The virulence factors ofBordetella pertussis: a matter of control

Pertussis Vaccines Scarcely Provide Protection against Bordetella parapertussis Infection in Children-A Systematic Review and Meta-Analysis

BACKGROUND

Pertussis, or whooping cough, is a global public health concern. Pertussis vaccines have demonstrated good protection against Bordetella pertussis infections, but their effectiveness against Bordetella parapertussis remains debated due to conflicting study outcomes.

METHODS

A systematic review and meta-analysis were conducted to assess the effectiveness of pertussis vaccines in protecting children against B. parapertussis infection. A comprehensive search of PubMed, Web of Science, and Scopus databases was conducted, and randomized controlled trials (RCTs) and observational studies that met inclusion criteria were included in the analysis.

RESULTS

The meta-analysis, involving 46,533 participants, revealed no significant protective effect of pertussis vaccination against B. parapertussis infection (risk ratio: 1.10, 95% confidence interval: 0.83 to 1.44). Subgroup analyses by vaccine type and study design revealed no significant protection. The dearth of recent data and a limited pool of eligible studies, particularly RCTs, underscore a critical gap that warrants future research in the domain.

CONCLUSIONS

These findings offer crucial insights into the lack of effectiveness of pertussis vaccines against B. parapertussis. Given the rising incidence of cases and outbreaks, coupled with the lack of cross-protection by the existing vaccines, there is an urgent need to develop vaccines that include specific antigens to protect against B. parapertussis.

Innate Lymphoid Cells and Their Role in the Immune Response to Infections

Over the past decade, a group of lymphocyte-like cells called innate lymphoid cells (ILCs) has gained considerable attention due to their crucial role in regulating immunity and tissue homeostasis. ILCs, lacking antigen-specific receptors, are a group of functionally differentiated effector cells that act as tissue-resident sentinels against infections. Numerous studies have elucidated the characteristics of ILC subgroups, but the mechanisms controlling protective or pathological responses to pathogens still need to be better understood. This review summarizes the functions of ILCs in the immunology of infections caused by different intracellular and extracellular pathogens and discusses their possible therapeutic potential.

Comparison of Two Different Methods for the Extraction of Outer Membrane Vesicles from the Bordetella pertussis as a Vaccine Candidate

Despite the availability of a vaccine, pertussis is still a worldwide health problem. Outer membrane vesicles (OMVs) in gram-negative bacteria can stimulate the immune system due to several outer membrane proteins and are very good candidates in vaccine development. OMVs obtained from Bordetella pertussis contain several antigens, which are considered immunogenic, and could make them a potential candidate for vaccine production. The current study aimed to compare the current OMV extraction method (with ultracentrifuge) and a modified extraction method (without ultracentrifuge) and to evaluate the physicochemical properties as well as the expression of their main virulence factors. Vaccinal strain BP134 grown on Bordet Gengo agar were inoculated in Modified Stainer-Scholte medium for mass cultivation. OMVs were prepared using two different methods. They were then stained and examined with a transmission electron microscope. Protein contents were measured by the Bradford method, and then the protein profile was evaluated by SDS-PAGE. The presence of immunogenic antigens was detected by Western blotting. The size and shape of the OMVs obtained from the modified method without the use of ultracentrifuge were similar to the current method and had a size between 40 and 200 nm. The total protein yields of the OMV isolated using the current and modified methods were 800 and 600 µg/ml, respectively. Evaluating the protein profile of extracted OMVs showed the presence of different proteins. Finally, the presence of PTX, PRN, and FHA was observed in OMVs extracted from both methods. Comparison of the two OMV extraction methods showed that the obtained vesicles have a suitable and similar shape and size as well as the expression of three important pathogenic factors as immunogens. Despite the relatively low reduction in protein yield as the modified method does not require ultracentrifuge, this extraction method can be used as a suitable alternative for extracting the outer membrane vesicles from B. pertussis, especially in developing countries. It should be noted that further experiments including immunogenicity determination of OMVs obtained as vaccine candidates in animal models are required.

Evaluation of Outer Membrane Vesicles Obtained from Predominant Local Isolate of Boredetella pertussis as a Vaccine Candidate

Background:

Pertussis is a current contagious bacterial disease caused by Bp. Given the prevalence of pertussis, development of new vaccines is important. This study was attempted to evaluate the expression of main virulence factors (PTX, PRN, and FHA) from Bp predominant strains and also compare the expression of these factors in the OMVs obtained from predominant circulating Bp isolate.

Methods:

The physicochemical features of the prepared OMVs were analyzed by electron microscopy and SDS-PAGE. The presence of the mentioned virulence factors was confirmed by Western blotting. BALB/c mice (n = 21) immunized with characterized OMVs were challenged intranasally with sublethal doses of Bp, to examine their protective capacity.

Results:

Electron microscopic examination of the OMVs indicated vesicles within the range of 40 to 200 nm. SDS-PAGE and Western blotting demonstrated the expression of all three main protective immunogens (PTX, PRN, and FHA), prevalent in the predominant, challenge, and vaccine strains, and OMVs of the predominant IR37 strain and BP134 vaccine strain. Significant differences were observed in lung bacterial counts between the immunized mice with OMV (30 CFU/lung) compared to the negative control group ((6 10⁴ CFU/lung; p < 0.001). In mice immunized with OMVs (3 µg), the number of lungs recovered colonies after five days dropped at least five orders of magnitude compared to the control group.

Conclusion:

OMVs obtained from circulating isolates with the predominant profile may constitute a highly promising vaccine quality. They also can be proposed as a potential basic material for the development of new pertussis vaccine candidate.

Fha Deficient Bordetella pertussis Isolates in Iran with 50 Years Whole Cell Pertussis Vaccination

Background:

Bordetella pertussis, a highly contagious respiratory. Notably, the resurgence of pertussis has recently been associated with the lacking production of vaccine virulence factors. This study aimed to screen pertactin (Prn) and filamentous hemagglutinin (Fha) production in Iran with 50 years’ whole cell vaccine (WCV) immunization program.

Methods:

Overall, 130 B. pertussis isolates collected from Pertussis Reference Laboratory of Iran during 2005–2018. Real-time PCR was performed by targeting IS481, ptxP, IS1001 and IS1002 for species confirmation of B. pertussis. Western-blot was used to evaluate the expression of virulence factors (pertactin and filamentous hemagglutinin).

Results:

All tested B. pertussis isolates expressed Prn and all except two isolates expressed Fha. We have sequenced genomes of these strains and identified differences compared with genome reference B. pertussis Tohama I.

Conclusion:

Many countries reporting Prn and Fha-deficiency due to acellular vaccine (ACV) pressure. Our results demonstrate in a country with WCV history, Fha-deficient isolates may rise independently. However, Prn-deficient isolates are more under the ACV pressure in B. pertussis isolates. Continues surveillance will provide a better understanding of the effect of WCV on the evolution of the pathogen deficiency.

Molecular epidemiology of Bordetella pertussis and analysis of vaccine antigen genes from clinical isolates from Shenzhen, China

Background

Although pertussis cases globally have been controlled through the Expanded Programme on Immunization (EPI), the incidence of pertussis has increased significantly in recent years, with a “resurgence” of pertussis occurring in developed countries with high immunization coverage. Attracted by its fast-developing economy, the population of Shenzhen has reached 14 million and has become one of the top five largest cities by population size in China. The incidence of pertussis here was about 2.02/100,000, far exceeding that of the whole province and the whole country (both < 1/100,000). There are increasing numbers of reports demonstrating variation in Bordetella pertussis antigens and genes, which may be associated with the increased incidence. Fifty strains of Bordetella pertussis isolated from 387 suspected cases were collected in Shenzhen in 2018 for genotypic and molecular epidemiological analysis.

