Pneumococcal virulence factors: structure and function

Serum antibodies to putative proteinase maturation protein A in children with acute otitis media

The pneumococcal genes encoding for the surface associated proteins have been proposed to be important for pneumococcal protein vaccine development. We cloned the full-length putative proteinase maturation protein A gene SP098l/ppmA (as published by Tettelin et al. in 2001) and produced the encoded protein in high levels in E. coli. The purified recombinant PpmA was used as an antigen in Western blotting to study systemic antibody responses to PpmA in animals and in children with acute otitis media (AOM). In children, the geometric mean titers of serum IgG antibodies against PpmA increased with age and differed significantly in relation to pneumococcal findings in middle ear fluid and/or nasopharyngeal aspirate. The serum IgG antibody titers against PpmA were low in children with Streptococcus pneumoniae cultured in the middle ear, and the highest in children with pneumococci in the nasopharynx, without them being found in the middle ear fluid. We conclude that PpmA is immunogenic in humans, and therefore an interesting antigen to study further in developing pneumococcal multicomponent protein vaccines.

Involvement of potD in Streptococcus pneumoniae polyamine transport and pathogenesis

Polyamines such as putrescine, spermidine, and cadaverine are small, polycationic molecules that are required for optimal growth in all cells. The intracellular concentrations of these molecules are maintained by de novo synthesis and transport pathways. The human pathogen Streptococcus pneumoniae possesses a putative polyamine transporter (pot) operon that consists of the four pot-specific genes potABCD. The studies presented here examined the involvement of potD in polyamine transport and in pneumococcal pathogenesis. A potD-deficient mutant was created in the mouse-virulent serotype 3 strain WU2 by insertion duplication mutagenesis. The growth of the WU2DeltapotD mutant was identical to that of the wild-type strain WU2 in vitro in rich media. However, WU2DeltapotD possessed severely delayed growth compared to wild-type WU2 in the presence of the polyamine biosynthesis inhibitors DFMO (alpha-dimethyl-fluoroornitithine) and MGBG [methylgloxal-bis (guanyl hydrazone)]. The mutant strain also showed a significant attenuation in virulence within murine models of systemic and pulmonary infection regardless of the inoculation route or location. These data suggest that potD is involved in pneumococcal polyamine transport and is important for pathogenesis within various infection models.

Induction of systemic and mucosal immune response and decrease in Streptococcus pneumoniae colonization by nasal inoculation of mice with recombinant lactic acid bacteria expressing pneumococcal surface antigen A

Mucosal epithelia constitute the first barriers to be overcome by pathogens during infection. The induction of protective IgA in this location is important for the prevention of infection and can be achieved through different mucosal immunization strategies. Lactic acid bacteria have been tested in the last few years as live vectors for the delivery of antigens at mucosal sites, with promising results. In this work, Streptococcus pneumoniae PsaA antigen was expressed in different species of lactic acid bacteria, such as Lactococcus lactis, Lactobacillus casei, Lactobacillus plantarum, and Lactobacillus helveticus. After nasal inoculation of C57Bl/6 mice, their ability to induce both systemic (IgG in serum) and mucosal (IgA in saliva, nasal and bronchial washes) anti-PsaA antibodies was determined. Immunization with L. lactis MG1363 induced very low levels of IgA and IgG, possibly by the low amount of PsaA expressed in this strain and its short persistence in the nasal mucosa. All three lactobacilli persisted in the nasal mucosa for 3 days and produced a similar amount of PsaA protein (150–250 ng per 10⁹ CFU). However, L. plantarum NCDO1193 and L. helveticus ATCC15009 elicited the highest antibody response (IgA and IgG). Vaccination with recombinant lactobacilli but not with recombinant L. lactis led to a decrease in S. pneumoniae recovery from nasal mucosa upon a colonization challenge. Our results confirm that certain Lactobacillus strains have intrinsic properties that make them suitable candidates for mucosal vaccination experiments.

Adherence molecules of pathogenic pneumococci

Adherence molecules are key players in pathogen-host interactions. These are usually surface-exposed structures that facilitate adherence to host cells, or target host serum proteins of the extracellular matrix. Our knowledge of the function of pneumococcal cell-surface structures, and the basic mechanisms underlying their interaction with host receptor molecules has dramatically increased, through molecular and structural analysis of adherence molecules. In particular, choline-binding proteins have received considerable attention because of their versatility, and their sophisticated role in the interaction with host proteins. Interestingly, subversion of host-protein functions to facilitate host invasion and immune evasion has also been attributed to intracellular or surface-exposed proteins of the pathogen. Many of these molecules do not possess the classic features of bacterial surface proteins.

Immunization with recombinant Streptococcus pneumoniae neuraminidase NanA protects chinchillas against nasopharyngeal colonization

Immunization with recombinant S. pneumoniae neuraminidase NanA (rNanA) resulted in a significant reduction in pneumococcal colonization in the chinchilla model. The bacteria were eliminated from the nasopharynx 1 week earlier than that from the control cohort. Our data suggest that rNanA affords protection against pneumococcal nasopharyngeal colonization.

Pneumococci induced TLR- and Rac1-dependent NF-kappaB-recruitment to the IL-8 promoter in lung epithelial cells

Streptococcus pneumoniae is the major pathogen of community-acquired pneumonia. The respiratory epithelium constitutes the first line of defense against invading lung pathogens, including pneumococci. We analyzed the involvement of Toll-like receptors (TLR) and Rho-GTPase signaling in the activation of human lung epithelial cells by pneumococci. S. pneumoniae induced release of interleukin-8 (IL-8) by human bronchial epithelial cell line BEAS-2B. Specific inhibition of Rac1 by Nsc23766 or a dominant-negative mutant of Rac1 strongly reduced cytokine release. In addition, pneumococci-related cell activation (IL-8 release, NF-kappaB-activation) depended on MyD88, phosphatidylinositol 3-kinase, and Cdc42 but not on RhoA. Pneumococci enhanced TLR1 and TLR2 mRNA expression in BEAS-2B cells, whereas TLR4 and TLR6 expression was constitutively high. TLR1 and 2 synergistically recognized pneumococci in cotransfection experiments. TLR4, TLR6, LPS-binding protein, and CD14 seem not to be involved in pneumococci-dependent cell activation. At the IL-8 gene promoter, recruitment of phosphorylated NF-kappaB subunit p65 was blocked by inhibition of Rac1, whereas binding of the phosphorylated activator protein-1 subunit c-Jun to the promoter was not diminished. In summary, these results suggest that S. pneumoniae activate human epithelial cells by TLR1/2 and a phosphatidylinositol 3-kinase- and Rac1-dependent NF-kappaB-recruitment to the IL-8 promoter.

