The recent emergence of a highly related virulent Clostridium difficile clade with unique characteristics

OBJECTIVES

Clostridium difficile is a major global human pathogen divided into five clades, of which clade 3 is the least characterized and consists predominantly of PCR ribotype (RT) 023 strains. Our aim was to analyse and characterize this clade.

METHODS

In this cohort study the clinical presentation of C. difficile RT023 infections was analysed in comparison with known 'hypervirulent' and non-hypervirulent strains, using data from the Netherlands national C. difficile surveillance programme. European RT023 strains of diverse origin were collected and whole-genome sequenced to determine the genetic similarity between isolates. Distinctive features were investigated and characterized.

RESULTS

Clinical presentation of C. difficile RT023 infections show severe infections akin to those seen with 'hypervirulent' strains from clades 2 (RT027) and 5 (RT078) (35%, 29% and 27% severe CDI, respectively), particularly with significantly more bloody diarrhoea than RT078 and non-hypervirulent strains (RT023 8%, other RTs 4%, p 0.036). The full genome sequence of strain CD305 is presented as a robust reference. Phylogenetic comparison of CD305 and a further 79 previously uncharacterized European RT023 strains of diverse origin revealed minor genetic divergence with >99.8% pairwise identity between strains. Analyses revealed distinctive features among clade 3 strains, including conserved pathogenicity locus, binary toxin and phage insertion toxin genotypes, glycosylation of S-layer proteins, presence of the RT078 four-gene trehalose cluster and an esculinase-negative genotype.

CONCLUSIONS

Given their recent emergence, virulence and genomic characteristics, the surveillance of clade 3 strains should be more highly prioritized.

In vitro and in vivo properties of the bovine antimicrobial peptide, Bactenecin 5

Antimicrobial peptides (AMP), part of the innate immune system, are well studied for their ability to kill pathogenic microorganisms. However, many also possess important immunomodulatory effects, and this area has potential for the development of novel therapies to supplement traditional methods such as the use of antibiotics. Here, we characterise the microbicidal and immunomodulatory potential of the proline-rich bovine AMP, Bactenecin 5 (Bac5). We demonstrate broad antimicrobial activity, including against some mycobacterial species, which are important pathogens of fish, cattle and humans. Bac5 is able to activate macrophage-like THP-1 cells and can synergistically trigger the upregulation of tnf-α when co-stimulated with M. marinum. Furthermore, Bac5 sensitises A549 epithelial cells to stimulation with TNF-α. For the first time, we characterise the activity of Bac5 in vivo, and show it to be a potent chemokine for macrophages in the zebrafish (Danio rerio) embryo model of infection. Bac5 also supports the early recruitment of neutrophils in the presence of M. marinum. In the absence of host adaptive immunity, exogenous injected Bac5 is able to slow, although not prevent, infection of zebrafish with M. marinum.

Zoonotic Transfer of Clostridium difficile Harboring Antimicrobial Resistance between Farm Animals and Humans

The emergence of Clostridium difficile as a significant human diarrheal pathogen is associated with the production of highly transmissible spores and the acquisition of antimicrobial resistance genes (ARGs) and virulence factors. Unlike the hospital-associated C. difficile RT027 lineage, the community-associated C. difficile RT078 lineage is isolated from both humans and farm animals; however, the geographical population structure and transmission networks remain unknown. Here, we applied whole-genome phylogenetic analysis of 248 C. difficile RT078 strains from 22 countries. Our results demonstrate limited geographical clustering for C. difficile RT078 and extensive coclustering of human and animal strains, thereby revealing a highly linked intercontinental transmission network between humans and animals. Comparative whole-genome analysis reveals indistinguishable accessory genomes between human and animal strains and a variety of antimicrobial resistance genes in the pangenome of C. difficile RT078. Thus, bidirectional spread of C. difficile RT078 between farm animals and humans may represent an unappreciated route disseminating antimicrobial resistance genes between humans and animals. These results highlight the importance of the "One Health" concept to monitor infectious disease emergence and the dissemination of antimicrobial resistance genes.

Molecular detection identified a type six secretion system in Campylobacter jejuni from various sources but not from human cases

AIM

To determine the presence of the T6SS in Campylobacter jejuni from diverse sources.

METHODS AND RESULTS

The recently identified type VI secretion system (T6SS) is a bacterial injection machinery that plays a role in virulence, symbiosis, bacterial interactions and environmental stress responses. This system has been recently discovered in the major enteric pathogen Camp. jejuni. In this study, we used multiplex PCR (mPCR), based on conserved genetic markers of the T6SS, to screen 366 Pakistani Camp. jejuni isolates from humans, poultry, cattle, wildlife or waste-water sources. We identified the T6SS in isolates from all of these sources except humans. The overall prevalence of the T6SS among the isolates was 17/366 (4·6%) and the T6SS positive isolates clustered into four different groups. Transcription of the T6SS genes, determined using RT-PCR, was observed in bacteria cultured at 37 or 42°C but not in 37°C cultures adjusted to pH3.

CONCLUSIONS

Campylobacter jejuni isolates harbouring T6SS markers genes were identified in livestock and non-livestock sources but in this study we did not identify human diarrhoeal isolates which possessed the T6SS. We demonstrated down-regulation of T6SS in an acidic environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study questions the role of the T6SS in human diarrhoeal disease. Moreover this study did not identify a clear association of Camp. jejuni isolates harbouring T6SS with any of the niches tested. Our study highlights the need to establish the role of the T6SS in environmental survival or virulence.

