Vaccination with FimA from Streptococcus parasanguis protects rats from endocarditis caused by other viridans streptococci

Identification and genetic engineering of pneumococcal capsule-like polysaccharides in commensal oral streptococci

Capsular polysaccharides (CPS) in Streptococcus pneumoniae are pivotal for bacterial virulence and present extensive diversity. While oral streptococci show pronounced antigenicity toward pneumococcal capsule-specific sera, insights into evolution of capsule diversity remain limited. This study reports a pneumococcal CPS-like genetic locus in Streptococcus parasanguinis, a predominant oral Streptococcus. The discovered locus comprises 15 genes, mirroring high similarity to those from the Wzy-dependent CPS locus of S. pneumoniae. Notably, S. parasanguinis elicited a reaction with pneumococcal 19B antiserum. Through nuclear magnetic resonance analysis, we ascertained that its CPS structure matches the chemical composition of the pneumococcal 19B capsule. By introducing the glucosyltransferase gene cps19cS from a pneumococcal serotype 19C, we successfully transformed S. parasanguinis antigenicity from 19B to 19C. Furthermore, substituting serotype-specific genes, cpsI and cpsJ, with their counterparts from pneumococcal serotype 19A and 19F enabled S. parasanguinis to generate 19A- and 19F-specific CPS, respectively. These findings underscore that S. parasanguinis harbors a versatile 19B-like CPS adaptable to other serotypes. Remarkably, after deleting the locus's initial gene, cpsE, responsible for sugar transfer, we noted halted CPS production, elongated bacterial chains, and diminished biofilm formation. A similar phenotype emerged with the removal of the distinct gene cpsZ, which encodes a putative autolysin. These data highlight the importance of S. parasanguinis CPS for biofilm formation and propose a potential shared ancestry of its CPS locus with S. pneumoniae.

IMPORTANCE

Diverse capsules from Streptococcus pneumoniae are vital for bacterial virulence and pathogenesis. Oral streptococci show strong responses to a wide range of pneumococcal capsule-specific sera. Yet, the evolution of this capsule diversity in relation to microbe-host interactions remains underexplored. Our research delves into the connection between commensal oral streptococcal and pneumococcal capsules, highlighting the potential for gene transfer and evolution of various capsule types. Understanding the genetic and evolutionary factors that drive capsule diversity in S. pneumoniae and its related oral species is essential for the development of effective pneumococcal vaccines. The present findings provide fresh perspectives on the cross-reactivity between commensal streptococci and S. pneumoniae, its influence on bacteria-host interactions, and the development of new strategies to manage and prevent pneumococcal illnesses by targeting and modulating commensal streptococci.

Prediction of Burkholderia pseudomallei DsbA substrates identifies potential virulence factors and vaccine targets

Identification of bacterial virulence factors is critical for understanding disease pathogenesis, drug discovery and vaccine development. In this study we used two approaches to predict virulence factors of Burkholderia pseudomallei, the Gram-negative bacterium that causes melioidosis. B. pseudomallei is naturally antibiotic resistant and there are no clinically available melioidosis vaccines. To identify B. pseudomallei protein targets for drug discovery and vaccine development, we chose to search for substrates of the B. pseudomallei periplasmic disulfide bond forming protein A (DsbA). DsbA introduces disulfide bonds into extra-cytoplasmic proteins and is essential for virulence in many Gram-negative organism, including B. pseudomallei. The first approach to identify B. pseudomallei DsbA virulence factor substrates was a large-scale genomic analysis of 511 unique B. pseudomallei disease-associated strains. This yielded 4,496 core gene products, of which we hypothesise 263 are DsbA substrates. Manual curation and database screening of the 263 mature proteins yielded 81 associated with disease pathogenesis or virulence. These were screened for structural homologues to predict potential B-cell epitopes. In the second approach, we searched the B. pseudomallei genome for homologues of the more than 90 known DsbA substrates in other bacteria. Using this approach, we identified 15 putative B. pseudomallei DsbA virulence factor substrates, with two of these previously identified in the genomic approach, bringing the total number of putative DsbA virulence factor substrates to 94. The two putative B. pseudomallei virulence factors identified by both methods are homologues of PenI family β-lactamase and a molecular chaperone. These two proteins could serve as high priority targets for future B. pseudomallei virulence factor characterization.

