Group A streptococcus adheres to pharyngeal epithelial cells with salivary proline-rich proteins via GrpE chaperone protein

The Pneumococcal Protein SufC Binds to Host Plasminogen and Promotes Its Conversion into Plasmin

Streptococcus pneumoniae causes otitis media, sinusitis, and serious diseases such as pneumonia and bacteremia. However, the in vivo dynamics of S. pneumoniae infections and disease severity are not fully understood. In this study, we investigated pneumococcal proteins detected in the bronchoalveolar lavage fluid of an S. pneumoniae-infected mouse, which were assumed to be expressed during infection. Analysis of three proteins with unknown infection-related functions revealed that recombinant Fe-S cluster assembly ATP-binding protein (SufC) binds to the host plasminogen and promotes its conversion into plasmin. SufC was detected in the bacterial cell-surface protein fraction, but it had no extracellular secretory signal. This study suggests that S. pneumoniae releases SufC extracellularly through LytA-dependent autolysis, binding to the bacterial cell surface and host plasminogen and promoting its conversion into plasmin. The recruitment of plasmin by S. pneumoniae is considered useful for bacterial survival and spread, and SufC is suggested to facilitate this process.

GrpE and ComD contribute to the adherence, biofilm formation, and pathogenicity of Streptococcus suis

Streptococcus suis is a major bacterial pathogen of swine and an emerging zoonotic agent that has to date resulted in substantial economic losses to the swine industry worldwide, and can cause persistent infection by forming biofilms. GrpE and histidine protein kinase ComD are important proteins implicated in the pathogenicity of S. suis, although whether they play roles in adhesion and biofilm formation has yet to be sufficiently clarified. In this study, we constructed grpE and comD deletion strains of S. suis by homologous recombination, and examined their cell adhesion and biofilm formation capacities compared with those of the wild-type strain. The pathogenicity of the grpE and comD deletion strains was evaluated using a mouse infection model, which revealed that compared with the wild-type, these deletion strains induced milder symptoms and lower bacteremia, as well as comparatively minor organ (brain, spleen, liver, and lung) lesions, in the infected mice. Moreover, the deletion of grpE and comD significantly reduced the pro-inflammatory cytokine (IL-6, IL-1β, and TNF-α) induction capacity of S. suis. Collectively, the findings of this study indicate that the GrpE and ComD proteins of Streptococcus suis play key roles in the adherence to PK-15 cells and the formation of biofilms, thereby contributing to the virulence of this pathogen.

Investigating the functional role of a buried interchain aromatic cluster in Escherichia coli GrpE dimer

Aromatic clusters in the core of proteins are often involved in imparting structural stability to proteins. However, their functional importance is not always clear. In this study, we investigate the thermosensing role of a phenylalanine cluster present in the GrpE homodimer. GrpE, which acts as a nucleotide exchange factor for the molecular chaperone DnaK, is well known for its thermosensing activity resulting from temperature-dependent structural changes that allow control of chaperone function. Using mutational analysis, we show that an interchain phenylalanine cluster in a four-helix bundle of the GrpE homodimer assists in the thermosensing ability of the co-chaperone. Substitution of aromatic residues with hydrophobic ones in the core of the four-helix bundle reduces the thermal stability of the bundle and that of a connected coiled-coil domain, which impacts thermosensing. Cell growth assays and SEM images of the mutants show filamentous growth of Escherichia coli cells at 42°C, which corroborates with the defect in thermosensing. Our work suggests that the interchain edge-to-face aromatic cluster is important for the propagation of the structural signal from the coiled-coil domain to the four-helical bundle of GrpE, thus facilitating GrpE-mediated thermosensing in bacteria.