Prevalence of Type VI Secretion System in Spanish Campylobacter jejuni Isolates

Infections from Campylobacter jejuni pose a serious public health problem and are now considered the leading cause of foodborne bacterial gastroenteritis throughout the world. Sequencing of C. jejuni genomes has previously allowed a number of loci to be identified, which encode virulence factors that aid survival and pathogenicity. Recently, a Type VI secretion system (T6SS) consisting of 13 conserved genes was described in C. jejuni strains and recognised to promote pathogenicity and adaptation to the environment. In this study, we determined the presence of this T6SS in 63 Spanish C. jejuni isolates from the food chain and urban effluents using whole-genome sequencing. Our findings demonstrated that nine (14%) strains harboured the 13 ORFs found in prototype strain C. jejuni 108. Further studies will be necessary to determine the prevalence and importance of T6SS-positive C. jejuni strains.

Campylobacter jejuni gene cj0511 encodes a serine peptidase essential for colonisation

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A novel peptidase Cj0511 in an important human bacterial pathogen Campylobacter jejuni has been characterized.

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Proteolytic properties of Cj0511 protein were detected in whole cell lysates using zymography.

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Enzymatic studies conducted with a purified protein confirmed the prediction of a serine peptidase.

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The cj0511 mutant was severely attenuated in a chicken colonisation model, suggesting a role in infection.

According to MEROPS peptidase database, Campylobacter species encode 64 predicted peptidases. However, proteolytic properties of only a few of these proteins have been confirmed experimentally. In this study we identified and characterised a Campylobacter jejuni gene cj0511 encoding a novel peptidase. The proteolytic activity associated with this enzyme was demonstrated in cell lysates. Moreover, enzymatic studies conducted with a purified protein confirmed a prediction of it being a serine peptidase. Furthermore, cj0511 mutant was found to be severely attenuated in chicken colonisation model, suggesting a role of the Cj0511 protein in infection.

Development of signature-tagged mutagenesis in Burkholderia pseudomallei to identify genes important in survival and pathogenesis

Burkholderia pseudomallei, the causative agent of melioidosis, is an important human pathogen in Southeast Asia and northern Australia for which a vaccine is unavailable. A panel of 892 double signature-tagged mutants was screened for virulence using an intranasal BALB/c mouse model of infection. A novel DNA tag microarray identified 33 mutants as being attenuated in spleens, while 6 were attenuated in both lungs and spleens. The transposon insertion sites in spleen-attenuated mutants revealed genes involved in several stages of capsular polysaccharide biosynthesis and DNA replication and repair, a putative oxidoreductase, ABC transporters, and a lipoprotein that may be important in intercellular spreading. The six mutants identified as missing in both lungs and spleens were found to have insertions in recA involved in the SOS response and DNA repair; putative auxotrophs of leucine, threonine, p-aminobenzoic acid, and a mutant with an insertion in aroB causing auxotrophy for aromatic compounds were also found. Murine challenge studies revealed partial protection in BALB/c mice vaccinated with the aroB mutant. The refined signature-tagged mutagenesis approach developed in this study was used to efficiently identify attenuating mutants from this highly pathogenic species and could be applied to other organisms.

Comparative phylogenomics of Clostridium difficile reveals clade specificity and microevolution of hypervirulent strains

Clostridium difficile is the most frequent cause of nosocomial diarrhea worldwide, and recent reports suggested the emergence of a hypervirulent strain in North America and Europe. In this study, we applied comparative phylogenomics (whole-genome comparisons using DNA microarrays combined with Bayesian phylogenies) to model the phylogeny of C. difficile, including 75 diverse isolates comprising hypervirulent, toxin-variable, and animal strains. The analysis identified four distinct statistically supported clusters comprising a hypervirulent clade, a toxin A(-) B(+) clade, and two clades with human and animal isolates. Genetic differences among clades revealed several genetic islands relating to virulence and niche adaptation, including antibiotic resistance, motility, adhesion, and enteric metabolism. Only 19.7% of genes were shared by all strains, confirming that this enteric species readily undergoes genetic exchange. This study has provided insight into the possible origins of C. difficile and its evolution that may have implications in disease control strategies.

Biofilm formation in Campylobacter jejuni

The major gastrointestinal pathogen Campylobacter jejuni is shown to exist as three forms of monospecies biofilm in liquid culture. It attaches to a glass surface; forms an unattached aggregate (floc); and forms a pellicle at the liquid-gas interface. The three forms of biofilm resemble each other when examined by scanning electron microscopy. The biofilm mode of growth confers protection against environmental stress, the microaerobic bacteria in flocs surviving up to 24 days at ambient temperature and atmosphere compared to 12 days survival by planktonic bacteria. The wild-type strains C. jejuni 33106, 32799, 33084 and 31485 did not form flocs, and floc formation was reduced in strains mutant in a putative flagellar protein (FliS) and in a phosphate acetyltransferase (Cj0688). All other strains tested, including strains with mutations affecting capsular polysaccharide (kpsM), flagella (maf5), protein glycosylation (pglH) and lipo-oligosaccharide (neuB1) formed flocs. Similarly, all strains tested formed a pellicle and attached to glass except the aflagellate mutant maf5; pellicle formation was reduced in fliS and cj0688 mutants. Different mechanisms, therefore, may control formation of different forms of biofilm. It is proposed that these poorly characterized forms of growth are important for the persistence of C. jejuni in the environment and may in part explain the high incidence of Campylobacter-associated food borne disease.

Development and application of an insertional system for gene delivery and expression in Campylobacter jejuni

The genetic investigation of Campylobacter jejuni, an important gastrointestinal pathogen, has been hampered by the lack of an efficient system for introduction of exogenous genetic information, as commonly used vectors designed for Escherichia coli and other bacteria cannot be maintained in Campylobacter cells. Additionally, gene expression in Campylobacter requires the presence of species-specific promoters. In this study we exploited the availability of several conserved copies of rRNA gene clusters for insertion of various genes into the chromosome by homologous recombination. The high conservation of the rRNA sequences means that the procedure can be applied to other Campylobacter strains. The presence of a Campylobacter-derived promoter in this vector ensures expression of exogenous genes in target cells. The efficiency of the procedure was demonstrated by complementation of mutations in two strains of Campylobacter. In addition, we applied the system for introduction and expression of a green fluorescent protein (GFP). GFP-expressing Campylobacter allowed visualization of sessile bacteria attached to a glass surface in stationary liquid culture. The study demonstrated that the attached bacteria contained an assemblage of coccoid and spiral forms with liquid channels preserving viable highly motile cells. We demonstrate a novel universal procedure for gene delivery and expression that can be used as an efficient tool to study this poorly understood pathogen. The principles developed in this study could be more widely applied for the manipulation of other bacteria that are refractory to genetic analysis.