Adaptation to Adversity: the Intermingling of Stress Tolerance and Pathogenesis in Enterococci

Enterococcus is a diverse and rugged genus colonizing the gastrointestinal tract of humans and numerous hosts across the animal kingdom. Enterococci are also a leading cause of multidrug-resistant hospital-acquired infections. In each of these settings, enterococci must contend with changing biophysical landscapes and innate immune responses in order to successfully colonize and transit between hosts. Therefore, it appears that the intrinsic durability that evolved to make enterococci optimally competitive in the host gastrointestinal tract also ideally positioned them to persist in hospitals, despite disinfection protocols, and acquire new antibiotic resistances from other microbes. Here, we discuss the molecular mechanisms and regulation employed by enterococci to tolerate diverse stressors and highlight the role of stress tolerance in the biology of this medically relevant genus.

Current Concepts of Prophylactic Antibiotics for Dental Patients

Despite numerous guidelines, joint interprofessional collaboration, and years of data collection, the use of antibiotic prophylaxis before dental procedures remains controversial. There continues to be disagreement on indications, justification, and outcome of the use of various antibiotic prophylaxis regiments. This is complicated by the lack of data demonstrating any positive or negative impact on the care of patients. The dental community has distanced itself from a leadership role in this conversation, based on multiple concerns including fear of litigation, lack of clear pathophysiology, and unclear cause-effect relationship.

Antibodies Targeting Hsa and PadA Prevent Platelet Aggregation and Protect Rats against Experimental Endocarditis Induced by Streptococcus gordonii

Streptococcus gordonii and related species of oral viridans group streptococci (VGS) are common etiological agents of infective endocarditis (IE). We explored vaccination as a strategy to prevent VGS-IE, using a novel antigen-presenting system based on non-genetically modified Lactococcus lactis displaying vaccinogens on its surface. Hsa and PadA are surface-located S. gordonii proteins implicated in platelet adhesion and aggregation, which are key steps in the pathogenesis of IE. This function makes them ideal targets for vaccination against VGS-IE. In the present study, we report the use of nonliving L. lactis displaying at its surface the N-terminal region of Hsa or PadA by means of the cell wall binding domain of Lactobacillus casei A2 phage lysine LysA2 (Hsa-LysA2 and PadA-LysA2, respectively) and investigation of their ability to elicit antibodies in rats and to protect them from S. gordonii experimental IE. Immunized and control animals with catheter-induced sterile aortic valve vegetations were inoculated with 10⁶ CFU of S. gordonii The presence of IE was evaluated 24 h later. Immunization of rats with L. lactis Hsa-LysA2, L. lactis PadA-LysA2, or both protected 6/11 (55%), 6/11 (55%), and 11/12 (91%) animals, respectively, from S. gordonii IE (P < 0.05 versus controls). Protection correlated with the induction of high levels of functional antibodies against both Hsa and PadA that delayed or totally inhibited platelet aggregation by S. gordonii These results support the value of L. lactis as a system for antigen delivery and of Hsa and PadA as promising candidates for a vaccine against VGS-IE.

Infective endocarditis

Infective endocarditis (IE) is a rare, life-threatening disease that has long-lasting effects even among patients who survive and are cured. IE disproportionately affects those with underlying structural heart disease and is increasingly associated with health care contact, particularly in patients who have intravascular prosthetic material. In the setting of bacteraemia with a pathogenic organism, an infected vegetation may form as the end result of complex interactions between invading microorganisms and the host immune system. Once established, IE can involve almost any organ system in the body. The diagnosis of IE may be difficult to establish and a strategy that combines clinical, microbiological and echocardiography results has been codified in the modified Duke criteria. In cases of blood culture-negative IE, the diagnosis may be especially challenging, and novel microbiological and imaging techniques have been developed to establish its presence. Once diagnosed, IE is best managed by a multidisciplinary team with expertise in infectious diseases, cardiology and cardiac surgery. Antibiotic prophylaxis for the prevention of IE remains controversial. Efforts to develop a vaccine that targets common bacterial causes of IE are ongoing, but have not yet yielded a commercially available product.