The streptococcal lipoprotein rotamase A (SlrA) is a functional peptidyl-prolyl isomerase involved in pneumococcal colonization

Streptococcus pneumoniae expresses two surface-exposed lipoproteins, PpmA and SlrA, which share homology with distinct families of peptidyl-prolyl isomerases (PPIases). In this study, we demonstrated for the first time that the lipoprotein cyclophilin, SlrA, can catalyze the cis-trans isomerization of proline containing tetrapeptides and that SlrA contributes to pneumococcal colonization. The substrate specificity of SlrA is typical for prokaryotic and eukaryotic cyclophilins, with Suc-Ala-Ala-Pro-Phe-p-nitroanilide (pNA) being the most rapidly catalyzed substrate. In a mouse pneumonia model the slrA knock-out D39DeltaslrA did not cause significant differences in the survival times of mice compared with the isogenic wild-type strain. In contrast, a detailed analysis of bacterial outgrowth over time in the nasopharynx, airways, lungs, blood, and spleen showed a rapid elimination of slrA mutants from the upper airways but did not reveal significant differences in the lungs, blood, and spleen. These results suggested that SlrA is involved in colonization but does not contribute significantly to invasive pneumococcal disease. In cell culture infection experiments, the absence of SlrA impaired adherence to pneumococcal disease-specific epithelial and endothelial non-professional cell lines. Adherence of the slrA mutant could not be restored by exogenously added SlrA. Strikingly, deficiency in SlrA did not reduce binding activity to host target proteins, but resulted in enhanced uptake by professional phagocytes. In conclusion, SlrA is a functional, cyclophilin-type PPIase and contributes to pneumococcal virulence in the first stage of infection, namely, colonization of the upper airways, most likely by modulating the biological function of important virulence proteins.

DC-SIGN specifically recognizes Streptococcus pneumoniae serotypes 3 and 14

The Gram-positive bacterium Streptococcus pneumoniae is the leading causative pathogen in community-acquired pneumonia. The ever-increasing frequency of antibiotic-resistant S. pneumoniae strains severely hampers effective treatments. Thus, a better understanding of the mechanisms involved in the pathogenesis of pneumococcal disease is needed; in particular, of the initial interactions that take place between the host and the bacterium. Recognition of pathogens by dendritic cells is one of the most crucial steps in the induction of an immune response. For efficient pathogen recognition, dendritic cells express various kinds of receptors, including the DC-specific C-type lectin DC-SIGN. Pathogens such as Mycobacterium tuberculosis and HIV target DC-SIGN to escape immunity. Here the in vitro binding of DC-SIGN with S. pneumoniae was investigated. DC-SIGN specifically interacts with S. pneumoniae serotype 3 and 14 in contrast to other serotypes such as 19F. While the data described here suggest that DC-SIGN interacts with S. pneumoniae serotype 14 through a ligand expressed by the capsular polysaccharide, the binding to S. pneumoniae serotype 3 appears to depend on an as yet unidentified ligand. Despite the binding capacity of the capsular polysaccharide of S. pneumoniae 14 to DC-SIGN, no immunomodulatory effects on the dendritic cells were observed. The immunological consequences of the serotype-specific capacity to interact with DC-SIGN should be further explored and might result in new insights in the development of new and more potent vaccines.

Biochemical characterization of the pneumococcal glucose 1-phosphate uridylyltransferase (GalU) essential for capsule biosynthesis

The glucose 1-phosphate uridylyltransferase (GalU) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of Streptococcus pneumoniae. The pneumococcal GalU protein was overexpressed in Escherichia coli, and purified. GalU showed a pI of 4.23, and catalyzed the reversible formation of UDP-glucose and pyrophosphate from UTP and glucose 1-phosphate with K(m) values of 0.4 mM: for UDP-glucose, 0.26 mM: for pyrophosphate, 0.19 mM: for glucose 1-phosphate, and 0.24 mM: for UTP. GalU has an optimum pH of 8-8.5, and requires Mg(2+) for activity. Neither ADP-glucose nor TDP-glucose is utilized as substrates in vitro. The purification of GalU represents a fundamental step to provide insights on drug design to control the biosynthesis of the main pneumococcal virulence factor.

Mechanisms of resistance to telithromycin in Streptococcus pneumoniae

Reports of ketolide resistance remain scarce, however, a few laboratory-derived and clinical isolates of resistant Streptococcus pneumoniae have been documented. Mutations in key telithromycin-binding sites such as domains II and V of the 23S rRNA and ribosomal proteins L4 and L22, as well as mutations of the resistance determinant erm(B) are associated with elevated telithromycin MICs. Mutations in the secondary binding site of domain II coupled with ribosomal methylation may have serious resistance consequences should the domain II binding site be lost. Although ketolides are purported to maintain excellent activity against efflux-positive isolates, laboratory-derived telithromycin-resistant strains have been generated. As telithromycin usage increases, ketolide-resistant isolates of S. pneumoniae may well increase.

Release of DNA into the medium by competent Streptococcus pneumoniae: kinetics, mechanism and stability of the liberated DNA

The release of chromosomal DNA into culture media has been reported for several naturally transformable bacterial species, but a direct link between competence development and the liberation of DNA is generally lacking. Based on the analysis of strains with mutations in competence-regulatory genes and the use of conditions favouring or preventing competence, we provide evidence that DNA release is triggered by the induction of competence in Streptococcus pneumoniae. Kinetic analyses revealed that whereas competence was maximal 20 min after addition of competence-stimulating peptide, and then decreased, the amount of liberated DNA continued to increase and reached a maximum in stationary phase, when cells are no longer competent for DNA uptake. These data are not consistent with the proposal that release of DNA by a fraction of the population is coordinated with uptake by the remainder. Moreover, we observed that an unidentified DNase was specifically induced or released in competent cultures, and that together with the major pneumococcal endonuclease, EndA, it could degrade released DNA. Nearby complete abolition of release in a mutant lacking both the major autolysin, LytA, and the autolytic lysozyme, LytC, indicated that DNA liberation occurs by LytA-LytC-dependent cell lysis. These observations suggest that competence-dependent DNA release is one facet of a more general phenomenon of sensitization to autolysis that reaches its maximum in stationary phase.

Competence-programmed predation of noncompetent cells in the human pathogen Streptococcus pneumoniae: genetic requirements

Natural competence for genetic transformation is the best-characterized feature of the major human pathogen Streptococcus pneumoniae. Recent studies have shown the virulence of competence-deficient mutants to be attenuated, but the nature of the connection between competence and virulence remained unknown. Here we document the release, triggered by competent cells, of virulence factors (e.g., the cytolytic toxin pneumolysin) from noncompetent cells. This phenomenon, which we name allolysis, involves a previously undescribed bacteriocin system consisting of a two-peptide bacteriocin, CibAB, and its immunity factor, CibC; the major autolysin, LytA, and lysozyme, LytC; and a proposed new amidase, CbpD. We show that CibAB are absolutely required for allolysis, whereas LytA and LytC can be supplied either by the competent cells or by the targeted cells. We propose that allolysis constitutes a competence-programmed mechanism of predation of noncompetent cells, which benefits to the competent cells and contributes to virulence by coordinating the release of virulence factors.