Campylobacter jejuni gene expression in the chick cecum: evidence for adaptation to a low-oxygen environment

Transcriptional profiling of Campylobacter jejuni during colonization of the chick cecum identified 59 genes that were differentially expressed in vivo compared with the genes in vitro. The data suggest that C. jejuni regulates electron transport and central metabolic pathways to alter its physiological state during establishment in the chick cecum.

The Campylobacter jejuni general glycosylation system is important for attachment to human epithelial cells and in the colonization of chicks

It has recently been shown that the enteropathogenCampylobacter jejunihas anN-linked generalproteinglycosylation pathway (Pgl) that modifies many of the organism's proteins. To determine the role of theN-linked general glycosylation inC jejuni, the authors studied thepglHgene, which shows high similarity to a family of sugar transferases.pglHmutants were constructed in strains 81116 and 11168H. Both mutants were shown to be deficient in their ability to glycosylate a number ofC. jejuniproteins, but their lipooligosaccharide and capsule were unaffected. ThepglHmutants had significantly reduced ability to adhere to and invade human epithelial Caco-2 cells. Additionally, the 81116pglHmutant was severely affected in its ability to colonize chicks. These results suggest that glycosylation is important for the attachment ofC. jejunito human and chicken host cells and imply a role for glycoproteins in the pathogenesis ofC. jejuni.

A Caenorhabditis elegans model of Yersinia infection: biofilm formation on a biotic surface

To investigate Yersinia pathogenicity and the evolutionary divergence of the genus, the effect of pathogenic yersiniae on the model organism Caenorhabditis elegans was studied. Three strains of Yersinia pestis, including a strain lacking pMT1, caused blockage and death of C. elegans; one strain, lacking the haemin storage (hms) locus, caused no effect. Similarly, 15 strains of Yersinia enterocolitica caused no effect. Strains of Yersinia pseudotuberculosis showed different levels of pathogenicity. The majority of strains (76 %) caused no discernible effect; 5 % caused a weak infection, 9.5 % an intermediate infection, and 9.5 % a severe infection. There was no consistent relationship between serotype and severity of infection; nor was there any relationship between strains causing infection of C. elegans and those able to form a biofilm on an abiotic surface. Electron microscope and cytochemical examination of infected worms indicated that the infection phenotype is a result of biofilm formation on the head of the worm. Seven transposon mutants of Y. pseudotuberculosis strain YPIII pIB1 were completely or partially attenuated; mutated genes included genes encoding proteins involved in haemin storage and lipopolysaccharide biosynthesis. A screen of 15 defined C. elegans mutants identified four where mutation caused (complete) resistance to infection by Y. pseudotuberculosis YPIII pIB1. These mutants, srf-2, srf-3, srf-5 and the dauer pathway gene daf-1, also exhibit altered binding of lectins to the nematode surface. This suggests that biofilm formation on a biotic surface is an interactive process involving both bacterial and invertebrate control mechanisms.

Immunization with a DNA vaccine expressing a truncated form of varicella zoster virus glycoprotein E

The gE glycoprotein of varicella zoster virus (VZV) is involved with cell entry and it is the most abundant glycoprotein produced in VZV-infected cells. It is also the first glycoprotein to be recognized by the immune system and induces neutralizing antibodies and cellular immunity. We have shown previously that immunization with a DNA vaccine encoding full length gE induces high antibody titres in BALB/c mice. In this study, we engineered a truncated form of gE to facilitate secretion of the glycoprotein, which is thought to increase the quantity of antigen available for B cells to mount an immune response. This hypothesis was tested by using inverse PCR mutagenesis (IPCRM) to engineer a mutated form of gE that was secreted from the cell. This construct was then evaluated as a potential DNA vaccine. Following immunization studies, the magnitude of the immune response induced with the mutant form of gE was found to be similar to that induced by membrane bound protein. This finding suggests that, in the case of VZV, a DNA vaccine expressing a secreted protein has no advantage over one expressing a membrane bound protein. However, mice immunized with the truncated form of gE (gED) displayed responses favouring IgG1 (Th2) in comparison with mice immunized with the full length gE construct, which generated an IgG2a (Th1) response. This observation indicates that immunization with a truncated form of a gene may induce immune modulation, a phenomenon that should be taken into account for the design of vaccines.

Application of high-density array-based signature-tagged mutagenesis to discover novel Yersinia virulence-associated genes

Yersinia pestis, the causative agent of plague, and the enteropathogen Yersinia pseudotuberculosis have nearly identical nucleotide similarity yet cause markedly different diseases. To investigate this conundrum and to study Yersinia pathogenicity, we developed a high-density oligonucleotide array-based modification of signature-tagged mutagenesis (STM). Y. pseudotuberculosis YPIII mutants constructed with the tagged transposons were evaluated in the murine yersiniosis infection model. The DNA tags were amplified using biotinylated primers and hybridized to high-density oligonucleotide arrays containing DNA complementary to the tags. Comparison of the hybridization signals from input pools and output pools identified a mutant whose relative abundance was significantly reduced in the output pool. Sequence data from 31 transposon insertion regions was compared to the complete Y. pestis CO92 genome sequence. The 26 genes present in both species were found to be almost identical, but five Y. pseudotuberculosis genes identified through STM did not have counterparts in the Y. pestis genome and may contribute to the different tropisms in these closely related pathogens. Potential virulence genes identified include those involved in lipopolysaccharide biosynthesis, adhesion, phospholipase activity, iron assimilation, and gene regulation. The phospholipase A (PldA) mutant exhibited reduced phospholipase activity compared to the wild-type strain and in vivo attenuation of the mutant was confirmed. The combination of optimized double tag sequences and high-density array hybridization technology offers improved performance, efficiency, and reliability over classical STM and permits quantitative analysis of data.