Methods

There were 387 suspected cases of pertussis enrolled at surveillance sites in Shenzhen from June to August 2018. Nasopharyngeal swabs from suspected pertussis cases were collected for bacterial culture and the identity of putative Bordetella pertussis isolates was confirmed by real-time PCR. The immunization history of each patient was taken. The acellular pertussis vaccine (APV) antigen genes for pertussis toxin (ptxA, ptxC), pertactin (prn) and fimbriae (fim2 and fim3) together with the pertussis toxin promoter region (ptxP) were analyzed by second-generation sequencing. Genetic and phylogenetic analysis was performed using sequences publicly available from GenBank, National Institutes of Health, Bethesda, MD, USA (https://www.ncbi.nlm.nih.gov/genbank/). The antimicrobial susceptibility was test by Kirby-Bauer disk diffusion.

Results

Fifty strains of Bordetella pertussis were successfully isolated from nasopharyngeal swabs of 387 suspected cases, with a positivity rate of 16.79%, including 28 males and 22 females, accounting for 56.0% and 44.0% respectively. Thirty-eight of the 50 (76%) patients were found to be positive for B. pertussis by culture. Among the positive cases with a history of vaccination, 30 of 42 (71.4%) cases had an incomplete pertussis vaccination history according to the national recommendation. Three phylogenetic groups (PG1-PG3) were identified each containing a predominant genotype. The two vaccines strains, CS and Tohama I, were distantly related to these three groups. Thirty-one out of fifty (62%) isolates belonged to genotype PG1, with the allelic profile prn2/ptxC2/ptxP3/ptxA1/fim3-1/fim2-1. Eighteen out of fifty (36%) isolates contained the A2047G mutation and were highly resistant to erythromycin, and all belonged to genotype PG3 (prn1/ptxA1/ptxP1/ptxC1/fim3-1/fim2-1), which is closely related to the recent epidemic strains found in northern China.

Conclusions

The positive rate of cases under one-year-old was significantly higher than that of other age groups and should be monitored. The dominant antigen genotypes of 50 Shenzhen isolates are closely related to the epidemic strains in the United States, Australia and many countries in Europe. Despite high rates of immunization with APV, epidemics of pertussis have recently occurred in these countries. Therefore, genomic analysis of circulating isolates of B. pertussis should be continued, for it will benefit the control of whooping cough and development of improved vaccines and therapeutic strategies.

SEVERE PERTUSSIS IN CHILDHOOD: UPDATE AND CONTROVERSY - SYSTEMATIC REVIEW

Objective:

Through a systematic review, this essay aimed at revising the concepts of severe pertussis, updating the epidemiology, pathophysiology, clinical presentation, antibiotic therapy and auxiliary therapeutic options for symptomatology and complications.

Data sources:

This review considered publications from the last 30years in the databases US National Library of Medicine (PubMed), Scientific Electronic Library Online (SciELO), Literatura Latino-americana e do Caribe em Ciências da Saúde (LILACS), Cochrane, Google Scholar, as well as protocols of the Ministry of Health and recommendations of the Centers for Disease Control and Prevention, related to childhood pertussis (whooping cough), with emphasis on its severe form. This research was based on keywords derived from the terms “pertussis”, “azithromycin”, “antitussives”, “leukocyte reduction” in Portuguese and English. Duplicate studies and those with unavailable full-text were excluded.

Data synthesis:

Among 556 records found, 54 were selected for analysis. Pertussis, as a reemerging disease, has affected all age groups, evidencing the transient immunity conferred by infection and vaccination. Severe cases occur in neonates and infants, with secondary viral and bacterial complications and malignant pertussis, a longside hyperleukocytosis, respiratory failure and shock. Macrolides continue to be the chosen antibiotics, while antitussives for coughing remain without efficacy. The prompt treatment in Intensive Care Units improved the prognostic in severe cases, and transfusion was promising among procedures for leukoreduction.

Conclusions:

Approaching severe pertussis in childhood remains a challenge for diagnostic and therapy, as the available therapeutic options are still unsatisfactory. Strategies of prevention are expected to reduce the occurrence of severe cases, while new studies should confirm the role of auxiliary therapies.

Genetic analysis of clinical and vaccine strains of Bordetella pertussis by Pulsed-Field Gel Electrophoresis (PFGE), Multi Locus Sequence Typing (MLST) and serotyping

In spite of high vaccination coverage in the Expanded Program of Immunization (EPI), pertussis has not been eradicated yet and the re-emergence of the disease is still reported worldwide. The genetic divergence study of circulating clinical strains of Bordetella pertussis among the population with high vaccination coverage is a useful tool to have an insight in the understanding of genetic patterns of this bacterium and deviation of them from vaccine strains. Different methods are accessible for studying of Bordetella pertussis that can perform appropriate assessment between populations. Strains used in this study were a collection of two pertussis vaccine strains used to create killed pertussis vaccine over years at Razi Vaccine and Serum Research Institute, 10 clinical and 2 reference strains (ATCC9797 and Tohama I) in Multilocus Sequence Typing (MLST), Pulsed-Field Gel Electrophoresis (PFGE), and serotyping. The genetic profiles of vaccine working and master seeds showed no important change(s) in frequencies of fingerprint types investigated in the vaccine strains and had homogeneity in PFGE method where the clinical isolates showed diversity in genetic profile. Serotyping method showed that all of 10 clinical strains expressing Fim 3. In MLST study, seven housekeeping genes including adk, pgm, fum C, tyr B, gly A, pep A and icd were analyzed which showed no changes in the sequence of clinical and vaccine strains with 100% homology. The genes that cause pathogenicity like ptxC, tcfA and fhaB were also evaluated and the results illustrated heterogeneity in the vaccine and circulating strains.

Comparison of the Whole Cell Proteome and Secretome of Epidemic Bordetella pertussis Strains From the 2008-2012 Australian Epidemic Under Sulfate-Modulating Conditions

Sulfate is an important modulator for virulence factor expression in Bordetella pertussis, the causative organism for whooping cough. During infection, sulfate is released when respiratory epithelial cells are damaged which can affect gene expression. The current predominant strains in Australia are found in single nucleotide polymorphism (SNP) cluster I (ptxP3/prn2). It has been reported that ptxP3 strains have higher mRNA expression of virulence genes than ptxP1 strains under intermediate sulfate-modulating conditions (5 mM MgSO₄). Our previous proteomic study compared L1423 (cluster I, ptxP3) and L1191 (cluster II, ptxP1) in Thalen-IJssel (THIJS) media without sulfate modulation and identified an upregulation of transport proteins and a downregulation of immunogenic proteins. To determine whether proteomic differences exist between cluster I and cluster II strains in intermediate modulating conditions, this study compared the whole cell proteome and secretome between L1423 and L1191 grown in THIJS media with 5 mM MgSO₄ using iTRAQ and high-resolution multiple reaction monitoring (MRM-hr). Two proteins (BP0200 and BP1175) in the whole cell were upregulated in L1423 [fold change (FC) >1.2, false discovery rate (FDR) <0.05]. In the secretome, four proteins from the type III secretion system (T3SS) effectors were downregulated (FC < 0.8, FDR < 0.05) while six proteins, including two adhesins, pertactin (Prn) and tracheal colonization factor A (TcfA), were upregulated which were consistent with our previous proteomic study. The upregulation of Prn and TcfA in SNP cluster I may result in improved adhesion while the downregulation of the T3SS and other immunogenic proteins may reduce immune recognition, which may contribute to the increased fitness of cluster I B. pertussis strains.