Mycoplasma hyopneumoniae membrane protein Mhp271 interacts with host UPR protein GRP78 to facilitate infection

The unfolded protein response (UPR) plays a crucial role in Mycoplasma hyopneumoniae (M. hyopneumoniae) pathogenesis. We previously demonstrated that M. hyopneumoniae interferes with the host UPR to foster bacterial adhesion and infection. However, the underlying molecular mechanism of this UPR modulation is unclear. Here, we report that M. hyopneumoniae membrane protein Mhp271 interacts with host GRP78, a master regulator of UPR localized to the porcine tracheal epithelial cells (PTECs) surface. The interaction of Mhp271 with GRP78 reduces the porcine beta‐defensin 2 (PBD‐2) production, thereby facilitating M. hyopneumoniae adherence and infection. Furthermore, the R1‐2 repeat region of Mhp271 is crucial for GRP78 binding and the regulation of PBD‐2 expression. Intriguingly, a coimmunoprecipitation (Co‐IP) assay and molecular docking prediction indicated that the ATP, rather than the substrate‐binding domain of GRP78, is targeted by Mhp271 R1‐2. Overall, our findings identify host GRP78 as a target for M. hyopneumoniae Mhp271 modulating the host UPR to facilitate M. hyopneumoniae adherence and infection.

Triosephosphate isomerase of Streptococcus pneumoniae is released extracellularly by autolysis and binds to host plasminogen to promote its activation

Recruitment of plasminogen is an important infection strategy of the human pathogen Streptococcus pneumoniae to invade host tissues. In Streptococcus aureus, triosephosphate isomerase (TPI) has been reported to bind plasminogen. In this study, the TPI of S. pneumoniae (TpiA) was identified through proteomic analysis of bronchoalveolar lavage fluid from a murine pneumococcal pneumonia model. The binding kinetics of recombinant pneumococcal TpiA with plasminogen were characterized using surface plasmon resonance (SPR, Biacore), ligand blot analyses, and enzyme‐linked immunosorbent assay. Enhanced plasminogen activation and subsequent degradation by plasmin were also shown. Release of TpiA into the culture medium was observed to be dependent on autolysin. These findings suggest that S. pneumoniae releases TpiA via autolysis, which then binds to plasminogen and promotes its activation, thereby contributing to tissue invasion via degradation of the extracellular matrix.

Abiotrophia defectiva adhere to saliva-coated hydroxyapatite beads via interactions between salivary proline-rich-proteins and bacterial glyceraldehyde-3-phosphate dehydrogenase

Abiotrophia defectiva is a species of nutritionally variant streptococci that is found in human saliva and dental plaques and that has been associated with infective endocarditis. In our previous study, it was found that A. defectiva could bind specifically to saliva-coated hydroxyapatite beads (SHA). This study identified a cell surface component of A. defectiva that promotes adherence to SHA beads. The binding of A. defectiva to SHA was reduced in the presence of antibodies against human proline-rich protein (PRP); these results suggested that PRP may be a critical component mediating interactions between A. defectiva and the salivary pellicle. Two-dimensional gel electrophoresis of whole A. defectiva cells followed by Far-Western blotting was conducted by probing with synthetic peptides analogous to the binding region of PRP known as PRP-C. The results indicate that an A. defectiva protein of 37 kDa interacts with PRP-C. The results of amino-terminal sequencing of the adhesive A. defectiva protein revealed significant similarity to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Recombinant GAPDH bound to immobilized PRP-C in a dose-dependent manner and binding of A. defectiva to SHA or to PRP was reduced in the presence of anti-GAPDH antiserum. Western blotting or electron immunomicroscopic observations with anti-GAPDH antiserum revealed that this protein was expressed in both cytosolic and cell wall fractions. These results suggest that A. defectiva could specifically bind to PRP via interactions with cell surface GAPDH; the findings suggest a mechanism underlying A. defectiva-mediated adherence to saliva-coated tooth surfaces.

