Tracheal colonization factor: a Bordetella pertussis secreted virulence determinant

Cyclic di-GMP Regulates the Type III Secretion System and Virulence in Bordetella bronchiseptica

The second messenger cyclic di-GMP (c-di-GMP) is a ubiquitous molecule in bacteria that regulates diverse phenotypes. Among them, motility and biofilm formation are the most studied. Furthermore, c-di-GMP has been suggested to regulate virulence factors, making it important for pathogenesis. Previously, we reported that c-di-GMP regulates biofilm formation and swimming motility in Bordetella bronchiseptica. Here, we present a multi-omics approach for the study of B. bronchiseptica strains expressing different cytoplasmic c-di-GMP levels, including transcriptome sequencing (RNA-seq) and shotgun proteomics with label-free quantification. We detected 64 proteins significantly up- or downregulated in either low or high c-di-GMP levels and 358 genes differentially expressed between strains with high c-di-GMP levels and the wild-type strain. Among them, we found genes for stress-related proteins, genes for nitrogen metabolism enzymes, phage-related genes, and virulence factor genes. Interestingly, we observed that a virulence factor like the type III secretion system (TTSS) was regulated by c-di-GMP. B. bronchiseptica with high c-di-GMP levels showed significantly lower levels of TTSS components like Bsp22, BopN, and Bcr4. These findings were confirmed by independent methods, such as quantitative reverse transcription-PCR (q-RT-PCR) and Western blotting. Higher intracellular levels of c-di-GMP correlated with an impaired capacity to induce cytotoxicity in a eukaryotic cell in vitro and with attenuated virulence in a murine model. This work presents data that support the role that the second messenger c-di-GMP plays in the pathogenesis of Bordetella.

Pathogenicity and virulence of Bordetella pertussis and its adaptation to its strictly human host

The highly contagious whooping cough agent Bordetella pertussis has evolved as a human-restricted pathogen from a progenitor which also gave rise to Bordetella parapertussis and Bordetella bronchiseptica. While the latter colonizes a broad range of mammals and is able to survive in the environment, B. pertussis has lost its ability to survive outside its host through massive genome decay. Instead, it has become a highly successful human pathogen by the acquisition of tightly regulated virulence factors and evolutionary adaptation of its metabolism to its particular niche. By the deployment of an arsenal of highly sophisticated virulence factors it overcomes many of the innate immune defenses. It also interferes with vaccine-induced adaptive immunity by various mechanisms. Here, we review data from invitro, human and animal models to illustrate the mechanisms of adaptation to the human respiratory tract and provide evidence of ongoing evolutionary adaptation as a highly successful human pathogen.

RNase III and RNase E Influence Posttranscriptional Regulatory Networks Involved in Virulence Factor Production, Metabolism, and Regulatory RNA Processing in Bordetella pertussis

Bordetella pertussis has been shown to encode regulatory RNAs, yet the posttranscriptional regulatory circuits on which they act remain to be fully elucidated. We generated mutants lacking the endonucleases RNase III and RNase E and assessed their individual impact on the B. pertussis transcriptome. Transcriptome sequencing (RNA-Seq) analysis showed differential expression of ∼25% of the B. pertussis transcriptome in each mutant, with only 28% overlap between data sets. Both endonucleases exhibited substantial impact on genes involved in amino acid uptake (e.g., ABC transporters) and in virulence (e.g., the type III secretion system and the autotransporters vag8, tcfA, and brkA). Interestingly, mutations in RNase III and RNase E drove the stability of many transcripts, including those involved in virulence, in opposite directions, a result that was validated by qPCR and immunoblotting for tcfA and brkA. Of note, whereas similar mutations to RNase E in Escherichia coli have subtle effects on transcript stability, a striking >20-fold reduction in four gene transcripts, including tcfA and vag8, was observed in B. pertussis. We further compared our data set to the regulon controlled by the RNA chaperone Hfq to identify B. pertussis loci influenced by regulatory RNAs. This analysis identified ∼120 genes and 19 operons potentially regulated at the posttranscriptional level. Thus, our findings revealed how changes in RNase III- and RNase E-mediated RNA turnover influence pathways associated with virulence and cellular homeostasis. Moreover, we highlighted loci potentially influenced by regulatory RNAs, providing insights into the posttranscriptional regulatory networks involved in fine-tuning B. pertussis gene expression. IMPORTANCE Noncoding, regulatory RNAs in bacterial pathogens are critical components required for rapid changes in gene expression profiles. However, little is known about the role of regulatory RNAs in the growth and pathogenesis of Bordetella pertussis. To address this, mutants separately lacking ribonucleases central to regulatory RNA processing, RNase III and RNase E, were analyzed by RNA-Seq. Here, we detail the first transcriptomic analysis of the impact of altered RNA degradation in B. pertussis. Each mutant showed approximately 1,000 differentially expressed genes, with significant changes in the expression of pathways associated with metabolism, bacterial secretion, and virulence factor production. Our analysis suggests an important role for these ribonucleases during host colonization and provides insights into the breadth of posttranscriptional regulation in B. pertussis, further informing our understanding of B. pertussis pathogenesis.

Tracheal colonization factor A (TcfA) is a biomarker for rapid and specific detection of Bordetella pertussis

Pertussis is a highly contagious disease for which prompt, point-of-care diagnosis remains an unmet clinical need. Results from conventional test modalities (nucleic acid detection, serology, and culture) take hours to days. To overcome this challenge, we identified a new biomarker (tracheal colonization factor A, TcfA) for detection of Bordetella pertussis infection by lateral flow immunoassay (LFIA). We developed a library of 28 epitope-mapped monoclonal antibodies against TcfA and incorporated three antibodies into a LFIA. The LFIA did not cross-react with common bacterial or fungal organisms, but did react with nine distinct B. pertussis strains. The minimal linear epitope sequences targeted by the LFIA were conserved in 98% of 954 B. pertussis isolates collected across 12 countries from 1949–2017. The LFIA’s limit of detection was 3.0 × 10⁵ CFU/mL with B. pertussis cells in buffer, 6.2 × 10⁵ CFU/mL with nasopharyngeal washes from a non-human primate model, and 2.3 ng/mL with recombinant TcfA. The LFIA reacted with patient nasopharyngeal swab specimens containing as few as 1.8 × 10⁶B. pertussis genomes/mL and showed no false-positives. Rapid (< 20 min) LFIA detection of TcfA as a biomarker for B. pertussis infection is feasible and may facilitate early detection of pertussis.