Relationship between surface accessibility for PpmA, PsaA, and PspA and antibody-mediated immunity to systemic infection by Streptococcus pneumoniae

Antibodies to capsular polysaccharide (PS) are protective against systemic infection by Streptococcus pneumoniae, but the large number of pneumococcal serogroups and the age-related immunogenicity of pure PS limit the utility of PS-based vaccines. In contrast, cell wall-associated proteins from different capsular serotypes can be cross-reactive and immunogenic in all age groups. Therefore, we evaluated three pneumococcal proteins with respect to relative accessibility to antibody, in the context of intact pneumococci, and their ability to elicit protection against systemic infection by encapsulated S. pneumoniae. Sequences encoding pneumococcal surface adhesin A (PsaA), putative protease maturation protein A (PpmA), and the N-terminal region of pneumococcal surface protein A (PspA) from S. pneumoniae strain A66.1 were cloned and expressed in Escherichia coli. The presence of genes encoding PsaA, PpmA, and PspA in 11 clinical isolates was examined by PCR, and the expression of these proteins by each strain was examined by Western blotting with antisera raised to the respective recombinant proteins. We used flow cytometry to demonstrate that PspA was readily detectable on the surface of the pneumococcal strains analyzed, whereas PsaA and PpmA were not. Consistent with these observations, mice with passively or actively acquired antibodies to PspA or type 3 PS were equivalently protected from homologous systemic challenge with type 3 pneumococci, whereas mice with passively or actively acquired antibodies to PsaA or PpmA were not effectively protected. These experiments support the hypothesis that the extent of protection against systemic pneumococcal infection is influenced by target antigen accessibility to circulating host antibodies.

Ofloxacin-like antibiotics inhibit pneumococcal cell wall-degrading virulence factors

The search for new drugs against Streptococcus pneumoniae (pneumococcus) is driven by the 1.5 million deaths it causes annually. Choline-binding proteins attach to the pneumococcal cell wall through domains that recognize choline moieties, and their involvement in pneumococcal virulence makes them potential targets for drug development. We have defined chemical criteria involved in the docking of small molecules from a three-dimensional structural library to the major pneumococcal autolysin (LytA) choline binding domain. These criteria were used to identify compounds that could interfere with the attachment of this protein to the cell wall, and several quinolones that fit this framework were found to inhibit the cell wall-degrading activity of LytA. Furthermore, these compounds produced similar effects on other enzymes with different catalytic activities but that contained a similar choline binding domain; that is, autolysin (LytC) and the phage lytic enzyme (Cpl-1). Finally, we resolved the crystal structure of the complex between the choline binding domain of LytA and ofloxacin at a resolution of 2.6 Angstroms. These data constitute an important launch pad from which effective drugs to combat pneumococcal infections can be developed.

Drug treatment of pneumococcal pneumonia in the elderly

Streptococcus pneumoniae has been recognised as a major cause of pneumonia since the time of Sir William Osler. Drug-resistant S. pneumoniae (DRSP), which have gradually become resistant to penicillins as well as more recently developed macrolides and fluoroquinolones, have emerged as a consequence of indiscriminate use of antibacterials coupled with the ability of the pneumococcus to adapt to a changing antibacterial milieu. Pneumococci use cell wall choline components to bind platelet-activating factor receptors, colonise mucosal surfaces and evade innate immune defenses. Numerous virulence factors that include hyaluronidase, neuraminidase, iron-binding proteins, pneumolysin and autolysin then facilitate cytolysis of host cells and allow tissue invasion and bloodstream dissemination. Changes in pneumococcal cell wall penicillin-binding proteins account for resistance to penicillins, mutations in the ermB gene cause high-level macrolide resistance and mutations in topoisomerase IV genes coupled with GyrA gene mutations alter DNA gyrase and lead to high-level fluoroquinolone resistance. Risk factors for lower respiratory tract infections in the elderly include age-associated changes in oral clearance, mucociliary clearance and immune function. Other risks for developing pneumonia include poor nutrition, hypoalbuminaemia, bedridden status, aspiration, recent viral infection, the presence of chronic organ dysfunction syndromes including parenchymal lung disease and recent antibacterial therapy. Although the incidence of infections caused by DRSP is rising, the effect of an increase in the prevalence of resistant pneumococci on mortality is not clear. When respiratory infections occur, rapid diagnosis and prompt, empirical administration of appropriate antibacterial therapy that ensures adequate coverage of DRSP is likely to increase the probability of a successful outcome when treating community-acquired pneumonia in elderly patients, particularly those with multiple risk factors for DRSP. A chest x-ray is recommended for all patients, but other testing such as obtaining a sputum Gram's smear is not necessary and should not prolong the time gap between clinical suspicion of pneumonia and antibacterial administration. The selection of antibacterials should be based upon local resistance patterns of suspected organisms and the bactericidal efficacy of the chosen drugs. If time-dependent agents are chosen and DRSP are possible pathogens, dosing should keep drug concentrations above the minimal inhibitory concentration that is effective for DRSP. Treatment guidelines and recent studies suggest that combination therapy with a beta-lactam and macrolide may be associated with a better outcome in hospitalised patients, and overuse of fluoroquinolones as a single agent may promote quinolone resistance. The ketolides represent a new class of macrolide-like antibacterials that are highly effective in vitro against macrolide- and azalide-resistant pneumococci. Pneumococcal vaccination with the currently available polysaccharide vaccine is thought to confer some preventive benefit (preventing invasive pneumococcal disease), but more effective vaccines, such as nonconjugate protein vaccines, need to be developed that provide broad protection against pneumococcal infection.

Recent trends on the molecular biology of pneumococcal capsules, lytic enzymes, and bacteriophage

Streptococcus pneumoniae has re-emerged as a major cause of morbidity and mortality throughout the world and its continuous increase in antimicrobial resistance is rapidly becoming a leading cause of concern for public health. This review is focussed on the analysis of recent insights on the study of capsular polysaccharide biosynthesis, and cell wall (murein) hydrolases, two fundamental pneumococcal virulence factors. Besides, we have also re-evaluated the molecular biology of the pneumococcal phage, their possible role in pathogenicity and in the shaping of natural populations of S. pneumoniae. Precise knowledge of the topics reviewed here should facilitate the rationale to move towards the design of alternative ways to combat pneumococcal disease.

