Invasion and killing of human endothelial cells by viridans group streptococci

Insights into the enigma of oral streptococci in carcinogenesis

SUMMARYThe genus Streptococcus consists of a taxonomically diverse group of Gram-positive bacteria that have earned significant scientific interest due to their physiological and pathogenic characteristics. Within the genus Streptococcus, viridans group streptococci (VGS) play a significant role in the oral ecosystem, constituting approximately 80% of the oral biofilm. Their primary role as pioneering colonizers in the oral cavity with multifaceted interactions like adherence, metabolic signaling, and quorum sensing contributes significantly to the complex dynamics of the oral biofilm, thus shaping oral health and disease outcomes. Perturbations in oral streptococci composition drive oral dysbiosis and therefore impact host-pathogen interactions, resulting in oral inflammation and representing VGS as an opportunistic pathogen. The association of oral streptococci in tumors across distant organs, spanning the esophagus, stomach, pancreas, and colon, illuminates a potential association between oral streptococci, inflammation, and tumorigenesis. This finding emphasizes the need for further investigations into the role of oral streptococci in mucosal homeostasis and their involvement in carcinogenesis. Hence, here, we review the significance of oral streptococci in biofilm dynamics and how the perturbation may impact mucosal immunopathogenesis in the context of cancer, with a vision of exploiting oral streptococci for cancer intervention and for the development of non-invasive cancer diagnosis.

The oral microbiota and cardiometabolic health: A comprehensive review and emerging insights

There is mounting evidence demonstrating that oral dysbiosis causes periodontal disease and promotes the development of cardiovascular disease. The advancement of omics techniques has driven the optimization of oral microbiota species analysis and has provided a deeper understanding of oral pathogenic bacteria. A bi-directional relationship exists between the oral microbiota and the host, and oral-gut microbiota transfer is known to alter the composition of the gut microbiota and may cause local metabolic disorders. Furthermore, cardiovascular health can also be highly affected by oral microbiota functions and metabolites, including short-chain fatty acids (SCFAs), nitric oxide (NO), hydrogen sulfide (H2S), and some lipid metabolites. Studies have found that trimethylamine oxide (TMAO) may have adverse effects on cardiovascular health, whereas SCFAs, NO, and H2S have cardioprotective effects. SCFAs and H2S exert varying oral and cardiovascular effects, however reports on this specific topic remain controversial. Previous evidences are accustomed to summarizing the functions of oral microbiota in the context of periodontitis. The direct relationship between oral microbiota and cardiovascular diseases is insufficient. By systematically summarizing the methods associated with oral microbiota transplantation (OMT), this review facilitates an investigation into the causal links between oral microbiota and cardiovascular disease. The concomitant development of omics, bioinformatics, bacterial culture techniques, and microbiota transplantation techniques is required to gain a deeper understanding of the relationship between oral microbiota and cardiovascular disease occurrence.

Antibiotic susceptibility patterns of viridans group streptococci isolates in the United States from 2010 to 2020

Background

Viridans group streptococci (VGS) are typically part of the commensal flora but can also cause severe invasive diseases such as infective endocarditis. There are limited data available showing antibiotic susceptibility over time for VGS.

Objectives

To evaluate antibiotic susceptibility trends in VGS over time.

Methods

In vitro susceptibility patterns for 33 antibiotics were examined for Streptococcus mitis, Streptococcus oralis, and non-speciated VGS isolates from patients in Veterans Affairs (VA) Medical Centers in the United States between 2010 and 2020. Susceptibility determinations were made by the individual clinical microbiology laboratories and data were retrospectively collected from the VA Corporate Data Warehouse. Susceptibility trends were analysed using Poisson regression.

Results

A total of 14 981 VGS isolates were included of which 19.5%, 0.7% and 79.8% were S. mitis, S. oralis and non-speciated VGS isolates, respectively. Cumulative susceptibility rates across all years were similar between species for ceftriaxone (range: 96.0% to 100%), clindamycin (81.3% to 84.5%), and vancomycin (99.7% to 100%). For penicillin, susceptibility rates were 71.0%, 80.9% and 86.3% for S. mitis, S. oralis and non-speciated isolates, respectively. From 2010 to 2020, susceptibility of non-speciated VGS isolates decreased for erythromycin (P = 0.0674), penicillin (P = 0.0835), and tetracycline (P = 0.0994); though the decrease was only significant for clindamycin (P = 0.0033). For S. mitis, a significant susceptibility rate decrease was observed for erythromycin (P = 0.0112).

Conclusions

Susceptibility rates for some clinically relevant antibiotics declined between 2010 and 2020. This worrisome trend highlights the need to improve antimicrobial stewardship efforts to limit unnecessary antibiotic use and preserve empirical treatment options.

Diversity in Phenotypes Associated With Host Persistence and Systemic Virulence in Streptococcus sanguinis Strains

Streptococcus sanguinis is a pioneer commensal species of dental biofilms, abundant in different oral sites and commonly associated with opportunist cardiovascular infections. In this study, we addressed intra-species functional diversity to better understand the S. sanguinis commensal and pathogenic lifestyles. Multiple phenotypes were screened in nine strains isolated from dental biofilms or from the bloodstream to identify conserved and strain-specific functions involved in biofilm formation and/or persistence in oral and cardiovascular tissues. Strain phenotypes of biofilm maturation were independent of biofilm initiation phenotypes, and significantly influenced by human saliva and by aggregation mediated by sucrose-derived exopolysaccharides (EPS). The production of H2O2 was conserved in most strains, and consistent with variations in extracellular DNA (eDNA) production observed in few strains. The diversity in complement C3b deposition correlated with the rates of opsonophagocytosis by human PMN and was influenced by culture medium and sucrose-derived EPS in a strain-specific fashion. Differences in C3b deposition correlated with strain binding to recognition proteins of the classical pathway, C1q and serum amyloid protein (SAP). Importantly, differences in strain invasiveness into primary human coronary artery endothelial cells (HCAEC) were significantly associated with C3b binding, and in a lesser extent, with binding to host glycoproteins (such as fibrinogen, plasminogen, fibronectin, and collagen). Thus, by identifying conserved and strain-specific phenotypes involved in host persistence and systemic virulence, this study indicates potential new functions involved in systemic virulence and highlights the need of including a wider panel of strains in molecular studies to understand S. sanguinis biology.

Type IV Pili of Streptococcus sanguinis Contribute to Pathogenesis in Experimental Infective Endocarditis

Streptococcus sanguinis is a common cause of infective endocarditis (IE). Efforts by research groups are aimed at identifying and characterizing virulence factors that contribute to the ability of this organism to cause IE. This Gram-positive pathogen causes heart infection by gaining access to the bloodstream, adhering to host extracellular matrix protein and/or platelets, colonizing the aortic endothelium, and incorporating itself into the aortic vegetation. While many virulence factors have been reported to contribute to the ability of S. sanguinis to cause IE, it is noteworthy that type IV pili (T4P) have not been described to be a virulence factor in this organism, although S. sanguinis strains typically encode these pili. Type IV pili are molecular machines that are capable of mediating diverse virulence functions and surface motility. T4P have been shown to mediate twitching motility in some strains of S. sanguinis, although in most strains it has been difficult to detect twitching motility. While we found that T4P are dispensable for direct in vitro platelet binding and aggregation phenotypes, we show that they are critical to the development of platelet-dependent biofilms representative of the cardiac vegetation. We also observed that T4P are required for in vitro invasion of S. sanguinis into human aortic endothelial cells, which indicates that S. sanguinis may use T4P to take advantage of an intracellular niche during infection. Importantly, we show that T4P of S. sanguinis are critical to disease progression (vegetation development) in a native valve IE rabbit model. The results presented here expand our understanding of IE caused by S. sanguinis and identify T4P as an important virulence factor for this pathogen.

IMPORTANCE This work provides evidence that type IV pili produced by Streptococcus sanguinis SK36 are critical to the ability of these bacteria to attach to and colonize the aortic heart valve (endocarditis). We found that an S. sanguinis type IV pili mutant strain was defective in causing platelet-dependent aggregation in a 24-h infection assay but not in a 1-h platelet aggregation assay, suggesting that the type IV pili act at later stages of vegetation development. In a rabbit model of disease, a T4P mutant strain does not develop mature vegetations that form on the heart, indicating that this virulence factor is critical to disease and could be a target for IE therapy.