Analysis of multidrug resistance in Streptococcus suis ATCC 700794 under tylosin stress

Streptococcus suis is an important zoonotic pathogen. The massive use of tylosin and other antibiotics in swine production has led to the emergence of resistant phenotypes of S. suis. However, there are no adequate measures available to address the problem of bacterial resistance. This study involved the use of 1/4 MIC (0.125 µg/mL) of tylosin to investigate resistance-related proteins by S. suis ATCC 700794. Our results showed that 171 proteins were differentially expressed in S. suis tested with 1/4 MIC (0.125 µg/mL) of tylosin using iTRAQ-based quantitative proteomic methods. TCS, heat shock protein and elongation factors were differentially expressed at 1/4 MIC (0.125 µg/mL) of tylosin compared to non treated, control cells. Using quantitative RT-PCR analysis, we verified the relationship between the differentially expressed proteins in S. suis with different MIC values. The data showed that expression profile for elongation factor G (fusA), elongation factor Ts (tsf), elongation factor Tu (tuf), putative histidine kinase of the competence regulon, ComD (comD), putative competence-damage inducible protein (cinA) and protein GrpE (grpE), observed in tylosin-resistant S. suis, correlated with that of S. suis ATCC 700794 at 1/4 MIC (0.125 µg/mL). The MIC of tylosin-resistant showed high-level resistance in terramycin, chlortetracycline, ofloxacin and enrofloxacin. Our findings demonstrated the importance of elongation factors, TCS and heat shock protein during development of tylosin resistance in S. suis. Thus, our study will provide insight into new drug targets and help reduce bacterial multidrug resistance through development of corresponding inhibitors.

Intracellular Invasion by Streptococcus pyogenes: Invasins, Host Receptors, and Relevance to Human Disease

The human oral-nasal mucosa is the primary reservoir for Streptococcus pyogenes infections. Although the most common infection of consequence in temperate climates is pharyngitis, the past 25 years have witnessed a dramatic increase in invasive disease in many regions of the world. Historically, S. pyogenes has been associated with sepsis and fulminate systemic infections, but the mechanism by which these streptococci traverse mucosal or epidermal barriers is not understood. The discovery that S. pyogenes can be internalized by mammalian epithelial cells at high frequencies (1-3) and/or open tight junctions to pass between cells (4) provides potential explanations for changes in epidemiology and the ability of this species to breach such barriers. In this article, the invasins and pathways that S. pyogenes uses to reach the intracellular state are reviewed, and the relationship between intracellular invasion and human disease is discussed.

Human glycan expression patterns influence Group A streptococcal colonization of epithelial cells

Colonization of the oropharynx is the initial step in Group A Streptococcus (GAS) pharyngeal infection. We have previously reported that the highly virulent M1T1 GAS clone attaches to oral epithelial cells via M1 protein interaction with blood group antigen carbohydrate structures. Here, we have identified that colonization of human oral epithelial cells by GAS serotypes M3 and M12 is mediated by human blood group antigens [ABO(H)] and Lewis (Le) antigen expression. Removal of linkage-specific fucose, galactose, N-acetylgalactosamine, and sialic acid modulated GAS colonization, dependent on host ABO(H) blood group and Le expression profile. Furthermore, N-linked glycans from human salivary glycoproteins, when released and purified, were potent inhibitors of M1, M3, and M12 GAS colonization ex vivo. These data highlight the important role played by human protein glycosylation patterns in GAS attachment to oral epithelial cell surfaces.-De Oliveira, D. M. P., Everest-Dass, A., Hartley-Tassell, L., Day, C. J., Indraratna, A., Brouwer, S., Cleary, A., Kautto, L., Gorman, J., Packer, N. H., Jennings, M. P., Walker, M. J., Sanderson-Smith, M. L. Human glycan expression patterns influence Group A streptococcal colonization of epithelial cells.