Humanised monoclonal antibodies neutralise pertussis toxin by receptor blockade and reduced retrograde trafficking

Pertussis toxin (PTx) is a major protective antigen produced by Bordetella pertussis that is included in all current acellular vaccines. Of several well‐characterized monoclonal antibodies binding this toxin, the humanised hu1B7 and hu11E6 antibodies are highly protective in multiple in vitro and in vivo assays. In this study, we determine the molecular mechanisms of protection mediated by these antibodies. Neither antibody directly binds the B. pertussis bacterium nor supports antibody‐dependent complement cytotoxicity. Both antibodies, either individually or as a cocktail, form multivalent complexes with soluble PTx that bind the FcγRIIb receptor more tightly than antibody alone, suggesting that the antibodies may accelerate PTx clearance via immune complex formation. However, a receptor binding assay and cellular imaging indicate that the main mechanism used by hu11E6 is competitive inhibition of PTx binding to its cellular receptor. In contrast, the main hu1B7 neutralising mechanism appears to be inhibition of PTx internalisation and retrograde trafficking. We assessed the effects of hu1B7 on PTx retrograde trafficking in CHO‐K1 cells using quantitative immunofluorescence microscopy. In the absence of hu1B7 or after incubation with an isotype control antibody, PTx colocalizes to organelles in a manner consistent with retrograde transport. However, after preincubation with hu1B7, PTx appears restricted to the membrane surface with colocalization to organelles associated with retrograde transport significantly reduced. Together, these data support a model whereby hu11E6 and hu1B7 interfere with PTx receptor binding and PTx retrograde trafficking, respectively.

Diversion of complement-mediated killing by Bordetella

The complement cascade participates in protection against bacterial infections, and pathogens, including Bordetella pertussis, have developed complement-evading strategies. Here we discuss current knowledge on B. pertussis complement evasion strategies and the role of antibody-dependent complement-mediated killing in protection against B. pertussis infection pointing out important knowledge gaps for further research to improve current pertussis vaccines.

Block V RTX Domain of Adenylate Cyclase from Bordetella pertussis: A Conformationally Dynamic Scaffold for Protein Engineering Applications

The isolated Block V repeats-in-toxin (RTX) peptide domain of adenylate cyclase (CyaA) from Bordetella pertussis reversibly folds into a β-roll secondary structure upon calcium binding. In this review, we discuss how the conformationally dynamic nature of the peptide is being engineered and employed as a switching mechanism to mediate different protein functions and protein-protein interactions. The peptide has been used as a scaffold for diverse applications including: a precipitation tag for bioseparations, a cross-linking domain for protein hydrogel formation and as an alternative scaffold for biomolecular recognition applications. Proteins and peptides such as the RTX domains that exhibit natural stimulus-responsive behavior are valuable building blocks for emerging synthetic biology applications.

Presence of Bacterial Virulence Gene Homologues in the dibenzo-p-dioxins degrading bacterium Sphingomonas wittichii

Sphingomonas wittichii, a close relative of the human pathogen Sphingomonas paucimobilis, is a microorganism of great interest to the bioremediation community for its ability of biodegradation to a large number of toxic polychlorinated dioxins. In the present study we investigated the presence of different virulence factors and genes in S. wittichii. We utilized phylogenetic, comparative genomics and bioinformatics analysis to investigate the potentiality of S. wittichii as a potential virulent pathogen. The 16SrDNA phylogenetic tree showed that the closest bacterial taxon to S. wittichii is Brucella followed by Helicobacter, Campylobacter, Pseudomonas then Legionella. Despite their close phylogenetic relationship, S. wittichii did not share any virulence factors with Helicobacter or Campylobacter. On the contrary, in spite of the phylogenetic divergence between S. wittichii and Pseudomonas spp., they shared many major virulence factors, such as, adherence, antiphagocytosis, Iron uptake, proteases and quorum sensing. S. wittichii contains several major virulence factors resembling Pseudomonas sp., Legionella sp., Brucella sp. and Bordetella sp. virulence factors. Similarity of virulence factors did not match phylogenetic relationships. These findings suggest horizontal gene transfer of virulence factors rather than sharing a common pathogenic ancestor. S. wittichii is a potential virulent bacterium. Another possibility is that reductive evolution process attenuated S. wittichii pathogenic capabilities. Thus plenty of care must be taken when using this bacterium in soil remediation purposes.

Dynamics and Energy Contributions for Transport of Unfolded Pertactin through a Protein Nanopore

To evaluate the physical parameters governing translocation of an unfolded protein across a lipid bilayer, we studied protein transport through aerolysin, a passive protein channel, at the single-molecule level. The protein model used was the passenger domain of pertactin, an autotransporter virulence protein. Transport of pertactin through the aerolysin nanopore was detected as transient partial current blockades as the unfolded protein partially occluded the aerolysin channel. We compared the dynamics of entry and transport for unfolded pertactin and a covalent end-to-end dimer of the same protein. For both the monomer and the dimer, the event frequency of current blockades increased exponentially with the applied voltage, while the duration of each event decreased exponentially as a function of the electrical potential. The blockade time was twice as long for the dimer as for the monomer. The calculated activation free energy includes a main enthalpic component that we attribute to electrostatic interactions between pertactin and the aerolysin nanopore (despite the low Debye length), plus an entropic component due to confinement of the unfolded chain within the narrow pore. Comparing our experimental results to previous studies and theory suggests that unfolded proteins cross the membrane by passing through the nanopore in a somewhat compact conformation according to the "blob" model of Daoud and de Gennes.

In silico detection of virulence gene homologues in the human pathogen sphingomonas spp

There is an ongoing debate about the clinical significance of Sphingomonas paucimobilis as a virulent bacterial pathogen. In the present study, we investigated the presence of different virulence factors and genes in Sphingomonas bacteria. We utilized phylogenetic, comparative genomics and bioinformatics analysis to investigate the potentiality of Sphingomonas bacteria as virulent pathogenic bacteria. The 16S ribosomal RNA gene (16S rDNA) phylogenetic tree showed that the closest bacterial taxon to Sphingomonas is Brucella with a bootstrap value of 87 followed by Helicobacter, Campylobacter, Pseudomonas, and then Legionella. Sphingomonas shared no virulence factors with Helicobacter or Campylobacter, despite their close phylogenic relationship. In spite of the phylogenetic divergence between Sphingomonas and Pseudomonas, they shared many major virulence factors, such as adherence, antiphagocytosis, iron uptake, proteases, and quorum sensing. In conclusion, Sphingomonas spp. contains several major virulence factors resembling Pseudomonas sp., Legionella sp., Brucella sp., and Bordetella sp. virulence factors. Similarity of virulence factors did not match phylogenetic relationships. These findings suggest horizontal gene transfer of virulence factors rather than sharing a common pathogenic ancestor. Sphingomonas spp. is potential virulent bacterial pathogen.

Role of feedback and network architecture in controlling virulence gene expression in Bordetella

Bordetella is a Gram-negative bacterium responsible for causing whooping cough in a broad range of host organisms. For successful infection, Bordetella controls expression of four distinct classes of genes (referred to as class 1, 2, 3, and 4 genes) at distinct times in the infection cycle. This control is executed by a single two-component system, BvgAS. Interestingly, the transmembrane component of the two-component system, BvgS, consists of three phospho-transfer domains leading to phosphorylation of the response regulator, BvgA. Phosphorylated BvgA then controls expression of virulence genes and also controls bvgAS transcription. In this work, we perform simulations to characterize the role of the network architecture in governing gene expression in Bordetella. Our results show that the wild-type network is locally optimal for controlling the timing of expression of the different classes of genes involved in infection. In addition, the interplay between environmental signals and positive feedback aids the bacterium identify precise conditions for and control expression of virulence genes.

