Bordetella Adenylate Cyclase-Hemolysin Toxins

Pertussis vaccination in adults in France: Overview and suggestions for improvement

In France, the goal of the pertussis vaccination program is to protect newborns. All infants are vaccinated under the program and then given booster shots up to the age of 25 years. Pregnant women are likewise vaccinated, with the cocooning strategy reserved for infants born to unvaccinated mothers. Real-world data shows (i) inadequate coverage among adolescents and adults under 25; (ii) improper use of the tetanus, diphtheria, and polio (Td/IPV) vaccine in children under six years, adolescents, and young adults; and (iii) underdiagnosis of pertussis in adults. Older patients or those with specific chronic medical conditions are at risk of developing severe disease. Improving the diagnosis and surveillance of pertussis in adults and seniors would be one of the first steps in the right direction. Aligning pertussis vaccination in adults with the Td/IPV program (boosters at 45, 65 years of age, and then every 10 years) would make the vaccination schedule simpler, easier to understand, and easier to implement. Large-scale awareness campaigns targeting this population would increase coverage, thereby boosting the effectiveness of the other measures.

Bordetella bronchiseptica and Bordetella pertussis: Similarities and Differences in Infection, Immuno-Modulation, and Vaccine Considerations

Bordetella pertussis and Bordetella bronchiseptica belong to the genus Bordetella, which comprises 14 other species. B. pertussis is responsible for whooping cough in humans, a severe infection in children and less severe or chronic in adults. These infections are restricted to humans and currently increasing worldwide. B. bronchiseptica is involved in diverse respiratory infections in a wide range of mammals. For instance, the canine infectious respiratory disease complex (CIRDC), characterized by a chronic cough in dogs. At the same time, it is increasingly implicated in human infections, while remaining an important pathogen in the veterinary field. Both Bordetella can evade and modulate host immune responses to support their persistence, although it is more pronounced in B. bronchiseptica infection. The protective immune responses elicited by both pathogens are comparable, while there are important characteristics in the mechanisms that differ. However, B. pertussis pathogenesis is more difficult to decipher in animal models than those of B. bronchiseptica because of its restriction to humans. Nevertheless, the licensed vaccines for each Bordetella are different in terms of formulation, route of administration and immune responses induced, with no known cross-reaction between them. Moreover, the target of the mucosal tissues and the induction of long-lasting cellular and humoral responses are required to control and eliminate Bordetella. In addition, the interaction between both veterinary and human fields are essential for the control of this genus, by preventing the infections in animals and the subsequent zoonotic transmission to humans.

Genomic evidence and virulence properties decipher the extra-host origin of Bordetella bronchiseptica

Until recently, members of the classical Bordetella species comprised only pathogenic bacteria that were thought to live exclusively in warm-blooded animals. The close phylogenetic relationship of Bordetella with Achromobacter and Alcaligenes, which include primarily environmental bacteria, suggests that the ancestral Bordetellae were probably free-living. Eventually, the Bordetella species evolved to infect and live within warm-blooded animals. The modern history of pathogens related to the genus Bordetella started towards the end of the 19th century when it was discovered in the infected respiratory epithelium of mammals, including humans. The first identified member was Bordetella pertussis, which causes whooping cough, a fatal disease in young children. In due course, B. bronchiseptica was recovered from the trachea and bronchi of dogs with distemper. Later, a second closely related human pathogen, B. parapertussis, was described as causing milder whooping cough. The classical Bordetellae are strictly host-associated pathogens transmitted via the host-to-host aerosol route. Recently, the B. bronchiseptica strain HT200 has been reported from a thermal spring exhibiting unique genomic features that were not previously observed in clinical strains. Therefore, it advocates that members of classical Bordetella species have evolved from environmental sources. This organism can be transmitted via environmental reservoirs as it can survive nutrient-limiting conditions and possesses a motile flagellum. This study aims to review the molecular basis of origin and virulence properties of obligate host-restricted and environmental strains of classical Bordetella.

