Capsular polysaccharide of Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas, and its modification with phosphorylcholine

Broad specificity of monoclonal IgA (TEPC15-IgA) for enteric bacteria via phosphorylcholine-mediated interaction

Immunoglobulin A (IgA) is notable for its broad specificity toward multiple bacteria. Phosphorylcholine (PC) plays a role in the infection of pathogenic bacteria carrying PC and in the induction of IgA responses in the host immune system. The commercially available mouse monoclonal IgA, TEPC15-IgA, is a distinctive antibody with specificity for PC, warranting further exploration of its response to PC-bearing enteric bacteria. In this study, using 17 different enteric bacteria, including 3 aerobic and 14 anerobic bacteria that could be cultured in vitro, we confirmed that TEPC15-IgA recognizes 4 bacterial species: Lactobacillus taiwanensis, Limosilactobacillus frumenti, Streptococcus infantis, and Escherichia coli, although reactivity varied. Interestingly, TEPC15-IgA did not react with four of six Lactobacillus species used. Moreover, distinct target molecules associated with PC in L. taiwanensis and L. frumenti were evident, differing in molecular weight. These findings suggest that the natural generation of PC-specific IgA could prevent PC-mediated infections and potentially facilitate the formation of a microflora rich in indigenous bacteria with PC, particularly in the gastrointestinal tract.

β-l-Rhamnosylation and β-d-Mannosylation Mediated by 4-O-Ester Groups in a Weakly Nucleophilic Environment

eq-4-O-Acyl group directed β-rhamnosylation and β-mannosylation are achieved in a carborane or BARF anion formed weakly nucleophilic environment with the assistance of a 2,3-orthocarbonate group. The 4-O-acyl group plays a critical role in directing the β-selectivity, and the weakly coordinating anion is essential to amplify this direction. The orthocarbonate group could be readily removed with 1,3-propanediol in the presence of BF3·Et2O.

Analysis of Bacterial Phosphorylcholine-Related Genes Reveals an Association between Type-Specific Biosynthesis Pathways and Biomolecules Targeted for Phosphorylcholine Modification

Many bacterial surface proteins and carbohydrates are modified with phosphorylcholine (ChoP), which contributes to host mimicry and can also promote colonization and survival in the host. However, the ChoP biosynthetic pathways that are used in bacterial species that express ChoP have not been systematically studied. For example, the well-studied Lic-1 pathway is absent in some ChoP-expressing bacteria, such as Neisseria meningitidis and Neisseria gonorrhoeae. This raises a question as to the origin of the ChoP used for macromolecule biosynthesis in these species. In the current study, we used in silico analyses to identify the potential pathways involved in ChoP biosynthesis in genomes of the 26 bacterial species reported to express a ChoP-modified biomolecule. We used the four known ChoP biosynthetic pathways and a ChoP transferase as search terms to probe for their presence in these genomes. We found that the Lic-1 pathway is primarily associated with organisms producing ChoP-modified carbohydrates, such as lipooligosaccharide. Pilin phosphorylcholine transferase A (PptA) homologs were detected in all bacteria that express ChoP-modified proteins. Additionally, ChoP biosynthesis pathways, such as phospholipid N-methyltransferase (PmtA), phosphatidylcholine synthase (Pcs), or the acylation-dependent phosphatidylcholine biosynthesis pathway, which generate phosphatidylcholine, were also identified in species that produce ChoP-modified proteins. Thus, a major finding of this study is the association of a particular ChoP biosynthetic pathway with a cognate, target ChoP-modified surface factor; i.e., protein versus carbohydrate. This survey failed to identify a known biosynthetic pathway for some species that express ChoP, indicating that a novel ChoP biosynthetic pathway(s) may remain to be identified. IMPORTANCE The modification of bacterial surface virulence factors with phosphorylcholine (ChoP) plays an important role in bacterial virulence and pathogenesis. However, the ChoP biosynthetic pathways in bacteria have not been fully understood. In this study, we used in silico analysis to identify potential ChoP biosynthetic pathways in bacteria that express ChoP-modified biomolecules and found the association between a specific ChoP biosynthesis pathway and the cognate target ChoP-modified surface factor.