Group A Streptococcus-Mediated Host Cell Signaling

In the past decade, the field of the cellular microbiology of group A Streptococcus (S. pyogenes) infection has made tremendous advances and touched upon several important aspects of pathogenesis, including receptor biology, invasive and evasive phenomena, inflammasome activation, strain-specific autophagic bacterial killing, and virulence factor-mediated programmed cell death. The noteworthy aspect of S. pyogenes-mediated cell signaling is the recognition of the role of M protein in a variety of signaling events, starting with the targeting of specific receptors on the cell surface and on through the induction and evasion of NETosis, inflammasome, and autophagy/xenophagy to pyroptosis and apoptosis. Variations in reports on S. pyogenes-mediated signaling events highlight the complex mechanism of pathogenesis and underscore the importance of the host cell and S. pyogenes strain specificity, as well as in vitro/in vivo experimental parameters. The severity of S. pyogenes infection is, therefore, dependent on the virulence gene expression repertoire in the host environment and on host-specific dynamic signaling events in response to infection. Commonly known as an extracellular pathogen, S. pyogenes finds host macrophages as safe havens wherein it survives and even multiplies. The fact that endothelial cells are inherently deficient in autophagic machinery compared to epithelial cells and macrophages underscores the invasive nature of S. pyogenes and its ability to cause severe systemic diseases. S. pyogenes is still one of the top 10 causes of infectious mortality. Understanding the orchestration of dynamic host signaling networks will provide a better understanding of the increasingly complex mechanism of S. pyogenes diseases and novel ways of therapeutically intervening to thwart severe and often fatal infections.

Complete genome sequence of Lactobacillus pentosus SLC13, isolated from mustard pickles, a potential probiotic strain with antimicrobial activity against foodborne pathogenic microorganisms

Background

Lactobacillus pentosus SLC13 is a high exopolysaccharide (EPS)-producing strain with broad-spectrum antimicrobial activity and the ability to grow in simulated gastrointestinal conditions. SLC13 was isolated from mustard pickles in Taiwan for potential probiotic applications. To better understand the molecular base for its antimicrobial activity and high EPS production, entire genome of SLC13 was determined by PacBio SMRT sequencing.

Results

L. pentosus SLC13 contains a genome with a 3,520,510-bp chromosome and a 62,498-bp plasmid. GC content of the complete genome was 46.5% and that of plasmid pSLC13 was 41.3%. Sequences were annotated at the RAST prokaryotic genome annotation server, and the results showed that the genome contained 3172 coding sequences and 82 RNA genes. Seventy-six protein-coding sequences were identified on the plasmid pSLC13. A plantaricin gene cluster, which is responsible for bacteriosins biosynthesis and could be associated with its broad-spectrum antimicrobial activity, was identified based on comparative genomic analysis. Two gene clusters involved in EPS production were also identified.

Conclusion

This genomic sequence might contribute to a future application of this strain as probiotic in productive livestock potentially inhibiting competing and pathogenic organisms.

Streptococcus pyogenes adhesion and colonization

Streptococcus pyogenes (group A Streptococcus, GAS) is a human-adapted pathogen responsible for a wide spectrum of disease. GAS can cause relatively mild illnesses, such as strep throat or impetigo, and less frequent but severe life-threatening diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. GAS is an important public health problem causing significant morbidity and mortality worldwide. The main route of GAS transmission between humans is through close or direct physical contact, and particularly via respiratory droplets. The upper respiratory tract and skin are major reservoirs for GAS infections. The ability of GAS to establish an infection in the new host at these anatomical sites primarily results from two distinct physiological processes, namely bacterial adhesion and colonization. These fundamental aspects of pathogenesis rely upon a variety of GAS virulence factors, which are usually under strict transcriptional regulation. Considerable progress has been made in better understanding these initial infection steps. This review summarizes our current knowledge of the molecular mechanisms of GAS adhesion and colonization.

SILAC and LC-MS/MS identification of Streptococcus equi ssp. zooepidemicus proteins that contribute to mouse brain microvascular endothelial cell infection

Streptococcus equi ssp. zooepidemicus (SEZ) causes meningitis in both humans and animals. Some dissociative proteins of SEZ are cytotoxic to mouse brain microvascular endothelial cells (mBMECs) and may contribute to the penetration of SEZ across the blood-brain barrier (BBB). In this study, the ability of SEZ to penetrate across an in vitro BBB model was confirmed. We used stable isotope labeling with amino acids in cell culture (SILAC) to label SEZ proteins with heavy or light isotope-tagged amino acids, along with LC-MS/MS to determine which SEZ proteins were involved in interactions with mBMECs. The efficiency of SEZ protein isotope labeling was 94.7 %, which was sufficient for further analysis. Forty-nine labeled peptides were identified as binding to mBMECs, which matched to 25 SEZ proteins. Bioinformatic analysis indicated that most of these proteins were cytoplasmic. These proteins may have functions in breaching the host BBB, and some of them are known virulence factors in other bacteria. Indirect immunofluorescence results indicated that SEZ enolase had binding activity toward mBMECs. Protective test results showed that enolase was a protective antigen against SEZ infection. This research is the first application of SILAC combined with LC-MS/MS to identify SEZ proteins that may contribute to the infection of mBMECs and potentially show functions related to breaching the BBB. The outcomes provide many future avenues for research into the mechanism of SEZ-induced meningitis.