Fine-tuned production of hydrogen peroxide promotes biofilm formation of Streptococcus parasanguinis by a pathogenic cohabitant Aggregatibacter actinomycetemcomitans

Balanced bacterial biofilm communities help to maintain host health. Disturbance of such balance can lead to bacterial dysbiosis and pathogenesis. However, complex and dynamic bacterial interactions within the biofilm communities are poorly understood. In this study, we used a dual-species biofilm consisting of the periodontal pathogen Aggregatibacter actinomycetemcomitans, and a commensal Streptococcus parasanguinis to investigate bacterial interactions since the two organisms have been found to coexist during the development of localized aggressive periodontal disease. We report that A. actinomycetemcomitans promoted biofilm formation of S. parasanguinis in vitro and in vivo. Protein profiling of S. parasanguinis co-cultured with A. actinomycetemcomitans revealed a significant decrease in the protein level of pyruvate oxidase(PoxL), an enzyme required for the generation of hydrogen peroxide (H₂ O₂ ). Consistently, the H₂ O₂ concentration was concurrently decreased. However, the complete removal of H₂ O₂ impaired the biofilm formation. H₂ O₂ at a low concentration range regulated by A. actinomycetemcomitans enhanced the biofilm formation. These results demonstrate that A. actinomycetemcomitans promotes the S. parasanguinis biofilm formation through modulating the production of H₂ O₂ by fine-tuning the expression of poxL, indicating that H₂ O₂ functions as a signaling molecule. Taken together, this report revealed a previously unknown bacteria-bacteria interaction mechanism.

Three-dimensional structure and biophysical characterization of Staphylococcus aureus cell surface antigen-manganese transporter MntC

MntC is a metal-binding protein component of the Mn²⁺-specific mntABC transporter from the pathogen Staphylococcus aureus. The protein is expressed during the early stages of infection and was proven to be effective at reducing both S. aureus and Staphylococcus epidermidis infections in a murine animal model when used as a vaccine antigen. MntC is currently being tested in human clinical trials as a component of a multiantigen vaccine for the prevention of S. aureus infections. To better understand the biological function of MntC, we are providing structural and biophysical characterization of the protein in this work. The three-dimensional structure of the protein was solved by X-ray crystallography at 2.2Å resolution and suggests two potential metal binding modes, which may lead to reversible as well as irreversible metal binding. Precise Mn²⁺-binding affinity of the protein was determined from the isothermal titration calorimetry experiments using a competition approach. Differential scanning calorimetry experiments confirmed that divalent metals can indeed bind to MntC reversibly as well as irreversibly. Finally, Mn²⁺-induced structural and dynamics changes have been characterized using spectroscopic methods and deuterium-hydrogen exchange mass spectroscopy. Results of the experiments show that these changes are minimal and are largely restricted to the structural elements involved in metal coordination. Therefore, it is unlikely that antibody binding to this antigen will be affected by the occupancy of the metal-binding site by Mn²⁺.

Beneficial microbes for the oral cavity: time to harness the oral streptococci?

Indigenous microbes are known to influence human health outcomes and various approaches are now being made to positively modulate these microbe-induced outcomes via the administration of probiotics. The application of probiotics that are specific to the oral cavity is a relatively undeveloped field, and their emergence has largely occurred as a reasoned follow-up to initial studies in which probiotics that had already been developed and obtained regulatory approval for intestinal applications were then also evaluated for their putative influence on oral microbiota functionality. These attempts to extend the application of existing probiotics were probably at least in part motivated by recognition of the substantial safety and regulatory hurdles that must be overcome prior to the introduction of a novel probiotic agent. Nevertheless, from an efficacy perspective it appears more logical to develop microbes of oral origin as the specific providers of probiotic solutions for oral diseases, rather than attempting to adapt intestinally-derived strains for this role. Oral bacteria and their bioactive molecules have evolved to operate optimally in this environment and in some cases are known to persist only in oral sites. Amongst the bacteria of more than 700 species now identified within the human oral microbiota, it is the streptococci that are numerically predominant. Although this review highlights the development of the oral cavity bacterium Streptococcus salivarius as an oral probiotic, a number of other streptococcal species have also been shown to have considerable potential as probiotic candidates.