Substantial gaps in knowledge of Bordetella pertussis antibody and T cell epitopes relevant for natural immunity and vaccine efficacy

The recent increase in whooping cough in vaccinated populations has been attributed to waning immunity associated with the acellular vaccine. The Immune Epitope Database (IEDB) is a repository of immune epitope data from the published literature and includes T cell and antibody epitopes for human pathogens. The IEDB conducted a review of the epitope literature, which revealed 300 Bordetella pertussis-related epitopes from 39 references. Epitope data are currently available for six virulence factors of B. pertussis: pertussis toxin, pertactin, fimbrial 2, fimbrial 3, adenylate cyclase and filamentous hemagglutinin. The majority of epitopes were defined for antibody reactivity; fewer T cell determinants were reported. Analysis of available protective correlates data revealed a number of candidate epitopes; however few are defined in humans and few have been shown to be protective. Moreover, there are a limited number of studies defining epitopes from natural infection versus whole cell or acellular/subunit vaccines. The relationship between epitope location and structural features, as well as antigenic drift (SNP analysis) was also investigated. We conclude that the cumulative data is yet insufficient to address many fundamental questions related to vaccine failure and this underscores the need for further investigation of B. pertussis immunity at the molecular level.

Toxicity and potency evaluation of pertussis vaccines

Current methods for determining the potency and toxicity of pertussis vaccines are outdated and require improvement. The intracerebral challenge test is effective for determining the potency of whole-cell vaccines but is objectionable on animal welfare and technical grounds. The same applies to its modification for assaying acellular pertussis vaccines. Respiratory challenge methods offer an interim solution pending establishment of validated in vitro correlates of protection, for example nitric oxide induction. Their evaluation is being promoted by the World Health Organization through the Pertussis Vaccines Working Group. Current toxicity assays based on weight gain and histamine sensitization of mice are imprecise and need replacement. Limits need to be established for specific toxin content of both acellular and whole-cell vaccines and should be supported by specific assays. More precise methods based on determination of ribosyltransferase activity in tandem with receptor-binding assays are under evaluation. Genome sequence data and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to improved methods for assessing both toxicity and immunogenicity.

Protective Immunity againstBordetella pertussisby a Recombinant DNA Vaccine and the Effect of Coinjection with a Granulocyte-Macrophage Colony Stimulating Factor Gene

A recombinant pertussis DNA vaccine was described here with its immunogenicity and the ability to induce protection against B. pertussis infection in mice. Three immunodominant antigen gene fragments of pertussis, pertussis toxin subunit 1 (pts1), fragments of pertactin (prn) and filamentous hemagglutinin (fha), were recombined as fragment pts1-prn-fha named ppf, and it was cloned to plasmid pVAX1 as pVAX1/ppf. Compared to those injected with pVAX1, the mice injected with pVAX1/ppf significantly elicited more antigen specific antibody anti-PTS1, anti-PRN, anti-FHA and cytokine IL-10, IFN-gamma. When pGM-CSF was coinjected with pVAX1/ppf, the mice showed significantly increases of the three antibodies and cytokine IL-10, IL-4, IFN-gamma and TNF-alpha compared to those injected with pVAX1 only. The mice in group pVAX1/ppf & pGM-CSF, in particular; induced much more anti-PTS1, IL-4 and TNF-alpha than those in group pVAX1/ppf. In the intracerebral mouse protection test, the mice immunized with pVAX1/ppf or pVAX1/ppf & pGM-CSF induced protection to a lethal dose of B. pertussis. The results indicate that recombinant DNA vaccine and pGM-CSF coinjection can induce protective immunity against B. pertussis, demonstrating a valuable method to prevent pertussis.

Production of biomass and filamentous hemagglutinin by Bordetella bronchiseptica

The mammalian pathogen Bordetella bronchiseptica was grown under controlled batch conditions with glutamate as the primary carbon and nitrogen source. First, a Box-Behnken statistical design quantified the effect of Mg, sulfate, and nicotinate on the antigen filamentous hemagglutinin (FHA) formation. Using lactic acid as a secondary carbon source for pH control, Mg, and SO₄ each negatively affected antigen expression, while nicotinate positively affected antigen expression. Sulfate had a stronger negative effect than Mg with 10 mM eliminating FHA altogether; the highest FHA expression (about 1,000 ng/mL) occurred when either Mg concentration or SO₄ concentration, but not both, was about 0.1 mM. Using two Mg and SO₄ compositions modeled to yield the greatest antigen expression, three other organic acids were compared as the secondary carbon source: acetate, citrate, and succinate. Mixtures of acetate and glutamate resulted in the greatest organic acid consumption, OD, and FHA concentration (about 1,500 ng/mL), although significant acetate accumulated during these batch processes. The mechanism leading to elevated FHA expression when acetate is the secondary carbon source is unknown, particularly since these cultures were most prone to phase shift to Bvg(-) cultures.

Comparative genomics of the classical Bordetella subspecies: the evolution and exchange of virulence-associated diversity amongst closely related pathogens

Background

The classical Bordetella subspecies are phylogenetically closely related, yet differ in some of the most interesting and important characteristics of pathogens, such as host range, virulence and persistence. The compelling picture from previous comparisons of the three sequenced genomes was of genome degradation, with substantial loss of genome content (up to 24%) associated with adaptation to humans.

Results

For a more comprehensive picture of lineage evolution, we employed comparative genomic and phylogenomic analyses using seven additional diverse, newly sequenced Bordetella isolates. Genome-wide single nucleotide polymorphism (SNP) analysis supports a reevaluation of the phylogenetic relationships between the classical Bordetella subspecies, and suggests a closer link between ovine and human B. parapertussis lineages than has been previously proposed. Comparative analyses of genome content revealed that only 50% of the pan-genome is conserved in all strains, reflecting substantial diversity of genome content in these closely related pathogens that may relate to their different host ranges, virulence and persistence characteristics. Strikingly, these analyses suggest possible horizontal gene transfer (HGT) events in multiple loci encoding virulence factors, including O-antigen and pertussis toxin (Ptx). Segments of the pertussis toxin locus (ptx) and its secretion system locus (ptl) appear to have been acquired by the classical Bordetella subspecies and are divergent in different lineages, suggesting functional divergence in the classical Bordetellae.

Conclusions

Together, these observations, especially in key virulence factors, reveal that multiple mechanisms, such as point mutations, gain or loss of genes, as well as HGTs, contribute to the substantial phenotypic diversity of these versatile subspecies in various hosts.

FHA-mediated cell-substrate and cell-cell adhesions are critical for Bordetella pertussis biofilm formation on abiotic surfaces and in the mouse nose and the trachea

Bordetella spp. form biofilms in the mouse nasopharynx, thereby providing a potential mechanism for establishing chronic infections in humans and animals. Filamentous hemagglutinin (FHA) is a major virulence factor of B. pertussis, the causative agent of the highly transmissible and infectious disease, pertussis. In this study, we dissected the role of FHA in the distinct biofilm developmental stages of B. pertussis on abiotic substrates and in the respiratory tract by employing a murine model of respiratory biofilms. Our results show that the lack of FHA reduced attachment and decreased accumulation of biofilm biomass on artificial surfaces. FHA contributes to biofilm development by promoting the formation of microcolonies. Absence of FHA from B. pertussis or antibody-mediated blockade of surface-associated FHA impaired the attachment of bacteria to the biofilm community. Exogenous addition of FHA resulted in a dose-dependent inhibitory effect on bacterial association with the biofilms. Furthermore, we show that FHA is important for the structural integrity of biofilms formed on the mouse nose and trachea. Together, these results strongly support the hypothesis that FHA promotes the formation and maintenance of biofilms by mediating cell-substrate and inter-bacterial adhesions. These discoveries highlight FHA as a key factor in establishing structured biofilm communities in the respiratory tract.

Pertussis resurgence in Toronto, Canada: a population-based study including test-incidence feedback modeling

BACKGROUND

Pertussis continues to challenge medical professionals; recently described increases in incidence may be due to age-cohort effects, vaccine effectiveness, or changes in testing patterns. Toronto, Canada has recently experienced increases in pertussis incidence, and provides an ideal jurisdiction for evaluating pertussis epidemiology due to centralized testing. We evaluated pertussis trends in Toronto using all available specimen data, which allowed us to control for changing testing patterns and practices.