Erysipelothrix rhusiopathiae-specific T-cell responses after experimental infection of chickens selectively bred for high and low serum levels of mannose-binding lectin

Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER) is an important emerging disease in laying hens. We have earlier observed prominent mannose-binding lectin (MBL) acute phase responses in experimentally ER infected chickens. The present study aimed to further examine immune responses to ER by using chickens selectively bred for high (L10H) and low (L10L) serum MBL levels. Chickens were infected with ER at 3 weeks of age and immune parameters and bacterial load were monitored in blood until day 18 after infection. Blood and spleen leukocytes collected on day 18 were stimulated in vitro with ER antigens and blast transformation of different T-cell populations was assessed. The ER infection gave a very varied outcome and no clear differences were observed between L10H and L10L chickens with respect to leukocyte counts, bacterial load or clinical outcome. Nonetheless, rapid innate responses, e.g., heterophilia and increased serum MBL levels were noted in bacteraemic chickens. All ER infected chickens also showed transient increased expression of mannose receptor MRC1L-B and decreased expression of major histocompatibility complex II on monocytes day 1 after infection indicating monocyte activation or relocation. In vitro ER stimulation showed antigen specific blast transformation of CD4+, TCRγ/δ-CD8αβ+ and TCRγ/δ+CD8αβ+ spleen cells from all infected chickens. For CD4+ and TCRγ/δ-CD8αβ+ cells the proportions of blast transformed cells were significantly higher for samples from L10L chickens than those for samples from L10H chickens. This is the first observation of ER-specific T-cells in chickens and interestingly a Th1-type response comprising cytotoxic T-cells was indicated.

Immune responses upon experimental Erysipelothrix rhusiopathiae infection of naïve and vaccinated chickens

Erysipelas, a disease caused by Erysipelothrix rhusiopathiae (ER), is an increasing problem in laying hens housed in cage-free systems. This study aimed to monitor immune responses during ER infection of naïve chickens and chickens vaccinated intra muscularly with a commercial inactivated ER vaccine. Chickens were infected intra muscularly with ER at 30 days of age and blood leukocyte counts, serum levels of mannose binding lectin (MBL) and ER-specific IgY were monitored until the experiment was terminated at day 15 after infection. ER was detected in blood from more chickens and at higher bacterial counts in the naïve group (day 1: 1 of 7 chickens; day 3: 6 of 6 chickens) than in the vaccinated group (day 1: 0 of 7 chickens; day 3: 1 of 6 chickens). During the acute phase of infection transient increases in circulating heterophil numbers and serum MBL levels were detected in all ER infected chickens but these responses were prolonged in chickens from the naïve group compared to vaccinated chickens. Before infection IgY titers to ER in vaccinated chickens did not differ significantly from those of naïve chickens but vaccinated chickens showed significantly increased IgY titers to ER earlier after infection compared to chickens in the naïve group. In conclusion, the ER infection elicited prompt acute innate responses in all chickens. Vaccinated chickens did not have high IgY titers to ER prior to infection but did however show lower levels of bacteraemia and their acute immune responses were of shorter duration.