Bordetella parapertussis adenylate cyclase toxin promotes the bacterial survival to the encounter with macrophages

B. parapertussis is a whooping cough etiological agent, whose incidence in the population has increased remarkably. Virulence factors involved in the bacterial infection, however, remain poorly investigated. We here studied the role of adenylate cyclase (CyaA), the main toxin of B. parapertussis, in the outcome of the bacterial interaction with macrophages. Our results showed that B. parapertussis CyaA intoxicates human macrophages, prevents bacterial phagocytosis and precludes phago-lysosomal fusion eventually promoting the bacterial survival to the encounter with these immune cells. Accordingly, we found that B. parapertussis CyaA induces the transcriptional downregulation of host genes encoding for antimicrobial peptides, proteins involved in bacterial intracellular killing, and the pro-inflammatory cytokine TNF-α, while induces the upregulation of the anti-inflammatory cytokine IL-10. Together with previous reports suggesting a protective role of B. parapertussis CyaA against neutrophils bactericidal activity, the results of this study suggest a central role of CyaA in B. parapertussis immune evasion and persistence.

A Robust and Sensitive Spectrophotometric Assay for the Enzymatic Activity of Bacterial Adenylate Cyclase Toxins

Various bacterial pathogens are producing toxins that target the cyclic Nucleotide Monophosphate (cNMPs) signaling pathways in order to facilitate host colonization. Among them, several are exhibiting potent nucleotidyl cyclase activities that are activated by eukaryotic factors, such as the adenylate cyclase (AC) toxin, CyaA, from Bordetella pertussis or the edema factor, EF, from Bacillus anthracis. The characterization of these toxins frequently requires accurate measurements of their enzymatic activity in vitro, in particular for deciphering their structure-to-function relationships by protein engineering and site-directed mutagenesis. Here we describe a simple and robust in vitro assay for AC activity based on the spectrophotometric detection of cyclic AMP (cAMP) after chromatographic separation on aluminum oxide. This assay can accurately detect down to fmol amounts of B. pertussis CyaA and can even be used in complex media, such as cell extracts. The relative advantages and disadvantages of this assay in comparison with other currently available methods are briefly discussed.

Comparative proteomics and secretomics revealed virulence, and coresistance-related factors in non O1/O139 Vibrio cholerae recovered from 16 species of consumable aquatic animals

Vibrio cholerae can cause pandemic cholera in humans. The bacterium resides in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. In this study, we determined virulence-associated genes, cross-resistance between antibiotics and heavy metals, and genome fingerprinting profiles of non O1/O139 V. cholerae isolates (n = 20) recovered from 16 species of consumable aquatic animals. Secretomes and proteomes of V. cholerae with distinct genotypes and phenotypes were obtained by using two-dimensional gel electrophoresis (2D-GE) and/or liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Comparative secretomic analysis revealed 4 common and 45 differential extracellular proteins among 20 V. cholerae strains, including 13 virulence- and 8 resistance-associated proteins. A total of 21,972 intracellular proteins were identified, and comparative proteomic analysis revealed 215 common and 913 differential intracellular proteins, including 22 virulence- and 8 resistance-associated proteins. Additionally, different secretomes and proteomes were observed between V. cholerae isolates of fish and shellfish origins. A number of novel proteins with unknown function and strain-specific proteins were also discovered in the V. cholerae isolates. SIGNIFICANCE: V. cholerae can cause pandemic cholera in humans. The bacterium is distributed in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. Non-O1/O139 V. cholerae has been reported to cause sporadic cholera-like diarrhea and bacteremia diseases, which indicates virulence factors rather than the major cholera toxin (CT) exist. This study for the first time investigated proteomes and secretomes of non-O1/O139 V. cholerae originating from aquatic animals. This resulted in the identification of a number of virulence and coresistance-related factors, as well as novel proteins and strain-specific proteins in V. cholerae isolates recovered from 16 species of consumable aquatic animals. These results fill gaps for better understanding of pathogenesis and resistance of V. cholerae, and also support the increasing need for novel diagnosis and vaccine targets against the leading waterborne pathogen worldwide.

Design of a Quantitative LC-MS Method for Residual Toxins Adenylate Cyclase Toxin (ACT), Dermonecrotic Toxin (DNT) and Tracheal Cytotoxin (TCT) in Bordetella pertussis Vaccines

The antigens for acellular pertussis vaccines are made up of protein components that are purified directly from Bordetella pertussis (B. pertussis) bacterial fermentation. As such, there are additional B. pertussis toxins that must be monitored as residuals during process optimization. This paper describes a liquid chromatography mass spectrometry (LC-MS) method for simultaneous analysis of residual protein toxins adenylate cyclase toxin (ACT) and dermonecrotic toxin (DNT), as well as a small molecule glycopeptide, tracheal cytotoxin (TCT) in a Pertussis toxin vaccine antigen. A targeted LC-MS technique called multiple reaction monitoring (MRM) is used for quantitation of ACT and TCT, which have established limits in drug product formulations. However, DNT is currently monitored in an animal test, which does not have an established quantitative threshold. New approaches for DNT testing are discussed, including a novel standard based on concatenated quantitation sequences for ACT and DNT. Collectively, the method represents a “3-in-1” analytical simplification for monitoring process-related residuals during development of B. pertussis vaccines.