Comparative analysis of extractable proteins from Clostridium perfringens type A and type C strains showing varying degree of virulence

The prevailing scenario of bioterrorism warrants development of medical countermeasures with expanded coverage of select agents. Clostridium perfringens is a pathogen of medical, veterinary and military importance, and has been listed as Validated Biological Agent. We employed 2DE-MS approach to identify a total of 134 unique proteins (529 protein spot features) from the extractable proteome of four type A and type C strains. Proteins showing altered expression under host-simulated conditions from virulent type A strain (ATCC13124) were also elucidated. Significant among the differentially expressed proteins were elongation factor, molecular chaperones, ribosomal proteins, carbamoyl phosphate synthase, clpB protein, choloylglycine hydrolase, phosphopyruvate hydratase, and trigger factor. Predictive elucidation, of putative virulence associated proteins and sequence conservation pattern of selected candidates, was carried out using homologous proteins from other bacterial select agents to screen for the commonality of putative antigenic determinants. Pathogens (17 select agents) were observed to form three discrete clusters; composition of I and II being consistent in most of the phylogenetic reconstructions. This work provides a basis for further validation of putative candidate proteins as prophylactic agents and for their ability to provide protection against clusters of pathogenic select bacterial agents; aimed at mitigating the shadows of biothreat.

Antimicrobial peptides: an alternative for innovative medicines?

Antimicrobial peptides are small molecules with activity against bacteria, yeasts, fungi, viruses, bacteria, and even tumor cells that make these molecules attractive as therapeutic agents. Due to the alarming increase of antimicrobial resistance, interest in alternative antimicrobial agents has led to the exploitation of antimicrobial peptides, both synthetic and from natural sources. Thus, many peptide-based drugs are currently commercially available for the treatment of numerous ailments, such as hepatitis C, myeloma, skin infections, and diabetes. Initial barriers are being increasingly overcome with the development of cost-effective, more stable peptides. Herein, we review the available strategies for their synthesis, bioinformatics tools for the rational design of antimicrobial peptides with enhanced therapeutic indices, hurdles and shortcomings limiting the large-scale production of AMPs, as well as the challenges that the pharmaceutical industry faces on their use as therapeutic agents.

Molecular and genomic characterization of pathogenic traits of group A Streptococcus pyogenes

Group A streptococcus (GAS) or Streptococcus pyogenes causes various diseases ranging from self-limiting sore throat to deadly invasive diseases. The genome size of GAS is 1.85-1.9 Mb, and genomic rearrangement has been demonstrated. GAS possesses various surface-associated substances such as hyaluronic capsule, M proteins, and fibronectin/laminin/immunoglobulin-binding proteins. These are related to the virulence and play multifaceted and mutually reflected roles in the pathogenesis of GAS infections. Invasion of GAS into epithelial cells and deeper tissues provokes immune and non-immune defense or inflammatory responses including the recruitment of neutrophils, macrophages, and dendritic cells in hosts. GAS frequently evades host defense mechanisms by using its virulence factors. Extracellular products of GAS may perturb cellular and subcellular functions and degrade tissues enzymatically, which leads to the aggravation of local and/or systemic disorders in the host. In this review, we summarize some important cellular and extracellular substances that may affect pathogenic processes during GAS infections, and the host responses to these.