Erysipelothrix Spp.: Past, Present, and Future Directions in Vaccine Research

Erysipelothrix spp. comprise a group of small Gram-positive bacteria that can infect a variety of hosts including mammals, fish, birds, reptiles and insects. Among the eight Erysipelothrix species that have been described to date, only Erysipelothrix rhusiopathiae plays a major role in farmed livestock where it is the causative agent of erysipelas. E. rhusiopathiae also has zoonotic potential and can cause erysipeloid in humans with a clear occupational link to meat and fish industries. While there are 28 known Erysipelothrix serovars, over 80% of identified isolates belong to serovars 1 or 2. Vaccines to protect pigs against E. rhusiopathiae first became available in 1883 as a response to an epizootic of swine erysipelas in southern France. The overall vaccine repertoire was notably enlarged between the 1940s and 1960s following major outbreaks of swine erysipelas in the Midwest USA and has changed little since. Traditionally, E. rhusiopathiae serovar 1a or 2 isolates were inactivated (bacterins) or attenuated and these types of vaccines are still used today on a global basis. E. rhusiopathiae vaccines are most commonly used in pigs, poultry, and sheep where the bacterium can cause considerable economic losses. In addition, erysipelas vaccination is also utilized in selected vulnerable susceptible populations, such as marine mammals in aquariums, which are commonly vaccinated at regular intervals. While commercially produced erysipelas vaccines appear to provide good protection against clinical disease, in recent years there has been an increase in perceived vaccine failures in farmed animals, especially in organic outdoor operations. Moreover, clinical erysipelas outbreaks have been reported in animal populations not previously considered at risk. This has raised concerns over a possible lack of vaccine protection across various production species. This review focuses on summarizing the history and the present status of E. rhusiopathiae vaccines, the current knowledge on protection including surface antigens, and also provides an outlook into future directions for vaccine development.

Genome-Wide Identification of Virulence Genes in Erysipelothrix rhusiopathiae: Use of a Mutant Deficient in a tagF Homolog as a Safe Oral Vaccine against Swine Erysipelas

Swine erysipelas is caused by the Gram-positive pathogen Erysipelothrix rhusiopathiae The swine erysipelas live vaccine in Japan, the E. rhusiopathiae Koganei 65-0.15 strain (Koganei), has been reported to cause arthritis and endocarditis. To develop a vaccine with increased safety, we used a virulent Fujisawa strain to construct transposon mutants for a total of 651 genes, which covered 38% of the coding sequence of the genome. We screened the mutants for attenuation by inoculating mice with 108 CFU of each mutant and subsequently assessed protective capability by challenging the surviving mice with 103 CFU (102 times the 50% lethal dose) of the Fujisawa strain. Of the 23 attenuated mutants obtained, 6 mutants were selected and evaluated for protective capability in pigs by comparison to that of the Koganei strain. A mutant in the ERH_0432 (tagF) gene encoding a putative CDP-glycerol glycerophosphotransferase was found to be highly attenuated and to induce humoral and cell-mediated immune responses in conventional pigs. An in-frame deletion mutant of the gene, the Δ432 mutant, was constructed, and attenuation was further confirmed in germfree piglets; three of four piglets subcutaneously inoculated with 109 CFU of the Δ432 mutant showed no apparent clinical symptoms, whereas all four of the Koganei-inoculated piglets died 3 days after inoculation. It was confirmed that conventional pigs inoculated orally or subcutaneously with the Δ432 strain were almost completely protected against lethal challenge infection. Thus, the tagF homolog mutant of E. rhusiopathiae represents a safe vaccine candidate that can be administered via the oral and subcutaneous routes.

Identification of the Chromosomal Region Essential for Serovar-Specific Antigen and Virulence of Serovar 1 and 2 Strains of Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae causes swine erysipelas, an infection characterized by acute septicemia or chronic endocarditis and polyarthritis. Among 17 E. rhusiopathiae serovars, determined based on heat-stable peptidoglycan antigens, serovars 1 and 2 are most commonly associated with the disease; however, the molecular basis for the association between these serovars and virulence is unknown. To search for the genetic region defining serovar 1a (Fujisawa) strain antigenicity, we examined the 15-kb chromosomal region encompassing a putative pathway for polysaccharide biosynthesis, which was previously identified in the E. rhusiopathiae Fujisawa strain. Six transposon mutants of Fujisawa strain possessing a mutation in this region lost antigenic reactivity with serovar 1a-specific rabbit serum. Sequence analysis of this region in wild-type strains of serovars 1a, 1b, and 2 and serovar N, which lacks serovar-specific antigens, revealed that gene organization was similar among the strains and that serovar 2 strains showed variation. Serovar N strains displayed the same gene organization as the serovar 1a, 1b, or 2 strain and possessed certain mutations in this region. In two of the analyzed serovar N strains, restoration of the mutations via complementation with sequences derived from serovar 1a and 2 strains recovered antigenic reactivity with 1a- and 2-specific rabbit serum, respectively. Several gene mutations in this region resulted in altered capsule expression and attenuation of virulence in mice. These results indicate a functional connection between the biosynthetic pathways for the capsular polysaccharide and peptidoglycan antigens used for serotyping, which may explain variation in virulence among strains of different serovars.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Bacterial Genomics Reveal the Complex Epidemiology of an Emerging Pathogen in Arctic and Boreal Ungulates