Infective endocarditis

Infective endocarditis (IE) is lethal if not aggressively treated with antibiotics alone or in combination with surgery. The epidemiology of this condition has substantially changed over the past four decades, especially in industrialized countries. Once a disease that predominantly affected young adults with previously well-identified valve disease--mostly chronic rheumatic heart disease--IE now tends to affect older patients and new at-risk groups, including intravenous-drug users, patients with intracardiac devices, and patients exposed to healthcare-associated bacteremia. As a result, skin organisms (for example, Staphylococcus spp.) are now reported as the pathogen in these populations more often than oral streptococci, which still prevail in the community and in native-valve IE. Moreover, progress in molecular diagnostics has helped to improve the diagnosis of poorly cultivable pathogens, such as Bartonella spp. and Tropheryma whipplei, which are responsible for blood-culture-negative IE more often than expected. Epidemiological data indicate that IE mostly occurs independently of medico-surgical procedures, and that circumstantial antibiotic prophylaxis is likely to protect only a minute proportion of individuals at risk. Therefore, new strategies to prevent IE--including improvement of dental hygiene, decontamination of carriers of Staphylococcus aureus, vaccination, and, possibly, antiplatelet therapy--must be explored.

Pooled protein immunization for identification of cell surface antigens in Streptococcus sanguinis

Background

Available bacterial genomes provide opportunities for screening vaccines by reverse vaccinology. Efficient identification of surface antigens is required to reduce time and animal cost in this technology. We developed an approach to identify surface antigens rapidly in Streptococcus sanguinis, a common infective endocarditis causative species.

Methods and Findings

We applied bioinformatics for antigen prediction and pooled antigens for immunization. Forty-seven surface-exposed proteins including 28 lipoproteins and 19 cell wall-anchored proteins were chosen based on computer algorithms and comparative genomic analyses. Eight proteins among these candidates and 2 other proteins were pooled together to immunize rabbits. The antiserum reacted strongly with each protein and with S. sanguinis whole cells. Affinity chromatography was used to purify the antibodies to 9 of the antigen pool components. Competitive ELISA and FACS results indicated that these 9 proteins were exposed on S. sanguinis cell surfaces. The purified antibodies had demonstrable opsonic activity.

Conclusions

The results indicate that immunization with pooled proteins, in combination with affinity purification, and comprehensive immunological assays may facilitate cell surface antigen identification to combat infectious diseases.

Contribution of lipoproteins and lipoprotein processing to endocarditis virulence in Streptococcus sanguinis

Streptococcus sanguinis is an important cause of infective endocarditis. Previous studies have identified lipoproteins as virulence determinants in other streptococcal species. Using a bioinformatic approach, we identified 52 putative lipoprotein genes in S. sanguinis strain SK36 as well as genes encoding the lipoprotein-processing enzymes prolipoprotein diacylglyceryl transferase (lgt) and signal peptidase II (lspA). We employed a directed signature-tagged mutagenesis approach to systematically disrupt these genes and screen each mutant for the loss of virulence in an animal model of endocarditis. All mutants were viable. In competitive index assays, mutation of a putative phosphate transporter reduced in vivo competitiveness by 14-fold but also reduced in vitro viability by more than 20-fold. Mutations in lgt, lspA, or an uncharacterized lipoprotein gene reduced competitiveness by two- to threefold in the animal model and in broth culture. Mutation of ssaB, encoding a putative metal transporter, produced a similar effect in culture but reduced in vivo competiveness by >1,000-fold. [(3)H]palmitate labeling and Western blot analysis confirmed that the lgt mutant failed to acylate lipoproteins, that the lspA mutant had a general defect in lipoprotein cleavage, and that SsaB was processed differently in both mutants. These results indicate that the loss of a single lipoprotein, SsaB, dramatically reduces endocarditis virulence, whereas the loss of most other lipoproteins or of normal lipoprotein processing has no more than a minor effect on virulence.