Pneumococcal vaccines: an update on current strategies

Streptococcus pneumoniae is a major cause of morbidity and mortality in infants, children and the elderly. Despite the availability of excellent antimicrobial therapy and adequate health care systems, respiratory diseases and invasive infections caused by pneumococci still comprise a major health problem. The emerging resistance to penicillin and other commonly used antibiotics underscores the importance of the development of novel vaccine strategies to combat pneumococcal disease. Although the 23-valent polysaccharide (PS) vaccine is immunogenic and protective in most adults and children over 5 years of age, they fail to protect children under 2 years of age. Fortunately, the recent conjugate vaccines have shown to be highly efficacious in preventing invasive diseases in this risk group. Moreover, promising results regarding prevention of pneumonia and acute otitis media have been published. Unfortunately, protection is raised against a limited number of pneumococcal serotypes, and serotype replacement and subsequent vaccine failure have become a serious concern. Currently, several pneumococcal surface proteins are considered as alternative vaccine candidates because of their serotype-independence. Thus far, pneumococcal surface adhesin A (PsaA) has proven to be highly protective against colonization in animal models. Moreover, pneumococcal surface protein A (PspA) and pneumolysin have shown to elicit protection against invasive diseases. Future research will elucidate their true potential in protecting humans. In this paper we discuss the present knowledge on pneumococcal vaccines and the current status of novel vaccine strategies.

Sequence Analysis and Characterization of a Novel Fibronectin-Binding Repeat Domain from the Surface ofStreptococcus pneumoniae

Streptococcus pneumoniae open reading frame SP0082 encodes a surface protein that contains four copies of a novel conserved repeat domain that bears no significant sequence similarity to proteins of known function. Homologous sequences from other streptococci contain two to six of these repeats, designated the SSURE (streptococcal surface repeat) domain. To investigate the functional role(s) of this domain, the third SSURE repeat of SP0082 sequence has been expressed in Escherichia coli, purified to homogeneity and characterized by biochemical and immunological methods. The expressed protein fragment was found to bind to fibronectin, but not to collagen or submaxillary mucin. Anti-SSURE antibodies recognized the corresponding protein on the surface of pneumococcal cells. These data identify S. pneumoniae SP0082 protein and its homologs in other streptococci as fibronectin-binding surface adhesins. The SSURE domain is likely to contain a novel protein fold, which was tentatively modeled using ab initio modeling methods.

Pneumolysin in the immunopathogenesis and treatment of pneumococcal disease

Recent insights into the immunopathogenesis of pneumococcal infection, a common and significant cause of morbidity and mortality, have implicated pneumolysin as being a prominent virulence factor, which may play a role in microbial colonization, invasion and dissemination, as well as tissue inflammation. Being a highly immunogenic polypeptide produced by all clinically relevant pneumococcal isolates, pneumolysin is recognized as a potential carrier protein for polysaccharide conjugate vaccines, while in the setting of acute disease, promising pneumolysin-directed pharmacological strategies include, among others, macrolides and corticosteroids.

Microarray analysis of pneumococcal gene expression during invasive disease

Streptococcus pneumoniae is a leading cause of invasive bacterial disease. This is the first study to examine the expression of S. pneumoniae genes in vivo by using whole-genome microarrays available from The Institute for Genomic Research. Total RNA was collected from pneumococci isolated from infected blood, infected cerebrospinal fluid, and bacteria attached to a pharyngeal epithelial cell line in vitro. Microarray analysis of pneumococcal genes expressed in these models identified body site-specific patterns of expression for virulence factors, transporters, transcription factors, translation-associated proteins, metabolism, and genes with unknown function. Contributions to virulence predicted for several unknown genes with enhanced expression in vivo were confirmed by insertion duplication mutagenesis and challenge of mice with the mutants. Finally, we cross-referenced our results with previous studies that used signature-tagged mutagenesis and differential fluorescence induction to identify genes that are potentially required by a broad range of pneumococcal strains for invasive disease.

IMMUNOMODULATION AND SEPSIS: IMPACT OF THE PATHOGEN

Infection begins when microorganisms overcome host barriers and multiply within host tissues. To contain the infection, the host mounts an inflammatory response that mobilizes defense systems and kills the invading microorganisms. A focal inflammatory response is usually sufficient to eradicate the organisms. However, when it fails to contain the infection, the organisms, their toxins, and numerous host mediators are released into the bloodstream, producing a systemic inflammatory response and organ failure. Microorganisms have coevolved with their hosts, thereby acquiring means of overcoming host defense mechanisms or even taking advantage of innate host responses. Many pathogens avoid recognition by the host or dampen host immune responses via sophisticated pathogen-host interactions. Some pathogens benefit from the inflammatory response. According to current hypotheses regarding the pathogenesis of sepsis, the host generates both an innate immune response identical for all pathogens and an adaptive pathogen-specific response. Determining whether the innate response benefits the pathogen or the host is essential for understanding host-pathogen interactions. In this review, we discuss how pathogens interfere with innate and adaptive immune responses to escape eradication by the host.

l-Ascorbic Acid 6-Hexadecanoate, a Potent Hyaluronidase Inhibitor

Hyaluronidases are enzymes that degrade hyaluronan, an important component of the extracellular matrix. The mammalian hyaluronidases are considered to be involved in many (patho)physiological processes like fertilization, tumor growth, and metastasis. Bacterial hyaluronidases, also termed hyaluronate lyases, contribute to the spreading of microorganisms in tissues. Such roles for hyaluronidases suggest that inhibitors could be useful pharmacological tools. Potent and selective inhibitors are not known to date, although L-ascorbic acid has been reported to be a weak inhibitor of Streptococcus pneumoniae hyaluronate lyase (SpnHL). The x-ray structure of SpnHL complexed with L-ascorbic acid has been elucidated suggesting that additional hydrophobic interactions might increase inhibitory activity. Here we show that L-ascorbic acid 6-hexadecanoate (Vcpal) is a potent inhibitor of both streptococcal and bovine testicular hyaluronidase (BTH). Vcpal showed strong inhibition of Streptococcus agalactiae hyaluronate lyase with an IC(50) of 4 microM and weaker inhibition of SpnHL and BTH with IC(50) values of 100 and 56 microM, respectively. To date, Vcpal has proved to be one of the most potent inhibitors of hyaluronidase. We also determined the x-ray structure of the SpnHL-Vcpal complex and confirmed the hypothesis that additional hydrophobic interactions with Phe-343, His-399, and Thr-400 in the active site led to increased inhibition. A homology structural model of BTH was also generated to suggest binding modes of Vcpal to this hyaluronidase. The long alkyl chain seemed to interact with an extended, hydrophobic channel formed by mostly conserved amino acids Ala-84, Leu-91, Tyr-93, Tyr-220, and Leu-344 in BTH.