Acellular Pertussis Vaccines Induce Anti-pertactin Bactericidal Antibodies Which Drives the Emergence of Pertactin-Negative Strains

Despite high vaccination coverage, Bordetella pertussis the causative agent of whooping cough is still a health concern worldwide. A resurgence of pertussis cases has been reported, particularly in countries using acellular vaccines with waning immunity and pathogen adaptation thought to be responsible. A better understanding of protective immune responses is needed for the development of improved vaccines. In our study, B. pertussis strain B1917 variants presenting a single gene deletion were generated to analyze the role of vaccine components or candidate vaccine antigens as targets for bactericidal antibodies generated after acellular vaccination or natural infection. Our results show that acellular vaccination generates bactericidal antibodies that are only directed against pertactin. Serum bactericidal assay performed with convalescent samples show that disease induces bactericidal antibodies against Prn but against other antigen(s) as well. Four candidate vaccine antigens (CyaA, Vag8, BrkA, and TcfA) have been studied but were not targets for complement-mediated bactericidal antibodies after natural infection. We confirm that Vag8 and BrkA are involved in complement resistance and would be targeted by blocking antibodies. Our study suggests that the emergence and the widespread circulation of Prn-deficient strains is driven by acellular vaccination and the generation of bactericidal antibodies targeting Prn.

Bordetella pertussis Acetylome is Shaped by Lysine Deacetylase Bkd1

Post-translational modifications of proteins enable swift physiological adaptation of cells to altered growth conditions and stress. Aside from protein phosphorylation, acetylation on ε-amino groups of lysine residues (N-ε-lysine acetylation) represents another important post-translational modification of proteins. For many bacterial pathogens, including the whooping cough agent Bordetella pertussis, the role and extent of protein acetylation remain to be defined. We expressed in Escherichia coli the BP0960 and BP3063 genes encoding two putative deacetylases of B. pertussis and show that BP0960 encodes a lysine deacetylase enzyme, named Bkd1, that regulates acetylation of a range of B. pertussis proteins. Comparison of the proteome and acetylome of a Δbkd1 mutant with the proteome and acetylome of wild-type B. pertussis (PRIDE ID. PXD016384) revealed that acetylation on lysine residues may modulate activities or stabilities of proteins involved in bacterial metabolism and histone-like proteins. However, increased acetylation of the BvgA response regulator protein of the B. pertussis master virulence-regulating BvgAS two-component system affected neither the total levels of produced BvgA nor its phosphorylation status. Indeed, the Δbkd1 mutant was not impaired in the production of key virulence factors and its survival within human macrophages in vitro was not affected. The Δbkd1 mutant exhibited an increased growth rate under carbon source-limiting conditions and its virulence in the in vivo mouse lung infection model was somewhat affected. These results indicate that the lysine deacetylase Bkd1 and N-ε-lysine acetylation primarily modulate the general metabolism rather than the virulence of B. pertussis.

Outer Membrane Vesicles (OMV)-based and Proteomics-driven Antigen Selection Identifies Novel Factors Contributing to Bordetella pertussis Adhesion to Epithelial Cells

Despite high vaccination coverage world-wide, whooping cough, a highly contagious disease caused by Bordetella pertussis, is recently increasing in occurrence suggesting that novel vaccine formulations targeted at the prevention of colonization and transmission should be investigated. To identify new candidates for inclusion in the acellular formulation, we used spontaneously released outer membrane vesicles (OMV)1 as a potential source of key adhesins. The enrichment of Bvg+ OMV with adhesins and the ability of anti-OMV serum to inhibit the adhesion of B. pertussis to lung epithelial cells in vitro were demonstrated. We employed a proteomic approach to identify the differentially expressed proteins in OMV purified from bacteria in the Bvg+ and Bvg- virulence phases, thus comparing the outer membrane protein pattern of this pathogen in its virulent or avirulent state. Six of the most abundant outer membrane proteins were selected as candidates to be evaluated for their adhesive properties and vaccine potential. We generated E. coli strains singularly expressing the selected proteins and assessed their ability to adhere to lung epithelial cells in vitro Four out of the selected proteins conferred adhesive ability to E. coli Three of the candidates were specifically detected by anti-OMV mouse serum suggesting that these proteins are immunogenic antigens able to elicit an antibody response when displayed on the OMV. Anti-OMV serum was able to inhibit only BrkA-expressing E. coli adhesion to lung epithelial cells. Finally, stand-alone immunization of mice with recombinant BrkA resulted in significant protection against infection of the lower respiratory tract after challenge with B. pertussis Taken together, these data support the inclusion of BrkA and possibly further adhesins to the current acellular pertussis vaccines to improve the impact of vaccination on the bacterial clearance.

Bordetella Pertussis virulence factors in the continuing evolution of whooping cough vaccines for improved performance

Despite high vaccine coverage, whooping cough caused by Bordetella pertussis remains one of the most common vaccine-preventable diseases worldwide. Introduction of whole-cell pertussis (wP) vaccines in the 1940s and acellular pertussis (aP) vaccines in 1990s reduced the mortality due to pertussis. Despite induction of both antibody and cell-mediated immune (CMI) responses by aP and wP vaccines, there has been resurgence of pertussis in many countries in recent years. Possible reasons hypothesised for resurgence have ranged from incompliance with the recommended vaccination programmes with the currently used aP vaccine to infection with a resurged clinical isolates characterised by mutations in the virulence factors, resulting in antigenic divergence with vaccine strain, and increased production of pertussis toxin, resulting in dampening of immune responses. While use of these vaccines provide varying degrees of protection against whooping cough, protection against infection and transmission appears to be less effective, warranting continuation of efforts in the development of an improved pertussis vaccine formulations capable of achieving this objective. Major approaches currently under evaluation for the development of an improved pertussis vaccine include identification of novel biofilm-associated antigens for incorporation in current aP vaccine formulations, development of live attenuated vaccines and discovery of novel non-toxic adjuvants capable of inducing both antibody and CMI. In this review, the potential roles of different accredited virulence factors, including novel biofilm-associated antigens, of B. pertussis in the evolution, formulation and delivery of improved pertussis vaccines, with potential to block the transmission of whooping cough in the community, are discussed.