A conserved domain of previously unknown function in Gap1 mediates protein-protein interaction and is required for biogenesis of a serine-rich streptococcal adhesin

Fap1-like serine-rich proteins are a new family of bacterial adhesins found in a variety of streptococci and staphylococci that have been implicated in bacterial pathogenesis. A gene cluster encoding glycosyltransferases and accessory Sec components is required for Fap1 glycosylation and biogenesis in Streptococcus parasanguinis. Here we report that the glycosylation-associated protein, Gap1, contributes to glycosylation and biogenesis of Fap1 by interacting with another glycosylation-associated protein, Gap3. Gap1 shares structural homology with glycosyltransferases. The gap1 mutant, like the gap3 mutant, produced an aberrantly glycosylated Fap1 precursor and failed to produce mature Fap1, suggesting that Gap1 and Gap3 might function in concert in the Fap1 glycosylation and biogenesis. Indeed, Gap1 interacted with Gap3 in vitro and in vivo. A Gap1 N-terminal motif, within a highly conserved domain of unknown function (DUF1975) identified in many bacterial glycosyltransferases, was required for the Gap1-Gap3 interaction. Deletion of one, four and nine amino acids within the conserved motif gradually inhibited the Gap1-Gap3 interaction and diminished production of mature Fap1 and concurrently increased production of the Fap1 precursor. Consequently, bacterial adhesion to an in vitro tooth model was also reduced. These data demonstrate that the Gap1-Gap3 interaction is required for Fap1 biogenesis and Fap1-dependent bacterial adhesion.

Prophylaxis of Infective Endocarditis: Prevention of the Perfect Storm

Despite the availability of endocarditis prophylaxis guidelines for more than five decades, no prospective, randomised trial has ever been conducted to evaluate the efficacy and safety of this practice. This fact, in combination with mixed results from case-control investigations and other factors, has prompted a re-evaluation of the appropriateness of the guidelines. The update provided herein highlights recent revisions in guidelines promulgated by different countries.

Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group

BACKGROUND

The purpose of this statement is to update the recommendations by the American Heart Association (AHA) for the prevention of infective endocarditis, which were last published in 1997.

METHODS AND RESULTS

A writing group appointed by the AHA for their expertise in prevention and treatment of infective endocarditis (IE) with liaison members representing the American Dental Association, the Infectious Diseases Society of America and the American Academy of Pediatrics. The writing group reviewed input from national and international experts on IE. The recommendations in this document reflect analyses of relevant literature regarding procedure-related bacteremia and IE; in vitro susceptibility data of the most common microorganisms, which cause IE; results of prophylactic studies in animal models of experimental endocarditis; and retrospective and prospective studies of prevention of IE. MEDLINE database searches from 1950 through 2006 were done for English language articles using the following search terms: endocarditis, infective endocarditis, prophylaxis, prevention, antibiotic, antimicrobial, pathogens, organisms, dental, gastrointestinal, genitourinary, streptococcus, enterococcus, staphylococcus, respiratory, dental surgery, pathogenesis, vaccine, immunization and bacteremia. The reference lists of the identified articles were also searched. The writing group also searched the AHA online library. The American College of Cardiology/AHA classification of recommendations and levels of evidence for practice guidelines were used. The article subsequently was reviewed by outside experts not affiliated with the writing group and by the AHA Science Advisory and Coordinating Committee.

CONCLUSIONS

The major changes in the updated recommendations include the following. (1) The committee concluded that only an extremely small number of cases of IE might be prevented by antibiotic prophylaxis for dental procedures even if such prophylactic therapy were 100 percent effective. (2) IE prophylaxis for dental procedures should be recommended only for patients with underlying cardiac conditions associated with the highest risk of adverse outcome from IE. (3) For patients with these underlying cardiac conditions, prophylaxis is recommended for all dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. (4) Prophylaxis is not recommended based solely on an increased lifetime risk of acquisition of IE. (5) Administration of antibiotics solely to prevent endocarditis is not recommended for patients who undergo a genitourinary or gastrointestinal tract procedure. These changes are intended to define more clearly when IE prophylaxis is or is not recommended and to provide more uniform and consistent global recommendations.

Managing the infected heart

Most infective processes are straightforward and can be diagnosed from bacterial findings in a single test. IE does not always follow this tenet, so establishing the diagnosis can be difficult. The salient features of IE may present atypically or be obscured by the presence of preexisting and coexisting diseases. Flulike symptoms may mask the beginning of this devastating disease. Early diagnosis of IE is important because of its high risk of morbidity and mortality. Management of the patient who has IE is complex and requires interventions by infectious disease specialists, cardiologists, respiratory therapists, and critical care nurses to address the many multifaceted complications. Early evaluation, diagnostic validation, multidisciplinary management, prompt pharmaceutical initiation, and intense critical care nursing intervention are necessary to reduce the probability of long-standing complications and to improve patient outcomes.

Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group

BACKGROUND

The purpose of this statement is to update the recommendations by the American Heart Association (AHA) for the prevention of infective endocarditis that were last published in 1997.

METHODS AND RESULTS

A writing group was appointed by the AHA for their expertise in prevention and treatment of infective endocarditis, with liaison members representing the American Dental Association, the Infectious Diseases Society of America, and the American Academy of Pediatrics. The writing group reviewed input from national and international experts on infective endocarditis. The recommendations in this document reflect analyses of relevant literature regarding procedure-related bacteremia and infective endocarditis, in vitro susceptibility data of the most common microorganisms that cause infective endocarditis, results of prophylactic studies in animal models of experimental endocarditis, and retrospective and prospective studies of prevention of infective endocarditis. MEDLINE database searches from 1950 to 2006 were done for English-language papers using the following search terms: endocarditis, infective endocarditis, prophylaxis, prevention, antibiotic, antimicrobial, pathogens, organisms, dental, gastrointestinal, genitourinary, streptococcus, enterococcus, staphylococcus, respiratory, dental surgery, pathogenesis, vaccine, immunization, and bacteremia. The reference lists of the identified papers were also searched. We also searched the AHA online library. The American College of Cardiology/AHA classification of recommendations and levels of evidence for practice guidelines were used. The paper was subsequently reviewed by outside experts not affiliated with the writing group and by the AHA Science Advisory and Coordinating Committee.

CONCLUSIONS

The major changes in the updated recommendations include the following: (1) The Committee concluded that only an extremely small number of cases of infective endocarditis might be prevented by antibiotic prophylaxis for dental procedures even if such prophylactic therapy were 100% effective. (2) Infective endocarditis prophylaxis for dental procedures is reasonable only for patients with underlying cardiac conditions associated with the highest risk of adverse outcome from infective endocarditis. (3) For patients with these underlying cardiac conditions, prophylaxis is reasonable for all dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. (4) Prophylaxis is not recommended based solely on an increased lifetime risk of acquisition of infective endocarditis. (5) Administration of antibiotics solely to prevent endocarditis is not recommended for patients who undergo a genitourinary or gastrointestinal tract procedure. These changes are intended to define more clearly when infective endocarditis prophylaxis is or is not recommended and to provide more uniform and consistent global recommendations.

Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group

BACKGROUND

The purpose of this statement is to update the recommendations by the American Heart Association (AHA) for the prevention of infective endocarditis that were last published in 1997.

METHODS AND RESULTS

A writing group was appointed by the AHA for their expertise in prevention and treatment of infective endocarditis, with liaison members representing the American Dental Association, the Infectious Diseases Society of America, and the American Academy of Pediatrics. The writing group reviewed input from national and international experts on infective endocarditis. The recommendations in this document reflect analyses of relevant literature regarding procedure-related bacteremia and infective endocarditis, in vitro susceptibility data of the most common microorganisms that cause infective endocarditis, results of prophylactic studies in animal models of experimental endocarditis, and retrospective and prospective studies of prevention of infective endocarditis. MEDLINE database searches from 1950 to 2006 were done for English-language papers using the following search terms: endocarditis, infective endocarditis, prophylaxis, prevention, antibiotic, antimicrobial, pathogens, organisms, dental, gastrointestinal, genitourinary, streptococcus, enterococcus, staphylococcus, respiratory, dental surgery, pathogenesis, vaccine, immunization, and bacteremia. The reference lists of the identified papers were also searched. We also searched the AHA online library. The American College of Cardiology/AHA classification of recommendations and levels of evidence for practice guidelines were used. The paper was subsequently reviewed by outside experts not affiliated with the writing group and by the AHA Science Advisory and Coordinating Committee.

