The structure of the carbohydrate backbone of the core-lipid A region of the lipopolysaccharide from a clinical isolate of Yersinia enterocolitica O:9

Development of a Multiplex Bead Assay to Detect Serological Responses to Brucella Species in Domestic Pigs and Wild Boar with the Potential to Overcome Cross-Reactivity with Yersinia enterocolitica O:9

The aim of this study was to develop a multiplex bead assay using a Brucella rLPS antigen, a Brucella suis smooth antigen, and a Yersinia enterocolitica O:9 antigen that not only discriminates Brucella-infected from Brucella-uninfected pigs and wild boar, but also overcomes the cross reactivity with Y. enterocolitica O:9. Sera from 126 domestic pigs were tested: 29 pigs were Brucella infected, 80 were non-infected and 17 were confirmed to be false positive serological reactors (FPSR). Sera from 49 wild boar were tested: 18 were positive and 31 were negative. Using the rLPS antigen, 26/29 Brucella-infected domestic pigs and 15/18 seropositive wild boar were positive, while 75/80 non-Brucella infected domestic pigs, all FPSR, and all seronegative wild boar were negative. Using the smooth B. suis 1330 antigen, all Brucella-infected domestic pigs, 9/17 FPSR and all seropositive wild boar were positive, while all non-infected pigs and 30/31 seronegative wild boar were negative. The ratio of the readouts from the smooth B. suis antigen and Y. enterocolitica O:9 antigen enabled discriminating all Brucella infected individuals from the FPSR domestic pigs. These results demonstrate the potential of this assay for use in the surveillance of brucellosis, overcoming the cross-reactivity with Y. enterocolitica.

The Tip of Brucella O-Polysaccharide Is a Potent Epitope in Response to Brucellosis Infection and Enables Short Synthetic Antigens to Be Superior Diagnostic Reagents

Brucellosis is a global disease and the world’s most prevalent zoonosis. All cases in livestock and most cases in humans are caused by members of the genus Brucella that possess a surface O-polysaccharide (OPS) comprised of a rare monosaccharide 4-deoxy-4-formamido-D-mannopyranose assembled with α1,2 and α1,3 linkages. The OPS of the bacterium is the basis for serodiagnostic tests for brucellosis. Bacteria that also contain the same rare monosaccharide can induce antibodies that cross-react in serological tests. In previous work we established that synthetic oligosaccharides, representing elements of the Brucella A and M polysaccharide structures, were excellent antigens to explore the antibody response in the context of infection, immunisation and cross reaction. These studies suggested the existence of antibodies that are specific to the tip of the Brucella OPS. Sera from naturally and experimentally Brucella abortus-infected cattle as well as from cattle experimentally infected with the cross-reactive bacterium Yersinia enterocolitica O:9 and field sera that cross react in conventional serological assays were studied here with an expanded panel of synthetic antigens. The addition of chemical features to synthetic antigens that block antibody binding to the tip of the OPS dramatically reduced their polyclonal antibody binding capability providing conclusive evidence that the OPS tip (non-reducing end) is a potent epitope. Selected short oligosaccharides, including those that were exclusively α1,2 linked, also demonstrated superior specificity when evaluated with cross reactive sera compared to native smooth lipopolysaccharide (sLPS) antigen and capped native OPS. This surprising discovery suggests that the OPS tip epitope, even though common to both Brucella and Y. enterocolitica O:9, has more specific diagnostic properties than the linear portion of the native antigens. This finding opens the way to the development of improved serological tests for brucellosis.

Regulatory protein OmpR influences the serum resistance of Yersinia enterocolitica O:9 by modifying the structure of the outer membrane