Pathogenic and antimicrobial resistance genes in Streptococcus oralis strains revealed by comparative genome analysis

Streptococcus oralis is an early colonizer bacterium in dental plaques and is considered a potential pathogen of infective endocarditis (IE) disease. In this study, we built a complete genome map of Streptococcus oralis strain SOT, Streptococcus oralis strain SOD and Streptococcus infantis strain SO and performed comparative genomic analysis among these three strains. The results showed that there are five genomic islands (GIs) in strain SOT and one CRISPR in strain SOD. Each genome harbors various pathogenic genes related to diseases and drug resistance, while the antibiotic resistance genes in strains SOT and SOD were quite similar but different from those in strain SO. In addition, we identified 17 main virulence factors and capsule-related genes in three strains. These results suggest the pathogenic potential of Streptococcus strains, which lay a foundation for the prevention and treatment of a Streptococcus oralis infection.

Multidrug-Resistant Infections Among Hospitalized Adults With Community-Acquired Pneumonia In An Indonesian Tertiary Referral Hospital

Objectives

To evaluate the clinical and microbiological appearance among hospitalized pneumonia patients focusing on resistance and risk factors for mortality in a referral hospital.

Patients and methods

The study was an observational retrospective study on patients with CAP from 2014 to 2016 at Dr Soetomo referral hospital of Surabaya, Indonesia. All positive cultures with antimicrobial susceptibility results from blood and respiratory specimens were included. Patients infected with drug-susceptible pathogens and MDR organisms were also assessed in terms of clinical characteristics, day-3 clinical improvement, and 14-day mortality.

Results

Of 202 isolates, 181 possessed antimicrobial susceptibility data. S. pneumoniae was the most prevalent pathogen causing CAP (18.3%). Most patients were empirically treated with ceftriaxone (n=75; 41.4%). Among beta-lactam antibiotics, the susceptibility to the third-generation cephalosporins remained relatively high, between 67.4% and 82.3%, compared with the other beta-lactams such as amoxicillin/clavulanate and ampicillin/sulbactam (a sensitivity rate of 36.5% and 47.5, respectively). For carbapenem antibiotics, imipenem and meropenem susceptibility was 69.6% and 82.3% respectively. Approximately 22% of isolates were identified as MDR that showed significant differences in clinical outcomes of 14-day mortality rates (p<0.001). Notably, patients with day-3 improvement had a lower risk of mortality (OR= 0.06; 95% CI= 0.02–0.19).

Conclusion

One-fifth of causative agents among hospitalized CAP cases were identified as MDR organisms. The pathogens of MDR and non-MDR CAP remain susceptible to the third-generation cephalosporins. Together with additional consideration of culture findings and Pneumonia Severity Index (PSI) assessment, a 3-day clinical assessment is essential to predict the prognosis of 14-day mortality.

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DMBT1 involvement in the human aortic endothelial cell response to Streptococcus mutans

Streptococcus mutans is a causative organism of dental caries and has been reported to be associated with the development of cardiovascular disease (CVD). Previous studies have demonstrated that S. mutans invades human aortic endothelial cells (HAECs) and HAECs invaded by S. mutans produce higher levels of CVD-related cytokines than non-invaded HAECs. DMBT1 (deleted in malignant brain tumors 1), also known as salivary agglutinin or gp-340, belongs to the scavenger receptor cysteine-rich superfamily. DMBT1 is expressed in epithelial and non-epithelial tissues and has multiple functions. The interaction between S. mutans and DMBT1 has been demonstrated in cariogenesis, but DMBT1 involvement in CVD has not been examined. In this study, we investigated DMBT1 expression in HAECs stimulated with S. mutans and examined the role of DMBT1 in the interaction between S. mutans and HAECs. All of the tested S. mutans strains induced higher production levels of DMBT1 in HAECs than those in unstimulated HAECs. More S. mutans cells adhered to DMBT1 knock down HAECs than to DMBT1-producing HAECs. Invasion of DMBT1 knock down HAECs by S. mutans was stronger than that of DMBT1-producing HAECs, and externally added DMBT1 reduced bacterial invasion. Cytokine production by DMBT1 knock down HAECs by S. mutans stimulation was higher than that by DMBT1-producing HAECs. These phenomena seemed to be due to the effect of released DMBT1, namely, the inhibition of bacterial adherence to HAECs by DMBT1. These results suggest that DMBT1 plays a protective role against the S. mutans-induced CVD process in HAECs.

Streptococcus pneumoniae potently induces cell death in mesothelial cells

Pleural infection/empyema is common and its incidence continues to rise. Streptococcus pneumoniae is the commonest bacterial cause of empyema in children and among the commonest in adults. The mesothelium represents the first line of defense against invading microorganisms, but mesothelial cell responses to common empyema pathogens, including S. pneumoniae, have seldom been studied. We assessed mesothelial cell viability in vitro following exposure to common empyema pathogens. Clinical isolates of S. pneumoniae from 25 patients with invasive pneumococcal disease and three reference strains were tested. All potently induced death of cultured mesothelial cells (MeT-5A) in a dose- and time-dependent manner (>90% at 10⁷ CFU/mL after 24 hours). No significant mesothelial cell killing was observed when cells were co-cultured with Staphylococcus aureus, Streptococcus sanguinis and Streptococcus milleri group bacteria. S. pneumoniae induced mesothelial cell death via secretory product(s) as cytotoxicity could be: i) reproduced using conditioned media derived from S. pneumoniae and ii) in transwell studies when the bacteria and mesothelial cells were separated. No excess cell death was seen when heat-killed S. pneumoniae were used. Pneumolysin, a cytolytic S. pneumoniae toxin, induced cell death in a time- and dose-dependent manner. S. pneumoniae lacking the pneumolysin gene (D39 ΔPLY strain) failed to kill mesothelial cells compared to wild type (D39) controls, confirming the necessity of pneumolysin in D39-induced mesothelial cell death. However, pneumolysin gene mutation in other S. pneumoniae strains (TIGR4, ST3 and ST23F) only partly abolished their cytotoxic effects, suggesting different strains may induce cell death via different mechanisms.

Molecular mechanisms driving Streptococcus mitis entry into human gingival fibroblasts in presence of chitlac-nAg and saliva

The molecular mechanisms leading to Streptococcus mitis capability of entering oral cells were investigated in a co-culture of S. mitis and Human Gingival Fibroblasts (HGFs) in the presence of saliva. An innovative colloidal solution based on silver nanoparticles (Chitlac-nAg), a promising device for daily oral care, was added to the experimental system in order to study the effects of silver on the bacterial overgrowth and ability to enter non-phagocytic eukaryotic cells. The entry of bacteria into the eukaryotic cells is mediated by a signalling pathway involving FAK, integrin β1, and the two cytoskeleton proteins vinculin and F-actin, and down-regulated by the presence of saliva both at 3 and 48 h of culture, whereas Chitlac-n Ag exposure seems to influence, by incrementing it, the number of bacteria entering the fibroblasts only at 48 h. The formation of fibrillary extrusion from HGFs and the co-localization of bacteria and silver nanoparticles within the fibroblast vacuoles were also recorded. After longer experimental times (72 and 96 h), the number of S. mitis chains inside gingival cells is reduced, mainly in presence of saliva. The results suggest an escape of bacteria from fibroblasts to restore the microbial balance of the oral cavity.

