated with PTB through their interaction with the host immune system.

Evolutionary relationships among salivarius streptococci as inferred from multilocus phylogenies based on 16S rRNA-encoding, recA, secA, and secY gene sequences.

BackgroundStreptococci are divided into six phylogenetic groups, i.e, anginosus, bovis, mitis, mutans, pyogenic, and salivarius, with the salivarius group consisting of only three distinct species. Two of these species, Streptococcus salivarius and Streptococcus vestibularis, are members of the normal human oral microflora whereas the third, Streptococcus thermophilus, is found in bovine milk. Given that S. salivarius and S. vestibularis share several physiological characteristics, in addition to inhabiting the same ecosystem, one would assume that they would be more closely related to each other than to S. thermophilus. However, the few phylogenetic trees published so far suggest that S. vestibularis is more closely related to S. thermophilus. To determine whether this phylogenetic relationship is genuine, we performed phylogenetic inferences derived from secA and secY, the general secretion housekeeping genes, recA, a gene from a separate genetic locus that encodes a major component of the homologous recombinational apparatus, and 16S rRNA-encoding gene sequences using other streptococcal species as outgroups.ResultsThe maximum likelihood (ML) and maximum parsimony (MP) phylogenetic inferences derived from the secA and recA gene sequences provided strong support for the S. vestibularis/S. thermophilus sister-relationship, whereas 16S rRNA-encoding and secY-based analyses could not discriminate between alternate topologies. Phylogenetic analyses derived from the concatenation of these sequences unambiguously supported the close affiliation of S. vestibularis and S. thermophilus.ConclusionOur results corroborated the sister-relationship between S. vestibularis and S. thermophilus and the concomitant early divergence of S. salivarius at the base of the salivarius lineage.

Oral candidiasis-adhesion of non-albicans Candida species

Oral candidiasis is an opportunistic infection caused primarily by Candida albicans. However, in recent years, species of non-albicans Candida have been implicated more frequently in mucosal infection. Candida species usually reside as commensal organisms and are part of normal oral microflora. Determining exactly how transformation from commensal to pathogen takes place and how it can be prevented is continuous challenge for clinical doctors. Candidal adherence to mucosal surfaces is considered as a critical initial step in the pathogenesis of oral candidiasis. Acrylic dentures, acting as reservoirs, play an important role in increasing the risk from Candida colonisation. Thus, this review discusses what is currently known about the adhesion of non-albicans Candida species of oral origin to buccal epithelial cells and denture acrylics.

Will triclosan in toothpaste select for resistant oral streptococci?

The aims of the study were to determine the in vitro sensitivity of triclosan against viridans streptococci and the impact of triclosan on the normal oral microflora. Nine subjects used a triclosan-containing toothpaste for 2 weeks. Saliva samples were collected on days 0 and 14 and were analyzed quantitatively. The minimum inhibitory concentrations of triclosan and of several antimicrobial agents were determined for the streptococci isolated on days 0 and 14. No major changes occurred in the normal oral microflora during the study period. There were no differences in susceptibility between streptococcal strains collected at days 0 and 14 against triclosan or antimicrobial agents. Short-term use of triclosan has no major impact on normal oral microflora or on streptococcal susceptibility of antimicrobial agents. The effects of long-term use should be evaluated.

Possible association between amniotic fluid micro-organism infection and microflora in the mouth