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.

Almost half of the RTX domain is dispensable for complement receptor 3 binding and cell-invasive activity of the Bordetella adenylate cyclase toxin

The whooping cough agent Bordetella pertussis secretes an adenylate cyclase toxin (CyaA) that through its large carboxy-proximal Repeat-in-ToXin (RTX) domain binds the complement receptor 3 (CR3). The RTX domain consists of five blocks (I-V) of characteristic glycine and aspartate-rich nonapeptides that fold into five Ca2+-loaded parallel β-rolls. Previous work indicated that the CR3-binding structure comprises the interface of β-rolls II and III. To test if further portions of the RTX domain contribute to CR3 binding, we generated a construct with the RTX block II/III interface (CyaA residues 1132-1294) linked directly to the C-terminal block V fragment bearing the folding scaffold (CyaA residues 1562-1681). Despite deletion of 267 internal residues of the RTX domain, the Ca2+-driven folding of the hybrid block III/V β-roll still supported formation of the CR3-binding structure at the interface of β-rolls II and III. Moreover, upon stabilization by N- and C-terminal flanking segments, the block III/V hybrid-comprising constructs competed with CyaA for CR3 binding and induced formation of CyaA toxin-neutralizing antibodies in mice. Finally, a truncated CyaAΔ1295-1561 toxin bound and penetrated erythrocytes and CR3-expressing cells, showing that the deleted portions of RTX blocks III, IV, and V (residues 1295-1561) were dispensable for CR3 binding and for toxin translocation across the target cell membrane. This suggests that almost a half of the RTX domain of CyaA is not involved in target cell interaction and rather serves the purpose of toxin secretion.

Isolation, Antimicrobial Resistance Phenotypes, and Virulence Genes of Bordetella bronchiseptica From Pigs in China, 2018-2020

Bordetella bronchiseptica is a leading cause of respiratory diseases in pigs. However, epidemiological data of B. bronchiseptica in pigs particularly in China, the largest pig rearing country in the world is still limited. We isolated 181 B. bronchiseptica strains from 4259 lung samples of dead pigs with respiratory diseases in 14 provinces in China from 2018 to 2020. The average isolation rate of this 3-year period was 4.25% (181/4259). Antimicrobial susceptibility testing performed by disc diffusion method revealed that most of the B. bronchiseptica isolates in this study were resistant to ampicillin (83.98%), while a proportion of isolates were resistant to cefotaxime (30.39%%), chloramphenicol (12.71%), gentamicin (11.60%), florfenicol (11.60%), tetracycline (8.84%), amoxicillin (8.29%), tobramycin (6.63%), ceftriaxone (4.97%), and cefepime (0.55%). There were no isolates with resistant phenotypes to imipenem, meropenem, polymyxin B, ciprofloxacin, enrofloxacin, and amikacin. In addition, ~13.18% of the isolates showed phenotypes of multidrug resistance. Detection of antimicrobial resistance genes (ARGs) by PCR showed that 16.57% of the B. bronchiseptica isolates in this study was positive to aac(3)-IV, while 3.87%, 2.21%, 1.10%, 0.55%, 0.55%, and 0.55% of the isolates were positive to aac6'-Ib, rmtA, bla_TEM, bla_SHV, oqxB, and tetA, respectively. Detection of virulence factors encoding genes (VFGs) by conventional PCR showed that over 90% of the pig B. bronchiseptica isolates in this study were positive to the five VFGs examined (fhaB, 97.24%; prn, 91.16%; cyaA, 98.34%; dnt, 98.34%; betA, 92.82%). These results demonstrate B. bronchiseptica as an important pathogen associated with pig respiratory disorders in China. The present work contributes to the current understanding of the prevalence, antimicrobial resistance and virulence genes of B. bronchiseptica in pigs.