Salivary peptidomic as a tool to disclose new potential antimicrobial peptides

Antimicrobial peptides (AMPs) and peptidomimetics are among the new generation of antibiotics due to their broad spectrum of activity towards pathogenic agents. Considering the fact that the oral cavity is a relevant entryway for pathogenic microorganisms, it must be armed with several defenses in order to maintain homeostasis. Thus, we aimed at disclosing potential AMPs in saliva from humans, pigs and mice. We enriched salivary peptides by filtration and then separated and identified multiple peptides by nanoHPLC-MALDI-TOF/TOF. Using this approach, we identified 45 different peptides from mice's saliva and 94 from pig's saliva. Almost all peptides from pig and mice saliva were new assignments, encouraging the application of this technique to other mammals' saliva. The potential antimicrobial activity was then calculated in silico with an available CAMP's algorithm. Eight peptides from pig's basic proline-rich protein, as well as 6 peptides resulting from human's P-B peptide, 1 from P-C peptide fragmentation and 1 from statherin were found to have potential antimicrobial activity. Therefore, the peptides GPPPQGGRPQG and RFGYGYGPYQPVPEQPLYPQ were synthetically obtained and their antimicrobial properties evaluated in vitro for different bacterial strains. These showed to exert an antibacterial effect in Staphylococcus aureus. This report validates the prospection of mammal's saliva to find new alternatives to antibiotics.

BIOLOGICAL SIGNIFICANCE

With the growing problem of antibiotic resistance, the identification of new routes in antibiotic therapy is on the scientific agenda worldwide. Antimicrobial peptides (AMPs) and peptidomimetics are among the new generation of antibiotics due to their broad spectrum of activity towards pathogenic agents and owing to a less probable microbial resistance that can arise from their use. Thus, we explored the saliva from humans, pigs and mice to identify potential AMPs using a peptidomic approach. At the end, eight peptides from pig's basic proline-rich protein, six peptides resulting from human's P-B peptide, one from P-C peptide fragmentation and one from statherin were found to have potential antimicrobial activity. From this, the peptides GPPPQGGRPQG and RFGYGYGPYQPVPEQPLYPQ were tested showing to have antibacterial effect in S. aureus which highlights the potential of mammal's saliva to find new alternatives to antibiotics.

Proteomic analysis on the antibacterial activity of a Ru(II) complex against Streptococcus pneumoniae

Streptococcus pneumoniae is a Gram-positive pathogen that causes a variety of infection diseases in human. In this project, we determined the antibacterial activity of a Ru(II) complex X-03 against S. pneumoniae in vitro, by comparing its toxicity to host cells A549 and HBE. We performed two-dimensional gel electrophoresis (2-DE)-based proteomic analysis to characterize the protein alterations in S. pneumoniae after treatment with X-03. In total, 50 proteins exhibiting significant differential expressions were identified. RT-PCR was used to confirm the expression differences for selected proteins. Bioinformatics analysis on the proteomic alterations suggested that Ru(II) complex X-03 may obstruct bacterial fatty acid synthesis and oxidation-reduction process to suppress the growth of S. pneumoniae. Metal-uptake experiments revealed that iron-acquisition pathway in the bacterium may be interfered by X-03. These results provide useful clues for further investigations on the mechanism of the antibacterial action of metal compounds.

BIOLOGICAL SIGNIFICANCE

The appearance of bacterial strains with broad antibiotic resistance is becoming an alarming global health concern. The development of novel efficient antibacterial compound is urgently needed. In the present study, we found that Ru(II) complex X-03 has a significant antibacterial activity and applied proteomic technology combined with bioinformatics analysis to investigate its antimicrobial mechanism in S. pneumoniae. Many proteins were found to be dysregulated, implicating that X-03 may affect various molecular pathways leading to the inhibition of bacterial growth. Metal-uptake experiments demonstrated that X-03 treatment reduced the iron content in the bacterium, suggesting the interference with iron acquisition systems by the complex. This disturbance in iron acquisition may directly or indirectly induce the proteomic response that involved many pathways. In addition, X-03 could selectively suppress Gram-positive bacteria but execute less cytotoxicity to Gram-negative bacteria, with almost no effect on human cells, implicating its potential to be developed as a specific antimicrobial agent. These results provide useful information for further investigations on the mechanism of the antibacterial action of metal drugs and development of efficient antibacterial drugs.