Objective To determine whether oral bacteria are found in the amniotic cavity. Design Laboratory based analysis of clinical samples. Setting Royal London Hospital, Whitechapel. Population Forty-eight women attending for elective caesarean section. Methods Dental plaque, a high vaginal swab, amniotic fluid and chorioamnion tissue were taken from women with intact membranes. Main outcome measures Samples were investigated using culture and microscopy for the presence of micro-organisms. Amniotic fluid was analysed by polymerase chain reaction (PCR) for the presence of the ubiquitous 16S rRNA gene specific to most eubacteria. Samples were analysed using PCR genus and species specific primers directed to bacterial taxa found as part of the normal oral microflora ( Streptococcus spp. and Fusobacterium nucleatum). Levels of prostaglandin E 2 and cytokines were measured in amniotic fluid. Results Amniotic fluid was positive for universal bacteria PCR, Streptococcus spp. PCR and F. nucleatum PCR in 34/48, 20/48 and 7/48 of cases, respectively. Streptococcus spp. and F. nucleatum were cultured from the dental plaque, vagina and amniotic fluid of 48/48, 14/48, 0/48 and 29/48, 6/48, 0/48 subjects, respectively. A significant association was found between detection of microbial DNA (universal and F. nucletum) and complications in previous pregnancies including miscarriage, intrauterine death, neonatal death, preterm delivery and premature rupture of membranes ( P < 0.05 and P < 0.01, respectively). Prostaglandin E 2 and cytokine levels, with the exception of IL-1α, were not significantly different between women with and without evidence of infection. Conclusions The results indicate that Streptococcus spp. and F. nucleatum in the amniotic fluid may have an oral origin.

Possible association between amniotic fluid micro-organism infection and microflora in the mouth.

To determine whether oral bacteria are found in the amniotic cavity. Laboratory based analysis of clinical samples. Royal London Hospital, Whitechapel. Forty-eight women attending for elective caesarean section. Dental plaque, a high vaginal swab, amniotic fluid and chorioamnion tissue were taken from women with intact membranes. Samples were investigated using culture and microscopy for the presence of microorganisms. Amniotic fluid was analysed by polymerase chain reaction (PCR) for the presence of the ubiquitous 16S rRNA gene specific to most eubacteria. Samples were analysed using PCR genus and species specific primers directed to bacterial taxa found as part of the normal oral microflora (Streptococcus spp. and Fusobacterium nucleatum). Levels of prostaglandin E2 and cytokines were measured in amniotic fluid. Amniotic fluid was positive for universal bacteria PCR, Streptococcus spp. PCR and F. nucleatum PCR in 34/48, 20/48 and 7/48 of cases, respectively. Streptococcus spp. and F. nucleatum were cultured from the dental plaque, vagina and amniotic fluid of 48/48, 14/48, 0/48 and 29/48, 6/48, 0/48 subjects, respectively. A significant association was found between detection of microbial DNA (universal and F. nucletum) and complications in previous pregnancies including miscarriage, intrauterine death, neonatal death, preterm delivery and premature rupture of membranes (P < 0.05 and P < 0.01, respectively). Prostaglandin E2 and cytokine levels, with the exception of IL-1alpha, were not significantly different between women with and without evidence of infection. The results indicate that Streptococcus spp. and F. nucleatum in the amniotic fluid may have an oral origin.

PH-regulated secretion of a glyceraldehyde-3-phosphate dehydrogenase from Streptococcus gordonii FSS2: purification, characterization, and cloning of the gene encoding this enzyme.

Streptococcus gordonii and other viridans streptococci (VS) are primary etiologic agents of infective endocarditis, despite being part of the normal oral microflora. Recently, a surface-bound glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been found on the cells of all tested streptococcal species, where it has been implicated as a virulence factor. In contrast, we observed that a soluble extracellular GAPDH was the major secreted protein from S. gordonii FSS2, an endocarditis strain. The biochemical properties and gene sequence of S. gordonii GAPDH are almost identical to those of other streptococcal GAPDHs. Growth at defined pHs showed that secretion of GAPDH is regulated by environmental pH. GAPDH was primarily surface-associated at growth pH 6.5 and shifted to > 90% secreted at growth pH 7.5. Others have identified S. gordonii promoters that are up-regulated by a pH shift similar to that experienced by organisms entering the blood stream (neutral) from the oral cavity (slightly acid). Analysis of our results suggests that secretion of GAPDH may be a similar adaptation by S. gordonii.

Characteristic distribution pattern of Helicobacter pylori in dental plaque and saliva detected with nested PCR.