An Important Role for Polymeric Ig Receptor-Mediated Transport of IgA in Protection againstStreptococcus pneumoniaeNasopharyngeal Carriage

The importance of IgA for protection at mucosal surfaces remains unclear, and in fact, it has been reported that IgA-deficient mice have fully functional vaccine-induced immunity against several bacterial and viral pathogens. The role of respiratory Ab in preventing colonization by Streptococcus pneumoniae has now been examined using polymeric IgR knockout (pIgR(-/-)) mice, which lack the ability to actively secrete IgA into the mucosal lumen. Intranasal vaccination with a protein conjugate vaccine elicited serotype-specific anti-capsular polysaccharide Ab locally and systemically, and pIgR(-/-) mice produced levels of total serum Ab after vaccination that were similar to wild-type mice. However, pIgR(-/-) mice had approximately 5-fold more systemic IgA and 6-fold less nasal IgA Ab than wild-type mice due to defective transport into mucosal tissues. Wild-type, but not pIgR(-/-) mice were protected against infection with serotype 14 S. pneumoniae, which causes mucosal colonization but does not induce systemic inflammatory responses in mice. The relative importance of secretory IgA in host defense was further shown by the finding that intranasally vaccinated IgA gene-deficient mice were not protected from colonization. Although secretory IgA was found to be important for protection against nasal carriage, it does not appear to have a crucial role in immunity to systemic pneumococcus infection, because both vaccinated wild-type and pIgR(-/-) mice were fully protected from lethal systemic infection by serotype 3 pneumococci. The results demonstrate the critical role of secretory IgA in protection against pneumococcal nasal colonization and suggest that directed targeting to mucosal tissues will be needed for effective vaccination in humans.

Zymographic characterization of bacteriolytic enzymes produced by oral streptococci

Zymographic analysis was performed to know the bacteriolytic enzyme profiles of 4% SDS extracts of oral streptococci, Streptococcus mutans, S. sobrinus, S. sanguis, S. mitis and S. salivarius. We investigated the five strains in each species and found that the profile was very similar among strains of the same species except for S. salivarius(the profile was classified into two types). On the other hand, the profile was considerably different among species. Two major bacteriolytic enzymes of S. mutans showing molecular mass of 80 and 100 kDa were found using SDS-boiled S. mutans or S. sobrinus cells as substrate. These bacteriolytic activities were less apparent in the gel containing S. mitis or S. salivarius, and also not detectable in the gel containing S. sanguis. S. sobrinus extract showed only one bacteriolytic band (78 kDa) as strong activity using S. sobrinus cells as substrate. S. sanguis extract showed no bacteriolytic bands using any streptococcal cells. Extracts of either S. mitis or S. salivarius showed weak activity by using respective strains as substrate.

Streptococcus pneumoniae-induced caspase 6-dependent apoptosis in lung epithelium

Streptococcus pneumoniae is the major pathogen of community-acquired pneumonia and one of the most common causes of death due to infectious diseases in industrialized countries. Lung epithelium lines the airways and constitutes the first line of innate defense against respiratory pathogens. Little is known about the molecular interaction of pneumococci with lung epithelial cells. Apoptosis of lung epithelium is involved in some bacterial lung infections. In this study different pneumococcal strains specifically induced either apoptotic or necrotic death of human alveolar and bronchial epithelial cells. Pneumococcus-induced apoptosis did not depend on the virulence factors pneumolysin and H(2)O(2). Apoptotic cells showed increased activity of caspases 6, 8, and 9 but not increased activity of caspase 3. Moreover, programmed cell death could be strongly reduced by a caspase 6 inhibitor and a pan-caspase inhibitor. Inhibitors of calpain and chymotrypsin- and trypsin-like proteases also reduced pneumococcus-induced apoptosis. Furthermore, pneumococcus-infected human alveolar epithelial cells showed Bid cleavage and reduced levels of Bcl2 and Bax. Overexpression of Bcl2 in these cells reduced apoptosis significantly. Thus, pneumococci induced apoptosis of human alveolar and bronchial epithelial cells. Programmed cell death was executed by caspase 6 and noncaspase proteases, but not by caspase 3, and could be blocked by overexpression of Bcl2.

Differences in clinical manifestation of Streptococcus pneumoniae infection are not correlated with in vitro production and release of the virulence factors pneumolysin and lipoteichoic and teichoic acids

Production and release of the pneumococcal virulence factors pneumolysin and lipoteichoic and teichoic acid in 75 clinical isolates were investigated. No difference was found between strains causing systemic infection or localized respiratory infection and isolates from asymptomatic carriers. This suggests that the presence of pneumolysin and lipoteichoic and teichoic acid is a necessary but not a sufficient condition for pneumococcal infection and development of invasive disease.

Immunization with native or recombinant Streptococcus pneumoniae neuraminidase affords protection in the chinchilla otitis media model

Streptococcus pneumoniae neuraminidase has been implicated as a virulence factor in the pathogenesis of pneumococcal otitis media. In this study, native neuraminidase was partially purified from cultures of S. pneumoniae by serial chromatography with DEAE-Sepharose and Sephacryl S-200. Recombinant neuraminidase, a 3,038-bp fragment of the neuraminidase A (nanA) gene, was cloned into the pET-28b vector and then expressed at high levels in Escherichia coli. Chinchillas were immunized subcutaneously with either the gel-purified native or recombinant neuraminidase, and all responded with elevated titers of antineuraminidase antibody in serum. Immunization with neuraminidase resulted in a significant reduction in nasopharyngeal colonization as well as in the incidence of otitis media with effusion. These data demonstrate for the first time that neuraminidase affords protection against S. pneumoniae nasopharyngeal colonization and experimental otitis media.

Expression and characterization of cholera toxin B—pneumococcal surface adhesin A fusion protein in Escherichia coli: ability of CTB-PsaA to induce humoral immune response in mice

Cholera toxin B subunit (CTB) is responsible for CT holotoxin binding to the cell and has been described as a mucosal adjuvant for vaccines. In this work, the ctxB gene was genetically fused to the psaA gene from Streptococcus pneumoniae, a surface protein involved in its colonization in the host that is also considered a vaccine antigen candidate against this pathogen. The CTB-PsaA fusion protein was expressed in Escherichia coli, and the purified protein was used for intranasal immunization experiments in Balb/C mice. CTB-PsaA was able to induce both systemic and mucosal antibodies evaluated in serum, saliva, and in nasal and bronchial wash samples, showing that CTB-PsaA is a promising molecule to be investigated as S. pneumoniae vaccine antigen candidate.

Pneumolysin-Induced Lung Injury Is Independent of Leukocyte Trafficking into the Alveolar Space

Pneumolysin (PLY) is a major virulence factor released by Streptococcus pneumoniae and has been implicated in the pathogenesis of pneumococcal pneumonia. In this study, we evaluated the contribution of newly recruited neutrophils and monocytes and resident alveolar macrophages to the pathogenesis of PLY-induced lung injury. Mice received either adhesion-blocking Abs to inhibit alveolar leukocyte trafficking or liposomal clodronate to deplete alveolar macrophages before intratracheal application of native PLY or its noncytotoxic derivative PdB. We found that treatment with PLY but not PdB resulted in increased lung vascular permeability. In addition, PLY also induced a decrease in the resident alveolar macrophage population, and the recruitment of peripheral blood neutrophils and monocytes into the alveolar space. Blockade of PLY-induced alveolar leukocyte trafficking by pretreatment of mice with anti-CD18 plus anti-CD49d Abs or depletion of circulating neutrophils did not attenuate the increase in lung permeability observed in response to intratracheal PLY. In addition, depletion of resident alveolar macrophages with clodronated liposomes did not reduce alveolar injury developing in response to PLY. PLY-induced lung injury was associated with only a small increase in bronchoalveolar lavage concentrations of cytokines. These data indicate that PLY-induced lung injury results from direct pneumotoxic effects on the alveolar-capillary barrier and is independent of both resident and recruited phagocytic cells.