A High-Affinity Calmodulin-Binding Site in the CyaA Toxin Translocation Domain is Essential for Invasion of Eukaryotic Cells

The molecular mechanisms and forces involved in the translocation of bacterial toxins into host cells are still a matter of intense research. The adenylate cyclase (CyaA) toxin from Bordetella pertussis displays a unique intoxication pathway in which its catalytic domain is directly translocated across target cell membranes. The CyaA translocation region contains a segment, P454 (residues 454-484), which exhibits membrane-active properties related to antimicrobial peptides. Herein, the results show that this peptide is able to translocate across membranes and to interact with calmodulin (CaM). Structural and biophysical analyses reveal the key residues of P454 involved in membrane destabilization and calmodulin binding. Mutational analysis demonstrates that these residues play a crucial role in CyaA translocation into target cells. In addition, calmidazolium, a calmodulin inhibitor, efficiently blocks CyaA internalization. It is proposed that after CyaA binding to target cells, the P454 segment destabilizes the plasma membrane, translocates across the lipid bilayer and binds calmodulin. Trapping of CyaA by the CaM:P454 interaction in the cytosol may assist the entry of the N-terminal catalytic domain by converting the stochastic motion of the polypeptide chain through the membrane into an efficient vectorial chain translocation into host cells.

Bioengineering of Bordetella pertussis Adenylate Cyclase Toxin for Vaccine Development and Other Biotechnological Purposes

The adenylate cyclase toxin, CyaA, is one of the key virulent factors produced by Bordetella pertussis, the causative agent of whooping cough. This toxin primarily targets innate immunity to facilitate bacterial colonization of the respiratory tract. CyaA exhibits several remarkable characteristics that have been exploited for various applications in vaccinology and other biotechnological purposes. CyaA has been engineered as a potent vaccine vehicle to deliver antigens into antigen-presenting cells, while the adenylate cyclase catalytic domain has been used to design a robust genetic assay for monitoring protein-protein interactions in bacteria. These two biotechnological applications are briefly summarized in this chapter.

Omics Analysis of Blood-Responsive Regulon in Bordetella pertussis Identifies a Novel Essential T3SS Substrate

Bacterial pathogens sense specific cues associated with different host niches and integrate these signals to appropriately adjust the global gene expression. Bordetella pertussis is a Gram-negative, strictly human pathogen of the respiratory tract and the etiological agent of whooping cough (pertussis). Though B. pertussis does not cause invasive infections, previous results indicated that this reemerging pathogen responds to blood exposure. Here, omics RNA-seq and LC–MS/MS techniques were applied to determine the blood-responsive regulon of B. pertussis. These analyses revealed that direct contact with blood rewired global gene expression profiles in B. pertussis as the expression of almost 20% of all genes was significantly modulated. However, upon loss of contact with blood, the majority of blood-specific effects vanished, with the exception of several genes encoding the T3SS-secreted substrates. For the first time, the T3SS regulator BtrA was identified in culture supernatants of B. pertussis. Furthermore, proteomic analysis identified BP2259 protein as a novel secreted T3SS substrate, which is required for T3SS functionality. Collectively, presented data indicate that contact with blood represents an important cue for B. pertussis cells.

Expanding the role of bacterial vaccines into life-course vaccination strategies and prevention of antimicrobial-resistant infections

A crisis in bacterial infections looms as ageing populations, increasing rates of bacteraemia and healthcare-associated infections converge with increasing antimicrobial resistance and a paucity of new antimicrobial classes. New initiatives are needed to develop bacterial vaccines for older adults in whom immune senescence plays a critical role. Novel vaccines require an expanded repertoire to prevent mucosal diseases such as pneumonia, skin and soft tissue infections and urinary tract infections that are major causes of morbidity and mortality in the elderly, and key drivers of antimicrobial resistance. This review considers the challenges inherent to the prevention of bacterial diseases, particularly mucosal infections caused by major priority bacterial pathogens against which current vaccines are sub-optimal. It has become clear that prevention of many lung, urinary tract and skin infections requires more than circulating antibodies. Induction of Th1/Th17 cellular responses with tissue-resident memory (Trm) cells homing to mucosal tissues may be a pre-requisite for success.