The oral microbiome and the immunobiology of periodontal disease and caries

The composition of the oral microbiome differs from one intraoral site to another, reflecting in part the host response and immune capacity at each site. By focusing on two major oral infections, periodontal disease and caries, new principles of disease emerge. Periodontal disease affects the soft tissues and bone that support the teeth. Caries is a unique infection of the dental hard tissues. The initiation of both diseases is marked by an increase in the complexity of the microbiome. In periodontitis, pathobionts and keystone pathogens such as Porphyromonas gingivalis appear in greater proportion than in health. As a keystone pathogen, P. gingivalis impairs host immune responses and appears necessary but not sufficient to cause periodontitis. Historically, dental caries had been causally linked to Streptococcus mutans. Contemporary microbiome studies now indicate that singular pathogens are not obvious in either caries or periodontitis. Both diseases appear to result from a perturbation among relatively minor constituents in local microbial communities resulting in dysbiosis. Emergent consortia of the minor members of the respective microbiomes act synergistically to stress the ability of the host to respond and protect. In periodontal disease, host protection first occurs at the level of innate gingival epithelial immunity. Secretory IgA antibody and other salivary antimicrobial systems also act against periodontopathic and cariogenic consortia. When the gingival immune response is impaired, periodontal tissue pathology results when matrix metalloproteinases are released from neutrophils and T cells mediate alveolar bone loss. In caries, several species are acidogenic and aciduric and appear to work synergistically to promote demineralization of the enamel and dentin. Whereas technically possible, particularly for caries, vaccines are unlikely to be commercialized in the near future because of the low morbidity of caries and periodontitis.

Natural defense by saliva and mucosa against oral infection by Leptospira

Leptospirosis caused by drinking water has not been as frequently reported as percutaneous infection. Resistance to oral infection by pathogenic Leptospira was examined in an experimental hamster infection model. The results suggested some natural defenses against oral infection by Leptospira. First, we found that characteristic linear agglutination of Leptospira rapidly occurs when mixed with human saliva. That human saliva attenuated the infectivity of the treated leptospires by its agglutination activity suggested saliva to be the first line of defense against oral infection by leptospires. Second, only 10(1) Leptospira organisms caused death after submucosal injection into oral mucosa in hamsters, but oral infection with drinking water containing 10(5) organisms/mL did not cause death. This result showed that the mucosa plays the role of a physical barrier. Third, hamsters intragastrically infected by leptospires, with doses lethal to hamsters in oral infection, showed no signs of illness, which suggested that gastric acid plays an important role in preventing oral infection. Based on these results, saliva, mucosa, and gastric acid make up a natural defense, which confers high resistance to hosts against oral infection by leptospires.

Structural basis of the novel S. pneumoniae virulence factor, GHIP, a glycosyl hydrolase 25 participating in host-cell invasion

Pathogenic bacteria produce a wide variety of virulence factors that are considered to be potential antibiotic targets. In this study, we report the crystal structure of a novel S. pneumoniae virulence factor, GHIP, which is a streptococcus-specific glycosyl hydrolase. This novel structure exhibits an α/β-barrel fold that slightly differs from other characterized hydrolases. The GHIP active site, located at the negatively charged groove in the barrel, is very similar to the active site in known peptidoglycan hydrolases. Functionally, GHIP exhibited weak enzymatic activity to hydrolyze the PNP-(GlcNAc)5 peptidoglycan by the general acid/base catalytic mechanism. Animal experiments demonstrated a marked attenuation of S. pneumoniae-mediated virulence in mice infected by ΔGHIP-deficient strains, suggesting that GHIP functions as a novel S. pneumoniae virulence factor. Furthermore, GHIP participates in allowing S. pneumoniae to colonize the nasopharynx and invade host epithelial cells. Taken together, these findings suggest that GHIP can potentially serve as an antibiotic target to effectively treat streptococcus-mediated infection.