Genome sequence of Yersinia pestis, the causative agent of plague

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease classically referred to as plague, and has been responsible for three human pandemics: the Justinian plague (sixth to eighth centuries), the Black Death (fourteenth to nineteenth centuries) and modern plague (nineteenth century to the present day). The recent identification of strains resistant to multiple drugs and the potential use of Y. pestis as an agent of biological warfare mean that plague still poses a threat to human health. Here we report the complete genome sequence of Y. pestis strain CO92, consisting of a 4.65-megabase (Mb) chromosome and three plasmids of 96.2 kilobases (kb), 70.3 kb and 9.6 kb. The genome is unusually rich in insertion sequences and displays anomalies in GC base-composition bias, indicating frequent intragenomic recombination. Many genes seem to have been acquired from other bacteria and viruses (including adhesins, secretion systems and insecticidal toxins). The genome contains around 150 pseudogenes, many of which are remnants of a redundant enteropathogenic lifestyle. The evidence of ongoing genome fluidity, expansion and decay suggests Y. pestis is a pathogen that has undergone large-scale genetic flux and provides a unique insight into the ways in which new and highly virulent pathogens evolve.

Whole genome comparison of Campylobacter jejuni human isolates using a low-cost microarray reveals extensive genetic diversity

Campylobacter jejuni is the leading cause of bacterial food-borne diarrhoeal disease throughout the world, and yet is still a poorly understood pathogen. Whole genome microarray comparisons of 11 C. jejuni strains of diverse origin identified genes in up to 30 NCTC 11168 loci ranging from 0.7 to 18.7 kb that are either absent or highly divergent in these isolates. Many of these regions are associated with the biosynthesis of surface structures including flagella, lipo-oligosaccharide, and the newly identified capsule. Other strain-variable genes of known function include those responsible for iron acquisition, DNA restriction/modification, and sialylation. In fact, at least 21% of genes in the sequenced strain appear dispensable as they are absent or highly divergent in one or more of the isolates tested, thus defining 1300 C. jejuni core genes. Such core genes contribute mainly to metabolic, biosynthetic, cellular, and regulatory processes, but many virulence determinants are also conserved. Comparison of the capsule biosynthesis locus revealed conservation of all the genes in this region in strains with the same Penner serotype as strain NCTC 11168. By contrast, between 5 and 17 NCTC 11168 genes in this region are either absent or highly divergent in strains of a different serotype from the sequenced strain, providing further evidence that the capsule accounts for Penner serotype specificity. These studies reveal extensive genetic diversity among C. jejuni strains and pave the way toward identifying correlates of pathogenicity and developing improved epidemiological tools for this problematic pathogen.

Demonstration of polysaccharide capsule in Campylobacter jejuni using electron microscopy

Recently, we reported that Campylobacter jejuni, an important gastrointestinal pathogen, has the genetic determinants to produce a capsular polysaccharide (Karlyshev et al., Mol. Microbiol. 35:529-541, 2000). Despite these data, the presence of a capsule in these bacteria has remained controversial. In this study we stain C. jejuni cells with the cationic dye Alcian blue and demonstrate for the first time by electron microscopy that C. jejuni cells produce a polysaccharide capsule that is retained in the coccoid form but is absent in a kpsM mutant.

The failure of different strains of Yersinia pestis to produce lipopolysaccharide O-antigen under different growth conditions is due to mutations in the O-antigen gene cluster

The lipopolysaccharide (LPS) from eight strains of Yersinia pestis which had been cultured at 28 degrees C appeared to be devoid of an O-antigen when analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. LPS isolated from three of these strains which had been cultured at 37 degrees C also appeared to be devoid of an O-antigen. When the LPS from Y. pestis strain CO92 was purified and analysed by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry, the observed signals were in the mass range predicted for molecules containing lipid A plus the core oligosaccharide but lacking an O-antigen. The nucleotide sequence of Y. pestis strain CO92 revealed the presence of a putative O-antigen gene cluster. However, frame-shift mutations in the ddhB, gmd, fcl and ushA genes are likely to prevent expression of the O-antigen thus explaining the loss of phenotype.

Yersinia pestis pFra shows biovar-specific differences and recent common ancestry with a Salmonella enterica serovar Typhi plasmid

Population genetic studies suggest that Yersinia pestis, the cause of plague, is a clonal pathogen that has recently emerged from Yersinia pseudotuberculosis. Plasmid acquisition is likely to have been a key element in this evolutionary leap from an enteric to a flea-transmitted systemic pathogen. However, the origin of Y. pestis-specific plasmids remains obscure. We demonstrate specific plasmid rearrangements in different Y. pestis strains which distinguish Y. pestis bv. Orientalis strains from other biovars. We also present evidence for plasmid-associated DNA exchange between Y. pestis and the exclusively human pathogen Salmonella enterica serovar Typhi.