Pneumococcal surface protein C contributes to sepsis caused by Streptococcus pneumoniae in mice

The role of pneumococcal surface protein C (PspC; also called SpsA, CbpA, and Hic) in sepsis by Streptococcus pneumoniae was investigated in a murine infection model. The pspC gene was deleted in strains D39 (type 2) and A66 (type 3), and the mutants were tested by being injected intravenously into mice. The animals infected with the mutant strains showed a significant increase in survival, with the 50% lethal dose up to 250-fold higher than that for the wild type. Our findings indicate that PspC affords a decisive contribution to sepsis development.

Virulence ofStreptococcus pneumoniaemay be determined independently of capsular polysaccharide

Mice were inoculated intranasally with Streptococcus pneumoniae isolates of serotype 14 with different genetic backgrounds (14R, 14DW) and a capsular switch of 14R, strain 9VR (serotype 9V). Inoculation of the mice with 14R and 9VR resulted in 60% mortality. All the mice survived 14DW inoculation. No differences in lungs' bacterial loads were found 3 h following inoculation. Bacterial clearance of 5 logs was observed 48 h after inoculation with 14DW versus within 1 log 48 h after inoculation with 14R and 9VR. No significant differences in bacterial size or the capsular amount could be found between 14R and 14DW. We conclude that factor(s) in addition to the capsule, contribute to disease outcome.

Cell wall branches, penicillin resistance and the secrets of the MurM protein

Production of low-affinity forms of penicillin-binding proteins (PBPs), although essential, is not sufficient to protect pneumococci against the inhibitory action of penicillin. Resistance also requires the newly identified protein MurM which, together with MurN, is involved with the synthesis of short peptide branches in the pneumococcal cell wall. Cells in which murM was inactivated produced cell walls without branches and also completely lost penicillin resistance. To understand these surprising observations a 3D-model of MurM was constructed, which helped to put into structural context several of the biochemical and genetic observations made about this protein.

Expression of Streptococcus pneumoniae antigens, PsaA (pneumococcal surface antigen A) and PspA (pneumococcal surface protein A) by Lactobacillus casei

A number of recent research works in lactic acid bacteria aim towards the design of new strains that could be used as live vectors for the delivery of antigens for oral vaccination, or other therapeutic molecules. In this work, an inducible expression system based on the Lactobacillus casei lactose operon promoter was used to express three important surface antigens of Streptococcus pneumoniae in this lactic acid bacterium: a virulence-related pneumococcal surface antigen (PsaA) and two variants of the virulence factor PspA (pneumococcal surface protein A). Expression of the three proteins was induced upon growth on lactose and strongly repressed by glucose. These proteins were produced intracellularly. Also, secretion to the growth medium was achieved by means of a fusion to the secreting and processing signals from the L. casei surface proteinase. Interestingly, while secreted PspA proteins were found in the culture supernatants, PsaA remained trapped in the cell wall. Expression of pneumococcal antigens in a food-grade organism opens an alternative for mucosal vaccination against this important pathogen.

Hydrogen peroxide-mediated killing of Caenorhabditis elegans: a common feature of different streptococcal species

Recently, we reported that Streptococcus pyogenes kills Caenorhabditis elegans by the use of hydrogen peroxide (H2O2). Here we show that diverse streptococcal species cause death of C. elegans larvae in proportion to the level of H2O2 produced. H2O2 may mask the effects of other pathogenicity factors of catalase-negative bacteria in the C. elegans infection model.

A novel putative enterococcal pathogenicity island linked to the esp virulence gene of Enterococcus faecium and associated with epidemicity

Enterococcus faecalis harbors a virulence-associated surface protein encoded by the esp gene. This gene has been shown to be part of a 150-kb putative pathogenicity island. A gene similar to esp has recently been found in Enterococcus faecium isolates recovered from hospitalized patients. In the present study we analyzed the polymorphism in the esp gene of E. faecium, and we investigated the association of esp with neighboring chromosomal genes. The esp gene showed considerable sequence heterogeneity in the regions encoding the nonrepeat N- and C-terminal domains of the Esp protein as well as differences in the number of repeats. DNA sequencing of chromosomal regions flanking the esp gene of E. faecium revealed seven open reading frames, representing putative genes implicated in virulence, regulation of transcription, and antibiotic resistance. These flanking regions were invariably associated with the presence or absence of the esp gene in E. faecium, indicating that esp in E. faecium is part of a distinct genetic element. Because of the presence of virulence genes in this gene cluster, the lower G+C content relative to that of the genome, and the presence of esp in E. faecium isolates associated with nosocomial outbreaks and clinically documented infections, we conclude that this genetic element constitutes a putative pathogenicity island, the first one described in E. faecium. Except for the presence of esp and araC, this pathogenicity island is completely different from the esp-containing pathogenicity island previously disclosed in E. faecalis.

Pneumococcus virulence factor sialidase: a new direction in neuro-AIDS research?

The purpose of this presentation is to invite consideration by the research community of the hypothesis that sialidase, a virulence factor of Streptococcus pneumoniae (pneumococcus) and most other opportunistic co-infectious agents associated with HIV infection, advances progression of HIV infection to neuro-AIDS.

Vaccines against bacterial meningitis

Meningitis remains an important cause of morbidity and mortality among children >5 years of age and is especially prevalent in developing countries. Effective routine immunization against Hib, pneumococcus and serogroupC meningococcus has had a significant impact on both invasive disease and carriage caused by these encapsulated bacteria. The major challenge in prevention of meningitis remains the delivery of vaccines worldwide, especially to resource-poor regions with the greatest disease burden.

Pneumococcal surface protein A is expressed in vivo, and antibodies to PspA are effective for therapy in a murine model of pneumococcal sepsis

Pneumococcal surface protein A (PspA) is an immunogenic protein expressed on the surface of all strains of Streptococcus pneumoniae (pneumococcus) and induces antibodies which protect against invasive infection in mice. Pneumococci used for infectious challenge in protection studies are typically collected from cultures grown in semisynthetic medium in vitro. The purpose of these studies is to confirm that PspA is expressed by pneumococci during growth in vivo at a level sufficient for antibodies to PspA to be protective. Mice were actively immunized with purified PspA or by passive transfer of monoclonal antibody (MAb) and challenged with a capsular type 3 strain in diluted whole blood from bacteremic mice. All were protected against challenge with 10 times the 50% lethal dose (LD(50)), and mice challenged with 1,000 times the LD(50) had increased survival compared with controls. Additionally, nonimmune mice treated with MAbs to PspA or PspA immune serum at 6 and 12 h after infection with 10 times the LD(50) also showed increased survival. Northern blot analysis of RNA from pneumococci grown either in vitro or in vivo showed similar levels of PspA mRNA. These results demonstrate that PspA is expressed in vivo in a mouse model and that immunization with PspA induces antibodies to an antigen which is expressed during the course of invasive infection. Immunotherapy with antibodies to PspA may have some utility in treating pneumococcal infections in humans.