The EnvZ/OmpR two-component system constitutes a regulatory pathway involved in bacterial adaptive responses to environmental cues. Our previous findings indicated that the OmpR regulator in Yersinia enterocolitica O:9 positively regulates the expression of FlhDC, the master flagellar activator, which influences adhesion/invasion properties and biofilm formation. Here we show that a strain lacking OmpR grown at 37°C exhibits extremely high resistance to the bactericidal activity of normal human serum (NHS) compared with the wild-type strain. Analysis of OMP expression in the ompR mutant revealed that OmpR reciprocally regulates Ail and OmpX, two homologous OMPs of Y. enterocolitica, without causing significant changes in the level of YadA, the major serum resistance factor. Analysis of mutants in individual genes belonging to the OmpR regulon (ail, ompX, ompC and flhDC) and strains lacking plasmid pYV, expressing YadA, demonstrated the contribution of the respective proteins to serum resistance. We show that Ail and OmpC act in an opposite way to the OmpX protein to confer serum resistance to the wild-type strain, but are not responsible for the high resistance of the ompR mutant. The serum resistance phenotype of ompR seems to be multifactorial and mainly attributable to alterations that potentiate the function of YadA. Our results indicate that a decreased level of FlhDC in the ompR mutant cells is partly responsible for the serum resistance and this effect can be suppressed by overexpression of flhDC in trans. The observation that the loss of FlhDC enhances the survival of wild-type cells in NHS supports the involvement of FlhDC regulator in this phenotype. In addition, the ompR mutant exhibited a lower level of LPS, but this was not correlated with changes in the level of FlhDC. We propose that OmpR might alter the susceptibility of Y. enterocolitica O:9 to complement-mediated killing through remodeling of the outer membrane.

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) as a characteristic component of bacterial endotoxin — a review of its biosynthesis, function, and placement in the lipopolysaccharide core

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is a characteristic component of bacterial lipopolysaccharide (LPS, endotoxin). It connects the carbohydrate part of LPS with C6 of glucosamine or 2,3-diaminoglucose of lipid A by acid-labile α-ketosidic linkage. The number of Kdo units present in LPS, the way they are connected, and the occurrence of other substituents (P, PEtn, PPEtn, Gal, or β-l-Ara4N) account for structural diversity of the inner core region of endotoxin. In a majority of cases, Kdo is crucial to the viability and growth of bacterial cells. In this paper, the biosynthesis of Kdo and the mechanism of its incorporation into the LPS structure, as well as the location of this unique component in the endotoxin core structures, have been described.

Diversity-oriented synthesis of inner core oligosaccharides of the lipopolysaccharide of pathogenic Gram-negative bacteria

Lipopolysaccharide (LPS) is a potent virulence factor of pathogenic Gram-negative bacteria. To better understand the role of LPS in host-pathogen interactions and to elucidate the antigenic and immunogenic properties of LPS inner core region, a collection of well-defined L-glycero-D-manno-heptose (Hep) and 3-deoxy-α-D-manno-oct-2-ulosonic acid (Kdo)-containing inner core oligosaccharides is required. To address this need, we developed a diversity-oriented approach based on a common orthogonal protected disaccharide Hep-Kdo. Utilizing this new approach, we synthesized a range of LPS inner core oligosaccharides from a variety of pathogenic bacteria including Y. pestis, H. influenzae, and Proteus that cause plague, meningitis, and severe wound infections, respectively. Rapid access to these highly branched core oligosaccharides relied on elaboration of the disaccharide Hep-Kdo core as basis for the elongation with various flexible modules including unique Hep and 4-amino-4-deoxy-β-L-arabinose (Ara4N) monosaccharides and branched Hep-Hep disaccharides. A regio- and stereoselective glycosylation of Kdo 7,8-diol was key to selective installation of the Ara4N moiety at the 8-hydroxyl group of Kdo moiety of the Hep-Kdo disaccharide. The structure of the LPS inner core oligosaccharides was confirmed by comparison of (1)H NMR spectra of synthetic antigens and isolated fragments. These synthetic LPS core oligosaccharides can be covalently bound to carrier proteins via the reducing end pentyl amine linker, to explore their antigenic and immunogenic properties as well as potential applications such as diagnostic tools and vaccines.