The precise mode of transmission and the natural reservoir for Helicobacter pylori are unknown. PCR assays have proved to be highly sensitive and specific and are regarded as the method of choice for detecting H. pylori DNA in the oral cavity. The aim of this study was to investigate the prevalence and distribution of H. pylori in the oral cavity. Forty-two patients undergoing gastroscopy were investigated for the presence of H. pylori in dental plaque and saliva by nested PCR, and in the stomach by the 13C-urea breath test. Samples tested comprised dental plaque from molars, premolars and incisors and saliva. Two sets of primers homologous to the 860-bp fragment of H. pylori DNA, which have been shown previously to be highly sensitive and specific, were used for nested PCR. Eleven patients (26.2%) were infected with H. pylori in the stomach. H. pylori DNA was identified in dental plaque samples from 41 patients (97%) and in 23 saliva samples (55%). The prevalence in dental plaque from molars, premolars and incisors was 82%, 64% and 59%, with an odds ratio of 3.18, 1.24 and 1 (reference), respectively. In conclusion, H. pylori was present in the oral cavity of 97% of tested patients, with a characteristic distribution that was independent of the infection status of the stomach. Thus H. pylori may belong to the normal oral microflora.

Acetaldehyde production by non-pathogenicNeisseria in human oral microflora: Implications for carcinogenesis in upper aerodigestive tract

Many epidemiological studies have identified chronic alcohol consumption as a significant risk factor for cancer of the upper aerodigestive tract (UAT) in human. Although acetaldehyde, the first metabolite from ethanol by alcohol dehydrogenase (ADH), is regarded as a carcinogen, how systemic production of acetaldehyde particularly affects the UAT remains unclear. In our study, we searched for the regional source of acetaldehyde in UAT, especially the involvement of bacteria in the human normal oral microflora. Here we demonstrate that, among the bacterial species identified from the human oral cavity, genus Neisseria had extremely high ADH activity and produced significant amounts of acetaldehyde when cultured with medium containing ethanol in vitro. The ability to produce acetaldehyde was more than 100-fold higher than that produced by any other genera we studied. Furthermore, alcohol ingestion influences the bacterial composition of the oral microflora, resulting in an increased proportion of Neisseria. Although Neisseria present in normal oral microflora is generally non-pathogenic, these findings suggest that this microbe can be a regional source of carcinogenic acetaldehyde and thus potentially play an important role in alcohol-related carcinogenesis in human UAT.

Actinobacillus actinomycetemcomitans in the Human Oral Microflora

In this paper, the frequency of the microaerophilic gram-negative bacterium Actinobacillus actinomycetemcomitans (Ac) which is a component of the normal human oral microflora was investigated. Ac could be cultivated from oral material (molar sulcus and/or mucous membrane of the cheek) from 55 out of 405 healthy adults examined. This overall Ac frequency of 13.6% corresponds well to the few other reports existing in literature. A short discussion about the possible pathogenic potential of Ac is given at the end of the paper.

Comparative Effects of Levofloxacin and Ofloxacin on the Normal Oral and Intestinal Microflora

The aim of the study was to study the ecological effects of levofloxacin, compared to that of ofloxacin, on the oral and intestinal human microflora. 10 healthy volunteers received levofloxacin (500 mg) and 10 subjects were given ofloxacin (400 mg) perorally, once daily for 7 days. Saliva and stool samples were obtained prior to drug administration, during administration (days 2, 4 and 7), and after withdrawal of the agents (days 9, 11, 14 and 21). The concentrations of levofloxacin and ofloxacin in the saliva and faecal samples, respectively, were assayed, and quantitative and qualitative microbiological analyses were performed. Oral administration of levofloxacin and ofloxacin led to low drug concentrations in the saliva, which corresponded with mild disturbances in the oral microflora. High drug levels were obtained in the intestinal tract, and both agents caused a selective reduction in the normal microflora, mainly directed towards aerobic Gram-negative bacteria. There was no significant difference between levofloxacin and ofloxacin, regarding ecological effects on the normal oral and intestinal microflora. From an ecological point of view, these agents acted favourably, since no major selection of resistant strains occurred in the normal microflora during administration.

Highly toxic clone of Actinobacillus actinomycetemcomitans in geographically widespread cases of juvenile periodontitis in adolescents of African origin.