Contribution of Streptococcus mutans Strains with Collagen-Binding Proteins in the Presence of Serum to the Pathogenesis of Infective Endocarditis

Streptococcus mutans, a major pathogen of dental caries, is considered one of the causative agents of infective endocarditis (IE). Recently, bacterial DNA encoding 120-kDa cell surface collagen-binding proteins (CBPs) has frequently been detected from S. mutans-positive IE patients. In addition, some of the CBP-positive S. mutans strains lacked a 190-kDa protein antigen (PA), whose absence strengthened the adhesion to and invasion of endothelial cells. The interaction between pathogenic bacteria and serum or plasma is considered an important virulence factor in developing systemic diseases; thus, we decided to analyze the pathogenesis of IE induced by S. mutans strains with different patterns of CBP and PA expression by focusing on the interaction with serum or plasma. CBP-positive (CBP⁺)/PA-negative (PA^-) strains showed prominent aggregation in the presence of human serum or plasma, which was significantly greater than that with CBP⁺/PA-positive (PA⁺) and CBP-negative (CBP^-)/PA+ strains. Aggregation of CBP⁺/PA^- strains was also observed in the presence of a high concentration of type IV collagen, a major extracellular matrix protein in serum. In addition, aggregation of CBP⁺/PA^- strains was drastically reduced when serum complement was inactivated. Furthermore, an ex vivo adherence model and an in vivo rat model of IE showed that extirpated heart valves infected with CBP⁺/PA^- strains displayed prominent bacterial mass formation, which was not observed following infection with CBP⁺/PA⁺ and CBP^-/PA⁺ strains. These results suggest that CBP⁺/PA^-S. mutans strains utilize serum to contribute to their pathogenicity in IE.

Invasive Streptococcus mutans induces inflammatory cytokine production in human aortic endothelial cells via regulation of intracellular toll-like receptor 2 and nucleotide-binding oligomerization domain 2

Streptococcus mutans, the primary etiologic agent of dental caries, can gain access to the bloodstream and has been associated with cardiovascular disease. However, the roles of S. mutans in inflammation in cardiovascular disease remain unclear. The aim of this study was to examine cytokine production induced by S. mutans in human aortic endothelial cells (HAECs) and to evaluate the participation of toll-like receptors (TLRs) and cytoplasmic nucleotide-binding oligomerization domain (NOD) -like receptors in HAECs. Cytokine production by HAECs was determined using enzyme-linked immunosorbent assays, and the expression of TLRs and NOD-like receptors was evaluated by real-time polymerase chain reaction, flow cytometry and immunocytochemistry. The involvement of TLR2 and NOD2 in cytokine production by invaded HAECs was examined using RNA interference. The invasion efficiencies of S. mutans strains were evaluated by means of antibiotic protection assays. Five of six strains of S. mutans of various serotypes induced interleukin-6, interleukin-8 and monocyte chemoattractant protein-1 production by HAECs. All S. mutans strains upregulated TLR2 and NOD2 mRNA levels in HAECs. Streptococcus mutans Xc upregulated the intracellular TLR2 and NOD2 protein levels in HAECs. Silencing of the TLR2 and NOD2 genes in HAECs invaded by S. mutans Xc led to a reduction in interleukin-6, interleukin-8 and monocyte chemoattractant protein-1 production. Cytokine production induced by invasive S. mutans via intracellular TLR2 and NOD2 in HAECs may be associated with inflammation in cardiovascular disease.

Streptococcus mitis and Gemella haemolysans were simultaneously found in atherosclerotic and oral plaques of elderly without periodontitis-a pilot study

OBJECTIVES

Local infections may contribute to the initiation and progression of several clinical diseases in humans. Atherosclerotic plaques of subjects suffering from periodontitis are colonized by periopathogens; however, the presence of bacteria in atherosclerotic plaques in patients without severe forms of periodontitis is of high relevance for the general population.

MATERIALS AND METHODS

Patients who were electively treated for atherosclerotic lesions of the carotid artery and without clinical signs of periodontitis were eligible for the study. Oral and atherosclerotic plaques were sampled, processed, and analyzed for their microbial composition by 454-sequencing.

RESULTS

Seventeen patients were included in the analyses, and 76 % of all atherosclerotic plaque specimens were positive for bacterial DNA. In the oral plaques, 76,532 sequences were identified representing 1 phylum, 17 classes, 112 families, and 263 genera. In atherosclerotic plaques, 6112 sequences representing 1 phylum, 4 classes, 8 families, and 36 genera were found. The bacterial DNAs of the species Gemella haemolysans and Streptococcus mitis were simultaneously found in atherosclerotic as well as oral plaque samples of 3 patients.

CONCLUSIONS

These results indicated that in subjects without periodontitis, the transmission of oral bacteria to atherosclerotic plaques of the carotid artery is a feasible event.

CLINICAL RELEVANCE

The prevention of transient bacteremia from the oral cavity requires high levels of oral health.

Aggressive Surgical Therapy With Early Vitrectomy, Panretinal Photocoagulation, and Silicone Oil Tamponade for Streptococcus mitis Endophthalmitis

An 87-year-old woman presented with acute, painful vision loss in her right eye after intravitreal injection. Examination disclosed hypopyon and vitritis, as well as discrete inflammatory collections in the vitreous and widespread retinal hemorrhages. The patient underwent vitrectomy with injection of intravitreal antibiotics. Vitreous cultures were positive for Streptococcus mitis, a pathogen associated with severe tissue damage and poor clinical outcomes. Clinical deterioration prompted repeat vitrectomy with silicone oil tamponade and panretinal photocoagulation two weeks later, resulting in more favorable anatomic and visual outcomes. Endophthalmitis caused by exotoxin-producing bacterial species such as S. mitis is often associated with severe vision loss or loss of the eye. Aggressive surgical intervention--prompted by concerning clinical findings and vitreous cultures--may play a role in improving outcomes in these patients.

Endocytosis‒Mediated Invasion and Pathogenicity of Streptococcus agalactiae in Rat Cardiomyocyte (H9C2)

Streptococcus agalactiae infection causes high mortality in cardiovascular disease (CVD) patients, especially in case of setting prosthetic valve during cardiac surgery. However, the pathogenesis mechanism of S. agalactiae associate with CVD has not been well studied. Here, we have demonstrated the pathogenicity of S. agalactiae in rat cardiomyocytes (H9C2). Interestingly, both live and dead cells of S. agalactiae were uptaken by H9C2 cells. To further dissect the process of S. agalactiae internalization, we chemically inhibited discrete parts of cellular uptake system in H9C2 cells using genistein, chlorpromazine, nocodazole and cytochalasin B. Chemical inhibition of microtubule and actin formation by nocodazole and cytochalasin B impaired S. agalactiae internalization into H9C2 cells. Consistently, reverse‒ transcription PCR (RT‒PCR) and quantitative real time‒PCR (RT-qPCR) analyses also detected higher levels of transcripts for cytoskeleton forming genes, Acta1 and Tubb5 in S. agalactiae‒infected H9C2 cells, suggesting the requirement of functional cytoskeleton in pathogenesis. Host survival assay demonstrated that S. agalactiae internalization induced cytotoxicity in H9C2 cells. S. agalactiae cells grown with benzyl penicillin reduced its ability to internalize and induce cytotoxicity in H9C2 cells, which could be attributed with the removal of surface lipoteichoic acid (LTA) from S. agalactiae. Further, the LTA extracted from S. agalactiae also exhibited dose‒dependent cytotoxicity in H9C2 cells. Taken together, our data suggest that S. agalactiae cells internalized H9C2 cells through energy‒dependent endocytic processes and the LTA of S. agalactiae play major role in host cell internalization and cytotoxicity induction.

Effects of surface reaction-type pre-reacted glass ionomer on oral biofilm formation of Streptococcus gordonii

Streptococcus gordonii, a bacterium involved in the initial colonization of tooth surfaces, contributes to dental biofilm formation and is an important cause of infective endocarditis. This study aimed to investigate the influence of surface reaction-type pre-reacted glass ionomer (S-PRG) filler on oral bacterial growth and aggregation of S. gordonii. The effect of various concentrations of S-PRG eluate on the growth and the biofilm formation of S. gordonii and other oral microorganisms (Streptococcus mutans, Streptococcus oralis, Lactobacillus acidophilus, and Candida albicans) was assessed. In addition, the effect of S-PRG eluate on coaggregation of S. gordonii with both S. oralis and Fusobacterium nucleatum was assessed. The effect of S-PRG eluate treatment on autoaggregation of S. gordonii was also evaluated. Our results indicate that S-PRG eluate treatment reduced both for the growth and for biofilm of all organisms in a dose-dependent manner. Coaggregation of S. gordonii with both S. oralis and F. nucleatum was inhibited by S-PRG eluate, whereas autoaggregation of S. gordonii increased at certain concentrations of S-PRG eluate. These results indicate that the S-PRG filler possesses antimicrobial activity that is mediated by inhibiting growth and biofilm of oral microorganisms, and by suppressing coaggregation of S. gordonii. In addition, these findings indicate that coaggregation of S. gordonii with other bacteria is inhibited by increased autoaggregation of S. gordonii.