Helicobacter pylori pore-forming cytolysin orthologue TlyA possesses in vitro hemolytic activity and has a role in colonization of the gastric mucosa

Hemolysins have been found to possess a variety of functions in bacteria, including a role in virulence. Helicobacter pylori demonstrates hemolytic activity when cultured on unlysed blood agar plates which is increased under iron-limiting conditions. However, the role of an H. pylori hemolysin in virulence is unclear. Scrutiny of the H. pylori 26695 genome sequence suggests the presence of at least two distinct hemolysins, HP1086 and HP1490, in this strain. Previous studies have shown that the in vitro hemolytic activity of H. pylori is reduced when it is coincubated with dextran 5000, suggesting the presence of a pore-forming cytolysin. HP1086 has homology to pore-forming cytolysins (TlyA) from other bacterial species, and the introduction of the cloned H. pylori tlyA gene into a nonhemolytic Escherichia coli strain conferred hemolytic activity. An H. pylori tlyA defined mutant showed reduced in vitro hemolytic activity, which appears to be due to pore formation, as the hemolytic activity of the wild-type strain is reduced to the same level as the tlyA mutant by the addition of dextran 5000. The mutant also showed reduced adhesion to human gastric adenocarcinoma cells and failed to colonize the gastric mucosa of mice. These data clearly suggest a role in virulence for H. pylori TlyA, contrary to the suggestion that hemolytic activity is an in vitro phenomenon for this pathogen.

Sequencing of the Francisella tularensis strain Schu 4 genome reveals the shikimate and purine metabolic pathways, targets for the construction of a rationally attenuated auxotrophic vaccine

Francisella tularensis is the etiological agent of tularemia, a serious disease in several Northern hemisphere countries. The organism has fastidious growth requirements and is very poorly understood at the genetic and molecular levels. Given the lack of data on this organism, we undertook the sample sequencing of its genome. A random library of DNA fragments from a highly virulent strain (Schu 4) of F. tularensis was constructed and the nucleotide sequences of 13,904 cloned fragments were determined and assembled into 353 contigs. A total of 1.83 Mb of nucleotide sequence was obtained that had a G+C content of 33.2%. Genes located on plasmids pOM1 and pNFL10, which had been previously isolated from low virulence strains of F. tularensis, were absent but all of the other known F. tularensis genes were represented in the assembled data. F. tularensis Schu4 was able to grow in the absence of aromatic amino acids and orthologues of genes which could encode enzymes in the shikimate pathway in other bacteria were identified in the assembled data. Genes that could encode all of the enzymes in the purine biosynthetic and most of the en- zymes in the purine salvage pathways were also identified. This data will be used to develop defined rationally attenuated mutants of F. tularensis, which could be used as replacements for the existing genetically undefined live vaccine strain.

Deciphering Campylobacter jejuni cell surface interactions from the genome sequence

The completion of the Campylobacter jejuni genome sequence is a landmark in Campylobacter research. Discoveries directly arising from these data include the identification of a capsular polysaccharide, extensive capacity for phase variable gene expression and lipo-oligosaccharide structural phase variation. The recent identification of a unique system of general protein glycosylation in C. jejuni, a C. jejuni protein that is translocated into eukaryotic cells, and plasmid-encoded components of a putative type IV secretion system are likely to be significant in terms of the host-pathogen interaction.

Characterization of the lipopolysaccharide of Yersinia pestis

Lipopolysaccharide (LPS) extracted from eight strains of Yersinia pestis, which had been cultured at 28 or 37 degrees C, reacted equally well, in Western blots, with four monoclonal antibodies generated against the LPS from a single strain of Y. pestis cultured at 28 degrees C. LPS was extracted and purified from Y. pestis strain GB, which had been cultured at 28 degrees C. When the LPS was analysed by SDS-PAGE and MALDI-TOF mass spectrometry it was found to be devoid of an O-antigen. The LPS possessed activity of 2.7 endotoxin units/ng in the Limulus amoebocyte lysate assay. The LPS stimulated the production of TNFalpha and IL-6 from mouse macrophages, but was less active in these assays than LPS isolated from Escherichia coli strain 0111. Y. pestis LPS, either alone or with cholera toxin B subunit, was used to immunize mice. Either immunization schedule resulted in the development of an antibody response to LPS. However, this response did not provide protection against 100 MLD of Y. pestis strain GB.

Detection and initial characterization of novel capsular polysaccharide among diverse Campylobacter jejuni strains using alcian blue dye

We have recently demonstrated that most strains of Campylobacter jejuni produce capsular polysaccharide (CPS), which can be detected by immunoblotting with homologous Penner antisera on polyvinylidene difluoride membranes (A. V. Karlyshev, D. Linton, N. A. Gregson, A. J. Lastovica, and B. W. Wren, Mol. Microbiol. 35:529-541, 2000). In this report, we describe a universal and rapid staining procedure using Alcian blue for C. jejuni CPS, which does not rely on the availability of antisera and identifies CPS in untypeable strains. Furthermore, Alcian blue staining identified CPS in its lipid-free form directly on Tricine gels, and we demonstrate that CPS is thermostable and is accumulated in the culture supernatant in a lipid-free form. The identification of a newly described CPS and its lipid-free form in C. jejuni should prove invaluable in studying the pathogenesis and epidemiology of this important pathogen.

Helicobacter pylori vaccine strategies--triggering a gut reaction

Helicobacter pylori causes peptic ulcer disease and some forms of gastric cancer; it is one of the most common chronic bacterial infections of humans. Although several prototype protein-based vaccines have shown promising results, they have not cleared infection and/or prevented reinfection. Nucleic acid vaccination offers a useful alternative to protein immunization, especially now that two complete H. pylori genome sequences are available, and facilitates the selection of antigenic targets.

Microbial genome analysis: insights into virulence, host adaptation and evolution

Genome analysis of microbial pathogens has provided unique insights into their virulence, host adaptation and evolution. Common themes have emerged, including lateral gene transfer among enteric pathogens, genome decay among obligate intracellular pathogens and antigenic variation among mucosal pathogens. The advent of post-genomic approaches and the sequencing of the human genome will enable scientists to investigate the complex and dynamic interplay between host and pathogen. This wealth of information will catalyse the development of new intervention strategies to reduce the burden of microbial-related disease.