The bacterium Actinobacillus actinomycetemcomitans has been implicated in the pathogenesis of juvenile periodontitis as the etiologic agent on the basis of several lines of circumstantial evidence. A matter of extensive debate is whether A. actinomycetemcomitans is an exogenous contagious pathogen or an opportunistic pathogen that resides in the normal oral microflora. Here we show evidence of a single clone of A. actinomycetemcomitans isolated from multiple patients with juvenile periodontitis in members of families of African origin living in geographically widespread areas. The clone is characterized by a 530-bp deletion in the leukotoxin gene operon, resulting in a significantly increased production of leukotoxin.

Antimicrobial treatment of periodontal diseases disturbs the human ecology: a review.

Periodontal diseases are associated with specific pathogenic microorganisms and therefore antimicrobial agents are often used in the treatment of patients with periodontitis refractory to conventional mechanical therapy. Perorally administered antimicrobial agents often lead to ecological disturbances in the normal oral and intestinal microflora with overgrowth of potentially pathogenic microorganisms, which may spread within the host or from patient to patient, causing infections. The use of antimicrobial agents also promotes the emergence of bacterial drug resistance, both in the periodontal pocket and in the normal oral and intestinal microflora. Topical administration of antimicrobial agents in the periodontal pockets causes restricted disturbances in the intestinal microflora, although there is a substantial risk of development of resistance at the site of application. A number of clinical studies imply that correct use of antimicrobial agents might be beneficial for a subset of patients with adult or juvenile periodontitis. The choice of antimicrobial agent should always be based on accurate microbial analyses of the subgingival microflora and in vitro antimicrobial susceptibility tests of the most important periodontal pathogens. Preferably, agents with low potential of causing ecological disturbances should be used.

Effect of chlorhexidine varnish on streptococci in dental plaque from occlusal fissures.

The treatment of tooth surfaces with chlorhexidine varnish may lead to long-lasting suppression of mutants streptococci in dental plaque. Microbiological observations following varnish treatment suggest that this prolonged suppression might be caused by bacterial interference. To investigate whether physiologically related organisms, such as other Streptococcus species, compete with mutans streptococci in the ecosystem, we have analyzed streptococcal populations on the tooth surface before and after chlorhexidine varnish treatment. Occlusal surfaces with high numbers of mutans streptococci were selected in human volunteers and treated with chlorhexidine varnish. Analyses of sequentially collected plaque samples confirmed that S. oralis-group streptococci returned to baseline levels shortly after the chlorhexidine application, while Actinomyces naeslundii populations reached prestudy or even higher levels only several days after treatment. Mutans streptococci, however, were below the detection level in the 14-day samples, except in 1 individual. The pattern of recolonization by individual Streptococcus species after chlorhexidine application closely resembled that of cleaned enamel surfaces: S. oralis and S. sanguis were primary colonizers while S. gordonii became dominant at a later stage. It is concluded that after intensive chlorhexidine treatment, a normal oral microflora reestablished, characterized by low proportions of mutans streptococci.

A microbiological and clinical review of the acute dentoalveolar abscess

Early microbiological studies of acute suppurative dental infection implicated streptococci or staphylococci as the causative microorganisms but recent studies suggest that the microbial flora of acute dentoalveolar abscess is usually polymicrobial, predominately involving CO 2-dependent streptococci, strictly anaerobic Gram-positive cocci and strictly anaerobic Gram-negative bacilli. These differences are probably due to poor sampling techniques and inadequate culture methods used in the early investigations. It is now accepted that specimens should be obtained by aspiration to avoid contamination and processed promptly using strict anaerobic culture. Traditionally the bacterial strains isolated have been regarded as members of the normal oral commensal microflora but it is becoming increasingly apparent from experimental infections that they have pathogenic properties. Although the vast majority of isolates have been found to be sensitive to a variety of antimicrobial agents there would not appear to be a uniformly effective drug. At the present time a penicillin, such as amoxycillin, would probably be the first choice antimicrobial agent with the addition of metronidazole if clinical improvement does not occur.