METHODS

Data included all pertussis culture and PCR test records for Greater Toronto from 1993 to 2007. We estimated incidence trends using Poisson regression models; complex relationships between disease incidence and test submission were explored with vector autoregressive models.

RESULTS

From 1993 to 2007, 26988 specimens were submitted for testing; 2545 (9.4%) were positive. Pertussis incidence was 2 per 100,000 from 1993 to 2004 and increased to 10 per 100,000 from 2005-2007, with a concomitant 6-fold surge in test specimen submissions after the introduction of a new, more sensitive PCR assay. The relative change in incidence was less marked after adjustment for testing volumes. Bidirectional feedbacks between test positivity and test submissions were identified.

CONCLUSIONS

Toronto's recent surge in pertussis reflects a true increase in local disease activity; the apparent size of the outbreak has likely been magnified by increasing use of pertussis testing by clinicians, and by improved test sensitivity since 2005. These findings may be applicable to changes in pertussis epidemiology that have been noted elsewhere in North America.

Multilocus Sequence Analysis of Housekeeping Genes and Antigenic Determinant Genes in Bordetella pertussis Strains Isolated in Korea

OBJECTIVES

To confirm genotype diversities of clinical isolates of Bordetella pertussis and to evaluate the risk of pertussis outbreak in Korea.

METHODS

Seven housekeeping genes and 10 antigenic determinant genes from clinical B. pertussis isolates were analyzed by Multilocus sequence typing (MLST).

RESULTS

More variant pattern was observed in antigenic determinant genes. Especially, PtxS1 gene was the most variant gene; five genotypes were observed from eight global genotypes. In the bacterial type, the number of observed sequence types in the isolates was seven and the most frequent form was type 1 (79.6%). This major sequence type also showed a time-dependent transition pattern. Older isolates (1968 and 1975) showed type 1 and 6 in housekeeping genes and antigenic determinant genes, respectively. However, these were changed to type 2 and 1 in isolates 1999-2008. This transition was mainly attributed to genotype change of PtxS1 and Fim3 gene; the tendency of genotype change was to avoid vaccine-derived genotype. In addition, there was second transition in 2009. In this period, only the sequence type of antigenic determinant genes was changed to type 2. Based Upon Related Sequence Types (BURST) analysis confirmed that there were two clonal complexes (ACCI and ACCII) in the Korean isolates. Moreover, the recently increased sequence type was revealed as AST2 derived from AST 3 in ACCI.

CONCLUSIONS

Genotype changes in Korean distributing strains are still progressing and there was a specific driving force in antigenic determinant genes. Therefore continuous surveillance of genotype change of the distributing strains should be performed to confirm interrelationship of genotype change with vaccine immunity.

Adhesion mechanisms of plant-pathogenic Xanthomonadaceae

The family Xanthomonadaceae is a wide-spread family of bacteria belonging to the gamma subdivision of the Gram-negative proteobacteria, including the two plant-pathogenic genera Xanthomonas and Xylella, and the related genus Stenotrophomonas. Adhesion is a widely conserved virulence mechanism among Gram-negative bacteria, no matter whether they are human, animal or plant pathogens, since attachment to the host tissue is one of the key early steps of the bacterial infection process. Bacterial attachment to surfaces is mediated by surface structures that are anchored in the bacterial outer membrane and cover a broad group of fimbrial and non-fimbrial structures, commonly known as adhesins. In this chapter, we discuss recent findings on candidate adhesins of plant-pathogenic Xanthomonadaceae, including polysaccharidic (lipopolysaccharides, exopolysaccharides) and proteineous structures (chaperone/usher pili, type IV pili, autotransporters, two-partner-secreted and other outer membrane adhesins), their involvement in the formation of biofilms and their mode of regulation via quorum sensing. We then compare the arsenals of adhesins among different Xanthomonas strains and evaluate their mode of selection. Finally, we summarize the sparse knowledge on specific adhesin receptors in plants and the possible role of RGD motifs in binding to integrin-like plant molecules.

Interactions between Bordetella pertussis and the complement inhibitor factor H

Bordetella pertussis causes whooping cough in humans, a highly contagious disease of the upper respiratory tract. An increase in cases of whooping cough in adolescents and adults in many countries has been reported, despite high immunization rates in children. To efficiently colonize the host the bacteria have to resist complement, the first defence line of innate immunity. B. pertussis has previously been shown to bind the classical pathway inhibitors C4b-binding protein and C1-inhibitor being thereby able to escape the classical pathway of complement. In this study recent clinical isolates of B. pertussis and B. parapertussis were found to survive alternative pathway attack in fresh non-immune serum better than the reference B. pertussis strain, Tohama I. By using adsorption assays, flow cytometry and a radioligand binding assay we observed that both B. pertussis and B. parapertussis bound the alternative pathway inhibitor factor H (FH) from normal human serum. The surface attached FH maintained its complement regulatory activity and promoted factor I-mediated cleavage of C3b. The main binding region was located to the C-terminal part of FH, into short consensus repeat domains 19-20. In contrast, the avian pathogen B. avium did not bind FH and was sensitive to the alternative pathway of human complement. In conclusion, the human pathogens B. pertussis and B. parapertussis are able to evade the alternative complement pathway by surface acquisition of the host complement regulator FH.

Characterization of the CpxRA regulon in Haemophilus ducreyi

The Haemophilus ducreyi 35000HP genome encodes a homolog of the CpxRA two-component cell envelope stress response system originally characterized in Escherichia coli. CpxR, the cytoplasmic response regulator, was shown previously to be involved in repression of the expression of the lspB-lspA2 operon (M. Labandeira-Rey, J. R. Mock, and E. J. Hansen, Infect. Immun. 77:3402-3411, 2009). In the present study, the H. ducreyi CpxR and CpxA proteins were shown to closely resemble those of other well-studied bacterial species. A cpxA deletion mutant and a CpxR-overexpressing strain were used to explore the extent of the CpxRA regulon. DNA microarray and real-time reverse transcriptase (RT) PCR analyses indicated several potential regulatory targets for the H. ducreyi CpxRA two-component regulatory system. Electrophoretic mobility shift assays (EMSAs) were used to prove that H. ducreyi CpxR interacted with the promoter regions of genes encoding both known and putative virulence factors of H. ducreyi, including the lspB-lspA2 operon, the flp operon, and dsrA. Interestingly, the use of EMSAs also indicated that H. ducreyi CpxR did not bind to the promoter regions of several genes predicted to encode factors involved in the cell envelope stress response. Taken together, these data suggest that the CpxRA system in H. ducreyi, in contrast to that in E. coli, may be involved primarily in controlling expression of genes not involved in the cell envelope stress response.

Hemolytic uremic syndrome caused by Bordetella pertussis infection

We report the case of a 4-week-old infant with severe Bordetella pertussis infection resulting in hemolytic anemia, thrombocytopenia, and acute renal failure leading to a diagnosis of hemolytic uremic syndrome (HUS) associated with pertussis. In addition to antibiotic and supportive therapy, he was treated with plasma transfusions based on the possibility of underlying complement defect, and he improved. The association of B. pertussis infection and HUS has previously been described in a patient with a mutation in the gene encoding complement factor H (CFH). However, whereas a genetic workup for complement regulator mutations was performed, no mutation was found in our patient. This case demonstrates the possible association between pertussis infection and HUS and highlights the need for increased vigilance for renal complications in this diagnosis. Despite negative results in this case, in-depth workup of the complement system may be important to guide treatment efforts and strategies.