Northern ecosystems are currently experiencing unprecedented ecological change, largely driven by a rapidly changing climate. Pathogen range expansion, and emergence and altered patterns of infectious disease, are increasingly reported in wildlife at high latitudes. Understanding the causes and consequences of shifting pathogen diversity and host-pathogen interactions in these ecosystems is important for wildlife conservation, and for indigenous populations that depend on wildlife. Among the key questions are whether disease events are associated with endemic or recently introduced pathogens, and whether emerging strains are spreading throughout the region. In this study, we used a phylogenomic approach to address these questions of pathogen endemicity and spread for Erysipelothrix rhusiopathiae, an opportunistic multi-host bacterial pathogen associated with recent mortalities in arctic and boreal ungulate populations in North America. We isolated E. rhusiopathiae from carcasses associated with large-scale die-offs of muskoxen in the Canadian Arctic Archipelago, and from contemporaneous mortality events and/or population declines among muskoxen in northwestern Alaska and caribou and moose in western Canada. Bacterial genomic diversity differed markedly among these locations; minimal divergence was present among isolates from muskoxen in the Canadian Arctic, while in caribou and moose populations, strains from highly divergent clades were isolated from the same location, or even from within a single carcass. These results indicate that mortalities among northern ungulates are not associated with a single emerging strain of E. rhusiopathiae, and that alternate hypotheses need to be explored. Our study illustrates the value and limitations of bacterial genomic data for discriminating between ecological hypotheses of disease emergence, and highlights the importance of studying emerging pathogens within the broader context of environmental and host factors.

Proteomic and Transcriptomic Analyses of Swine Pathogen Erysipelothrix rhusiopathiae Reveal Virulence Repertoire

E. rhusiopathiae is the causative agent of erysipelas in animals and erysipeloid in humans, but its pathogenicity is poorly understood. To identify virulence factors associated with E. rhusiopathiae and screen engineered vaccine candidates, we used proteomics and transcriptomics to compare the highly virulent strain HX130709 with an isogenic avirulent derivative, HX130709a. 1,299 proteins and 1,673 transcribed genes were identified and 1,292 of the proteins could be associated with genes. In a comparison between HX130907 and HX130709a, 168 proteins and 475 genes exhibited differences in regulation level. Among these, levels for 61 proteins and transcripts were positively or negatively correlated. Gene Ontology (GO) analysis suggests that many of the down-regulated proteins in the attenuated strain have catalytic or binding functions. Potential protein-protein interactions suggest that some of the down-regulated proteins may regulate PTS, GMP synthase and ribosomal proteins. Morphological results showed that HX130709 and HX130709a have similar colony and capsule morphology. Growth curves and pyruvate measurements suggest that TCA cycle and saccharide phosphorylation levels were decreased and gluconeogenesis was increased in HX130709a. Our study confirms that SpaA and neuraminidase, but not hyaluronidase and capsule, are associated with virulence in E. rhusiopathiae. We conclude that the virulence of E. rhusiopathiae may be associated with slow reactions of the TCA cycle and down-regulation of selected proteins.