An evaluation of the capability of existing and novel serodiagnostic methods for porcine brucellosis to reduce false positive serological reactions

Porcine brucellosis is a zoonotic disease of truly global significance because even in countries without the disease the occurrence of false positive serological reactions (FPSRs) creates significant problems. Statutory diagnostic testing is required in many disease free countries or regions and is often a prerequisite for the movement of live animals. Currently this testing is dependent almost entirely on serological assays and these may result in a significant number of FPSRs. The aim of this study was to examine existing and novel serodiagnostic assays to evaluate their diagnostic sensitivity and resilience to FPSRs. The existing assays evaluated were the RBT, smooth lipopolysaccharide (sLPS) indirect (i) ELISA, sLPS competitive (c) ELISA, and the FPA. The novel assays evaluated were the sLPS TR-FRET assay, a rough (r) LPS iELISA, a recombinant protein BP26 iELISA and a cytoplasmic protein extract (Brucellergene™) iELISA. Four populations of sera were evaluated: those from Brucella suis infected swine (n=34), randomly selected samples from non-infected swine (n=161), sera from non-infected swine within herds exhibiting FPSRs (n=132) and sera from swine experimentally infected with Yersinia enterocolitica O:9 (n=4). The results show that all the assays dependent on the sLPS O-polysaccharide (OPS) for their sensitivity (the RBT, sLPS ELISAs, FPA and the sLPS TR-FRET) had significantly reduced diagnostic specificity when applied to the FPSR population, the RBT being most affected. Of the two rapid homogeneous assays, the TR-FRET was diagnostically superior to the FPA in this study. Neither of the protein based iELISAs demonstrated sufficient diagnostic sensitivity to resolve the FPSRs. The rLPS iELISA showed no cross reaction with the FPSRs and had diagnostic sensitivity similar to that of the OPS based assays.

Bacterial cell surface structures in Yersinia enterocolitica

Yersinia enterocolitica is a widespread member of the family of Enterobacteriaceae that contains both non-virulent and virulent isolates. Pathogenic Y. enterocolitica strains, especially belonging to serotypes O:3, O:5,27, O:8 and O:9 are etiologic agents of yersiniosis in animals and humans. Y. enterocolitica cell surface structures that play a significant role in virulence have been subject to many investigations. These include outer membrane (OM) glycolipids such as lipopolysaccharide (LPS) and enterobacterial common antigen (ECA) and several cell surface adhesion proteins present only in virulent Y. enterocolitica, i.e., Inv, YadA and Ail. While the yadA gene is located on the Yersinia virulence plasmid the Ail, Inv, LPS and ECA are chromosomally encoded. These structures ensure the correct architecture of the OM, provide adhesive properties as well as resistance to antimicrobial peptides and to host innate immune response mechanisms.

Exploiting the Campylobacter jejuni protein glycosylation system for glycoengineering vaccines and diagnostic tools directed against brucellosis

Background

Immune responses directed towards surface polysaccharides conjugated to proteins are effective in preventing colonization and infection of bacterial pathogens. Presently, the production of these conjugate vaccines requires intricate synthetic chemistry for obtaining, activating, and attaching the polysaccharides to protein carriers. Glycoproteins generated by engineering bacterial glycosylation machineries have been proposed to be a viable alternative to traditional conjugation methods.

Results

In this work we expressed the C. jejuni oligosaccharyltansferase (OTase) PglB, responsible for N-linked protein glycosylation together with a suitable acceptor protein (AcrA) in Yersinia enterocolitica O9 cells. MS analysis of the acceptor protein demonstrated the transfer of a polymer of N-formylperosamine to AcrA in vivo. Because Y. enterocolitica O9 and Brucella abortus share an identical O polysaccharide structure, we explored the application of the resulting glycoprotein in vaccinology and diagnostics of brucellosis, one of the most common zoonotic diseases with over half a million new cases annually. Injection of the glycoprotein into mice generated an IgG response that recognized the O antigen of Brucella, although this response was not protective against a challenge with a virulent B. abortus strain. The recombinant glycoprotein coated onto magnetic beads was efficient in differentiating between naïve and infected bovine sera.

Conclusion

Bacterial engineered glycoproteins show promising applications for the development on an array of diagnostics and immunoprotective opportunities in the future.