Characterisation of Bordetella bronchiseptica isolated from rabbits in Fujian, China

Bordetella bronchiseptica is a potential zoonotic pathogen, which mainly causes respiratory diseases in humans and a variety of animal species. B. bronchiseptica is one of the important pathogens isolated from rabbits in Fujian Province. However, the knowledge of the epidemiology and characteristics of the B. bronchiseptica in rabbits in Fujian Province is largely unknown. In this study, 219 B. bronchiseptica isolates recovered from lung samples of dead rabbits with respiratory diseases in Fujian Province were characterised by multi-locus sequencing typing, screening virulence genes and testing antimicrobial susceptibility. The results showed that the 219 isolates were typed into 11 sequence types (STs) including five known STs (ST6, ST10, ST12, ST14 and ST33) and six new STs (ST88, ST89, ST90, ST91, ST92 and ST93) and the ST33 (30.14%, 66/219), ST14 (26.94%, 59/219) and ST12 (16.44%, 36/219) were the three most prevalent STs. Surprisingly, all the 219 isolates carried the five virulence genes (fhaB, prn, cyaA, dnt and bteA) in the polymerase chain reaction screening. Moreover, the isolates were resistant to cefixime, ceftizoxime, cefatriaxone and ampicillin at rates of 33.33%, 31.05%, 11.87% and 3.20%, respectively. This study showed the genetic diversity of B. bronchiseptica in rabbits in Fujian Province, and the colonisation of the human-associated ST12 strain in rabbits in Fujian Province. The results might be useful for monitoring the epidemic strains, developing preventive methods and preventing the transmission of epidemic strains from rabbits to humans.

Functional and structural consequences of epithelial cell invasion by Bordetella pertussis adenylate cyclase toxin

Bordetella pertussis, the causative agent of whopping cough, produces an adenylate cyclase toxin (CyaA) that plays a key role in the host colonization by targeting innate immune cells which express CD11b/CD18, the cellular receptor of CyaA. CyaA is also able to invade non-phagocytic cells, via a unique entry pathway consisting in a direct translocation of its catalytic domain across the cytoplasmic membrane of the cells. Within the cells, CyaA is activated by calmodulin to produce high levels of cyclic adenosine monophosphate (cAMP) and alter cellular physiology. In this study, we explored the effects of CyaA toxin on the cellular and molecular structure remodeling of A549 alveolar epithelial cells. Using classical imaging techniques, biochemical and functional tests, as well as advanced cell mechanics method, we quantify the structural and functional consequences of the massive increase of intracellular cyclic AMP induced by the toxin: cell shape rounding associated to adhesion weakening process, actin structure remodeling for the cortical and dense components, increase in cytoskeleton stiffness, and inhibition of migration and repair. We also show that, at low concentrations (0.5 nM), CyaA could significantly impair the migration and wound healing capacities of the intoxicated alveolar epithelial cells. As such concentrations might be reached locally during B. pertussis infection, our results suggest that the CyaA, beyond its major role in disabling innate immune cells, might also contribute to the local alteration of the epithelial barrier of the respiratory tract, a hallmark of pertussis.

Bordetella Dermonecrotic Toxin Is a Neurotropic Virulence Factor That Uses CaV3.1 as the Cell Surface Receptor

Dermonecrotic toxin (DNT) is one of the representative toxins produced by Bordetella pertussis, but its role in pertussis, B. pertussis infection, remains unknown. In this study, we identified the T-type voltage-gated Ca2+ channel CaV3.1 as the DNT receptor by CRISPR-Cas9-based genome-wide screening. As CaV3.1 is highly expressed in the nervous system, the neurotoxicity of DNT was examined. DNT affected cultured neural cells and caused flaccid paralysis in mice after intracerebral injection. No neurological symptoms were observed by intracerebral injection with the other major virulence factors of the organisms, pertussis toxin and adenylate cyclase toxin. These results indicate that DNT has aspects of the neurotropic virulence factor of B. pertussis The possibility of the involvement of DNT in encephalopathy, which is a complication of pertussis, is also discussed.IMPORTANCEBordetella pertussis, which causes pertussis, a contagious respiratory disease, produces three major protein toxins, pertussis toxin, adenylate cyclase toxin, and dermonecrotic toxin (DNT), for which molecular actions have been elucidated. The former two toxins are known to be involved in the emergence of some clinical symptoms and/or contribute to the establishment of bacterial infection. In contrast, the role of DNT in pertussis remains unclear. Our study shows that DNT affects neural cells through specific binding to the T-type voltage-gated Ca2+ channel that is highly expressed in the central nervous system and leads to neurological disorders in mice after intracerebral injection. These data raise the possibility of DNT as an etiological agent for pertussis encephalopathy, a severe complication of B. pertussis infection.