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Immunoproteomic Profiling of Bordetella pertussis Outer Membrane Vesicle Vaccine Reveals Broad and Balanced Humoral Immunogenicity

The current resurgence of whooping cough is alarming, and improved pertussis vaccines are thought to offer a solution. Outer membrane vesicle vaccines (omvPV) are potential vaccine candidates, but omvPV-induced humoral responses have not yet been characterized in detail. The purpose of this study was to determine the antigen composition of omvPV and to elucidate the immunogenicity of the individual antigens. Quantitative proteome analysis revealed the complex composition of omvPV. The omvPV immunogenicity profile in mice was compared to those of classic whole cell vaccine (wPV), acellular vaccine (aPV), and pertussis infection. Pertussis-specific antibody levels, antibody isotypes, IgG subclasses, and antigen specificity were determined after vaccination or infection by using a combination of multiplex immunoassays, two-dimensional immunoblotting, and mass spectrometry. The vaccines and infection raised strong antibody responses, but large quantitative and qualitative differences were measured. The highest antibody levels were obtained by omvPV. All IgG subclasses (IgG1/IgG2a/IgG2b/IgG3) were elicited by omvPV and in a lower magnitude by wPV, but not by aPV (IgG1) or infection (IgG2a/b). The majority of omvPV-induced antibodies were directed against Vag8, BrkA, and LPS. The broad and balanced humoral response makes omvPV a promising pertussis vaccine candidate.

Structural and functional studies of BapC protein of Bordetella pertussis

Bordetella pertussis, the causative agent of whooping cough, attaches to mucosal surface in upper respiratory tract, where it produces a variety of surface associated and secreted autotransporter molecules among others. In this study we have cloned newly identified member of autotransporter family BapC (B. pertussis autotransporter protein C); expressed it in Escherichia coli and characterized it for its different properties. We have also raised antisera to BapC protein; the antisera were used in immunofluorescence assay to determine the surface association of the protein. Results suggest that BapC in B. pertussis Taberman parent is surface exposed when compared with the respective BapC mutant. The neutralizing effect of anti-BapC serum was also evaluated in the presence of active complement proteins and results suggest that antiserum can potentiate the killing of B. pertussis cells in the presence of added source of complement. Structure of the protein was also studied, both α and β domains of the protein were modeled, β domain exhibits typical transmembrane β-barrel porin topology whereas α domain behaves as a characteristic bacterial autotransporter passenger domain.

Pathogenesis and histopathology of pertussis: implications for immunization

Pertussis is a unique infectious disease in that it can be severe and fatal but occurs without fever and other evidence of an inflammatory illness. The authors with others have studied the histopathology of fatal pertussis and also the unique characteristics of severe pertussis in young infants. Histopathologic observations from approximately 100 years ago, and from recent evaluation, indicate that the histopathologic changes of the upper respiratory tract of patients with fatal pertussis are often relatively normal unless there is a secondary bacterial infection. Bordetella pertussis contains many protein antigens and perhaps a polysaccharide capsule which contribute to the infectious process. However, only two of these antigens contribute to clinical illness. These antigens are pertussis toxin and the yet to be identified 'cough toxin'. The authors speculate as to the nature of the 'cough toxin' and discuss the implications of their observations and concepts for the future control of pertussis.

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.

Bordetella pertussis pathogenesis: current and future challenges

Pertussis, also known as whooping cough, has recently re-emerged as a major public health threat despite high levels of vaccination against the aetiological agent Bordetella pertussis. In this Review, we describe the pathogenesis of this disease, with a focus on recent mechanistic insights into B. pertussis virulence-factor function. We also discuss the changing epidemiology of pertussis and the challenges facing vaccine development. Despite decades of research, many aspects of B. pertussis physiology and pathogenesis remain poorly understood. We highlight knowledge gaps that must be addressed to develop improved vaccines and therapeutic strategies.

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.

A Type VI secretion system encoding locus is required for Bordetella bronchiseptica immunomodulation and persistence in vivo

Type VI Secretion Systems (T6SSs) have been identified in numerous Gram-negative pathogens, but the lack of a natural host infection model has limited analysis of T6SS contributions to infection and pathogenesis. Here, we describe disruption of a gene within locus encoding a putative T6SS in Bordetella bronchiseptica strain RB50, a respiratory pathogen that circulates in a broad range of mammals, including humans, domestic animals, and mice. The 26 gene locus encoding the B. bronchiseptica T6SS contains apparent orthologs to all known core genes and possesses thirteen novel genes. By generating an in frame deletion of clpV, which encodes a putative ATPase required for some T6SS-dependent protein secretion, we observe that ClpV contributes to in vitro macrophage cytotoxicity while inducing several eukaryotic proteins associated with apoptosis. Additionally, ClpV is required for induction of IL-1β, IL-6, IL-17, and IL-10 production in J774 macrophages infected with RB50. During infections in wild type mice, we determined that ClpV contributes to altered cytokine production, increased pathology, delayed lower respiratory tract clearance, and long term nasal cavity persistence. Together, these results reveal a natural host infection system in which to interrogate T6SS contributions to immunomodulation and pathogenesis.

Identification of Ata, a multifunctional trimeric autotransporter of Acinetobacter baumannii

Acinetobacter baumannii has recently emerged as a highly troublesome nosocomial pathogen, especially in patients in intensive care units and in those undergoing mechanical ventilation. We have identified a surface protein adhesin of A. baumannii, designated the Acinetobacter trimeric autotransporter (Ata), that contains all of the typical features of trimeric autotransporters (TA), including a long signal peptide followed by an N-terminal, surface-exposed passenger domain and a C-terminal domain encoding 4 β-strands. To demonstrate that Ata encoded a TA, we created a fusion protein in which we replaced the entire passenger domain of Ata with the epitope tag V5, which can be tracked with specific monoclonal antibodies, and demonstrated that the C-terminal 101 amino acids of Ata were capable of exporting the heterologous V5 tag to the surface of A. baumannii in a trimeric form. We found that Ata played a role in biofilm formation and bound to various extracellular matrix/basal membrane (ECM/BM) components, including collagen types I, III, IV, and V and laminin. Moreover, Ata mediated the adhesion of whole A. baumannii cells to immobilized collagen type IV and played a role in the survival of A. baumannii in a lethal model of systemic infection in immunocompetent mice. Taken together, these results reveal that Ata is a TA of A. baumannii involved in virulence, including biofilm formation, binding to ECM/BM proteins, mediating the adhesion of A. baumannii cells to collagen type IV, and contributing to the survival of A. baumannii in a mouse model of lethal infection.