Characterization and biological role of the O-polysaccharide gene cluster of Yersinia enterocolitica serotype O:9

Yersinia enterocolitica serotype O:9 is a gram-negative enteropathogen that infects animals and humans. The role of lipopolysaccharide (LPS) in Y. enterocolitica O:9 pathogenesis, however, remains unclear. The O:9 LPS consists of lipid A to which is linked the inner core oligosaccharide, serving as an attachment site for both the outer core (OC) hexasaccharide and the O-polysaccharide (OPS; a homopolymer of N-formylperosamine). In this work, we cloned the OPS gene cluster of O:9 and identified 12 genes organized into four operons upstream of the gnd gene. Ten genes were predicted to encode glycosyltransferases, the ATP-binding cassette polysaccharide translocators, or enzymes required for the biosynthesis of GDP-N-formylperosamine. The two remaining genes within the OPS gene cluster, galF and galU, were not ascribed a clear function in OPS biosynthesis; however, the latter gene appeared to be essential for O:9. The biological functions of O:9 OPS and OC were studied using isogenic mutants lacking one or both of these LPS parts. We showed that OPS and OC confer resistance to human complement and polymyxin B; the OPS effect on polymyxin B resistance could be observed only in the absence of OC.

Serological discrimination by indirect enzyme immunoassay between the antibody response to Brucella sp. and Yersinia enterocolitica O:9 in cattle and pigs

A rapid, inexpensive and rugged serological test that distinguishes cattle and swine infected with Brucella sp. or Yersinia enterocolitica O:9 is described. The test protocol, which is an indirect enzyme immunoassay uses a high concentration of divalent cation chelating agents to minimize binding of Y. enterocolitica O:9 antibody to rough lipopolysaccharide antigen derived from B. abortus RB51. No false positive reactions were observed when testing 100 Canadian cattle and swine without any evidence of brucellosis. The assay detected 91.6% of cattle (n=155) and 93.5% (n=31) of swine infected with Brucella sp. Sera from 58 cattle and 38 swine exposed to Y. enterocolitica O:9 were negative while only 20 sera from 121 'false positive' reactors of unspecified origin gave low level positive reactions, eliminating 84% of the false positive reactions.

Temperature-Dependent Variations and Intraspecies Diversity of the Structure of the Lipopolysaccharide of Yersinia pestis,

Yersinia pestis spread throughout the Americas in the early 20th century, and it occurs predominantly as a single clone within this part of the world. However, within Eurasia and parts of Africa there is significant diversity among Y. pestis strains, which can be classified into different biovars (bv.) and/or subspecies (ssp.), with bv. orientalis/ssp. pestis most closely related to the American clone. To determine one aspect of the relatedness of these different Y. pestis isolates, the structure of the lipopolysaccharide (LPS) of four wild-type and one LPS-mutant Eurasian/African strains of Y. pestis was determined, evaluating effects of growth at mammalian (37 degrees C) or flea (25 degrees C) temperatures on the structure and composition of the core oligosaccharide and lipid A. In the wild-type clones of ssp. pestis, a single major core glycoform was synthesized at 37 degrees C whereas multiple core oligosaccharide glycoforms were produced at 25 degrees C. Structural differences occurred primarily in the terminal monosaccharides. Only tetraacyl lipid A was made at 37 degrees C, whereas at 25 degrees C additional pentaacyl and hexaacyl lipid A structures were produced. 4-Amino-4-deoxyarabinose levels in lipid A increased with lower growth temperatures or when bacteria were cultured in the presence of polymyxin B. In Y. pestis ssp. caucasica, the LPS core lacked D-glycero-D-manno-heptose and the content of 4-amino-4-deoxyarabinose showed no dependence on growth temperature, whereas the degree of acylation of the lipid A and the structure of the oligosaccharide core were temperature dependent. A spontaneous deep-rough LPS mutant strain possessed only a disaccharide core and a slightly variant lipid A. The diversity and differences in the structure of the Y. pestis LPS suggest important contributions of these variations to the pathogenesis of this organism, potentially related to innate and acquired immune recognition of Y. pestis and epidemiologic means to detect, classify, control and respond to Y. pestis infections.