Epitope mapping of pneumococcal surface protein A of strain Rx1 using monoclonal antibodies and molecular structure modelling

Pneumococcal surface protein A (PspA) is an antigenic variable vaccine candidate of Streptococcus pneumoniae. Epitope similarities between PspA from the American vaccine candidate strain Rx1 and Norwegian clinical isolates were studied using PspA specific monoclonal antibodies (mAbs) made against clinical Norwegian strains. Using recombinant PspA/Rx1 fragments and immunoblotting the epitopes for mAbs were mapped to two regions of amino acids, 1-67 and 67-236. The discovered epitopes were visualized by modelling of the PspA:Fab part of mAb in three dimensions. Flow cytometric analysis showed that the epitopes for majority of mAbs were accessible for antibody binding on live pneumococci. Also, the epitopes for majority of the mAbs are widely expressed among clinical Norwegian isolates.

Structures of Streptococcus pneumoniae Hyaluronate Lyase in Complex with Chondroitin and Chondroitin Sulfate Disaccharides

Streptococcus pneumoniae hyaluronate lyase is a surface enzyme of this Gram-positive bacterium. The enzyme degrades hyaluronan and chondroitin/chondroitin sulfates by cleaving the beta1,4-glycosidic linkage between the glycan units of these polymeric substrates. This degradation helps spreading of this bacterial organism throughout the host tissues and facilitates the disease process caused by pneumococci. The mechanism of this degradative process is based on beta-elimination, is termed proton acceptance and donation, and involves selected residues of a well defined catalytic site of the enzyme. The degradation of hyaluronan alone is thought to proceed through a processive mode of action. The structures of complexes between the enzyme and chondroitin as well as chondroitin sulfate disaccharides allowed for the first detailed insights into these interactions and the mechanism of action on chondroitins. This degradation of chondroitin/chondroitin sulfates is nonprocessive and is selective for the chondroitin sulfates only with certain sulfation patterns. Chondroitin sulfation at the 4-position on the nonreducing site of the linkage to be cleaved or 2-sulfation prevent degradation due to steric clashes with the enzyme. Evolutionary studies suggest that hyaluronate lyases evolved from chondroitin lyases and still retained chondroitin/chondroitin sulfate degradation abilities while being specialized in the degradation of hyaluronan. The more efficient processive degradation mechanism has come to be preferred for the unsulfated substrate hyaluronan.

SecA2-dependent secretion of autolytic enzymes promotes Listeria monocytogenes pathogenesis

Pathogenic bacteria secrete proteins that promote invasion of host tissues and resistance to immune responses. However, secretion mechanisms that contribute to the enormous morbidity and mortality of Gram-positive bacteria are largely undefined. An auxiliary protein secretion system (SecA2) has recently emerged in Listeria monocytogenes and eight other Gram-positive pathogens. Here, a proteomics approach identified seventeen SecA2-dependent secreted and surface proteins of L. monocytogenes, the two most abundant of which [the p60 and N-acetylmuramidase (NamA) autolysins] hydrolyze bacterial peptidoglycan (PGN) and contribute to host colonization. SecA2-deficient (DeltaSecA2) bacteria were rapidly cleared after systemic infection of murine hosts, and in cultured cells showed reduced cell-cell spread. p60 or NamA deficiencies (Deltap60 and DeltaNamA) caused intermediate reductions in bacterial virulence in vivo, yet showed no defect for infection of cultured cells. Restoration of virulence in Deltap60 bacteria required full-length p60 with an intact catalytic domain, suggesting that PGN hydrolysis by p60 is crucial for L. monocytogenes virulence. Coordinated PGN hydrolysis by p60 and NamA activities is predicted to generate a muramyl glycopeptide, glucosaminylmuramyl dipeptide (GMDP), which is known to modify host inflammatory responses. Thus, SecA2-dependent secretion may promote release of muramyl peptides that subvert host pattern recognition.

Differential activation of the immune system by virulent Streptococcus pneumoniae strains determines recovery or death of the host

Streptococcus pneumoniae infection may result in asymptomatic carriage, mucosal or invasive disease. We hypothesize that self-limiting or fatal disease outcome follows infection with S. pneumoniae differential activation of the host immune response. BALB/c and C57BL/6 mice were inoculated intranasally with S. pneumoniae serotype 3 strain WU2 and serotype 14 strain DW14 and mortality, bacterial load, pathological changes in the lungs and cytokines mRNA levels in the spleen were analysed. No differences between the C57BL/6 and the BALB/c inbred mice were observed except for the severity of their lung pathology and IL-4 expression. Infection of the two mouse strains with S. pneumoniae WU2 resulted in sepsis and death that occurred within 4 days post-inoculation. This death was preceded, in both mouse strains, in an increase over time of the lung bacterial load and bacteraemia. The lung pathology was characterized by diffuse pneumonia with marked congestion of the lungs. Analysis of mRNA expression of cytokines in the spleen revealed no alterations in tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, interleukin (IL)-12 and interferon (IFN)-gamma and induction of IL-10 and IL-4. The two strains of mice survived infection with S. pneumoniae DW14. This was accompanied by a reduction over time of lung bacterial load and bacteraemia. The lung pathology was characterized by focal lymphocyte infiltration and preserved architecture of the organ. Analysis of mRNA expression of cytokines in the spleen revealed a significant decrease in the levels of TNF-alpha, TGF-beta, IL-12 and IFN-gamma mRNA expression, which usually precedes cytokine protein expression. Interestingly, a significant increase in the levels of IL-4 mRNA expression was found in BALB/c mice only. This study suggests that differential activation or evasion of cytokine expression by S. pneumoniae virulent strains determines disease outcome regardless of the host's immunogenetic background.