Post-translational acylation controls the folding and functions of the CyaA RTX toxin

The adenylate cyclase (CyaA) toxin is a major virulence factor of Bordetella pertussis, the causative agent of whooping cough. CyaA is synthetized as a pro-toxin, pro-CyaA, and converted into its cytotoxic form upon acylation of two lysines. After secretion, CyaA invades eukaryotic cells and produces cAMP, leading to host defense subversion. To gain further insights into the effect of acylation, we compared the functional and structural properties of pro-CyaA and CyaA proteins. HDX-MS results show that the refolding process of both proteins upon progressive urea removal is initiated by calcium binding to the C-terminal RTX domain. We further identified a critical hydrophobic segment, distal from the acylation region, that folds at higher urea concentration in CyaA than in pro-CyaA. Once refolded into monomers, CyaA is more compact and stable than pro-CyaA, due to a complex set of interactions between domains. Our HDX-MS data provide direct evidence that the presence of acyl chains in CyaA induces a significant stabilization of the apolar segments of the hydrophobic domain and of most of the acylation region. We propose a refolding model dependent on calcium and driven by local and distal acylation-dependent interactions within CyaA. Therefore, CyaA acylation is not only critical for cell intoxication, but also for protein refolding into its active conformation. Our data shed light on the complex relationship between post-translational modifications, structural disorder and protein folding. Coupling calcium-binding and acylation-driven folding is likely pertinent for other repeat-in-toxin cytolysins produced by many Gram-negative bacterial pathogens.-O'Brien, D. P., Cannella, S. E., Voegele, A., Raoux-Barbot, D., Davi, M., Douché, T., Matondo, M., Brier, S., Ladant, D., Chenal, A. Post-translational acylation controls the folding and functions of the CyaA RTX toxin.

Association between the timing of maternal vaccination and newborns' anti-pertussis toxin antibody levels

BACKGROUND

Pertussis remains an important global public health concern, despite the presence of extensive immunization programs. Incidence and severity of pertussis are typically higher in neonates and young infants. As a strategy to protect these young infants, maternal vaccination with Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) has been recommended in Brazil. The objective of this study was to evaluate the effects of Tdap vaccination during pregnancy on the anti-pertussis toxin (PT) IgG response in mothers and their infants at birth.

MATERIAL AND METHODS

Maternal and cord blood samples were collected from vaccinated (n = 243) and unvaccinated (n = 75) pregnant women, at the time of delivery, from July 2015 to August 2016 in São Paulo, Brazil. Anti-PT IgG antibodies were quantified by Enzyme-Linked Immunosorbent Assay (ELISA) and geometric mean concentrations (GMC) were calculated. Relationship between timing of vaccination and antibody concentrations were evaluated.

RESULTS

Maternal and cord blood GMCs among the vaccinated group were 5.4 and 5.6 fold higher [66.5 International Units (IU)/mL and 89.8 IU/mL] compared to the unvaccinated group (12.4 IU/mL and 16.1 IU/mL), respectively (p < 0.001). Higher anti-PT IgG GMCs were observed when vaccination occurred ≥60 days before delivery compared to <60 days, suggesting that vaccination early in the third trimester may be more effective than later in pregnancy.

CONCLUSION

Tdap maternal vaccination results in significantly higher anti-PT IgG in newborn infants and supports the current recommendation of the Brazilian Immunization Program.

The Adenylate Cyclase (CyaA) Toxin from Bordetella pertussis Has No Detectable Phospholipase A (PLA) Activity In Vitro

The adenylate cyclase (CyaA) toxin produced in Bordetella pertussis is the causative agent of whooping cough. CyaA exhibits the remarkable capacity to translocate its N-terminal adenyl cyclase domain (ACD) directly across the plasma membrane into the cytosol of eukaryotic cells. Once translocated, calmodulin binds and activates ACD, leading to a burst of cAMP that intoxicates the target cell. Previously, Gonzalez-Bullon et al. reported that CyaA exhibits a phospholipase A activity that could destabilize the membrane to facilitate ACD membrane translocation. However, Bumba and collaborators lately reported that they could not replicate these results. To clarify this controversy, we assayed the putative PLA activity of two CyaA samples purified in two different laboratories by using two distinct fluorescent probes reporting either PLA2 or both PLA1 and PLA2 activities, as well as in various experimental conditions (i.e., neutral or negatively charged membranes in different buffers.) However, we could not detect any PLA activity in these CyaA batches. Thus, our data independently confirm that CyaA does not possess any PLA activity.