Regulation of expression of the Haemophilus ducreyi LspB and LspA2 proteins by CpxR

The LspA1, LspA2, and LspB proteins of Haemophilus ducreyi comprise a two-partner secretion system that has been shown to be necessary for H. ducreyi to inhibit phagocytosis by immune cells in vitro. Inactivation of lspA1 resulted in increased levels of LspA2, suggesting that these two proteins are differentially controlled (C. J. Ward et al., Infect. Immun. 71:2478-2486, 2003). Expression of LspA2 but not LspA1 was shown to be both growth phase dependent and affected by the presence of fetal calf serum (FCS) in the growth medium. In addition, neither LspA1 nor LspA2 could be detected in culture supernatant fluid in the absence of FCS. DNA microarray analysis revealed that 324 H. ducreyi genes were differentially regulated after growth in the presence of FCS. Among these, the CpxRA two-component sensory transduction system was downregulated by the presence of FCS. Inactivation of cpxR resulted in increased expression of both LspB and LspA2. Electrophoretic mobility shift assays showed that a recombinant H. ducreyi CpxR protein bound the promoter region of the lspB-lspA2 operon. The cpxR and cpxA genes were shown to be part of an operon containing two additional genes in H. ducreyi 35000HP. This is the first description of a two-component sensory transduction system regulating a proven virulence factor of H. ducreyi.

Lessons from nature: "Pathogen-Mimetic" systems for mucosal nano-medicines

Mucosal surfaces establish an interface with external environments that provide a protective barrier with the capacity to selectively absorb and secrete materials important for homeostasis of the organism. In man, mucosal surfaces such as those in the gastrointestinal tract, respiratory tree and genitourinary system also represent significant barrier to the successful administration of certain pharmaceutical agents and the delivery of newly designed nano-scale therapeutic systems. This review examines morphological, physiological and biochemical aspects of these mucosal barriers and presents currently understood mechanisms used by a variety of virulence factors used by pathogenic bacteria to overcome various aspects of these mucosal barriers. Such information emphasizes the impediments that biologically active materials must overcome for absorption across these mucosal surfaces and provides a template for strategies to overcome these barriers for the successful delivery of nano-scale bioactive materials, also known as nano-medicines.

Bordetella pertussis isolates in Finland: serotype and fimbrial expression

BACKGROUND

Bordetella pertussis causes whooping cough or pertussis in humans. It produces several virulence factors, of which the fimbriae are considered adhesins and elicit immune responses in the host. B. pertussis has three distinct serotypes Fim2, Fim3 or Fim2,3. Generally, B. pertussis Fim2 strains predominate in unvaccinated populations, whereas Fim3 strains are often isolated in vaccinated populations. In Finland, pertussis vaccination was introduced in 1952. The whole-cell vaccine contained two strains, 18530 (Fim3) since 1962 and strain 1772 (Fim2,3) added in 1976. After that the vaccine has remained the same until 2005 when the whole-cell vaccine was replaced by the acellular vaccine containing pertussis toxin and filamentous hemagglutinin. Our aims were to study serotypes of Finnish B. pertussis isolates from 1974 to 2006 in a population with > 90% vaccination coverage and fimbrial expression of the isolates during infection. Serotyping was done by agglutination and serotype-specific antibody responses were determined by blocking ELISA.

RESULTS

Altogether, 1,109 isolates were serotyped. Before 1976, serotype distributions of Fim2, Fim3 and Fim2,3 were 67%, 19% and 10%, respectively. From 1976 to 1998, 94% of the isolates were Fim2 serotype. Since 1999, the frequency of Fim3 strains started to increase and reached 83% during a nationwide epidemic in 2003. A significant increase in level of serum IgG antibodies against purified fimbriae was observed between paired sera of 37 patients. The patients infected by Fim3 strains had antibodies which blocked the binding of monoclonal antibodies to Fim3 but not to Fim2. Moreover, about one third of the Fim2 strain infected patients developed antibodies capable of blocking of binding of both anti-Fim2 and Fim3 monoclonal antibodies.

CONCLUSION

Despite extensive vaccinations in Finland, B. pertussis Fim2 strains were the most common serotype. Emergence of Fim3 strains started in 1999 and coincided with nationwide epidemics. Results of serotype-specific antibody responses suggest that Fim2 strains could express Fim3 during infection, showing a difference in fimbrial expression between in vivo and in vitro.

In vivo colonization profile study of Bordetella bronchiseptica in the nasal cavity

Bordetella bronchiseptica chronically infects a wide range of mammals, and resides primarily in the nasal cavity of the infected host. Multiple virulence factors of Bordetella species have been studied in the context of lower respiratory tract infections, but relatively less is known about the bacterial life cycle in the nasal cavity. Evidences were discovered for Bvg intermediate (Bvgⁱ) phase expression in vivo and that the major adhesin filamentous hemagglutinin plays a major role in the colonization of B. bronchiseptica in the unciliated olfactory epithelia of the nasal cavity.

PAT for vaccines: The first stage of PAT implementation for development of a well-defined whole-cell vaccine against whooping cough disease

Since variation in process time and process output is commonly accepted to be inevitable for biological processes, application of Process Analytical Technologies (PAT) on these processes is challenging. In this paper the applicability of PAT on the cultivation of Bordetella pertussis bacteria as part of the manufacture of a vaccine against whooping cough disease is investigated. Scrutinizing and eliminating the most prominent sources of variance make the cultivation process step highly reproducible. Furthermore, the use of DNA microarrays allows investigation of how disturbances influence cellular physiology and product quality. Marker genes for product quality were identified, providing the means to quantitatively assess product quality, which is hardly possible using the mandatory animal tests for product quality. The tools and results described in this paper, combined with suitable on line measurements, can make full PAT application for this process step possible. Ultimately, the process can be designed and controlled towards consistent end product quality.

Integrated regulation of the type III secretion system and other virulence determinants in Ralstonia solanacearum

In many plant and animal bacterial pathogens, the Type III secretion system (TTSS) that directly translocates effector proteins into the eukaryotic host cells is essential for the development of disease. In all species studied, the transcription of the TTSS and most of its effector substrates is tightly regulated by a succession of consecutively activated regulators. However, the whole genetic programme driven by these regulatory cascades is still unknown, especially in bacterial plant pathogens. Here, we have characterised the programme triggered by HrpG, a host-responsive regulator of the TTSS activation cascade in the plant pathogen Ralstonia solanacearum. We show through genome-wide expression analysis that, in addition to the TTSS, HrpG controls the expression of a previously undescribed TTSS-independent pathway that includes a number of other virulence determinants and genes likely involved in adaptation to life in the host. Functional studies revealed that this second pathway co-ordinates the bacterial production of plant cell wall-degrading enzymes, exopolysaccharide, and the phytohormones ethylene and auxin. We provide experimental evidence that these activities contribute to pathogenicity. We also show that the ethylene produced by R. solanacearum is able to modulate the expression of host genes and can therefore interfere with the signalling of plant defence responses. These results provide a new, integrated view of plant bacterial pathogenicity, where a common regulator activates synchronously upon infection the TTSS, other virulence determinants and a number of adaptive functions, which act co-operatively to cause disease.

Most pathogenic bacteria have the ability to switch between free-living growth and life within the host tissues. However, the mechanisms that co-ordinate changes in gene expression during the passage between these alternative ecological niches are still largely unknown. A well-studied regulation pathway triggered in response to the host environment is that controlling the transcription of the Type III secretion system (TTSS) genes. The TTSS is a major pathogenicity determinant that delivers bacterial effector proteins directly into the host cell cytosol to promote disease. Here, Valls and colleagues show that the TTSS regulatory pathway is directly connected with other circuits driving the expression of diverse pathogenicity and host-adaptation activities. The authors have identified and characterised the genes co-regulated along with the TTSS via the HrpG regulator. They have found that, in addition to the TTSS, HrpG controls the transcription of a previously unknown TTSS-independent pathway that is essential to pathogenicity and alters the bacterial production of plant cell wall-degrading enzymes, exopolysaccharide, and the phytohormones ethylene and auxin. These findings reveal an important degree of co-ordination between adaptation and virulence functions at the transcriptional level and contribute to a better understanding of the infection process.