Genome-based bioinformatic selection of chromosomal Bacillus anthracis putative vaccine candidates coupled with proteomic identification of surface-associated antigens

Bacillus anthracis (Ames strain) chromosome-derived open reading frames (ORFs), predicted to code for surface exposed or virulence related proteins, were selected as B. anthracis-specific vaccine candidates by a multistep computational screen of the entire draft chromosome sequence (February 2001 version, 460 contigs, The Institute for Genomic Research, Rockville, Md.). The selection procedure combined preliminary annotation (sequence similarity searches and domain assignments), prediction of cellular localization, taxonomical and functional screen and additional filtering criteria (size, number of paralogs). The reductive strategy, combined with manual curation, resulted in selection of 240 candidate ORFs encoding proteins with putative known function, as well as 280 proteins of unknown function. Proteomic analysis of two-dimensional gels of a B. anthracis membrane fraction, verified the expression of some gene products. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analyses allowed identification of 38 spots cross-reacting with sera from B. anthracis immunized animals. These spots were found to represent eight in vivo immunogens, comprising of EA1, Sap, and 6 proteins whose expression and immunogenicity was not reported before. Five of these 8 immunogens were preselected by the bioinformatic analysis (EA1, Sap, 2 novel SLH proteins and peroxiredoxin/AhpC), as vaccine candidates. This study demonstrates that a combination of the bioinformatic and proteomic strategies may be useful in promoting the development of next generation anthrax vaccine.

Reduced release of pneumolysin by Streptococcus pneumoniae in vitro and in vivo after treatment with nonbacteriolytic antibiotics in comparison to ceftriaxone

Pneumolysin, a virulence factor of Streptococcus pneumoniae with cytotoxic and proinflammatory activities, occurs at concentrations from 0.85 to 180 ng/ml in cerebrospinal fluid (CSF) of meningitis patients. In pneumococcal cultures and in a rabbit meningitis model, the concentrations of pneumolysin in supernatant and CSF were lower after addition of nonbacteriolytic bactericidal antibiotics (rifampin and clindamycin) than after incubation with ceftriaxone.

Streptococcus pneumoniae hyaluronate lyase contains two non-cooperative independent folding/unfolding structural domains: characterization of functional domain and inhibitors of enzyme

Hyaluronate lyase contributes directly to bacterial invasion by degrading hyaluronan, the major component of host extracellular matrix of connective tissues. Streptococcus pneumoniae hyaluronate lyase (SpnHL) is built from two structural domains that interact through interface residues, in addition to being connected by a peptide linker. For the first time we demonstrate that the N- and C-terminal domains of SpnHL fold/unfold independent of each other suggesting the absence of any significant cooperative interactions between them. The C-terminal domain of SpnHL is less stable than the N-terminal domain against thermal and guanidine hydrochloride denaturation. The intact N-terminal domain was purified after limited proteolysis of SpnHL under conditions where only the C-terminal domain was unfolded. Isolated N-terminal domain of SpnHL had similar thermal stability as when present in the native enzyme and was found to be enzymatically active demonstrating that it is capable of carrying out enzymatic reaction on its own. Functional studies demonstrated that guanidine hydrochloride, guanidine isothiocyanate, l-arginine methyl ester, and l-arginine inhibit the enzymatic activity of SpnHL at very low concentrations. This provides a lead for new chemical entities that can be exploited for designing effective inhibitors of SpnHL.

Immunity to Streptococcus pneumoniae: Factors affecting production and efficacy

Streptococcus pneumoniae is a complex human pathogen and a major cause of morbidity and mortality. The genetic background of pneumococci and the chemical structure of their capsules is largely unraveled as well as the basic role of anticapsular antibodies and other opsonins interacting to enhance phagocytosis. Many experimental studies are improving our knowledge on the complex molecular mechanisms underlying those events. Pneumococcal optimal clearance requires the cooperation of a plethora of reactions from both innate and adaptive immunity. The last advances in the complexity of the immune response and protection are reviewed: phagocyte-pneumococcus interactions mediated by opsonins; the role of complement, reactive C protein and natural antibodies; details of novel immune evasion mechanisms; the complex role of the inflammatory mediators in the susceptibility to pneumococcal infections; why capsular polysaccharides do not yield an anamnestic response after primary immunization; the central question of whether T cells regulate in-vivo anti-polysaccharide immunoglobulin responses to intact pathogens. All of these are topics where new data and some answers are offered. The state of the art on the research of pneumococcal protein vaccines as an alternative to plain polysaccharide or conjugated vaccine and the establishment of immunologic correlates of protection to facilitate efficacy trial assessment are also reviewed.

Inactivation of the srtA gene affects localization of surface proteins and decreases adhesion of Streptococcus pneumoniae to human pharyngeal cells in vitro

Inactivation of sortase gene srtA in Streptococcus pneumoniae strain R6 caused the release of beta-galactosidase and neuraminidase A (NanA) from the cell wall into the surrounding medium. Both of these surface proteins contain the LPXTG motif in the C-terminal domain. Complementation with plasmid-borne srtA reversed protein release. Deletion of murM, a gene involved in the branching of pneumococcal peptidoglycan, also caused partial release of beta-galactosidase, suggesting preferential attachment of the protein to branched muropeptides in the cell wall. Inactivation of srtA caused decreased adherence to human pharyngeal cells in vitro but had no effect on the virulence of a capsular type III strain of S. pneumoniae in the mouse intraperitoneal model. The observations suggest that--as in other gram-positive bacteria--sortase-dependent display of proteins occurs in S. pneumoniae and that some of these proteins may be involved in colonization of the human host.

The future of meningitis vaccines

Without effective vaccines meningitis remains a substantial worldwide threat with major health-care implications. A number of advances have been made in vaccine design and implementation over the last decade, with new vaccine initiatives providing substantial promise for the future reduction of global disease burden.

The function of hydrophobic residues in the catalytic cleft of Streptococcus pneumoniae hyaluronate lyase. Kinetic characterization of mutant enzyme forms

Streptococcus pneumoniae hyaluronate lyase is a surface antigen of this Gram-positive human bacterial pathogen. The primary function of this enzyme is the degradation of hyaluronan, which is a major component of the extracellular matrix of the tissues of vertebrates and of some bacteria. The enzyme degrades its substrate through a beta-elimination process called proton acceptance and donation. The inherent part of this degradation is a processive mode of action of the enzyme degrading hyaluronan into unsaturated disaccharide hyaluronic acid blocks from the reducing to the nonreducing end of the polymer following the initial random endolytic binding to the substrate. The final degradation product is the unsaturated disaccharide hyaluronic acid. The residues of the enzyme that are involved in various aspects of such degradation were identified based on the three-dimensional structures of the native enzyme and its complexes with hyaluronan substrates of various lengths. The catalytic residues were identified to be Asn(349), His(399), and Tyr(408). The residues responsible for the release of the product of the reaction were identified as Glu(388), Asp(398), and Thr(400), and they were termed negative patch. The hydrophobic residues Trp(291), Trp(292), and Phe(343) were found to be responsible for the precise positioning of the substrate for enzyme catalysis and named hydrophobic patch. The comparison of the specific activities and kinetic properties of the wild type and the mutant enzymes involving the hydrophobic patch residues W292A, F343V, W291A/W292A, W292A/F343V, and W291A/W292A/F343V allowed for the characterization of every mutant and for the correlation of the activity and kinetic properties of the enzyme with its structure as well as the mechanism of catalysis.