CONCLUSIONS

The major changes in the updated recommendations include the following: (1) The Committee concluded that only an extremely small number of cases of infective endocarditis might be prevented by antibiotic prophylaxis for dental procedures even if such prophylactic therapy were 100% effective. (2) Infective endocarditis prophylaxis for dental procedures is reasonable only for patients with underlying cardiac conditions associated with the highest risk of adverse outcome from infective endocarditis. (3) For patients with these underlying cardiac conditions, prophylaxis is reasonable for all dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. (4) Prophylaxis is not recommended based solely on an increased lifetime risk of acquisition of infective endocarditis. (5) Administration of antibiotics solely to prevent endocarditis is not recommended for patients who undergo a genitourinary or gastrointestinal tract procedure. These changes are intended to define more clearly when infective endocarditis prophylaxis is or is not recommended and to provide more uniform and consistent global recommendations.

Analysis of recombinant group B streptococcal protein ScaAB and evaluation of its immunogenicity

Group B streptococcal (GBS) gene encoding the putative lipoprotein and adherence factor ScaAB was cloned and expressed in E. coli. Recombinant ScaAB protein was isolated. Signal sequence of ScaAB was found to be cleaved in the E. coli host. ScaAB recombinant protein was immunogenic in mice and antibodies against this protein were discovered in mice sera after GBS infection. The perspectives of the use of ScaAB protein in GBS vaccine are discussed.

The changing face of infective endocarditis

Infective endocarditis (IE) is an evolving disease with a persistently high mortality and morbidity, even in the modern era of advanced diagnostic imaging, improved antimicrobial chemotherapy, and potentially curative surgery. Despite these improvements in health care, the incidence of the disease has remained unchanged over the past two decades and may even be increasing. Chronic rheumatic heart disease is now an uncommon antecedent, whereas degenerative valve disease of the elderly, mitral valve prolapse, intravenous drug misuse, preceding valve replacement, and vascular instrumentation have become increasingly common, coinciding with an increase in staphylococcal infections and those caused by fastidious organisms. The current understanding of this difficult condition is reviewed and recent developments in medical and surgical management are updated.

Protection of laying hens against Salmonella Enteritidis by immunization with type 1 fimbriae

Eighteen chickens were immunized subcutaneously with purified type 1 fimbriae from Salmonella enterica serotype Enteritidis at 18 and 21 weeks of age. Evidence of IgG and IgA responses was found in the eggs and in the sera of the immunized hens. Three weeks later, immunized and non-immunized chickens (n=18) were challenged intravenously with 2x10(7) live Salmonella enterica serotype Enteritidis. There was no significant difference in the numbers of eggs laid by immunized and non-immunized birds. The percentage of Salmonella contaminated eggs was significantly higher in the non-immunized group than in the immunized group due to a higher percentage of contamination of the externally disinfected egg shells. There were no statistical differences in the percentages of contaminated yolks and egg whites between control and immunized birds. No differences in the number of colonizing bacteria could be found in the spleen nor in the liver between the immunized and the control groups throughout the experiment. Salmonella was cleared from the ovary of the immunized birds in the second week p.i., in contrast to the control birds where Salmonella was isolated till the third week after infection. Oviducts were significantly more infected in the control group than in the immunized group. Salmonella was cleared from the oviducts at 3 weeks p.i. in the immunized hens but not in the control hens. In conclusion, we demonstrated that the immunization of laying hens with type 1 fimbriae reduced the number of contaminated eggs and reduced the colonization of the reproductive organs.

Investigating the role of secA2 in secretion and glycosylation of a fimbrial adhesin in Streptococcus parasanguis FW213

Adhesion of Streptococcus parasanguis FW213, a primary colonizer, to the tooth surface is mediated mainly by peritrichous long fimbriae. The fimbrial structural unit, Fap1, is indispensable for fimbriae biogenesis, adhesion to an in vitro tooth model and biofilm formation. Mature Fap1 is a glycoprotein with an apparent molecular mass of 200 kDa. Glycosylated Fap1 is not present in some mutants screened from a transposon mutant library. Localization of the transposition sites revealed a gene determined to be secA2, which is distinct from the canonical secA gene. In FW213, glycosylated Fap1 was present in all the subcellular fractions including the cytoplasm. In VT1574, a non-polar mutant of secA2 generated by in frame deletion, Fap1 was not secreted. Glycosylated Fap1 was present in the membrane and cytoplasm of the mutant, although in greatly reduced amounts. Fap1 secretion and abundance were restored when VT1574 was complemented by a plasmid-borne secA2. The secretion defect of the secA2 mutation appears to be limited to a small group of proteins such as Fap1 and FimA. These data suggested that Fap1 secretion rather than glycosylation was the major effect of the deletion of secA2; however, this deletion also had an impact on Fap1 abundance. Two more secA2 mutants with different regions deleted were tested for their ability to secrete Fap1. One mutant was completely unable to secrete Fap1 while the other was able to secrete, but in a decreased amount. These data suggest that the region deleted in the latter mutant (nucleotides 2032-2337) is dispensable for Fap1 secretion.