Expression of the lipopolysaccharide-modifying enzymes PagP and PagL modulates the endotoxic activity of Bordetella pertussis

Lipopolysaccharide (LPS) is one of the major constituents of the gram-negative bacterial cell envelope. Its endotoxic activity causes the relatively high reactogenicity of whole-cell vaccines. Several bacteria harbor LPS-modifying enzymes that modulate the endotoxic activity of the LPS. Here we evaluated whether two such enzymes, i.e., PagP and PagL, could be useful tools for the development of an improved and less reactogenic whole-cell pertussis vaccine. We showed that expression of PagP and PagL in Bordetella pertussis leads to increased and decreased endotoxic activity of the LPS, respectively. As expected, PagP activity also resulted in increased endotoxic activity of whole bacterial cells. However, more unexpectedly, this was also the case for PagL. This paradoxical result may be explained, in part, by an increased release of LPS, which we observed in the PagL-expressing cells.

The genome sequence of Mannheimia haemolytica A1: insights into virulence, natural competence, and Pasteurellaceae phylogeny

The draft genome sequence of Mannheimia haemolytica A1, the causative agent of bovine respiratory disease complex (BRDC), is presented. Strain ATCC BAA-410, isolated from the lung of a calf with BRDC, was the DNA source. The annotated genome includes 2,839 coding sequences, 1,966 of which were assigned a function and 436 of which are unique to M. haemolytica. Through genome annotation many features of interest were identified, including bacteriophages and genes related to virulence, natural competence, and transcriptional regulation. In addition to previously described virulence factors, M. haemolytica encodes adhesins, including the filamentous hemagglutinin FhaB and two trimeric autotransporter adhesins. Two dual-function immunoglobulin-protease/adhesins are also present, as is a third immunoglobulin protease. Genes related to iron acquisition and drug resistance were identified and are likely important for survival in the host and virulence. Analysis of the genome indicates that M. haemolytica is naturally competent, as genes for natural competence and DNA uptake signal sequences (USS) are present. Comparison of competence loci and USS in other species in the family Pasteurellaceae indicates that M. haemolytica, Actinobacillus pleuropneumoniae, and Haemophilus ducreyi form a lineage distinct from other Pasteurellaceae. This observation was supported by a phylogenetic analysis using sequences of predicted housekeeping genes.

Granulocyte-macrophage colony-stimulating factor DNA prime-protein boost strategy to enhance efficacy of a recombinant pertussis DNA vaccine

AIM

To investigate a new strategy to enhance the efficacy of a recombinant pertussis DNA vaccine. The strategy is co-injection with cytokine plasmids as prime, and boosted with purified homologous proteins.

METHOD

A recombinant pertussis DNA vaccine containing the pertussis toxin subunit 1 (PTS1), fragments of the filamentous hemagglutinin (FHA) gene and pertactin (PRN) gene encoding filamentous hemagglutinin and pertactin were constructed. Balb/c mice were immunized with several DNA vaccines and antigen-specific antibodies anti-PTS1,anti-PRN, anti-FHA,cytokines interleukin (IL)-10, IL-4, IFN-gamma,TNF-alpha,and splenocyte-proliferation assay were used to describe immune responses.

RESULTS

The recombinant DNA vaccine could elicit similar immune responses in mice as that of separate plasmids encoding the 3 fragments, respectively. Mice immunized with DNA and boosted with the corresponding protein elicited more antibodies than those that received DNA as boost. In particular, when the mice were co-immunized with murine granulocyte-macrophage colony-stimulating factor plasmids and boosted with proteins, all 4 cytokines and the 3 antigen-specific antibodies were significantly increased compared to the pVAX1 group. Anti-PTS1, anti- FHA, IL-4 and TNF-alpha elicited in the colony stimulating factor (CSF) prime-protein boost group showed significant increase compared to all the other groups.

CONCLUSION

This prime and boost strategy has proven to be very useful in improving the immunogenicity of DNA vaccines against pertussis.

Population dynamics of Bordetella pertussis in Finland and Sweden, neighbouring countries with different vaccination histories

Pertussis is an infectious disease of the respiratory tract in humans caused by Bordetella pertussis. Despite extensive vaccinations, pertussis has remained endemic and re-emerged. In Finland, a whole-cell pertussis vaccine has been used since 1952 with high coverage. In Sweden, whole-cell vaccinations were introduced in 1953 but ceased in 1979, and pertussis vaccinations with acellular vaccines were introduced in 1996. Two epidemic peaks occurred in Sweden in 1999 and 2002 and in Finland in 1999 and 2003. We compared Finnish (N=193) and Swedish (N=455) B. pertussis isolates circulating in 1998-2003 together with vaccine strains used in these neighbouring countries with different vaccination histories. The isolates were analysed by serotyping, genotyping of pertussis toxin S1 subunit and pertactin, and pulsed-field gel electrophoresis. The results suggest that the sequential epidemics were caused by clonal expansion of a certain B. pertussis strain possibly transmitted from Sweden to Finland. The roles of antigenic variation in immunity-driven evolution of B. pertussis in both countries are discussed.

Polar localization of the autotransporter family of large bacterial virulence proteins

Autotransporters are an extensive family of large secreted virulence-associated proteins of gram-negative bacteria. Secretion of such large proteins poses unique challenges to bacteria. We demonstrate that autotransporters from a wide variety of rod-shaped pathogens, including IcsA and SepA of Shigella flexneri, AIDA-I of diffusely adherent Escherichia coli, and BrkA of Bordetella pertussis, are localized to the bacterial pole. The restriction of autotransporters to the pole is dependent on the presence of a complete lipopolysaccharide (LPS), consistent with known effects of LPS composition on membrane fluidity. Newly synthesized and secreted BrkA is polar even in the presence of truncated LPS, and all autotransporters examined are polar in the cytoplasm prior to secretion. Together, these findings are consistent with autotransporter secretion occurring at the poles of rod-shaped gram-negative organisms. Moreover, NalP, an autotransporter of spherically shaped Neisseria meningitidis contains the molecular information to localize to the pole of Escherichia coli. In N. meningitidis, NalP is secreted at distinct sites around the cell. These data are consistent with a model in which the secretion of large autotransporters occurs via specific conserved pathways located at the poles of rod-shaped bacteria, with profound implications for the underlying physiology of the bacterial cell and the nature of bacterial pathogen-host interactions.

Pertactin beta-helix folding mechanism suggests common themes for the secretion and folding of autotransporter proteins

Many virulence factors secreted from pathogenic Gram-negative bacteria are autotransporter proteins. The final step of autotransporter secretion is C --> N-terminal threading of the passenger domain through the outer membrane (OM), mediated by a cotranslated C-terminal porin domain. The native structure is formed only after this final secretion step, which requires neither ATP nor a proton gradient. Sequence analysis reveals that, despite size, sequence, and functional diversity among autotransporter passenger domains, >97% are predicted to form parallel beta-helices, indicating this structural topology may be important for secretion. We report the folding behavior of pertactin, an autotransporter passenger domain from Bordetella pertussis. The pertactin beta-helix folds reversibly in isolation, but folding is much slower than expected based on size and native-state topology. Surprisingly, pertactin is not prone to aggregation during folding, even though folding is extremely slow. Interestingly, equilibrium denaturation results in the formation of a partially folded structure, a stable core comprising the C-terminal half of the protein. Examination of the pertactin crystal structure does not reveal any obvious reason for the enhanced stability of the C terminus. In vivo, slow folding would prevent premature folding of the passenger domain in the periplasm, before OM secretion. Moreover, the extra stability of the C-terminal rungs of the beta-helix might serve as a template for the formation of native protein during OM secretion; hence, vectorial folding of the beta-helix could contribute to the energy-independent translocation mechanism. Coupled with the sequence analysis, the results presented here suggest a general mechanism for autotransporter secretion.