BapC autotransporter protein is a virulence determinant of Bordetella pertussis

A protein designated Bap-5 (GenBank accession no. AF081494) or BapC (GenBank accession no. AJ277634) has been identified as a member of the Bordetella pertussis autotransporter family and the present work suggests that this protein, like the previously characterised BrkA, is a Bvg-regulated serum resistance factor and virulence determinant. B. pertussis bapC and brkA, bapC mutants were created and, like a brkA mutant, showed greater sensitivity to killing by normal human serum than their parent strains but they were not as sensitive as a bvg mutant. Competition assays also showed an important role for BapC, like BrkA, in virulence of B. pertussis in mice after intranasal infection. Moreover, the bapC and brkA, bapC mutants, like the brkA mutant, were found to be more sensitive to the antimicrobial peptide cecropin P1 than the parent strains. In the genome sequence of B. pertussis strain Tohama, bapC is designated as a pseudogene due, in part, to a frameshift in a poly(C) tract near the 5' end of the gene which creates a truncated BapC protein. Sequence analyses of the bapC region spanning the poly(C) tract of a number of B. pertussis strains showed minor nucleotide and amino acid polymorphisms but it appeared that all had an ORF that would be able to produce BapC.

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.

Virulence factor secretion and translocation by Bordetella species

Here we review the Bordetella virulence secretome with an emphasis on factors that translocate into target cells. Recent advances in understanding the functions of adenylate cyclase toxin, a type 1 secretion system (T1SS) substrate, and pertussis toxin, a type IV secretion system (T4SS) substrate, are briefly described and a compilation of additional secretion systems and secreted factors is provided. Particular attention is devoted to the Bsc type III secretion system (T3SS) and controversies surrounding it. Efforts to identify effector proteins, characterize in vitro and in vivo phenotypes, and the potential role of type III secretion during human infections are discussed.

Serendipitous discovery of an immunoglobulin-binding autotransporter in Bordetella species

We describe the serendipitous discovery of BatB, a classical-type Bordetella autotransporter (AT) protein with an approximately 180-kDa passenger domain that remains noncovalently associated with the outer membrane. Like genes encoding all characterized protein virulence factors in Bordetella species, batB transcription is positively regulated by the master virulence regulatory system BvgAS. BatB is predicted to share similarity with immunoglobulin A (IgA) proteases, and we showed that BatB binds Ig in vitro. In vivo, a Bordetella bronchiseptica DeltabatB mutant was unable to overcome innate immune defenses and was cleared from the lower respiratory tracts of mice more rapidly than wild-type B. bronchiseptica. This defect was abrogated in SCID mice, suggesting that BatB functions to resist clearance during the first week postinoculation in a manner dependent on B- and T-cell-mediated activities. Taken together with the previous demonstration that polymorphonuclear neutrophils (PMN) are critical for the control of B. bronchiseptica in mice, our data support the hypothesis that BatB prevents nonspecific antibodies from facilitating PMN-mediated clearance during the first few days postinoculation. Neither of the strictly human-adapted Bordetella subspecies produces a fully functional BatB protein; nucleotide differences within the putative promoter region prevent batB transcription in Bordetella pertussis, and although expressed, the batB gene of human-derived Bordetella parapertussis (B. parapertussis(hu)) contains a large in-frame deletion relative to batB of B. bronchiseptica. Taken together, our data suggest that BatB played an important role in the evolution of virulence and host specificity among the mammalian-adapted bordetellae.

Bordetella pertussis expresses a functional type III secretion system that subverts protective innate and adaptive immune responses

Certain bacteria use a type III secretion system (TTSS) to deliver effector proteins that interfere with cell function into host cells. While transcription of genes encoding TTSS components has been demonstrated, studies to date have failed to identify TTSS effector proteins in Bordetella pertussis. Here we present the first evidence of a functionally active TTSS in B. pertussis. Three known TTSS effectors, Bsp22, BopN, and BopD, were identified as TTSS substrates in B. pertussis 12743. We found expression of Bsp22 in a significant proportion of clinical isolates but not in common laboratory-adapted strains of B. pertussis. We generated a TTSS mutant of B. pertussis 12743 and showed that it induced significantly lower respiratory tract colonization in mice than the wild-type bacteria. Respiratory infection of mice with the mutant bacteria induced significantly greater innate proinflammatory cytokine production in the lungs soon after challenge, and this correlated with significantly higher antigen-specific interleukin-17, gamma interferon, and immunoglobulin G responses later in infection. Our findings suggest that the TTSS subverts innate and adaptive immune responses during infection of the lungs and may be a functionally important virulence factor for B. pertussis infection of humans.

Phase variation and microevolution at homopolymeric tracts in Bordetella pertussis

BACKGROUND

Bordetella pertussis, the causative agent of whooping cough, is a highly clonal pathogen of the respiratory tract. Its lack of genetic diversity, relative to many bacterial pathogens, could limit its ability to adapt to a hostile and changing host environment. This limitation might be overcome by phase variation, as observed for other mucosal pathogens. One of the most common mechanisms of phase variation is reversible expansion or contraction of homopolymeric tracts (HPTs).

RESULTS

The genomes of B. pertussis and the two closely related species, B. bronchiseptica and B. parapertussis, were screened for homopolymeric tracts longer than expected on the basis of chance, given their nucleotide compositions. Sixty-nine such HPTs were found in total among the three genomes, 74% of which were polymorphic among the three species. Nine HPTs were genotyped in a collection of 90 geographically and temporally diverse B. pertussis strains using the polymerase chain reaction/ligase detection reaction (PCR/LDR) assay. Six HPTs were polymorphic in this collection of B. pertussis strains. Of note, one of these polymorphic HPTs was found in the fimX promoter, where a single base insertion variant was present in seven strains, all of which were isolated prior to introduction of the pertussis vaccine. Transcript abundance of fimX was found to be 3.8-fold lower in strains carrying the longer allele. HPTs in three other genes, tcfA, bapC, and BP3651, varied widely in composition across the strain collection and displayed allelic polymorphism within single cultures.

CONCLUSION

Allelic polymorphism at homopolymeric tracts is common within the B. pertussis genome. Phase variability may be an important mechanism in B. pertussis for evasion of the immune system and adaptation to different niches in the human host. High sensitivity and specificity make the PCR/LDR assay a powerful tool for investigating allelic variation at HPTs. Using this method, allelic diversity and phase variation were demonstrated at several B. pertussis loci.