Mutational analysis of genes encoding the early flagellar components of Helicobacter pylori: evidence for transcriptional regulation of flagellin A biosynthesis

We investigated the roles of fliF, fliS, flhB, fliQ, fliG, and fliI of Helicobacter pylori, predicted by homology to encode structural components of the flagellar basal body and export apparatus. Mutation of these genes resulted in nonmotile, nonflagellate strains. Western blot analysis showed that all the mutants had considerably reduced levels of both flagellin subunits and of FlgE, the flagellar hook protein. RNA slot blot hybridization showed reduced levels of flaA mRNA, indicating that transcription of the major flagellin gene is inhibited in the absence of the early components of the flagellar-assembly pathway. This is the first demonstration of a checkpoint in H. pylori flagellar assembly.

Phase variation of a beta-1,3 galactosyltransferase involved in generation of the ganglioside GM1-like lipo-oligosaccharide of Campylobacter jejuni

Ganglioside mimicry by Campylobacter jejuni lipo-oligosaccharide (LOS) is thought to be a critical factor in the triggering of the Guillain-Barré and Miller-Fisher syndrome neuropathies after C. jejuni infection. The combination of a completed genome sequence and a ganglioside GM1-like LOS structure makes C. jejuni NCTC 11168 a useful model strain for the identification and characterization of the genes involved in the biosynthesis of ganglioside-mimicking LOS. Genome analysis identified a putative LOS biosynthetic cluster and, from this, we describe a putative gene (ORF Cj1139c), which we have termed wlaN, with a significant level of similarity to a number of bacterial glycosyltransferases. Mutation of this gene in C. jejuni NCTC 11168 resulted in a LOS molecule of increased electrophoretic mobility, which also failed to bind cholera toxin. Comparison of LOS structural data from wild type and the mutant strain indicated lack of a terminal beta-1,3-linked galactose residue in the latter. The wlaN gene product was demonstrated unambiguously as a beta-1,3 galactosyltransferase responsible for converting GM2-like LOS structures to GM1-like by in vitro expression. We also show that the presence of an intragenic homopolymeric tract renders the expression of a functional wlaN gene product phase variable, resulting in distinct C. jejuni NCTC 11168 cell populations with alternate GM1 or GM2 ganglioside-mimicking LOS structures. The distribution of wlaN among a number of C. jejuni strains with known LOS structure was determined and, for C. jejuni NCTC 12500, similar wlaN gene phase variation was shown to occur, so that this strain has the potential to synthesize a GM1-like LOS structure as well as the ganglioside GM2-like LOS structure proposed in the literature.

The response regulator PhoP is important for survival under conditions of macrophage-induced stress and virulence in Yersinia pestis

The two-component regulatory system PhoPQ has been identified in many bacterial species. However, the role of PhoPQ in regulating virulence gene expression in pathogenic bacteria has been characterized only in Salmonella species. We have identified, cloned, and sequenced PhoP orthologues from Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. To investigate the role of PhoP in the pathogenicity of Y. pestis, an isogenic phoP mutant was constructed by using a reverse-genetics PCR-based strategy. The protein profiles of the wild-type and phoP mutant strains, grown at either 28 or 37 degrees C, revealed more than 20 differences, indicating that PhoP has pleiotrophic effects on gene expression in Y. pestis. The mutant showed a reduced ability to survive in J774 macrophage cell cultures and under conditions of low pH and oxidative stress in vitro. The mean lethal dose of the phoP mutant in mice was increased 75-fold in comparison with that of the wild-type strain, indicating that the PhoPQ system plays a key role in regulating the virulence of Y. pestis.

Investigation into the role of the serine protease HtrA in Yersinia pestis pathogenesis

The HtrA stress response protein has been shown to play a role in the virulence of a number of pathogens. For some organisms, htrA mutants are attenuated in the animal model and can be used as live vaccines. A Yersinia pestis htrA orthologue was identified, cloned and sequenced, showing 86% and 87% similarity to Escherichia coli and Salmonella typhimurium HtrAs. An isogenic Y. pestis htrA mutant was constructed using a reverse genetics approach. In contrast to the wild-type strain, the mutant failed to grow at an elevated temperature of 39 degrees C, but showed only a small increase in sensitivity to oxidative stress and was only partially attenuated in the animal model. However, the mutant exhibited a different protein expression profile to that of the wild-type strain when grown at 28 degrees C to simulate growth in the flea.

Helicobacter pylori possesses two CheY response regulators and a histidine kinase sensor, CheA, which are essential for chemotaxis and colonization of the gastric mucosa

Infection of the mucous layer of the human stomach by Helicobacter pylori requires the bacterium to be motile and presumably chemotactic. Previous studies have shown that fully functional flagella are essential for motility and colonization, but the role of chemotaxis remains unclear. The two-component regulatory system CheA/CheY has been shown to play a major role in chemotaxis in other enteric bacteria. Scrutiny of the 26695 genome sequence suggests that H. pylori has two CheY response regulators: one a separate protein (CheY1) and the other (CheY2) fused to the histidine kinase sensor CheA. Defined deletion mutations were introduced into cheY1, cheY2, and cheA in H. pylori strains N6 and SS1. Video tracking revealed that the wild-type H. pylori strain moves in short runs with frequent direction changes, in contrast to movement of cheY2, cheAY2, and cheAY2 cheY1 mutants, whose motion was more linear. The cheY1 mutant demonstrated a different motility phenotype of rapid tumbling. All mutants had impaired swarming and greatly reduced chemotactic responses to hog gastric mucin. Neither cheY1 nor cheAY2 mutants were able to colonize mice, but they generated a significant antibody response, suggesting that despite impaired chemotaxis, these mutants were able to survive in the stomach long enough to induce an immune response before being removed by gastric flow. Additionally, we demonstrated that cheY1 failed to colonize gnotobiotic piglets. This study demonstrates the importance of the roles of cheY1, cheY2, and cheA in motility and virulence of H. pylori.