Role in virulence of a Brucella abortus protein exhibiting lectin-like activity

Brucella abortus is a facultative, intracellular zoonotic pathogen which can cause undulant fever in humans and abortions in cattle. A 14-kDa protein of B. abortus was previously identified to be immunogenic in animals infected with Brucella spp. In this study, we discovered that the 14-kDa protein possessed immunoglobulin binding and hemagglutination properties that appeared to be based on the protein's lectin-like properties. Hemagglutination inhibition experiments suggested that the 14-kDa protein has affinity towards mannose. Disruption of the gene encoding the 14-kDa protein in virulent B. abortus strain 2308 induced a rough-like phenotype with an altered smooth lipopolysaccharide (LPS) immunoblot profile and a significant reduction in the bacterium's ability to replicate in mouse spleens. However, the mutant strain was stably maintained in mouse spleens at 2.0 to 2.6 log(10) CFU/spleen from day 1 to week 6 after intraperitoneal inoculation with 4.65 log(10) CFU. In contrast to the case for the smooth virulent strain 2308, in the rough attenuated strain RB51 disruption of the 14-kDa protein's gene had no effect on the mouse clearance pattern. These findings indicate that the 14-kDa protein of B. abortus possesses lectin-like properties and is essential for the virulence of the species, probably because of its direct or indirect role in the synthesis of smooth LPS.

Epitope of the vaccine-type Bordetella pertussis strain 186 lipooligosaccharide and antiendotoxin activity of antibodies directed against the terminal pentasaccharide-tetanus toxoid conjugate

Lipooligosaccharides (LOS) isolated from Bordetella pertussis strains 186 and 606 were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-resolution magic angle spinning nuclear magnetic resonance (NMR). These analyses distinguished between the LOS of strains 186 and 606, suggesting that the structure of LOS in B. pertussis is heterogeneous. The pentasaccharide was selectively cleaved from LOS of B. pertussis strain 186, purified, and covalently linked to a monomer fraction of tetanus toxoid. Injection of rabbits with the neoglycoconjugate emulsified in complete Freund's adjuvant yielded immunoglobulin G antibodies that were reactive with the LOS. These antibodies reacted strongly with B. pertussis LOS possessing the complete dodecasaccharide, as determined by an enzyme-linked immunosorbent assay, immunoblotting, and flow cytometry with intact, live bacterial cells. The binding epitope within the pentasaccharide was investigated by saturation transfer difference (STD) NMR spectroscopy. Protons H-1 and H-4 of the terminal alpha-D-GlcpNAc and proton H-6 and protons of an N-methyl group at H-4 of 3-substituted beta-L-FucpNAc4NMe exhibited the largest saturation transfers. STD NMR experiments confirmed that the immunodominant epitope recognized by the antineoglycoconjugate antibodies is located predominantly in the distal trisaccharide of B. pertussis 186 LOS. The antipentasaccharide antibodies induced by the conjugate inhibited the secretion of tumor necrosis factor alpha, interleukin-6, and NO by LOS-stimulated J774A.1 cells.

Adenylate cyclase toxin (ACT) from Bordetella hinzii: characterization and differences from ACT of Bordetella pertussis

Bordetella hinzii is a commensal respiratory microorganism in poultry but is increasingly being recognized as an opportunistic pathogen in immunocompromised humans. Although associated with a variety of disease states, practically nothing is known about the mechanisms employed by this bacterium. In this study, we show by DNA sequencing and reverse transcription-PCR that both commensal and clinical strains of B. hinzii possess and transcriptionally express cyaA, the gene encoding adenylate cyclase toxin (ACT) in other pathogenic Bordetella species. By Western blotting, we also found that B. hinzii produces full-length ACT protein in quantities that are comparable to those made by B. pertussis. In contrast to B. pertussis ACT, however, ACT from B. hinzii is less extractable from whole bacteria, nonhemolytic, has a 50-fold reduction in adenylate cyclase activity, and is unable to elevate cyclic AMP levels in host macrophages (nontoxic). The decrease in enzymatic activity is attributable, at least in part, to a decreased binding affinity of B. hinzii ACT for calmodulin, the eukaryotic activator of B. pertussis ACT. In addition, we demonstrate that the lack of intoxication by B. hinzii ACT may be due to the absence of expression of cyaC, the gene encoding the accessory protein required for the acylation of B. pertussis ACT. These results demonstrate the expression of ACT by B. hinzii and represent the first characterization of a potential virulence factor of this organism.

Pathogen adaptation under imperfect vaccination: implications for pertussis

Mass vaccination campaigns have drastically reduced the burden of infectious diseases. Unfortunately, in recent years several infectious diseases have re-emerged. Pertussis poses a well-known example. Inspired by pertussis, we study, by means of an epidemic model, the population and evolutionary dynamics of a pathogen population under the pressure of vaccination. A distinction is made between infection in immunologically naive individuals (primary infection) and infection in individuals whose immune system has been primed by vaccination or infection (secondary infection). The results show that (i) vaccination with an imperfect vaccine may not succeed in reducing the infection pressure if the transmissibility of secondary infections is higher than that of primary infections; (ii) pathogen strains that are able to evade the immunity induced by vaccination can only spread if escape mutants incur no or only a modest fitness cost and (iii) the direction of evolution depends crucially on the distribution of the different types of susceptibles in the population. We discuss the implications of these results for the design and use of vaccines that provide temporary immunity.

Type III secretion: more systems than you think

The type III secretion (T3S) pathway allows bacteria to inject effector proteins into the cytosol of target animal or plant cells. T3S systems evolved into seven families that were distributed among Gram-negative bacteria by horizontal gene transfer. There are probably a few hundred effectors interfering with control and signaling in eukaryotic cells and offering a wealth of new tools to cell biologists.

Strain variation among Bordetella pertussis isolates in finland, where the whole-cell pertussis vaccine has been used for 50 years

Pertussis is an infectious disease of the respiratory tract caused by Bordetella pertussis. Despite the introduction of mass vaccination against pertussis in Finland in 1952, pertussis has remained an endemic disease with regular epidemics. To monitor changes in the Finnish B. pertussis population, 101 isolates selected from 1991 to 2003 and 21 isolates selected from 1953 to 1982 were studied together with two Finnish vaccine strains. The analyses included serotyping of fimbriae (Fim), genotyping of the pertussis toxin S1 subunit (ptxA) and pertactin (prn), and pulsed-field gel electrophoresis (PFGE) after digestion of B. pertussis genomic DNA with XbaI restriction enzyme. Strains isolated before 1977 were found to harbor the same ptxA as the strains used in the Finnish whole-cell pertussis vaccine, and strains isolated before 1982 harbored the same prn as the strains used in the Finnish whole-cell pertussis vaccine. All recent isolates, however, represented genotypes distinct from those of the two vaccine strains. A marked shift of predominant serotype from Fim serotype 2 (Fim2) to Fim3 has been observed since the late 1990s. Temporal changes were seen in the genome of B. pertussis by PFGE analysis. Three PFGE profiles (BpSR1, BpSR11, and BpSR147) were distinguished by their prevalence between 1991 and 2003. The yearly emergence of the three profiles was distributed periodically. Our study stresses the importance of the continuous monitoring of emerging strains of B. pertussis and the need to obtain a better understanding of the relationship of the evolution of B. pertussis in vaccinated populations.

Adhesins and invasins of pathogenic bacteria: a structural view

Adhesion and invasion of pathogenic bacteria represent the important initial step of infection. Pathogens utilize surface-located adhesins/invasins for specific interaction with host cell receptors. The three-dimensional structures of a number of adhesins/invasins show that many are elongated molecules containing domains commonly found in eukaryotic proteins. Similar folds are employed repeatedly to target different receptors.