Changes of the Swedish Bordetella pertussis population in incidence peaks during an acellular pertussis vaccine period between 1997 and 2004

In a surveillance programme undertaken from 1997 through 2004, Bordetella pertussis isolates and clinical information were collected after introduction of acellular pertussis vaccines (Pa) in 1996. Changes in the B. pertussis population were studied in three incidence peaks: 1999-2000, 2002 and 2004. Available isolates from 158 fully vaccinated children representing all of Sweden, plus 37 from the Gothenburg area 2003-2004, were analysed by pulsed-field gel electrophoresis (PFGE), serotyping and sequencing of the virulence factor genes pertussis toxin subunits 1 and 3 (ptxA, ptxC), pertactin (prn), tracheal colonisation factor (tcfA) and fimbria3 (fim3). Allele ptxA1 was found in all isolates. There was a statistically significant increasing trend in three out of five studied genes, ptxC, prn and tcfA, and for a fourth, Fim3, if Gothenburg strains were included. The PFGE profile BpSR11 appearing in the 1999-2000 peak dominated by >or=23% during the entire period, bringing with it the allele combination 1/2/2/2/B (ptxA1/ptxC2/prn2/tcfA2/fim3B). Other BpSR11-related profiles with the same allele combination and more than 82% similarity--BpSR5 in the 2002 peak and BpSR12 in the 2004 peak--appeared with an increasing trend. Although vaccination with Pa has reduced disease, new variants have emerged representing clones surviving in the immunized population.

Adhesion mediated by autotransporters of Gram-negative bacteria: Structural and functional features

The ability of bacterial proteins to promote adhesion to biological surfaces is a fundamental step in bacterial infections. Some bacterial adhesins belong to the family of autotransporters, which are secreted to the surface of Gram-negative bacteria by an elegantly simple mechanism. This review will summarize their functional and structural features.

Legal and policy lessons from the Schiavo case: Is our right to choose the medical care we want seriously at risk?

The article explores the individual patient's right to refuse, withdraw, or insist on medical treatment where there is conflict over these issues involving health care personnel or institutions, family members, legal requirements, or third parties concerned with public policy or religious/ideological/political interests. Issues of physician assistance in dying and medical futility are considered. The basis and the current legal status of these rights is examined, and it is concluded that threats to the autonomy of patients, to the privacy of the doctor/patient relationship, and to the quality of medical care should be taken seriously by individuals, medical practitioners, and others concerned with developing and maintaining reasonable, effective, and ethical health care policy.

Bordetella pertussis, the causative agent of whooping cough, evolved from a distinct, human-associated lineage of B. bronchiseptica

Bordetella pertussis, B. bronchiseptica, B. parapertussis(hu), and B. parapertussis(ov) are closely related respiratory pathogens that infect mammalian species. B. pertussis and B. parapertussis(hu) are exclusively human pathogens and cause whooping cough, or pertussis, a disease that has resurged despite vaccination. Although it most often infects animals, infrequently B. bronchiseptica is isolated from humans, and these infections are thought to be zoonotic. B. pertussis and B. parapertussis(hu) are assumed to have evolved from a B. bronchiseptica-like ancestor independently. To determine the phylogenetic relationships among these species, housekeeping and virulence genes were sequenced, comparative genomic hybridizations were performed using DNA microarrays, and the distribution of insertion sequence elements was determined, using a collection of 132 strains. This multifaceted approach distinguished four complexes, representing B. pertussis, B. parapertussis(hu), and two distinct B. bronchiseptica subpopulations, designated complexes I and IV. Of the two B. bronchiseptica complexes, complex IV was more closely related to B. pertussis. Of interest, while only 32% of the complex I strains were isolated from humans, 80% of the complex IV strains were human isolates. Comparative genomic hybridization analysis identified the absence of the pertussis toxin locus and dermonecrotic toxin gene, as well as a polymorphic lipopolysaccharide biosynthesis locus, as associated with adaptation of complex IV strains to the human host. Lipopolysaccharide structural diversity among these strains was confirmed by gel electrophoresis. Thus, complex IV strains may comprise a human-associated lineage of B. bronchiseptica from which B. pertussis evolved. These findings will facilitate the study of pathogen host-adaptation. Our results shed light on the origins of the disease pertussis and suggest that the association of B. pertussis with humans may be more ancient than previously assumed.

Phg, a novel member of the autotransporter family present in Bordetella species

Several proteins encoded in the genomes of Bordetella species show significant sequence similarity to the autotransporter domains of surface exposed or secreted virulence factors of bordetellae such as pertactin, tracheal colonization factor or Vag8. One of these putative autotransporters, provisionally termed Phg, is encoded by the pertactin homologous gene (phg), which is highly conserved in Bordetella pertussis, B. bronchiseptica and B. parapertussis, but absent in B. avium and B. petrii. In contrast to homologues with documented functions in host interaction and virulence, several key amino acids probably involved in proteolytic processing of the autotransporter domain are not conserved in Phg. The transcription start site of phg was identified by primer extension analysis, but differential transcription of phg could not be detected in B. bronchiseptica strains under conditions that lead to enhanced expression of other known Bordetella autotransporter proteins. A mutant of B. pertussis was constructed in which major parts of phg are substituted by a kanamycin resistance cassette. Virulence testing of this mutant in a mouse respiratory infection model showed the same colonization properties as the wild-type strain.

Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies

Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.

Activation of the vrg6 promoter of Bordetella pertussis by RisA

The BvgAS two-component system positively regulates the expression of the virulence genes of Bordetella pertussis and negatively regulates a second set of genes whose function is unknown. The BvgAS-mediated regulation of the bvg-repressed genes is accomplished through the activation of expression of the negative regulator, BvgR. A second two-component regulatory system, RisAS, is required for expression of the bvg-repressed surface antigens VraA and VraB. We examined the roles of BvgR and RisA in the regulation of four bvg-repressed genes in B. pertussis. Our analyses demonstrated that all four genes are repressed by the product of the bvgR locus and are activated by the product of the risA locus. Deletion analysis of the vrg6 promoter identified the upstream and downstream boundaries of the promoter and, in contrast to previously published results, demonstrated that sequences downstream of the start of transcription are not required for the regulation of expression of vrg6. Gel mobility-shift experiments demonstrated sequence-specific binding of RisA to the vrg6 and vrg18 promoters, and led to the identification of two putative RisA binding sites. Finally, transcriptional analysis and Western blot analysis demonstrated that BvgR regulates neither the expression nor the stability of RisA.

Type V protein secretion pathway: the autotransporter story

Gram-negative bacteria possess an outer membrane layer which constrains uptake and secretion of solutes and polypeptides. To overcome this barrier, bacteria have developed several systems for protein secretion. The type V secretion pathway encompasses the autotransporter proteins, the two-partner secretion system, and the recently described type Vc or AT-2 family of proteins. Since its discovery in the late 1980s, this family of secreted proteins has expanded continuously, due largely to the advent of the genomic age, to become the largest group of secreted proteins in gram-negative bacteria. Several of these proteins play essential roles in the pathogenesis of bacterial infections and have been characterized in detail, demonstrating a diverse array of function including the ability to condense host cell actin and to modulate apoptosis. However, most of the autotransporter proteins remain to be characterized. In light of new discoveries and controversies in this research field, this review considers the autotransporter secretion process in the context of the more general field of bacterial protein translocation and exoprotein function.