Multiple N-acetyl neuraminic acid synthetase (neuB) genes in Campylobacter jejuni: identification and characterization of the gene involved in sialylation of lipo-oligosaccharide

N-acetyl neuraminic acid (NANA) is a common constituent of Campylobacter jejuni lipo-oligosaccharide (LOS). Such structures often mimic human gangliosides and are thought to be involved in the triggering of Guillain-Barré syndrome (GBS) and Miller-Fisher syndrome (MFS) following C. jejuni infection. Analysis of the C. jejuni NCTC 11168 genome sequence identified three putative NANA synthetase genes termed neuB1, neuB2 and neuB3. The NANA synthetase activity of all three C. jejuni neuB gene products was confirmed by complementation experiments in an Escherichia coli neuB-deficient strain. Isogenic mutants were created in all three neuB genes, and for one such mutant (neuB1) LOS was shown to have increased mobility. C. jejuni NCTC 11168 wild-type LOS bound cholera toxin, indicating the presence of NANA in a LOS structure mimicking the ganglioside GM1. This property was lost in the neuB1 mutant. Gas chromatography-mass spectrometry and fast atom bombardment-mass spectrometry analysis of LOS from wild-type and the neuB1 mutant strain demonstrated the lack of NANA in the latter. Expression of the neuB1 gene in E. coli confirmed that NeuB1 was capable of in vitro NANA biosynthesis through condensation of N-acetyl-D-mannosamine and phosphoenolpyruvate. Southern analysis demonstrated that the neuB1 gene was confined to strains of C. jejuni with LOS containing a single NANA residue. Mutagenesis of neuB2 and neuB3 did not affect LOS, but neuB3 mutants were aflagellate and non-motile. No phenotype was evident for neuB2 mutants in strain NCTC 11168, but for strain G1 the flagellin protein from the neuB2 mutant showed an apparent reduction in molecular size relative to the wild type. Thus, the neuB genes of C. jejuni appear to be involved in the biosynthesis of at least two distinct surface structures: LOS and flagella.

Immunization with a DNA expression vector encoding the varicella zoster virus glycoprotein E (gE) gene via intramuscular and subcutaneous routes

In this study we constructed a plasmid containing the gene encoding varicella-zoster virus transmembrane glycoprotein gE (VZV gE) and evaluated its utility for DNA immunization in mice. Our initial work demonstrates that intramuscular and subcutaneous injection of VZV gE DNA, without the use of costimulatory molecules or other adjuvant materials, results in the generation of antigen-specific antibodies of primarily the IgG2a subclass, indicating that this vaccine can stimulate Th1 type immunity. This is the first report of a prototype DNA vaccine for varicella-zoster virus.

The genome sequence of the food-borne pathogen Campylobacter jejuni reveals hypervariable sequences

Campylobacter jejuni, from the delta-epsilon group of proteobacteria, is a microaerophilic, Gram-negative, flagellate, spiral bacterium-properties it shares with the related gastric pathogen Helicobacter pylori. It is the leading cause of bacterial food-borne diarrhoeal disease throughout the world. In addition, infection with C. jejuni is the most frequent antecedent to a form of neuromuscular paralysis known as Guillain-Barré syndrome. Here we report the genome sequence of C. jejuni NCTC11168. C. jejuni has a circular chromosome of 1,641,481 base pairs (30.6% G+C) which is predicted to encode 1,654 proteins and 54 stable RNA species. The genome is unusual in that there are virtually no insertion sequences or phage-associated sequences and very few repeat sequences. One of the most striking findings in the genome was the presence of hypervariable sequences. These short homopolymeric runs of nucleotides were commonly found in genes encoding the biosynthesis or modification of surface structures, or in closely linked genes of unknown function. The apparently high rate of variation of these homopolymeric tracts may be important in the survival strategy of C. jejuni.

Genetic and biochemical evidence of a Campylobacter jejuni capsular polysaccharide that accounts for Penner serotype specificity

Campylobacter jejuni, a Gram-negative spiral bacterium, is the most common bacterial cause of acute human gastroenteritis and is increasingly recognized for its association with the serious post-infection neurological complications of the Miller-Fisher and Guillain-Barré syndromes. C. jejuni lipopolysaccharide (LPS) is thought to be involved in the pathogenesis of both uncomplicated infection and more serious sequelae, yet the LPS remains poorly characterized. Current studies on C. jejuni suggest that all strains produce lipooligosaccharide (LOS), with about one-third of strains also producing high-molecular-weight LPS (referred to as O-antigen). In this report, we demonstrate the presence of the high-molecular-weight LPS in all C. jejuni strains tested. Furthermore, we show that this LPS is biochemically and genetically unrelated to LOS and is similar to group II and group III capsular polysaccharides. All tested kpsM, kpsS and kpsC mutants of C. jejuni lost the ability to produce O-antigen. Moreover, this correlated with serotype changes. We demonstrate for the first time that the previously described O-antigen of C. jejuni is a capsular polysaccharide and a common component of the thermostable antigen used for serotyping of C. jejuni.

Characterization of Helicobacter pylori PldA, a phospholipase with a role in colonization of the gastric mucosa

BACKGROUND & AIMS

Phospholipase activity may play a role in the pathogenicity of Helicobacter pylori. Furthermore, some drugs that are effective against H. pylori infection are phospholipase inhibitors. Scrutiny of the H. pylori 26695 genome sequence revealed the presence of a putative protein with homology to Esherichia coli outer membrane phospholipase A (PldA). The aim of this study was to investigate the role of this putative PldA in the pathogenicity of H. pylori.

METHODS

An isogenic pldA mutant was constructed and analyzed for in vitro phospholipase A(2) and hemolytic activity. Adherence of the mutant to human gastric adenocarcinoma cells and the ability to colonize mice were also investigated.

RESULTS

The pldA mutant showed a marked reduction in phospholipase A(2) and hemolytic activity compared with the wild-type strain. The mutant was unable to colonize mice at 2 and 8 weeks, but it did induce a significant immune response. In contrast, the ability of the mutant to adhere to human gastric adenocarcinoma cells was unaffected.