Infective endocarditis

Despite improvements in health care, the incidence of infective endocarditis has not decreased over the past decades. This apparent paradox is explained by a progressive evolution in risk factors; while classic predisposing conditions such as rheumatic heart disease have been all but eradicated, new risk factors for infective endocarditis have emerged. These include intravenous drug use, sclerotic valve disease in elderly patients, use of prosthetic valves, and nosocomial disease. Newly identified pathogens, which are difficult to cultivate--eg, Bartonella spp and Tropheryma whipplei--are present in selected individuals, and resistant organisms are challenging conventional antimicrobial therapy. Keeping up with these changes depends on a comprehensive approach, allying understanding of the pathogenesis of disease with the development of new drugs for infective endocarditis. Infection by staphylococci and streptococci is being dissected at the molecular level. New ideas for antimicrobial agents are being developed. These novel insights should help redefine preventive and therapeutic strategies against infective endocarditis.

The sloABCR operon of Streptococcus mutans encodes an Mn and Fe transport system required for endocarditis virulence and its Mn-dependent repressor

Streptococcus mutans belongs to the viridans group of oral streptococci, which is the leading cause of endocarditis in humans. The LraI family of lipoproteins in viridans group streptococci and other bacteria have been shown to function as virulence factors, adhesins, or ABC-type metal transporters. We previously reported the identification of the S. mutans LraI operon, sloABCR, which encodes components of a putative metal uptake system composed of SloA, an ATP-binding protein, SloB, an integral membrane protein, and SloC, a solute-binding lipoprotein, as well as a metal-dependent regulator, SloR. We report here the functional analysis of this operon. By Western blotting, addition of Mn to the growth medium repressed SloC expression in a wild-type strain but not in a sloR mutant. Other metals tested had little effect. Cells were also tested for aerobic growth in media stripped of metals then reconstituted with Mg and either Mn or Fe. Fe at 10 micro M supported growth of the wild-type strain but not of a sloA or sloC mutant. Mn at 0.1 micro M supported growth of the wild-type strain and sloR mutant but not of sloA or sloC mutants. The combined results suggest that the SloABC proteins transport both metals, although the SloR protein represses this system only in response to Mn. These conclusions are supported by (55)Fe uptake studies with Mn as a competitor. Finally, a sloA mutant demonstrated loss of virulence in a rat model of endocarditis, suggesting that metal transport is required for endocarditis pathogenesis.

MtsABC is important for manganese and iron transport, oxidative stress resistance, and virulence of Streptococcus pyogenes

MtsABC is a Streptococcus pyogenes ABC transporter which was previously shown to be involved in iron and zinc accumulation. In this study, we showed that an mtsABC mutant has impaired growth, particularly in a metal-depleted medium and an aerobic environment. In metal-depleted medium, growth was restored by the addition of 10 microM MnCl(2), whereas other metals had modest or no effect. A characterization of metal radioisotope accumulation showed that manganese competes with iron accumulation in a dose-dependent manner. Conversely, iron competes with manganese accumulation but to a lesser extent. The mutant showed a pronounced reduction (>90%) of (54)Mn accumulation, showing that MtsABC is also involved in Mn transport. Using paraquat and hydrogen peroxide to induce oxidative stress, we show that the mutant has an increased susceptibility to reactive oxygen species. Moreover, activity of the manganese-cofactored superoxide dismutase in the mutant is reduced, probably as a consequence of reduced intracellular availability of manganese. The enzyme functionality was restored by manganese supplementation during growth. The mutant was also attenuated in virulence, as shown in animal experiments. These results emphasize the role of MtsABC and trace metals, especially manganese, for S. pyogenes growth, susceptibility to oxidative stress, and virulence.