Cloning, overexpression, and characterization of a serine/threonine protein kinase pknI from Mycobacterium tuberculosis H37Rv

Protein phosphorylation-dephosphorylation is the principal mechanism for translation of external signals into cellular responses. Eukaryotic-like serine/threonine kinases have been reported to play important roles in bacterial development and/or virulence. The PknI protein is one of the 11 eukaryotic-like serine/threonine kinases in Mycobacterium tuberculosis H37Rv. From the bioinformatic studies, PknI protein has been shown to have an N-terminal cytoplasmic domain followed by a transmembrane region and an extracellular C-terminus suggestive of a sensor molecule. In this study, we have cloned, overexpressed, and characterized the entire coding region and the cytoplasmic domain of PknI as a fusion protein with an N-terminal histidine tag, and used immobilized metal affinity chromatography for purification of recombinant proteins. The purified recombinant proteins were found to be functionally active through in vitro phosphorylation assay and phosphoamino acid analysis. In vitro kinase assay of both proteins revealed that PknI is capable of autophosphorylation and showed manganese-dependent activity. Phosphoamino acid analysis indicated phosphorylation at serine and threonine residues. Southern blot analysis with genomic DNA highlighted the conserved nature of pknI among the various mycobacterial species. In silico analysis revealed a close homology of PknI to Stk1 from Streptococcus agalactiae, shown to have a role in virulence and cell segregation of the organism.

Sequence variation and conservation in virulence-related genes of Bordetella pertussis isolates from the UK

To determine the value of gene markers for surveillance and to assess the genetic stability of potential acellular pertussis vaccine components, the sequence variation in ten virulence-related genes of Bordetella pertussis was investigated in strains isolated in the UK between 1920 and 2002. These genes encode: pertactin (prnA); pertussis toxin subunits S1 (ptxA) and S3 (ptxC); tracheal colonization factor (tcfA); bordetella autotransporter protein C (bapC); bordetella resistance to killing protein (brkA); fimbrial antigen 2 (fim2); outer-membrane protein Q (ompQ); virulence-activated gene 8 (vag8) and adenylate cyclase toxin (cyaA). The encoded proteins are either components of current acellular vaccines (ACVs), or potential virulence markers for B. pertussis. Three strains used in the pertussis UK whole-cell vaccine (WCV), strain Tohama-I used for production of ACV components and the type strain of B. pertussis (18323(T)) were also analysed. Several novel alleles were found. The UK isolates were assigned multi-locus sequence types (MLSTs) according to a previously described scheme for B. pertussis based on three of these genes (ptxA, ptxC and tcfA). Compared with isolates from other countries, the UK clinical strains showed a distinct distribution of MLSTs. Apart from one strain that was MLST-3, all other recent isolates (2000-2002) were identified as MLST-5. These isolates differed from the three WCV strains, which were MLST-2 or MLST-3, the Tohama-I strain (MLST-2) and the type strain of B. pertussis (MLST-9). MLST-3 and MLST-5 differ only by a single synonymous mutation, but this method does indicate that currently circulating strains of B. pertussis are not identical to the vaccine types, and they may differ in other important characteristics. Two new MLSTs were identified amongst historical UK isolates. Sequence-based typing offers a convenient method of analysing and comparing populations of B. pertussis from different time periods and from different countries. The variation exhibited by prnA and fim2 suggests that they could be useful, additional epidemiological markers in such a typing scheme.

Analysis of bvgR expression in Bordetella pertussis

Bordetella pertussis, the causative agent of whooping cough, produces a wide array of factors that are associated with its ability to cause disease. The expression and regulation of these virulence factors are dependent upon the bvg locus, which encodes three proteins: BvgA, a 23-kDa cytoplasmic protein; BvgS, a 135-kDa transmembrane protein; and BvgR, a 32-kDa protein. It is hypothesized that BvgS responds to environmental signals and interacts with BvgA, a transcriptional regulator, which upon modification by BvgS binds to specific promoters and activates transcription. An additional class of genes is repressed by the products of the bvg locus. The repression of these genes is dependent upon the third gene, bvgR. Expression of bvgR is dependent upon the function of BvgA and BvgS. This led to the hypothesis that the binding of phosphorylated BvgA to the bvgR promoter activates the expression of bvgR. We undertook an analysis of the transcriptional activation of bvgR expression. We identified the bvgR transcript by Northern blot analysis and identified the start site of transcription by primer extension. We determined that transcriptional activation of the bvgR promoter in an in vitro transcription system requires the addition of phosphorylated BvgA. Additionally, we have identified cis-acting regions that are required for BvgA activation of the bvgR promoter by in vitro footprinting and in vivo deletion and linker scanning analyses. A model of BvgA binding to the bvgR promoter is presented.

Vir90, a virulence-activated gene coding for a Bordetella pertussis iron-regulated outer membrane protein

Bordetella pertussis undergoes phenotypic changes modulated by the bvgAS locus, which regulates the expression of many genes related to virulence and immunogenicity. We previously reported the N-terminal sequence of a 90 kDa bvg-regulated outer membrane protein (OMP) of B. pertussis (SWISS-PROT accession No. p81549), a novel potential virulence factor that we named Vir90. The open reading frames (ORFs) which potentially code for Vir90 in B. pertussis, B. parapertussis and B. bronchiseptica were identified by computer analysis of the genomic sequences available for the three Bordetella species. Nucleotide sequence analysis of the vir90 upstream region revealed the presence of a putative promoter, a BvgA binding site and a putative Fur binding site. The B. pertussis Vir90 protein showed significant homology with ferrisiderophore receptors from Gram-negative bacteria. An antiserum raised against Vir90His recombinant protein recognized the 90-kDa protein in immunoblots of OMPs from these three virulent Bordetella species. The accumulation of the Vir90 protein increased 4-fold under low iron growth conditions. Therefore, the vir90 gene is expressed in the tested species and its expression is regulated positively by the BvgAS system and negatively under high iron concentration, likely by Fur.