CONCLUSIONS

The results suggest a role for PldA in colonization of the gastric mucosa and possibly tissue damage after colonization.

Nucleic acid immunization: concepts and techniques associated with third generation vaccines

A radical change in vaccine methodology arrived nine years ago with the advent of nucleic acid immunization. Aspects such as plasmid design, gene selection, the use of immunostimulatory complexes and clinical trials are discussed in this review. Furthermore, concepts and protocols involved in the construction, evaluation and immunization of a DNA vaccine have been examined as new strategies to enhance this technology continues to grow.

Local and systemic neutralizing antibody responses induced by intranasal immunization with the nontoxic binding domain of toxin A from Clostridium difficile

Fourteen of the 38 C-terminal repeats from Clostridium difficile toxin A (14CDTA) were cloned and expressed either with an N-terminal polyhistidine tag (14CDTA-HIS) or fused to the nontoxic binding domain from tetanus toxin (14CDTA-TETC). The recombinant proteins were successfully purified by bovine thyroglobulin affinity chromatography. Both C. difficile toxin A fusion proteins bound to known toxin A ligands present on the surface of rabbit erythrocytes. Intranasal immunization of BALB/c mice with three separate 10-microg doses of 14CDTA-HIS or -TETC generated significant levels of anti-toxin A serum antibodies compared to control animals. The coadministration of the mucosal adjuvant heat labile toxin (LT) from Escherichia coli (1 microg) significantly increased the anti-toxin A response in the serum and at the mucosal surface. Importantly, the local and systemic antibodies generated neutralized toxin A cytotoxicity. Impressive systemic and mucosal anti-toxin A responses were also seen following coadministration of 14CDTA-TETC with LTR72, an LT derivative with reduced toxicity which shows potential as a mucosal adjuvant for humans.

Investigation into the role of the response regulator NtrC in the metabolism and virulence of Brucella suis

During infection, Brucella species have to adapt to a range of different environments. Environmental sensing in bacteria often involves the concerted action of two-component regulatory systems consisting of sensor and response regulator components. In this study, we identified, cloned and sequenced four independent response regulator gene fragments from Brucella melitensis. One amplified gene fragment showed nearly 90% identity to the response regulator subfamily of NtrC transcriptional activators, and further analysis revealed the presence of an adjacent gene encoding the sensor protein NtrB. The NtrBC two-component regulatory system has been shown to play varying roles in nitrogen metabolism and potentially in virulence in other bacterial species. A B. suis ntrC isogenic mutant was constructed which showed no significant differences in growth rates compared to the wild-type strain when grown at different temperatures in vitro. However, the mutant exhibited a reduction in metabolic activity in the presence of many amino acids. The mutation did not affect survival or multiplication of B. suis in macrophages, but during the initial stages of infection in the murine brucellosis model, the ntrC mutant showed a reduced ability to multiply rapidly in splenic tissue.

A novel Campylobacter jejuni two-component regulatory system important for temperature-dependent growth and colonization

Campylobacter jejuni colonizes the intestines of domestic and wild animals and is a common cause of human diarrheal disease. We identified a two-component regulatory system, designated the RacR-RacS (reduced ability to colonize) system, that is involved in a temperature-dependent signalling pathway. A mutation of the response regulator gene racR reduced the organism's ability to colonize the chicken intestinal tract and resulted in temperature-dependent changes in its protein profile and growth characteristics.

Functional analysis of the roles of FliQ and FlhB in flagellar expression in Helicobacter pylori

Expression of the two Helicobacter pylori flagellin proteins FlaA and FlaB is required for full motility and persistent infection of the gastric mucosa. The mechanisms and regulation of the biosynthesis and export of flagella in H. pylori are still poorly understood. Scrutiny of the H. pylori 26695 genome sequence revealed homologues of FliQ and FlhB. The roles of the fliQ and flhB genes in H. pylori were investigated by the construction and characterisation of defined isogenic mutants. The results indicate that these genes are involved in the flagellar expression, adhesion to and colonisation of the gastric mucosa.

Immunogenicity of a Salmonella typhimurium aroA aroD vaccine expressing a nontoxic domain of Clostridium difficile toxin A

The C-terminal repeat domain of Clostridium difficile toxin A harbors toxin-neutralizing epitopes and is considered to be a candidate component of a vaccine against C. difficile-associated disease (CDAD). Fourteen of the 38 C-terminal toxin A repeats (14CDTA) were cloned into pTECH-1 in frame with the immunogenic fragment C of tetanus toxin (TETC) to generate plasmid p56TETC. Expression of the TETC-14CDTA fusion protein was driven from the anaerobically inducible nirB promoter within attenuated Salmonella typhimurium BRD509 (aroA aroD). The TETC-14CDTA fusion protein was purified and shown to bind to known toxin A receptors found on the surface of rabbit erythrocytes. Intranasal (i.n.) and intragastric (i.g.) immunization with 10(7) and 10(10) CFU, respectively, of BRD509(p56TETC) generated significant (P < 0.05) anti-toxin A serum responses after a single dose. Antibody titers were elevated following a boosting dose with either live vaccine or a subcutaneous injection of 0.5 microgram of purified 14CDTA protein. Importantly, serum from mice immunized with BRD509(p56TETC) neutralized toxin A cytotoxicity. Both i.n. and i.g. immunizations also generated toxin A-specific immunoglobulin A on the pulmonary and intestinal mucosa, respectively. Intranasal vaccination induced consistently higher serum and mucosal anti-toxin A antibody responses. Significant anti-tetanus toxoid serum and mucosal antibodies were also generated by both immunization routes. The availability of live attenuated Salmonella typhi for human use may allow the development of a multivalent mucosal vaccine against CDAD, tetanus, and typhoid.