Prophylactic effect of human lactoferrin against Streptococcus mutans bacteremia in lactoferrin knockout mice

Streptococcus mutans is the primary agent of dental caries, which is often detected in transient bacteremia. Lactoferrin is a multifunctional glycoprotein showing antibacterial activities against several Streptococcus species. We reported here the prophylactic effect of human lactoferrin (hLF) in a lactoferrin knockout mouse (LFKO-/-) bacteremic model. The hLF treatment significantly cleared S. mutans from the blood and organs of bacteremic mice when compared to the non-hLF treated mice. Further, analysis of serum cytokines, spleen and liver cytokine mRNA levels revealed that hLF prophylaxis modulates their release differently when compared to the non-hLF treated group. C-reactive protein level (P = 0.003) also decreased following hLF prophylaxis in S. mutans induced bacteremic mice. Additional quantitative RT-PCR analysis revealed that hLF prophylaxis significantly decreased the expression level of IFN-γ, TNF-α, IL-1β, IL-6, MPO and iNOS in spleen and liver. These results suggested that the hLF protects the host against S. mutans-induced experimental bacteremia.

Colonisation of gingival epithelia by subgingival biofilms in vitro: role of "red complex" bacteria

OBJECTIVES

Biofilm formation on tooth surface results in colonisation and invasion of the juxtaposed gingival tissue, eliciting strong inflammatory responses that lead to periodontal disease. This in vitro study investigated the colonisation of human gingival multi-layered epithelium by multi-species subgingival biofilms, and evaluated the relative effects of the "red complex" species (Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola).

METHODS

The grown biofilm consisted of Fusobacterium nucleatum, Campylobacter rectus, Veillonella dispar, P. gingivalis, Prevotella intermedia, T. forsythia, T. denticola, Actinomyces oris, Streptococcus anginosus and Streptococcus oralis, or its variant lacking the "red complex". After 48h in co-culture with the gingival epithelia, the bacterial species in the biofilm were quantified, whereas their localisation on the cell surface was investigated by combining confocal-laser scanning microscopy (CLSM) and fluorescence in situ hybridisation (FISH), as well as by scanning electron microscopy (SEM).

RESULTS

Exclusion of the "red complex" quantitatively affected S. oralis, but not other species. The "red-complex" species were all able to colonise the gingival epithelial cells. A co-localisation trend was observed between P. gingivalis and T. denticola, as determined by FISH. However, in the absence of all three "red complex" bacteria from the biofilm, an immense colonisation of streptococci (potentially S. oralis) was observed on the gingival epithelia, as confirmed by both CLSM and SEM.

CONCLUSIONS

While the "red complex" species synergise in colonizing gingival epithelia, their absence from the biofilm enhances streptococcal colonisation. This antagonism with streptococci reveals that the "red complex" may regulate biofilm virulence, with potential implications in periodontal pathogenesis.

Group B streptococcal serine-rich repeat proteins promote interaction with fibrinogen and vaginal colonization

Group B streptococcus (GBS) can cause severe disease in susceptible hosts, including newborns, pregnant women, and the elderly. GBS serine-rich repeat (Srr) surface glycoproteins are important adhesins/invasins in multiple host tissues, including the vagina. However, exact molecular mechanisms contributing to their importance in colonization are unknown. We have recently determined that Srr proteins contain a fibrinogen-binding region (BR) and hypothesize that Srr-mediated fibrinogen binding may contribute to GBS cervicovaginal colonization. In this study, we observed that fibrinogen enhanced wild-type GBS attachment to cervical and vaginal epithelium, and that this was dependent on Srr1. Moreover, purified Srr1-BR peptide bound directly to host cells, and peptide administration in vivo reduced GBS recovery from the vaginal tract. Furthermore, a GBS mutant strain lacking only the Srr1 "latching" domain exhibited decreased adherence in vitro and decreased persistence in a mouse model of GBS vaginal colonization, suggesting the importance of Srr-fibrinogen interactions in the female reproductive tract.

Phenotypic diversity of multicellular filamentation in oral Streptococci

Filamentous multicellular bacteria are among the most ancient multicellular organisms. They inhabit a great variety of environments and are present in the human body, including the oral cavity. Beside the selective advantages related to the larger size achieved through filamentation, the development of multicellular bacteria can be also driven by simple ecological factors such as birth and death rates at the cellular level. In order to extend earlier results obtained in aquatic species, we investigate the filamentation process of four different strains of oral streptococci, namely S. mutans, S. salivarius, S. oralis and S. anginosus. The results indicate differences in the capacities of different streptococcus species to form filaments, manifested in terms of length and the time-scale of filament elongation. The filamentation pattern of these oral streptococci resembles that of aquatic bacteria, whereby filaments reach a peak length during exponential growth and become short when the population reaches a steady state. Hence, this study validates that multicellularity can be an emergent property of filamentous bacteria of different ecological niches, and that phenotypic differences in filamentation can occur within species of the same genus, in this case oral streptococci. Moreover, given the role that specific oral streptococci can play in the etiology of oral diseases, these results can possibly open new perspectives in the study of the virulence properties of these species.

Streptococcus tigurinus is highly virulent in a rat model of experimental endocarditis

Streptococcus tigurinus is responsible for systemic infections in humans including infective endocarditis. We investigated whether the invasive trait of S. tigurinus in humans correlated with an increased ability to induce IE in rats. Rats with catheter-induced aortic vegetations were inoculated with 10⁴ CFU/ml of either of four S. tigurinus strains AZ_3a(T), AZ_4a, AZ_8 and AZ_14, isolated from patients with infective endocarditis or with the well known IE pathogen Streptococcus gordonii (Challis). Aortic infection was assessed after 24 h. S. tigurinus AZ_3a(T), AZ_4a and AZ_14 produced endocarditis in ≥80% of rats whereas S. gordonii produced endocarditis in only 33% of animals (P<0.05). S. tigurinus AZ_8 caused vegetation infection in 56% of the animals. The capacity of S. tigurinus to induce aortic infection was not related to their ability to bind extracellular matrix proteins (fibrinogen, fibronectin or collagen) or to trigger platelet aggregation. However, all S. tigurinus isolates showed an enhanced resistance to phagocytosis by macrophages and two of them had an increased ability to enter endothelial cells, key attributes of invasive streptococcal species.

Hydrogen peroxide produced by oral Streptococci induces macrophage cell death

Hydrogen peroxide (H₂O₂) produced by members of the mitis group of oral streptococci plays important roles in microbial communities such as oral biofilms. Although the cytotoxicity of H₂O₂ has been widely recognized, the effects of H₂O₂ produced by oral streptococci on host defense systems remain unknown. In the present study, we investigated the effect of H₂O₂ produced by Streptococcus oralis on human macrophage cell death. Infection by S. oralis was found to stimulate cell death of a THP-1 human macrophage cell line at multiplicities of infection greater than 100. Catalase, an enzyme that catalyzes the decomposition of H₂O₂, inhibited the cytotoxic effect of S. oralis. S. oralis deletion mutants lacking the spxB gene, which encodes pyruvate oxidase, and are therefore deficient in H₂O₂ production, showed reduced cytotoxicity toward THP-1 macrophages. Furthermore, H₂O₂ alone was capable of inducing cell death. The cytotoxic effect seemed to be independent of inflammatory responses, because H₂O₂ was not a potent stimulator of tumor necrosis factor-α production in macrophages. These results indicate that streptococcal H₂O₂ plays a role as a cytotoxin, and is implicated in the cell death of infected human macrophages.