Comparison of bipA alleles within and across Bordetella species

The Bordetella BvgAS signal transduction system controls the expression of at least three phenotypic phases, the Bvg(+) or virulent phase, the Bvg(-) or avirulent phase, and the Bvg(i) or Bvg intermediate phase, which has been hypothesized to be important for transmission. bipA, the first identified Bvg(i)-phase gene, encodes a protein with similarity to the well-characterized bacterial adhesins intimin and invasin. Proteins encoded by the bipA genes present in Bordetella pertussis Tohama I and Bordetella bronchiseptica RB50 differ in the number of 90-amino-acid repeats which they possess and in the sequence of the C-terminal domain. To investigate the possibility that bipA alleles segregate according to host specificity and to gain insight into the role of BipA and the Bvg(i) phase in the Bordetella infectious cycle, we compared bipA alleles across members of the B. bronchiseptica cluster, which includes both human-infective (B. pertussis and B. parapertussis(hu)) and non-human-infective (B. bronchiseptica and B. parapertussis(ov)) strains. bipA genes were present in most, but not all, strains. All bipA genes present in B. bronchiseptica strains were identical to bipA of RB50 (at least with regard to the DNA sequence of the 3' C-terminal-domain-encoding region, the number of 90-amino-acid repeats encoded, and expression patterns). Although all bipA genes present in the other Bordetella strains were identical in the 3' C-terminal-domain-encoding region to bipA of B. pertussis Tohama I, they varied in the number of 90-amino-acid repeats that they encoded and in expression level. Notably, the genes present in B. parapertussis(hu) strains were pseudogenes, and the genes present in B. parapertussis(ov) strains were expressed at significantly reduced levels compared with the levels in B. pertussis and B. bronchiseptica strains. Our results indicate that there is a correlation between specific bipA alleles and specific hosts. They also support the hypothesis that both horizontal gene transfer and fine-tuning of gene expression patterns contribute to the evolution of host adaptation in lineages of the B. bronchiseptica cluster.

Role of adhesin release for mucosal colonization by a bacterial pathogen

Pathogen attachment is a crucial early step in mucosal infections. This step is mediated by important virulence factors called adhesins. To exert these functions, adhesins are typically surface-exposed, although, surprisingly, some are also released into the extracellular milieu, the relevance of which has previously not been studied. To address the role of adhesin release in pathogenesis, we used Bordetella pertussis as a model, since its major adhesin, filamentous hemagglutinin (FHA), partitions between the bacterial surface and the extracellular milieu. FHA release depends on its maturation by the specific B. pertussis protease SphB1. We constructed SphB1-deficient mutants and found that they were strongly affected in their ability to colonize the mouse respiratory tract, although they adhered even better to host cells in vitro than their wild-type parent strain. The defect in colonization could be overcome by prior nasal instillation of purified FHA or by coinfection with FHA-releasing B. pertussis strains, but not with SphB1-producing FHA-deficient strains, ruling out a nonspecific effect of SphB1. These results indicate that the release of FHA is important for colonization, as it may facilitate the dispersal of bacteria from microcolonies and the binding to new sites in the respiratory tract.

A conserved region within the Bordetella pertussis autotransporter BrkA is necessary for folding of its passenger domain

Autotransporter secretion represents a unique mechanism that Gram-negative bacteria employ to deliver proteins to their cell surface. BrkA is a Bordetella pertussis autotransporter protein that mediates serum resistance and contributes to adherence of the bacterium to host cells. BrkA is a 103 kDa protein that is cleaved to form a 73 kDa alpha-domain and a 30 kDa beta domain. The alpha domain, also referred to as the passenger domain, is responsible for the effector functions of the protein, whereas the beta domain serves as a transporter. In an effort to characterize BrkA secretion, we have shown that BrkA has a 42 amino acid signal peptide for transit across the cytoplasmic membrane, and a translocation unit made up of a short linker region fused to the beta-domain to ferry the passenger domain to the bacterial surface through a channel formed by the beta-domain. In this report, we provide genetic, biochemical and structural evidence demonstrating that a region within the BrkA passenger (Glu601-Ala692) is necessary for folding the passenger. This region is not required for surface display in the outer membrane protease OmpT-deficient Escherichia coli strain UT5600. However, a BrkA mutant protein bearing a deletion in this region is susceptible to digestion when expressed in E. coli strains expressing OmpT suggesting that the region is required to maintain a stable structure. The instability of the deletion mutant can be rescued by surface expressing Glu601-Ala692in trans suggesting that this region is acting as an intramolecular chaperone to effect folding of the passenger concurrent with or following translocation across the outer membrane.

Differential regulation of the Bordetella bipA gene: distinct roles for different BvgA binding sites

The BvgAS signal transduction system of Bordetella controls an entire spectrum of gene expression states in response to differences in environmental conditions. In particular, the Bordetella Bvg-intermediate-phase gene bipA displays a complex regulatory pattern in response to various concentrations of modulators. Expression of bipA is low in the absence of modulating signals, maximal at intermediate concentrations of modulators, and near background levels at high concentrations of modulators. bipA is regulated at the transcriptional level, and the bipA promoter contains multiple BvgA binding sites present both upstream and downstream of the transcriptional initiation site. In vivo transcriptional analyses, utilizing several mutant promoter fusions to the reporter enzyme beta-galactosidase, suggest that the upstream binding site IR1 is essential for expression and that the downstream binding sites IR2 and IR3 are involved in transcriptional repression. Mutations of IR2 or IR3 convert the expression profile of bipA from that of a Bvg-intermediate-specific-phase gene to that of a Bvg(+)-phase gene. To gain insight into the mechanism responsible for differential bipA regulation, DNase I protection studies were conducted with various mutant promoters. These analyses suggest that IR1 and IR2 function as core binding sites and are the primary determinants for the phosphorylation-induced oligomerization of BvgA to the adjacent regions.

Multilocus sequence typing of Bordetella pertussis based on surface protein genes

Despite more than 50 years of vaccination, Bordetella pertussis has remained endemic in The Netherlands, causing epidemic outbreaks every 3 to 5 years. Strain variation may play a role in the persistence of B. pertussis and was studied by sequencing 15 genes coding for surface proteins, including genes for all five components of acellular pertussis vaccines: pertussis toxin (Ptx), pertactin (Prn), filamentous hemagglutinin, and fimbriae (Fim2 and Fim3). A low level of allelic variation was observed, confirming a recent evolutionary origin of B. pertussis. In modern isolates, polymorphism was observed only in prn, ptxS1, ptxS3, and tcfA. Polymorphism in ptxS1, ptxS3, and tcfA was used to categorize isolates in multilocus sequence types (MLSTs). Analysis of Dutch isolates from 1949 to 1999 revealed five MLSTs, which showed a highly dynamic temporal behavior. We observed significant changes in the MLSTs after the introduction of pertussis vaccination in The Netherlands. Epidemic years were found to be associated with the expansion of MLST-4 or MLST-5. MLST-5 showed a remarkable expansion from 10% in 1997 to 80% in 1999. The MLST analysis was extended to a number of widely separated geographic regions: Finland, Italy, Japan, and the United States. MLST-4 and MLST-5 were found to dominate in Italy and the United States. In Finland and Japan, MLST-3 and MLST-2, respectively, were predominant. Thus, although each region showed distinctive MLST frequencies, in three of the five regions MLST-4 and MLST-5 were predominant. These types may represent newly emerged, successful clones. The identification of highly successful clones may shed light on the question of how B. pertussis is able to maintain itself in vaccinated populations.