Effect of lomefloxacin on the normal oral and intestinal microflora

Ten healthy volunteers received 400 mg of lomefloxacin orally once daily for seven days. Saliva and faecal samples were collected on days 0, 2, 4, 7, 9, 11, 14 and 21 to investigate the effect of lomefloxacin on the normal oral and intestinal microflora. The mean concentration of lomefloxacin in faeces on day 7 was 203 mg/kg, while saliva levels were low, less than 0.6 mg/l in nine of ten volunteers. Aerobic gram-negative microorganisms were almost completely eradicated, while aerobic gram-positive and anaerobic microorganisms were virtually unaffected by the lomefloxacin administration. Two weeks after lomefloxacin was discontinued, the oral and intestinal microflora had returned to normal levels.

Growth of Oral Microflora on Saliva from Different Glands

In this study we have investigated the growth of batch-wise enrichment cultures of supragingival plaque on parotid, (PAR) submandibular-sublingual (SM-SL) and clarified whole (CHW) saliva from one volunteer, who also donated the plaque sample. All three salivas supported rapid growth of a mixed oral microflora. Salivary glycoproteins were completely deglycosylated during growth, while most proteins were left intact. The enrichment cultures on PAR and SM-SL salivas had different microbial compositions. B. oralis was dominant in the culture on PAR saliva, but absent in the culture on SM-SL saliva. In contrast E. lentum was found in a high proportion in SM-SL saliva, but was absent in the culture on PAR saliva. S. mitis was a dominant organism in both cultures, but the isolates from PAR and SM-SL saliva belonged to different biotypes. The enrichment on CHW saliva appeared to have an intermediate composition and most species and biotypes isolated either from the culture on PAR or from SM-SL saliva were found in CHW saliva. The various glycosidase and peptidase activities produced in the enrichment were largely cell-associated and found to be the same as those normally found in saliva and dental plaque in vivo . Taken together the results support the contention that the normal oral microflora maintains itself in the oral cavity by using salivary glycoproteins as a substrate. Moreover saliva seems to act as a selective force in the oral cavity, since different types of glycoproteins as found in PAR and SM-SL saliva supported the growth of different microfloras. Keywords: Saliva; Glycoproteins; Glycosidases; Peptidases; Oral microflora; Streptococci; Bacteroides; Adhesion.

The role of black-pigmented Bacteroides in human oral infections.

Today, 10 black-pigmented Bacteroides (BPB) species are recognized. The majority of these species can be isolated from the oral cavity. BPB species are involved in anaerobic infections of oral and non-oral sites. In the oral cavity, BPB species are associated with gingivitis, periodontitis, endodontal infections and odontogenic abscesses. Cultural studies suggest a specific role of the various BPB species in the different types of infection. Bacteroides gingivalis is closely correlated with destructive periodontitis in adults as well as in juveniles. Bacteroides intermedius seems to be less specific since it is found in gingivitis, periodontitis, endodontal infections and odontogenic abscesses. The recently described Bacteroides endodontalis is closely associated with endodontal infections and odontogenic abscesses of endodontal origin. There are indications that these periodontopathic BPB species are only present in the oral cavity of subjects suffering from periodontal breakdown, being absent on the mucosal surfaces of subjects without periodontal breakdown. BPB species associated with healthy oral conditions are Bacteroides melaninogenicus, Bacteroides denticola and Bacteroides loescheii. There are indications that these BPB species are part of the normal indigenous oral microflora. Many studies in the past have documented the pathogenic potential and virulence of BPB species. This virulence can be explained by the large numbers of virulence factors demonstrated in this group of micro-organisms. Among others, the proteolytic activity seems to be one of the most important features. Several artificial substrates as well as numerous biological proteins are degraded. These include anti-inflammatory proteins such as alpha-2-macroglobulin, alpha-1-antitrypsin, C3 and C5 complement factors and immunoglobulins. B. gingivalis is by far the most proteolytic species, followed by B. endodontalis. Like other bacteria, the lipopolysaccharide of B. gingivalis has shown to be active in bone resorption in vitro and is capable in stimulating interleukin-1 production in human peripheral monocytes. Based on the well documented association with periodontal disease and the possession of relevant virulence factors, BPB species must be considered as important micro-organisms in the etiology of oral infections. B. gingivalis seems to be the most pathogenic and virulent species.