Differential interactions of Streptococcus gordonii and Staphylococcus aureus with cultured osteoblasts

The impedance of normal osteoblast function by microorganisms is at least in part responsible for the failure of dental or orthopedic implants. Staphylococcus aureus is a major pathogen of bone, and exhibits high levels of adhesion and invasion of osteoblasts. In this article we show that the commensal oral bacterium Streptococcus gordonii also adheres to and is internalized by osteoblasts. Entry of S. gordonii cells had typical features of phagocytosis, similar to S. aureus, with membrane protrusions characterizing initial uptake, and closure of the osteoblast membrane leading to engulfment. The sensitivities of S. gordonii internalization to inhibitors cytochalasin D, colchicine and monensin indicated uptake through endocytosis, with requirement for actin accumulation. Internalization levels of S. gordonii were enhanced by expression of S. aureus fibronectin-binding protein A (FnBPA) on the S. gordonii cell surface. Lysosomal-associated membrane protein-1 phagosomal membrane marker accumulated with intracellular S. aureus and S. gordonii FnBPA, indicating trafficking of bacteria into the late endosomal/lysosomal compartment. Streptococcus gordonii cells did not survive intracellularly for more than 12 h, unless expressing FnBPA, whereas S. aureus showed extended survival times (>48 h). Both S. aureus and S. gordonii DL-1 elicited a rapid interleukin-8 response by osteoblasts, whereas S. gordonii FnBPA was slower. Only S. aureus elicited an interleukin-6 response. Hence, S. gordonii invades osteoblasts by a mechanism similar to that exhibited by S. aureus, and elicits a proinflammatory response that may promote bone resorption.

Protective mechanisms of respiratory tract Streptococci against Streptococcus pyogenes biofilm formation and epithelial cell infection

Streptococcus pyogenes (group A streptococci [GAS]) encounter many streptococcal species of the physiological microbial biome when entering the upper respiratory tract of humans, leading to the question how GAS interact with these bacteria in order to establish themselves at this anatomic site and initiate infection. Here we show that S. oralis and S. salivarius in direct contact assays inhibit growth of GAS in a strain-specific manner and that S. salivarius, most likely via bacteriocin secretion, also exerts this effect in transwell experiments. Utilizing scanning electron microscopy documentation, we identified the tested strains as potent biofilm producers except for GAS M49. In mixed-species biofilms, S. salivarius dominated the GAS strains, while S. oralis acted as initial colonizer, building the bottom layer in mixed biofilms and thereby allowing even GAS M49 to form substantial biofilms on top. With the exception of S. oralis, artificial saliva reduced single-species biofilms and allowed GAS to dominate in mixed biofilms, although the overall two-layer structure was unchanged. When covered by S. oralis and S. salivarius biofilms, epithelial cells were protected from GAS adherence, internalization, and cytotoxic effects. Apparently, these species can have probiotic effects. The use of Affymetrix array technology to assess HEp-2 cell transcription levels revealed modest changes after exposure to S. oralis and S. salivarius biofilms which could explain some of the protective effects against GAS attack. In summary, our study revealed a protection effect of respiratory tract bacteria against an important airway pathogen and allowed a first in vitro insight into local environmental processes after GAS enter the respiratory tract.

Enterococcus faecalis internalization in human umbilical vein endothelial cells (HUVEC)

Initial Enterococcus faecalis-endothelial cell molecular interactions which lead to enterococci associating in the host endothelial tissue, colonizing it and proliferating there can be assessed using in vitro models. Cultured human umbilical vein endothelial cells (HUVEC) have been used to study other Gram-positive bacteria-cell interactions; however, few studies have been aimed at establishing the relationship of E. faecalis with endothelial cells. The aggregation substance (AS) family of adhesins represents an E. faecalis virulence factor which has been implicated in endocarditis severity and bacterial persistence. The Asc10 protein (a member of this family) promotes bacterium-bacterium aggregation and bacterium-host cell binding. Evaluating Asc10 role in bacterial internalization by cultured enterocytes has shown that this adhesin facilitates E. faecalis endocytosis by HT-29 cells. A few eukaryotic cell structural components, such as cytoskeletal proteins, have been involved in E. faecalis entry into cell-lines; it is thus relevant to determine whether Asc10, as well as microtubules and actin microfilaments, play a role in E. faecalis internalization by cultured endothelial cells. The role of Asc10 and cytoskeleton proteins in E. faecalis ability to enter HUVEC was assessed in the present study, as well as cell apoptosis induction by enterococcal internalization by HUVEC; the data indicated increased cell apoptosis and that cytoskeleton components were partially involved in E. faecalis entry to endothelial cells, thereby suggesting that E. faecalis Asc10 protein would not be a critical factor for bacterial entry to cultured HUVEC.

Sutures coated with antiseptic pomade to prevent bacterial colonization: a randomized clinical trial

OBJECTIVE

The aim of this study was to assess if an antiseptic pomade could reduce the bacterial colonization on multifilament sutures.

STUDY DESIGN

A randomized clinical trial was conducted with 40 volunteer patients of both sexes aged 18-70, randomly separated into experimental (n = 20) and control (n = 20) groups. The experimental group received pomade-coated sutures (iodoform + calendula) and the control group uncoated sutures. Two millimeters of the suture was harvested from each patient from the 1st to the 15th postoperative day. The bacteria that had adhered to them were cultured. The number of colony-forming units per milliliter (CFU/mL) was determined and the groups were compared using the Mann-Whitney statistical test (P < .05).

RESULTS

The experimental group showed a significant reduction in bacterial growth compared with the control group (P = .002).

CONCLUSIONS

In this experimental model, the antiseptic pomade was effective in reducing bacterial colonization on silk braided sutures.

Adherence and invasion of streptococci to eukaryotic cells and their role in disease pathogenesis

Streptococcal adhesion, invasion, intracellular trafficking, dissemination, and persistence in eukaryotic cells have a variety of implications in the infection pathogenesis. While cell adhesion establishes the initial host contact, adhering bacteria exploit the host cell for their own benefit. Internalization into the host cell is an essential step for bacterial survival and subsequent dissemination and persistence, thus playing a key role in the course of infection. This chapter summarizes the current knowledge about the diverse mechanisms of streptococcal adhesion to and invasion into different eukaryotic cells and the impact on dissemination and persistence which is reflected by consequences for the pathogenesis of streptococcal infections.

Antibiotic modulation of the plasminogen binding ability of viridans group streptococci

The ability of viridans group streptococci to bind human plasminogen and its subsequent activation into plasmin may contribute to the pathogenesis of infective endocarditis (IE) by leading to a decreased stability of the streptococcal vegetation and facilitating dehiscence of emboli. At levels greater than or equal to their MICs, penicillin, vancomycin, and linezolid are efficacious in the treatment of streptococcal endocarditis. However, at sub-MICs, antibiotics can modulate the expression of bacterial genes, including virulence-associated genes, which can have counterproductive effects on the treatment of endocarditis. The effects of 1/8× and 1/4× MICs of penicillin, vancomycin, and linezolid on the plasminogen binding ability of IE isolates Streptococcus mitis 881/956, Streptococcus oralis 12601, and Streptococcus sanguinis 12403 were assessed phenotypically and the expression of plasminogen receptors α-enolase and glyceraldehyde 3-phosphate dehydrogenase of S. oralis 12601 when exposed to 1/4× MIC of penicillin, was analyzed through quantitative reverse transcription (qRT)-PCR. The plasminogen binding ability of S. mitis 881/956 and S. sanguinis 12403 remained unaffected by exposure to sub-MICs of all of the antibiotics tested, while that of S. oralis 12601 was significantly enhanced by all of the antibiotics tested at sub-MICs. qRT-PCR analysis of S. oralis 12601 demonstrated an upregulation of the eno and gapdh genes, indicating an overexpression of plasminogen receptors. These findings suggest that for some endocarditis isolates, the effect of antibiotic sub-MICs, in addition to a reduced antibacterial effect, may influence the clinical response to nonsurgical therapy. It remains difficult to accurately predict isolate responses to sub-MIC antimicrobials since there appears to be interspecies variation.