Efficient chemical synthesis of both anomers of ADP L-glycero- and D-glycero-D-manno-heptopyranose

A series of anomeric phosphates and ADP-activated L-glycero- and D-glycero-D-manno-heptopyranoses has been prepared in high overall yields, which provided model compounds and substrates in the elucidation of biosynthetic pathways and glycosyl transfer reactions of nucleotide-activated bacterial heptoses. The alpha-anomers of the heptosyl phosphates were obtained in high yield and selectivity using the phosphoramidite procedure, whereas the beta-phosphates were formed preferentially employing acylation of reducing heptoses with diphenyl phosphorochloridate. An efficient route to the formation of the nucleotide diphosphate sugars was elaborated by coupling of the O-acetylated phosphates with AMP-morpholidate followed by alkaline deprotection to furnish ADP-L- and D-glycero-alpha-D-manno-heptose in 84 and 89% yield, respectively. Deacetylation of the O-acetylated beta-configured ADP heptoses was conducted at strictly controlled conditions (-28 degrees C at pH 10.5) to suppress formation of cyclic heptose-1,2-phosphodiesters with concomitant release of AMP. Isolation of the unstable beta-configured ADP-heptoses by anion-exchange chromatography and gel-filtration afforded ADP L- and D-glycero-beta-D-manno-heptose in high yields.

The core structure of the lipopolysaccharide from the causative agent of plague, Yersinia pestis

The rough-type lipopolysaccharide (LPS) of the plague pathogen, Yersinia pestis, was studied after mild-acid and strong-alkaline degradations by chemical analyses, NMR spectroscopy and electrospray-ionization mass spectrometry, and the following structure of the core region was determined:where L-alpha-D-Hep stands for L-glycero-alpha-D-manno-heptose, Sug1 for either 3-deoxy-alpha-D-manno-oct-2-ulosonic acid (alpha-Kdo) or D-glycero-alpha-D-talo-oct-2-ulosonic acid (alpha-Ko), and Sug2 for either beta-D-galactose or D-glycero-alpha-D-manno-heptose. A minority of the LPS molecules lacks GlcNAc.

Isolation and structural characterization of an R-form lipopolysaccharide from Yersinia enterocolitica serotype O:8

The lipopolysaccharide (LPS) of strain 8081-c-R2, a spontaneous R-mutant of Yersinia enterocolitica serotype O:8, was isolated using extraction with phenol/chloroform/light petroleum. Its compositional analysis indicated the presence of D-GlcN, D-Glc, L-glycero-D-manno- and D-glycero-D-manno-heptose, 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) and phosphate. From deacylated LPS obtained after successive treatment with hydrazine and potassium hydroxide, three oligosaccharides (1-3) were isolated using high-performance anion-exchange chromatography, the structures of which were determined by compositional analysis and one- and two-dimensional NMR spectroscopy as [carbohydrate structure see text] in which all sugars are pyranoses, and R and R' represent beta-D-Glc (in 1 and 2) and beta-D-GlcN (in 1 only), respectively. D-alpha-D-Hep is D-glycero-alpha-D-manno-heptose, L-alpha-D-Hep is L-glycero-alpha-D-manno-heptose, Kdo is 3-deoxy-D-manno-oct-2-ulosonic acid, and P is phosphate. The liberated lipid A was analyzed by compositional analyses and MALDI-TOF MS. Its beta-D-GlcN4P-(1-->6)-alpha-D-GlcN-1-->P backbone is mainly tetra-acylated with two amide- and one ester-linked (at O3 of the reducing GlcN) (R)-3-hydroxytetradecanoic acid residues, and one tetradecanoic acid that is attached to the 3-OH group of the amide-linked (R)-3-hydroxytetradecanoic acid of the nonreducing GlcN. Additionally, small amounts of tri- and hexa-acylated lipid A species occur.

Novel variation of lipid A structures in strains of different Yersinia species

The Yersinia genus includes human and animal pathogens (plague, enterocolitis). The fine structures of the endotoxin lipids A of seven strains of Yersinia enterocolitica, Yersinia ruckeri and Yersinia pestis were determined and compared using mass spectrometry. These lipids differed in secondary acylation at C-2': this was dodecanoic acid (C(12)) for two strains of Y. enterocolitica and Y. ruckeri, tetradecanoic acid (C(14)) in two other Y. enterocolitica and hexadecenoic acid (C(16:1)) in Y. pestis. The enterocolitica lipids having a mass identical to that of Escherichia coli were found to be structurally different. The results supported the idea of a relation between membrane fluidity and environmental adaptability in Yersinia.