Translocation and calmodulin-activation of the adenylate cyclase toxin (CyaA) of Bordetella pertussis

The adenylate cyclase toxin (CyaA) is a multi-domain protein secreted by Bordetella pertussis, the causative agent of whooping cough. CyaA is involved in the early stages of respiratory tract colonization by Bordetella pertussis. CyaA is produced and acylated in the bacteria, and secreted via a dedicated secretion system. The cell intoxication process involves a unique mechanism of transport of the CyaA toxin catalytic domain (ACD) across the plasma membrane of eukaryotic cells. Once translocated, ACD binds to and is activated by calmodulin and produces high amounts of cAMP, subverting the physiology of eukaryotic cells. Here, we review our work on the identification and characterization of a critical region of CyaA, the translocation region, required to deliver ACD into the cytosol of target cells. The translocation region contains a segment that exhibits membrane-active properties, i.e. is able to fold upon membrane interaction and permeabilize lipid bilayers. We proposed that this region is required to locally destabilize the membrane, decreasing the energy required for ACD translocation. To further study the translocation process, we developed a tethered bilayer lipid membrane (tBLM) design that recapitulate the ACD transport across a membrane separating two hermetic compartments. We showed that ACD translocation is critically dependent on calcium, membrane potential, CyaA acylation and on the presence of calmodulin in the trans compartment. Finally, we describe how calmodulin-binding triggers key conformational changes in ACD, leading to its activation and production of supraphysiological concentrations of cAMP.

The Eukaryotic Host Factor 14-3-3 Inactivates Adenylate Cyclase Toxins of Bordetella bronchiseptica and B. parapertussis, but Not B. pertussis

Bordetella pertussis, Bordetella bronchiseptica, and Bordetella parapertussis share highly homologous virulence factors and commonly cause respiratory infections in mammals; however, their host specificities and disease severities differ, and the reasons for this remain largely unknown. Adenylate cyclase toxin (CyaA) is a homologous virulence factor that is thought to play crucial roles in Bordetella infections. We herein demonstrate that CyaAs function as virulence factors differently between B. bronchiseptica/B. parapertussis and B. pertussis. B. bronchiseptica CyaA bound to target cells, and its enzyme domain was translocated into the cytosol similarly to B. pertussis CyaA. The hemolytic activity of B. bronchiseptica CyaA on sheep erythrocytes was also preserved. However, in nucleated target cells, B. bronchiseptica CyaA was phosphorylated at Ser³⁷⁵, which constitutes a motif (RSXpSXP [pS is phosphoserine]) recognized by the host factor 14-3-3, resulting in the abrogation of adenylate cyclase activity. Consequently, the cytotoxic effects of B. bronchiseptica CyaA based on its enzyme activity were markedly attenuated. B. parapertussis CyaA carries the 14-3-3 motif, indicating that its intracellular enzyme activity is abrogated similarly to B. bronchiseptica CyaA; however, B. pertussis CyaA has Phe³⁷⁵ instead of Ser, and thus, was not affected by 14-3-3. In addition, B. pertussis CyaA impaired the barrier function of epithelial cells, whereas B. bronchiseptica CyaA did not. Rat infection experiments suggested that functional differences in CyaA are related to differences in pathogenicity between B. bronchiseptica/B. parapertussis and B. pertussis.

Bordetella pertussis, B. bronchiseptica, and B. parapertussis are bacterial respiratory pathogens that are genetically close to each other and produce many homologous virulence factors; however, their host specificities and disease severities differ, and the reasons for this remain unknown. Previous studies attempted to explain these differences by the distinct virulence factors produced by each Bordetella species. In contrast, we indicated functional differences in adenylate cyclase toxin, a homologous virulence factor of Bordetella. The toxins of B. bronchiseptica and presumably B. parapertussis were inactivated by the host factor 14-3-3 after phosphorylation in target cells, whereas the B. pertussis toxin was not inactivated because of the lack of the phosphorylation site. This is the first study to show that 14-3-3 inactivates the virulence factors of pathogens. The present results suggest that pathogenic differences in Bordetella are attributed to the different activities of adenylate cyclase toxins.