Bacterial interactions in dental biofilm

Biofilms are masses of microorganisms that bind to and multiply on a solid surface, typically with a fluid bathing the microbes. The microorganisms that are not attached but are free floating in an aqueous environment are termed planktonic cells. Traditionally, microbiology research has addressed results from planktonic bacterial cells. However, many recent studies have indicated that biofilms are the preferred form of growth of most microbes and particularly those of a pathogenic nature. Biofilms on animal hosts have significantly increased resistance to various antimicrobials compared to planktonic cells. These microbial communities form microcolonies that interact with each other using very sophisticated communication methods (i.e., quorum-sensing). The development of unique microbiological tools to detect and assess the various biofilms around us is a tremendously important focus of research in many laboratories. In the present review, we discuss the major biofilm mechanisms and the interactions among oral bacteria.

Streptococcus sanguinis induces foam cell formation and cell death of macrophages in association with production of reactive oxygen species

Streptococcus sanguinis, a normal inhabitant of the human oral cavity, is a common streptococcal species implicated in infective endocarditis. Herein, we investigated the effects of infection with S. sanguinis on foam cell formation and cell death of macrophages. Infection with S. sanguinis stimulated foam cell formation of THP-1, a human macrophage cell line. At a multiplicity of infection >100, S. sanguinis-induced cell death of the macrophages. Viable bacterial infection was required to trigger cell death because heat-inactivated S. sanguinis did not induce cell death. The production of cytokines interleukin-1β and tumor necrosis factor-α from macrophages was also stimulated during bacterial infection. Inhibition of the production of reactive oxygen species (ROS) resulted in reduced cell death, suggesting an association of ROS with cell death. Furthermore, S. sanguinis-induced cell death appeared to be independent of activation of inflammasomes, because cleavage of procaspase-1 was not evident in infected macrophages.

Mechanisms involved in the association between periodontal diseases and cardiovascular disease

It is now well accepted that besides the cholesterol associated mechanisms of atherogenesis, inflammation plays a crucial role in all stages of the development of the atherosclerotic lesion. This 'inflammation hypothesis' raises the possibility that through systemic elevations of pro-inflammatory cytokines, periodontal diseases might also contribute to systemic inflammation and, therefore, to atherogenesis. In fact, there is evidence that periodontal diseases are associated with higher systemic levels of high-sensitivity C-reactive protein and a low grade systemic inflammation. This phenomenon has been explained based on mechanisms associated with either the infectious or the inflammatory nature of periodontal diseases. The purposes of this article were to review (1) the evidence suggesting a role for oral bacterial species, particularly periodontal pathogens, in atherogenesis; (2) the potential mechanisms explaining an etiological role for oral bacteria in atherosclerosis; (3) the evidence suggesting that periodontal infections are accompanied by a heightened state of systemic inflammation; (4) the potential sources of systemic inflammatory biomarkers associated with periodontal diseases; and (5) the effects of periodontal therapy on systemic inflammatory biomarkers and cardiovascular risk.

Carboxypeptidase activity common to viridans group streptococci cleaves angiotensin I to angiotensin II: an activity homologous to angiotensin-converting enzyme (ACE)

We have found that Streptococcus gordonii FSS2, an infective endocarditis (IE) isolate, expresses a dipeptidyl-carboxypeptidase with activity homologous to angiotensin-converting enzyme (ACE). The carboxypeptidase activity was purified to homogeneity as a complex/aggregate from a bacterial surface extract and was also active as a 165 kDa monomer. The specific activity for the carboxypeptidase activity was eightfold higher than that for recombinant human ACE. Selected ACE inhibitors, captopril, lisinopril and enalapril, did not inhibit the ACE activity. The carboxypeptidase also hydrolysed the Aα and Bβ-chains of human fibrinogen, which resulted in impaired fibrin formation by thrombin. The gene encoding ACE carboxypeptidase activity was sequenced and the inferred polypeptide product showed 99 % amino acid homology to SGO_0566, sgc, ‘challisin’ of S. gordonii CL1 Challis, and had no significant amino acid sequence homology to human ACE. Homologues of challisin ACE activity were commonly detected among the viridans group streptococci most often associated with IE.

Interaction of oral bacteria with gingival epithelial cell multilayers

Primary gingival epithelial cells were cultured in multilayers as a model for the study of interactions with oral bacteria associated with health and periodontal disease. Multilayers maintained at an air-liquid interface in low-calcium medium displayed differentiation and cytokeratin properties characteristic of junctional epithelium. Multilayers were infected with fluorescently labeled Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum or Streptococcus gordonii, and bacterial association was determined by confocal microscopy and quantitative image analysis. Porphyromonas gingivalis invaded intracellularly and spread from cell to cell; A. actinomycetemcomitans and F. nucleatum remained extracellular and showed intercellular movement through the multilayer; whereas S. gordonii remained extracellular and predominantly associated with the superficial cell layer. None of the bacterial species disrupted barrier function as measured by transepithelial electrical resistance. P. gingivalis did not elicit secretion of proinflammatory cytokines. However, A. actinomycetemcomitans and S. gordonii induced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6 and IL-8 secretion; and F. nucleatum stimulated production of IL-1β and TNF-α. Aggregatibacter actinomycetemcomitans, F. nucleatum and S. gordonii, but not P. gingivalis, increased levels of apoptosis after 24 h infection. The results indicate that the organisms with pathogenic potential were able to traverse the epithelium, whereas the commensal bacteria did not. In addition, distinct host responses characterized the interaction between the junctional epithelium and oral bacteria.

The collagen-binding protein Cnm is required for Streptococcus mutans adherence to and intracellular invasion of human coronary artery endothelial cells

Streptococcus mutans is considered the primary etiologic agent of dental caries, a global health problem that affects 60 to 90% of the population, and a leading causative agent of infective endocarditis. It can be divided into four different serotypes (c, e, f, and k), with serotype c strains being the most common in the oral cavity. In this study, we demonstrate that in addition to OMZ175 and B14, three other strains (NCTC11060, LM7, and OM50E) of the less prevalent serotypes e and f are able to invade primary human coronary artery endothelial cells (HCAEC). Invasive strains were also significantly more virulent than noninvasive strains in the Galleria mellonella (greater wax worm) model of systemic disease. Interestingly, the invasive strains carried an additional gene, cnm, which was previously shown to bind to collagen and laminin in vitro. Inactivation of cnm rendered the organisms unable to invade HCAEC and attenuated their virulence in G. mellonella. Notably, the cnm knockout strains did not adhere to HCAEC as efficiently as the parental strains did, indicating that the loss of the invasion phenotype observed for the mutants was linked to an adhesion defect. Comparisons of the invasive strains and their respective cnm mutants did not support a correlation between biofilm formation and invasion. Thus, Cnm is required for S. mutans invasion of endothelial cells and possibly represents an important virulence factor of S. mutans that may contribute to cardiovascular infections and pathologies.

Streptococcus mitis: walking the line between commensalism and pathogenesis

Streptococcus mitis is a viridans streptococcus and a normal commensal of the human oropharynx. However, S. mitis can escape from this niche and cause a variety of infectious complications including infective endocarditis, bacteraemia and septicaemia. It uses a variety of strategies to effectively colonize the human oropharynx. These include expression of adhesins, immunoglobulin A proteases and toxins, and modulation of the host immune system. These various colonization factors allow S. mitis to compete for space and nutrients in the face of its more pathogenic oropharyngeal microbial neighbours. However, it is likely that in vulnerable immune-compromised patients S. mitis will use the same colonization and immune modulation factors as virulence factors promoting its opportunistic pathogenesis. The recent publication of a complete genome sequence for S. mitis strain B6 will allow researchers to thoroughly investigate which genes are involved in S. mitis host colonization and pathogenesis. Moreover, it will help to give insight into where S. mitis fits in the complicated oral microbiome. This review will discuss the current knowledge of S. mitis factors involved in host colonization, their potential role in virulence and what needs to be done to fully understand how a an oral commensal successfully transitions to a virulent pathogen.

A case of fulminant peritonitis caused by Streptococcus mitis in a patient on peritoneal dialysis

A 54-year-old woman on peritoneal dialysis (PD) was hospitalized with peritonitis with a high body temperature, abdominal pain and cloudy peritoneal fluid. She progressively fell into septic-like shock within only 6 hours after onset. The causative bacteria were Streptococcus mitis (S. mitis), part of the normal flora of oral cavity, intestine, female genial tract and upper respiratory tract. S. mitis shows pathogenicity for diseases such as endocarditis, brain abscesses and sepsis in children with malignancy or transplantation. However, S. mitis rarely shows severe pathogenic responses in adults. We report herein a case of fulminant peritonitis caused by S. mitis in an adult PD patient.