Protein-translocating outer membrane porins of Gram-negative bacteria

Five families of outer membrane porins that function in protein secretion in Gram-negative bacteria are currently recognized. In this report, these five porin families are analyzed from structural and phylogenetic standpoints. They are the fimbrial usher protein (FUP), outer membrane factor (OMF), autotransporter (AT), two-partner secretion (TPS) and outer membrane secretin (Secretin) families. All members of these families in the current databases were identified, and all full-length homologues were multiply aligned for structural and phylogenetic analyses. The organismal distribution of homologues in each family proved to be unique with some families being restricted to proteobacteria and others being widespread in other bacterial kingdoms as well as eukaryotes. The compositions of and size differences between subfamilies provide evidence for specific orthologous relationships, which agree with available functional information and intra-subfamily phylogeny. The results reveal that horizontal transfer of genes encoding these proteins between phylogenetically distant organisms has been exceptionally rare although transfer within select bacterial kingdoms may have occurred. The resultant in silico analyses are correlated with available experimental evidence to formulate models relevant to the structures and evolutionary origins of these proteins.

Characterization of Streptococcus suis genes encoding proteins homologous to sortase of gram-positive bacteria

Many surface proteins which are covalently linked to the cell wall of gram-positive bacteria have a consensus C-terminal motif, Leu-Pro-X-Thr-Gly (LPXTG). This sequence is cleaved, and the processed protein is attached to an amino group of a cross-bridge in the peptidoglycan by a specific enzyme called sortase. Using the type strain of Streptococcus suis, NCTC 10234, we found five genes encoding proteins that were homologous to sortases of other bacteria and determined the nucleotide sequences of the genetic regions. One gene, designated srtA, was linked to gyrA, as were the sortase and sortase-like genes of other streptococci. Three genes, designated srtB, srtC, and srtD, were tandemly clustered in a different location, where there were three segments of directly repeated sequences of approximately 110 bp in close vicinity. The remaining gene, designated srtE, was located separately on the chromosome with a pseudogene which may encode a transposase. The deduced amino acid sequences of the five Srt proteins showed 18 to 31% identity with the sortases of Streptococcus gordonii and Staphylococcus aureus, except that SrtA of S. suis had 65% identity with that of S. gordonii. Isogenic mutants deficient for srtA, srtBCD, or srtE were generated by allelic exchanges. The protein fraction which was released from partially purified cell walls by digestion with N-acetylmuramidase was profiled by two-dimensional gel electrophoresis. More than 15 of the protein spots were missing in the profile of the srtA mutant compared with that of the parent strain, and this phenotype was completely complemented by srtA cloned from S. suis. Four genes encoding proteins corresponding to such spots were identified and sequenced. The deduced translational products of the four genes possessed the LPXTG motif in their C-terminal regions. On the other hand, the protein spots that were missing in the srtA mutant appeared in the profiles of the srtBCD and srtE mutants. These results provide evidence that the cell wall sorting system involving srtA is also present in S. suis.

Subtilisin-like autotransporter serves as maturation protease in a bacterial secretion pathway

Proteins of Gram-negative bacteria destined to the extracellular milieu must cross the two cellular membranes and then fold at the appropriate time and place. The synthesis of a precursor may be a strategy to maintain secretion competence while preventing aggregation or premature folding (especially for large proteins). The secretion of 230 kDa filamentous haemagglutinin (FHA) of Bordetella pertussis requires the synthesis and the maturation of a 367 kDa precursor that undergoes the proteolytic removal of its approximately 130 kDa C-terminal intramolecular chaperone domain. We have identified a specific protease, SphB1, responsible for the timely maturation of the precursor FhaB, which allows for extracellular release of FHA. SphB1 is a large exported protein with a subtilisin-like domain and a C-terminal domain typical of bacterial autotransporters. SphB1 is the first described subtilisin-like protein that serves as a specialized maturation protease in a secretion pathway of Gram-negative bacteria. This is reminiscent of pro-protein convertases of eukaryotic cells.

Bordetella pertussis binds to human C4b-binding protein (C4BP) at a site similar to that used by the natural ligand C4b

Human complement regulators are important targets for pathogenic microorganisms. In one such interaction, Bordetella pertussis binds human C4b-binding protein (C4BP), a high-molecular-weight plasma protein that acts as inhibitor of the classical pathway of complement activation. At least two different B. pertussis surface components, one of which is the virulence factor filamentous hemagglutinin (FHA), contribute to the binding. We used a set of C4BP mutants and monoclonal antibodies to characterize the region in C4BP that binds B. pertussis and analyzed the salt sensitivity of the interaction. These studies indicated that positively charged residues at the interface between complement control protein modules 1-2 in the C4BP alpha-chain are important for binding, and that the site in C4BP that binds B. pertussis is very similar, but not identical, to the C4b-binding site. Bacteria-bound C4BP retained its complement regulatory function and B. pertussis selectively bound C4BP in human plasma, indicating that binding occurs also in vivo. Together, these findings indicate that B. pertussis exploits a site in C4BP, resembling that used by the natural ligand C4b.

The virulence factors ofBordetella pertussis: a matter of control

Bordetella pertussis is the causative agent of whooping cough, a contagious childhood respiratory disease. Increasing public concern over the safety of whole-cell vaccines led to decreased immunisation rates and a subsequent increase in the incidence of the disease. Research into the development of safer, more efficacious, less reactogenic vaccine preparations was concentrated on the production and purification of detoxified B. pertussis virulence factors. These virulence factors include adhesins such as filamentous haemagglutinin, fimbriae and pertactin, which allow B. pertussis to bind to ciliated epithelial cells in the upper respiratory tract. Once attachment is initiated, toxins produced by the bacterium enable colonisation to proceed by interfering with host clearance mechanisms. B. pertussis co-ordinately regulates the expression of virulence factors via the Bordetella virulence gene (bvg) locus, which encodes a response regulator responsible for signal-mediated activation and repression. This strict regulation mechanism allows the bacterium to express different gene subsets in different environmental niches within the host, according to the stage of disease progression.