Mycoplasma agalactiae Secretion of β-(1→6)-Glucan, a Rare Polysaccharide in Prokaryotes, Is Governed by High-Frequency Phase Variation

Mycoplasmas are minimal, wall-less bacteria but have retained the ability to secrete complex carbohydrate polymers that constitute a glycocalyx. In members of the Mycoplasma mycoides cluster, which are important ruminant pathogens, the glycocalyx includes both cell-attached and cell-free polysaccharides. This report explores the potential secretion of polysaccharides by M. agalactiae, another ruminant pathogen that belongs to a distant phylogenetic group. Comparative genomic analyses showed that M. agalactiae possesses all the genes required for polysaccharide secretion. Notably, a putative synthase gene (gsmA) was identified, by in silico reconstruction of the biosynthetic pathway, that could be involved in both polymerization and export of the carbohydrate polymers. M. agalactiae polysaccharides were then purified in vitro and found to be mainly cell attached, with a linear β-(1→6)-glucopyranose structure [β-(1→6)-glucan]. Secretion of β-(1→6)-glucan was further shown to rely on the presence of a functional gsmA gene, whose expression is subjected to high-frequency phase variation. This event is governed by the spontaneous intraclonal variation in length of a poly(G) tract located in the gsmA coding sequence and was shown to occur in most of the M. agalactiae clinical isolates tested in this study. M. agalactiae susceptibility to serum-killing activity appeared to be dictated by ON/OFF switching of β-(1→6)-glucan secretion, suggesting a role of this phenomenon in survival of the pathogen when it invades the host bloodstream. Finally, β-(1→6)-glucan secretion was not restricted to M. agalactiae but was detected also in M. mycoides subsp. capri PG3(T), another pathogen of small ruminants.

IMPORTANCE

Many if not all bacteria are able to secrete polysaccharides, either attached to the cell surface or exported unbound into the extracellular environment. Both types of polysaccharides can play a role in bacterium-host interactions. Mycoplasmas are no exception despite their poor overall metabolic capacity. We showed here that M. agalactiae secretes a capsular β-(1→6)-glucopyranose thanks to a specific glycosyltransferase with synthase activity. This secretion is governed by high-frequency ON/OFF phase variation that might be crucial in mycoplasma host dissemination, as cell-attached β-(1→6)-glucopyranose increases serum-killing susceptibility. Our results provide functional genetic data about mycoplasmal glycosyltransferases with dual functions, i.e., assembly and export of the sugar polymers across the cell membrane. Furthermore, we demonstrated that nonprotein epitopes can be subjected to surface antigenic variation in mycoplasmas. Finally, the present report contributes to unravel the role of secreted polysaccharides in the virulence and pathogenicity of these peculiar bacteria.

One-pot four-enzyme synthesis of thymidinediphosphate-l-rhamnose

A concise and effective one-pot four-enzyme synthesis of dTDP-Rha, the substrate of rhamnosyltransferases, is described.

Novel structural features of the immunocompetent ceramide phospho-inositol glycan core from Trichomonas vaginalis

The ceramide phosphoinositol glycan core (CPI-GC) of the lipophosphoglycan of Trichomonas vaginalis is a major virulent factor of this common genitourinary parasite. While its carbohydrate composition has been reported before, its structure has remained largely unknown. We isolated the glycan portions of CPI-GC by nitrous acid deamination and hydrofluoric acid treatment and investigated their structures by methylation analysis and 1- and 2-D NMR. We found that the α-anomer of galactose is a major constituent of CPI-GC. The β-anomer was found exclusively at the non-reducing end of CPI-GC side chains. Furthermore the data showed that the rhamnan backbone is more complex than previously thought and that the inositol residue at the reducing end is linked to a 4-linked α-glucuronic acid (GlcA) residue. This appears to be the most striking and novel feature of this GPI-anchor type molecule.

First report of macrolide resistance gene erm(T) harbored by a novel small plasmid from Erysipelothrix rhusiopathiae

The macrolide resistance gene erm(T) was identified for the first time in a porcine Erysipelothrix rhusiopathiae isolate from swine in China. The novel 3,749-bp small plasmid pER29, which carries erm(T), had a G+C content of 31% and four distinct open reading frames. The presence of pER29 increased by at least 128-fold the MICs of clindamycin and erythromycin for E. rhusiopathiae. The fitness cost of pER29 could be responsible for the low frequency of erm(T) in E. rhusiopathiae.