Invasion of human aortic endothelial cells by oral viridans group streptococci and induction of inflammatory cytokine production

Oral viridans group streptococci are the major commensal bacteria of the supragingival oral biofilm and have been detected in human atheromatous plaque. Atherosclerosis involves an ongoing inflammatory response, reportedly involving chronic infection caused by multiple pathogens. The aim of this study was to examine the invasion of human aortic endothelial cells (HAECs) by oral viridans group streptococci and the subsequent cytokine production by viable invaded HAECs. The invasion of HAECs by bacteria was examined using antibiotic protection assays and was visualized by confocal scanning laser microscopy. The inhibitory effects of catalase and cytochalasin D on the invasion of HAECs were also examined. The production of cytokines by invaded or infected HAECs was determined using enzyme-linked immunosorbent assays, and a real-time polymerase chain reaction method was used to evaluate the expression of cytokine messenger RNA. The oral streptococci tested were capable of invading HAECs. The number of invasive bacteria increased with the length of the co-culture period. After a certain co-culture period, some organisms were cytotoxic to the HAECs. Catalase and cytochalasin D inhibited the invasion of HAECs by the organism. HAECs invaded by Streptococcus mutans Xc, Streptococcus gordonii DL1 (Challis), Streptococcus gordonii ATCC 10558 and Streptococcus salivarius ATCC 13419 produced more cytokine(s) (interleukin-6, interleukin-8, monocyte chemoattractant protein-1) than non-invaded HAECs. The HAECs invaded by S. mutans Xc produced the largest amounts of cytokines, and the messenger RNA expression of cytokines by invaded HAECs increased markedly compared with that by non-invaded HAECs. These results suggest that oral streptococci may participate in the pathogenesis of atherosclerosis.

Streptococcus Mutans and Streptococcus Sobrinus are Able to Adhere and Invade Human Gingival Fibroblast Cell Line

Streptococcus mutans and Streptococcus sobrinus, the principal etiologic agents of caries decay of teeth, are generally acquired in oral cavity at the moment of tooth eruption. However, as S. mutans has been detected in oral cavity of predentate children, the eruption of teeth seems not to be a necessary prerequisite, suggesting that this species may be not confined to dental plaque. Here, we evaluate the ability of S. mutans and S. sobrinus in planktonic and biofilm lifestyle to adhere, invade and survive within human gingival fibroblast (HGF-1) cells. Planktonic and biofilm streptococci adhered and invaded host cells to different extents, showing higher efficiencies of biofilm than planktonic counterparts. Moreover, planktonic and biofilm streptococci showed the same percentage of survival within host cells. Transmission electron and confocal microscopy observations confirmed intracellular localization of planktonic and biofilm bacteria. The adhesion, invasion and survival abilities within human oral cells may be considered S. mutans and S. sobrinus virulence mechanisms to colonize and persist in the oral cavity in the absence of tooth surface.

Defect of glucosyltransferases reduces platelet aggregation activity of Streptococcus mutans: analysis of clinical strains isolated from oral cavities

OBJECTIVE

Streptococcus mutans is a major pathogen of dental caries and occasionally isolated from the blood of patients with infective endocarditis, though the association of its cell-surface glucosyltransferases (GTFB, GTFC, and GTFD) with pathogenicity for infective endocarditis remains to be elucidated. In this study, we investigated the contribution of S. mutans GTFs to platelet aggregation and analysed GTF expression profiles in a large number of clinical oral isolates.

DESIGN

The platelet aggregation properties of GTF-defective isogenic mutant strains constructed from S. mutans reference strain MT8148 were evaluated using whole blood and platelet-rich plasma (PRP) taken from mice, as well as human PRP. In addition, GTF expression profiles for 396 S. mutans strains isolated from the oral cavities of 396 subjects were analysed by western blotting using antisera specific for each GTF.

RESULTS

The platelet aggregation activities of the GTF-defective isogenic mutants were significantly lower than that of MT8148 when added to a large number of cells. Western blotting revealed no strains without GTF expression, though six strains had alterations of GTFB and GTFC as compared to MT8148. PCR analyses indicated that the gtfB-gtfC region length was approximately 4.5 kb shorter in those strains as compared to MT8148. These were designated as "GTFBC-fusion" strains and they demonstrated lower levels of platelet aggregation.

CONCLUSIONS

Our findings indicate that GTFs are associated with platelet aggregation. Although the clinical detection frequency of S. mutans strains with altered expressions is extremely low, GTFBC-fusion strains have activities similar to GTF-defective mutant strains.

Interactions between endocarditis-derived Streptococcus gallolyticus subsp. gallolyticus isolates and human endothelial cells

Background

Streptococcus gallolyticus subsp. gallolyticus is an important causative agent of infective endocarditis (IE) but the knowledge on virulence factors is limited and the pathogenesis of the infection is poorly understood. In the present study, we established an experimental in vitro IE cell culture model using EA.hy926 and HUVEC cells to investigate the adhesion and invasion characteristics of 23 Streptococcus gallolyticus subsp. gallolyticus strains from different origins (human IE-derived isolates, other human clinical isolates, animal isolates). Adhesion to eight components of the extracellular matrix (ECM) and the ability to form biofilms in vitro was examined in order to reveal features of S. gallolyticus subsp. gallolyticus endothelial infection. In addition, the strains were analyzed for the presence of the three virulence factors gtf, pilB, and fimB by PCR.

Results

The adherence to and invasion characteristics of the examined S. gallolyticus subsp. gallolyticus strains to the endothelial cell line EA.hy926 differ significantly among themselves. In contrast, the usage of three different in vitro models (EA.hy926 cells, primary endothelial cells (HUVECs), mechanical stretched cells) revealed no differences regarding the adherence to and invasion characteristics of different strains. Adherence to the ECM proteins collagen I, II and IV revealed the highest values, followed by fibrinogen, tenascin and laminin. Moreover, a strong correlation was observed in binding to these proteins by the analyzed strains. All strains show the capability to adhere to polystyrole surfaces and form biofilms. We further confirmed the presence of the genes of two known virulence factors (fimB: all strains, gtf: 19 of 23 strains) and demonstrated the presence of the gene of one new putative virulence factor (pilB: 9 of 23 strains) by PCR.

Conclusion

Our study provides the first description of S. gallolyticus subsp. gallolyticus adhesion and invasion of human endothelial cells, revealing important initial information of strain variability, behaviour and characteristics of this as yet barely analyzed pathogen.

The group B streptococcal serine-rich repeat 1 glycoprotein mediates penetration of the blood-brain barrier

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of bacterial meningitis in newborn infants. Because GBS is able to invade, survive, and cross the blood-brain barrier, we sought to identify surface-expressed virulence factors that contribute to blood-brain barrier penetration and the pathogenesis of meningitis.

METHODS

Targeted deletion and insertional mutants were generated in different GBS clinical isolates. Wild-type and mutant bacteria were analyzed for their capacity to adhere to and invade human brain microvascular endothelial cells (hBMECs) and to penetrate the blood-brain barrier using our model of hematogenous meningitis.

RESULTS

Analysis of a GBS (serotype V) clinical isolate revealed the presence of a surface-anchored serine-rich protein, previously designated serine-rich repeat 1 (Srr-1). GBS Srr-1 is a glycosylated protein with high molecular weight. Deletion of srr1 in NCTC 10/84 resulted in a significant decrease in adherence to and invasion of hBMECs. Additional mutants in other GBS serotypes commonly associated with meningitis showed a similar decrease in hBMEC invasion, compared with parental strains. Finally, in mice, wild-type GBS penetrated the blood-brain barrier and established meningitis more frequently than did the Deltasrr1 mutant strain.

CONCLUSIONS

Our data suggest that GBS Srr glycoproteins play an important role in crossing the blood-brain barrier and in the development of streptococcal meningitis.