Bioengineering of Bordetella pertussis Adenylate Cyclase Toxin for Antigen-Delivery and Immunotherapy

The adenylate cyclase toxin (CyaA) is one of the major virulence factors of Bordetella pertussis, the causative agent of whooping cough. CyaA is able to invade eukaryotic cells where, upon activation by endogenous calmodulin, it synthesizes massive amounts of cAMP that alters cellular physiology. The CyaA toxin is a 1706 residues-long bifunctional protein: the catalytic domain is located in the 400 amino-proximal residues, whereas the carboxy-terminal 1306 residues are implicated in toxin binding to the cellular receptor, the αMβ₂ (CD11b/CD18) integrin, and subsequently in the translocation of the catalytic domain across the cytoplasmic membrane of the target cells. Indeed, this protein is endowed with the unique capability of delivering its N-terminal catalytic domain directly across the plasma membrane of eukaryotic target cells. These properties have been exploited to engineer the CyaA toxin as a potent non-replicating vector able to deliver antigens into antigen presenting cells and elicit specific cell-mediated immune responses. Antigens of interest can be inserted into the CyaA protein to yield recombinant molecules that are targeted in vivo to dendritic cells, where the antigens are processed and presented by the major class I and class II histocompatibility complexes (MHC-I and II). CyaA turned out to be a remarkably effective and versatile vaccine vector capable of inducing all the components of the immune response (T-CD4, T-CD8, and antibody). In this chapter, we summarize the basic knowledge on the adenylate cyclase toxin and then describe the application of CyaA in vaccinology, including some recent results of clinical trials of immunotherapy using a recombinant CyaA vaccine.

Characterization of Post-Translational Modifications and Cytotoxic Properties of the Adenylate-Cyclase Hemolysin Produced by Various Bordetella pertussis and Bordetella parapertussis Isolates

Bordetella pertussis and Bordetella parapertussis are the causal agents of whooping cough in humans. They produce diverse virulence factors, including adenylate cyclase-hemolysin (AC-Hly), a secreted toxin of the repeat in toxins (RTX) family with cyclase, pore-forming, and hemolytic activities. Post-translational modifications (PTMs) are essential for the biological activities of the toxin produced by B. pertussis. In this study, we compared AC-Hly toxins from various clinical isolates of B. pertussis and B. parapertussis, focusing on (i) the genomic sequences of cyaA genes, (ii) the PTMs of partially purified AC-Hly, and (iii) the cytotoxic activity of the various AC-Hly toxins. The genes encoding the AC-Hly toxins of B. pertussis and B. parapertussis displayed very limited polymorphism in each species. Most of the sequence differences between the two species were found in the C-terminal part of the protein. Both toxins harbored PTMs, mostly corresponding to palmitoylations of the lysine 860 residue and palmoylations and myristoylations of lysine 983 for B. pertussis and AC-Hly and palmitoylations of lysine 894 and myristoylations of lysine 1017 for B. parapertussis AC-Hly. Purified AC-Hly from B. pertussis was cytotoxic to macrophages, whereas that from B. parapertussis was not.

Characterization of Post-Translational Modifications and Cytotoxic Properties of the Adenylate-Cyclase Hemolysin Produced by Various Bordetella pertussis and Bordetella parapertussis Isolates

Bordetella pertussis and Bordetella parapertussis are the causal agents of whooping cough in humans. They produce diverse virulence factors, including adenylate cyclase-hemolysin (AC-Hly), a secreted toxin of the repeat in toxins (RTX) family with cyclase, pore-forming, and hemolytic activities. Post-translational modifications (PTMs) are essential for the biological activities of the toxin produced by B. pertussis. In this study, we compared AC-Hly toxins from various clinical isolates of B. pertussis and B. parapertussis, focusing on (i) the genomic sequences of cyaA genes, (ii) the PTMs of partially purified AC-Hly, and (iii) the cytotoxic activity of the various AC-Hly toxins. The genes encoding the AC-Hly toxins of B. pertussis and B. parapertussis displayed very limited polymorphism in each species. Most of the sequence differences between the two species were found in the C-terminal part of the protein. Both toxins harbored PTMs, mostly corresponding to palmitoylations of the lysine 860 residue and palmoylations and myristoylations of lysine 983 for B. pertussis and AC-Hly and palmitoylations of lysine 894 and myristoylations of lysine 1017 for B. parapertussis AC-Hly. Purified AC-Hly from B. pertussis was cytotoxic to macrophages, whereas that from B. parapertussis was not.