Phosphorylcholine and SpaA, a choline-binding protein, are involved in the adherence of Erysipelothrix rhusiopathiae to porcine endothelial cells, but this adherence is not mediated by the PAF receptor

A crucial event in the initiation of many bacterial infections is the adherence of the bacteria to host cells, and bacterial surface structures and their interactions with host cell receptors play an important role in this process. Erysipelothrix rhusiopathiae is the causative agent of swine erysipelas, which may cause acute septicemia or chronic endocarditis and polyarthritis. To study the pathogenic mechanism of the widespread vascular disease observed in the acute form of swine erysipelas, we investigated the role of phosphorylcholine (PCho), a component of the E. rhusiopathiae capsule, in bacterial adherence to porcine endothelial cells (PECs) in vitro. We found that adherence of E. rhusiopathiae strain Fujisawa to PECs was twice that of adherence to control COS-7 cells and that the adherence rates of PCho-defective mutants were approximately 30-50% lower than those of the Fujisawa strain. The adherence of the Fujisawa strain to COS-7 cells transfected with the porcine platelet-activating factor receptor (PAFR) gene, which encodes a G protein-coupled receptor that has been shown to directly bind to Streptococcus pneumoniae via PCho in the bacterial cell wall, was not enhanced. Treatment with a PAFR antagonist (WEB-2086) did not inhibit bacterial adherence to PECs. Incubation of the bacterial cells with an antibody against PCho or SpaA, a choline-binding protein anchored to PCho of the Fujisawa strain, reduced the adherence of the strain to PECs. This effect was not observed when PCho-defective mutants were used. These results suggest that E. rhusiopathiae adheres to PECs via PCho and SpaA and that the PCho-mediated adherence is independent of PAFR.

Development of a loop-mediated isothermal amplification assay for rapid and simple detection of Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae is a causative agent of swine erysipelas. We developed a novel and highly specific loop-mediated isothermal amplification (LAMP) assay for sensitive and rapid detection of E. rhusiopathiae. The LAMP assay correctly detected 39 E. rhusiopathiae strains. No LAMP products were detected from 14 non-rhusiopathiae Erysipelothrix and 16 non-Erysipelothrix strains, including E. tonsillarum serovar 10 strains, which are difficult to be discriminated from E. rhusiopathiae strains. These results were consistent with those obtained by a conventional E. rhusiopathiae-specific PCR assay. Starting with DNA extraction from a single colony, the gel-based PCR assay took 4 h to provide a result, but the LAMP assay was faster, requiring only 37-80 min. The conventional culture test required more than 3-4 days to isolate and identify E. rhusiopathiae in the enrichment cultures. In contrast, the LAMP assay required less than 22 h from the beginning of the enrichment culture to final determination. These results suggest that the LAMP assay is useful as an adjunct to facilitate early diagnosis of swine erysipelas.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a loop-mediated isothermal amplification (LAMP) assay for simple and cost-effective detection of E. rhusiopathiae from swine samples. The LAMP assay provided more rapid detection of the bacterium than conventional PCR and biochemical-based assays, and it may potentially facilitate surveillance and early diagnosis of swine erysipelas in the field.

Characterization and identification of a novel candidate vaccine protein through systematic analysis of extracellular proteins of Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas, is a facultative intracellular Gram-positive bacterium. It has been shown that animals immunized with a filtrate from E. rhusiopathiae cultures are protected against lethal challenge. In this study, we identified and characterized the extracellular proteins of E. rhusiopathiae to search for novel vaccine antigens. A concentrated culture supernatant from the E. rhusiopathiae Fujisawa strain, which has been found to induce protection in mice, was analyzed using two-dimensional electrophoresis. From more than 40 confirmed protein spots, 16 major protein spots were selected and subjected to N-terminal amino acid sequence determination, and 14 protein spots were successfully identified. The identified proteins included housekeeping proteins and other metabolic enzymes. We searched for surface-localized proteins by analyzing the genomes of two E. rhusiopathiae strains: Fujisawa and ATCC 19414. Genome analysis revealed that the ATCC 19414 strain has three putative surface-exposed choline-binding proteins (CBPs): CbpA, CbpB, and CbpC. Each CBP contains a putative choline-binding domain. The CbpC gene is mutated in Fujisawa, becoming a nonfunctional pseudogene. Immunogold electron microscopy confirmed that CbpA and CbpB, as well as the majority of the metabolic enzymes examined, are associated with the cell surface of E. rhusiopathiae Fujisawa. Immunization with recombinant CbpB, but not with other recombinant CBPs or metabolic enzymes, protected mice against lethal challenge. A phagocytosis assay revealed that antiserum against CbpB promoted opsonin-mediated phagocytosis by murine macrophages in vitro. The protective capabilities of CbpB were confirmed in pigs, suggesting that CbpB could be used as a vaccine antigen.