Invasion of human coronary artery endothelial cells by Streptococcus mutans OMZ175

INTRODUCTION

Dissemination of oral bacteria into the bloodstream has been associated with eating, oral hygiene, and dental procedures; including tooth extraction, endodontic treatment, and periodontal surgery. Recently, studies identified Streptococcus mutans, the primary etiological agent of dental caries, as the most prevalent bacterial species found in clinical samples from patients who underwent heart valve and atheromatous plaque surgery.

METHODS

By using antibiotic protection assays, we tested the capacity of 14 strains of S. mutans to invade primary human coronary artery endothelial cells (HCAEC).

RESULTS

Serotype e strain B14 and serotype f strain OMZ175 of S. mutans were able to efficiently invade HCAEC. Among the tested strains, serotype f S. mutans OMZ175 was the most invasive, whereas strains of serotype c S. mutans, the most prevalent serotype in dental plaque, were not invasive. Based on its high invasion rate, we further investigated the invasive properties of serotype f OMZ175. Using transmission electron microscopy and antibiotic protection assays we demonstrate that S. mutans OMZ175 is capable of attaching to the HCAEC surface, entering the cells and surviving in HCAEC for at least 29 h.

DISCUSSION

Our findings highlight a potential role for S. mutans in the pathogenesis of certain cardiovascular diseases.

Cloning and characterization of an alpha-enolase of the oral pathogen Streptococcus mutans that binds human plasminogen

Streptococcus mutans is the etiologic agent of dental caries and is a causative agent of infective endocarditis. While the mechanisms by which S. mutans cells colonize heart tissue is not clear, it is thought that bacterial binding to extracellular matrix and blood components is crucial in the development of endocarditis. Previously, we have demonstrated that S. mutans cells have the capacity to bind and activate plasminogen to plasmin. Here we report the first cloning and characterization of an alpha-enolase of S. mutans that binds plasminogen. The functional identity of the purified recombinant alpha-enolase protein was confirmed by its ability to catalyze the conversion of 2-phosphoglycerate to phosphoenolpyruvate. The protein exhibited a Km of 9.5 mM and a Vmax of 31.0 mM/min/mg. The alpha-enolase protein was localized in the cytoplasmic, cell wall and extracellular fractions of S. mutans. Binding studies using an immunoblot analysis revealed that human plasminogen binds to the enolase enzyme of S. mutans. These findings identify S. mutans alpha-enolase as a binding molecule used by this oral pathogen to interact with the blood component, plasminogen. Further studies of this interaction may be critical to understand the pathogenesis of endocarditis caused by S. mutans.

Microbial Adherence on Various Intraoral Suture Materials in Patients Undergoing Dental Surgery

PURPOSE

Sutures used in oral surgery should avoid or limit bacterial adhesion and proliferation to those parts exposed to oral fluids. Hence, microbial colonization on various intraoral suture materials from patients undergoing dental surgery was compared.

PATIENTS AND METHODS

During dentoalveolar surgery, various suture materials were used in 60 patients, who were randomly divided into 5 groups of 12. In each group, silk was placed intraorally in association with a different type of suture (ie, Supramid, Synthofil, Ethibond Excel, Ti-cron, Monocryl) at the same site to compare microbial colonization intraindividually. Eight days postoperatively, the sutures were removed, and adhered micro-organisms were isolated, counted, and identified through enzymatic activities and fermentation of sugars.

RESULTS

In all 60 patients, silk sutures exhibited the smallest affinity toward the adhesion of bacteria compared with considerable proliferation with nonresorbable multifilament sutures (Supramid, Synthofil, Ethibond Excel, Ti-cron). On the contrary, the microbial load was significantly lower when absorbable monofilament Monocryl was used. A greater quantity of bacteria was found on nonresorbable sutures than on absorbable ones, and nearly 2 times more facultative anaerobic bacteria were isolated in total.

CONCLUSIONS

Our results show that bacteria adhere with different affinity to various types of suture materials. Absorbable silk and Monocryl exhibited the smallest number of adherent bacteria. Colonization by pathogens on sutures leads to the recommendation that sutures should be removed as early as possible after surgery is performed, to eliminate or to limit the reservoir for oral pathogens. This recommendation is dependent on whether the suture is absorbable.

Endothelial cell infection and hemostasis

As an important component of the vasculature, endothelial cell lining covers the inner surface of blood vessels and provides an active barrier interface between the vascular and perivascular compartments. In addition to maintaining vasomotor equilibrium and organ homeostasis and communicating with circulating blood cells, the vascular endothelium also serves as the preferred target for a number of infectious agents. This review article focuses on the roles of interactions between vascular endothelial cells and invading pathogens and resultant endothelial activation in the pathogenesis of important human diseases with viral and bacterial etiologies. In this perspective, the signal transduction events that regulate vascular inflammation and basis for endothelial cell tropism exhibited by certain specific viruses and pathogenic bacteria are also discussed.

Adherence and internalization of Streptococcus gordonii by epithelial cells involves beta1 integrin recognition by SspA and SspB (antigen I/II family) polypeptides

Streptococcus gordonii is a commensal bacterium that colonizes the hard and soft tissues present in the human mouth and nasopharynx. The cell wall-anchored polypeptides SspA and SspB expressed by S. gordonii mediate a wide range of interactions with host proteins and other bacteria. In this article we have determined the role of SspA and SspB proteins, which are members of the streptococcal antigen I/II (AgI/II) adhesin family, in S. gordonii adherence and internalization by epithelial cells. Wild-type S. gordonii DL1 expressing AgI/II polypeptides attached to and was internalized by HEp-2 cells, whereas an isogenic AgI/II- mutant was reduced in adherence and was not internalized. Association of S. gordonii DL1 with HEp-2 cells triggered protein tyrosine phosphorylation but no significant actin rearrangement. By contrast, Streptococcus pyogenes A40 showed 50-fold higher levels of internalization and this was associated with actin polymerization and interleukin-8 upregulation. Adherence and internalization of S. gordonii by HEp-2 cells involved beta1 integrin recognition but was not fibronectin-dependent. Recombinant SspA and SspB polypeptides bound to purified human alpha5beta1 integrin through sequences present within the NAV (N-terminal) region of AgI/II polypeptide. AgI/II polypeptides blocked interactions of S. gordonii and S. pyogenes with HEp-2 cells, and S. gordonii DL1 cells expressing AgI/II proteins inhibited adherence and internalization of S. pyogenes by HEp-2 cells. Conversely, S. gordonii AgI/II- mutant cells did not inhibit internalization of S. pyogenes. The results suggest that AgI/II proteins not only promote integrin-mediated internalization of oral commensal streptococci by host cells, but also potentially influence susceptibility of host tissues to more pathogenic bacteria.

Oral streptococci and cardiovascular disease: searching for the platelet aggregation-associated protein gene and mechanisms of Streptococcus sanguis-induced thrombosis

BACKGROUND

Pathogenic mechanisms in infective endocarditis, disseminated intravascular coagulation, and cardiovascular events involve the aggregation of platelets into thrombi. Attendant infection by oral bacteria contributes to these diseases. We have been studying how certain oral streptococci induce platelet aggregation in vitro and in vivo. Streptococcus sanguis expresses a platelet aggregation-associated protein (PAAP), which contributes little to adhesion to platelets. When specific antibodies or peptides block PAAP, S. sanguis fails to induce platelet aggregation in vitro or in vivo.

METHODS

We used subtractive hybridization to identify the gene encoding for PAAP.

RESULTS

After subtraction of strain L50 (platelet aggregation-negative), four strain 133-79 specific sequences were characterized. Sequence agg4 encoded a putative collagen-binding protein (CbpA), which was predicted to contain two PAAP collagen-like octapeptide sequences. S. sanguis CbpA- mutants were constructed and tested for induction of platelet aggregation in vitro. Platelet aggregation was substantially inhibited when compared to the wild-type using platelet-rich plasma from the principal donor, but adhesion was unaffected. Other donor platelets responded normally to the CbpA- strain, suggesting additional mechanisms of response to S. sanguis. In contrast, CshA- and methionine sulfoxide reductase-negative (MsrA-) strains neither adhered nor induced platelet aggregation.

CONCLUSIONS

CbpA was suggested to contribute to site 2 interactions in our two-site model of platelet aggregation in response to S. sanguis. Platelet polymorphisms were suggested to contribute to the thrombogenic potential of S. sanguis.