Gene content and diversity of the loci encoding biosynthesis of capsular polysaccharides of the 15 serovar reference strains of Haemophilus parasuis

Haemophilus parasuis is the causative agent of Glässer's disease, a systemic disease of pigs, and is also associated with pneumonia. H. parasuis can be classified into 15 different serovars. Here we report, from the 15 serotyping reference strains, the DNA sequences of the loci containing genes for the biosynthesis of the group 1 capsular polysaccharides, which are potential virulence factors of this bacterium. We contend that these loci contain genes for polysaccharide capsule structures, and not a lipopolysaccharide O antigen, supported by the fact that they contain genes such as wza, wzb, and wzc, which are associated with the export of polysaccharide capsules in the current capsule classification system. A conserved region at the 3' end of the locus, containing the wza, ptp, wzs, and iscR genes, is consistent with the characteristic export region 1 of the model group 1 capsule locus. A potential serovar-specific region (region 2) has been found by comparing the predicted coding sequences (CDSs) in all 15 loci for synteny and homology. The region is unique to each reference strain with the exception of those in serovars 5 and 12, which are identical in terms of gene content. The identification and characterization of this locus among the 15 serovars is the first step in understanding the genetic, molecular, and structural bases of serovar specificity in this poorly studied but important pathogen and opens up the possibility of developing an improved molecular serotyping system, which would greatly assist diagnosis and control of Glässer's disease.

Characterization of free exopolysaccharides secreted by Mycoplasma mycoides subsp. mycoides

Contagious bovine pleuropneumonia is a severe respiratory disease of cattle that is caused by a bacterium of the Mycoplasma genus, namely Mycoplasma mycoides subsp. mycoides (Mmm). In the absence of classical virulence determinants, the pathogenicity of Mmm is thought to rely on intrinsic metabolic functions and specific components of the outer cell surface. One of these latter, the capsular polysaccharide galactan has been notably demonstrated to play a role in Mmm persistence and dissemination. The free exopolysaccharides (EPS), also produced by Mmm and shown to circulate in the blood stream of infected cattle, have received little attention so far. Indeed, their characterization has been hindered by the presence of polysaccharide contaminants in the complex mycoplasma culture medium. In this study, we developed a method to produce large quantities of EPS by transfer of mycoplasma cells from their complex broth to a chemically defined medium and subsequent purification. NMR analyses revealed that the purified, free EPS had an identical β(1−>6)-galactofuranosyl structure to that of capsular galactan. We then analyzed intraclonal Mmm variants that produce opaque/translucent colonies on agar. First, we demonstrated that colony opacity was related to the production of a capsule, as observed by electron microscopy. We then compared the EPS extracts and showed that the non-capsulated, translucent colony variants produced higher amounts of free EPS than the capsulated, opaque colony variants. This phenotypic variation was associated with an antigenic variation of a specific glucose phosphotransferase permease. Finally, we conducted in silico analyses of candidate polysaccharide biosynthetic pathways in order to decipher the potential link between glucose phosphotransferase permease activity and attachment/release of galactan. The co-existence of variants producing alternative forms of galactan (capsular versus free extracellular galactan) and associated with an antigenic switch constitutes a finely tuned mechanism that may be involved in virulence.