Combined transcriptomic and ChIPseq analyses of the Bordetella pertussis RisA regulon

The regulation of Bordetella pertussis virulence is mediated by the two-component system BvgA/S, which activates the transcription of virulence-activated genes (vags). In the avirulent phase, the vags are not expressed, but instead, virulence-repressed genes (vrgs) are expressed, under the control of another two-component system, RisA/K. Here, we combined transcriptomic and chromatin immunoprecipitation sequencing (ChIPseq) data to examine the RisA/K regulon. We performed RNAseq analyses of RisA-deficient and RisA-phosphoablative B. pertussis mutants cultivated in virulent and avirulent conditions. We confirmed that the expression of most vrgs is regulated by phosphorylated RisA. However, the expression of some, including those involved in flagellum biosynthesis and chemotaxis, requires RisA independently of phosphorylation. Many RisA-regulated genes encode proteins with regulatory functions, suggesting multiple RisA regulation cascades. By ChIPseq analyses, we identified 430 RisA-binding sites, 208 within promoter regions, 201 within open reading frames, and 21 in non-coding regions. RisA binding was demonstrated in the promoter regions of most vrgs and, surprisingly, of some vags, as well as for other genes not identified as vags or vrgs. Unexpectedly, many genes, including some vags, like prn, brpL, bipA, and cyaA, contain a BvgA-binding site and a RisA-binding site, which increases the complexity of the RisAK/BvgAS network in B. pertussis virulence regulation.IMPORTANCEThe expression of virulence-activated genes (vags) of Bordetella pertussis, the etiological agent of whooping cough, is under the transcriptional control of the two-component system BvgA/S, which allows the bacterium to switch between virulent and avirulent phases. In addition, the more recently identified two-component system RisA/K is required for the expression of B. pertussis genes, collectively named vrgs, that are repressed during the virulent phase but activated during the avirulent phase. We have characterized the RisA/K regulon by combined transcriptomic and chromatin immunoprecipitation sequencing analyses. We identified more than 400 RisA-binding sites. Many of them are localized in promoter regions, especially vrgs, but some were found within open reading frames and in non-coding regions. Surprisingly, RisA-binding sites were also found in promoter regions of some vags, illustrating the previously underappreciated complexity of virulence regulation in B. pertussis.

Cytotoxicity of the effector protein BteA was attenuated in Bordetella pertussis by insertion of an alanine residue

Bordetella bronchiseptica and Bordetella pertussis are closely related respiratory pathogens that evolved from a common bacterial ancestor. While B. bronchiseptica has an environmental reservoir and mostly establishes chronic infections in a broad range of mammals, B. pertussis is a human-specific pathogen causing acute pulmonary pertussis in infants and whooping cough illness in older humans. Both species employ a type III secretion system (T3SS) to inject a cytotoxic BteA effector protein into host cells. However, compared to the high BteA-mediated cytotoxicity of B. bronchiseptica, the cytotoxicity induced by B. pertussis BteA (Bp BteA) appears to be quite low and this has been attributed to the reduced T3SS gene expression in B. pertussis. We show that the presence of an alanine residue inserted at position 503 (A503) of Bp BteA accounts for its strongly attenuated cytotoxic potency. The deletion of A503 from Bp BteA greatly enhanced the cytotoxic activity of B. pertussis B1917 on mammalian HeLa cells and expression of Bp BteAΔA503 was highly toxic to Saccharomyces cerevisiae cells. Vice versa, insertion of A503 into B. bronchiseptica BteA (Bb BteA) strongly decreased its cytotoxicity to yeast and HeLa cells. Moreover, the production of Bp BteAΔA503 increased virulence of B. pertussis B1917 in the mouse model of intranasal infection (reduced LD50) but yielded less inflammatory pathology in infected mouse lungs at sublethal infectious doses. This suggests that A503 insertion in the T3SS effector Bp BteA may represent an evolutionary adaptation that fine-tunes B. pertussis virulence and host immune response.

Pertussis remains the least-controlled vaccine-preventable infectious disease and the mechanisms by which Bordetella pertussis subverts defense mechanisms of human airway mucosa remain poorly understood. We found that B. pertussis had the cytotoxic activity of its type III secretion system-delivered effector BteA strongly attenuated by insertion of an alanine residue at position 503 as compared to the BteA homologue of the animal pathogen B. bronchiseptica. This functional adaptation reduced the capacity of B. pertussis to suppress host inflammatory response and may contribute to an acute course of the pulmonary form of human infant pertussis.

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.

Transcriptional profiling of human macrophages during infection with Bordetella pertussis

Bordetella pertussis, a strictly human re-emerging pathogen and the causative agent of whooping cough, exploits a broad variety of virulence factors to establish efficient infection. Here, we used RNA sequencing to analyse the changes in gene expression profiles of human THP-1 macrophages resulting from B. pertussis infection. In parallel, we attempted to determine the changes in intracellular B. pertussis-specific transcriptomic profiles resulting from interaction with macrophages. Our analysis revealed that global gene expression profiles in THP-1 macrophages are extensively rewired 6 h post-infection. Among the highly expressed genes, we identified those encoding cytokines, chemokines, and transcription regulators involved in the induction of the M1 and M2 macrophage polarization programmes. Notably, several host genes involved in the control of apoptosis and inflammation which are known to be hijacked by intracellular bacterial pathogens were overexpressed upon infection. Furthermore, in silico analyses identified large temporal changes in expression of specific gene subsets involved in signalling and metabolic pathways. Despite limited numbers of the bacterial reads, we observed reduced expression of majority of virulence factors and upregulation of several transcriptional regulators during infection suggesting that intracellular B. pertussis cells switch from virulent to avirulent phase and actively adapt to intracellular environment, respectively.

Bordetella pertussis Adenylate Cyclase Toxin Disrupts Functional Integrity of Bronchial Epithelial Layers

The airway epithelium restricts the penetration of inhaled pathogens into the underlying tissue and plays a crucial role in the innate immune defense against respiratory infections. The whooping cough agent, Bordetella pertussis, adheres to ciliated cells of the human airway epithelium and subverts its defense functions through the action of secreted toxins and other virulence factors. We examined the impact of B. pertussis infection and of adenylate cyclase toxin-hemolysin (CyaA) action on the functional integrity of human bronchial epithelial cells cultured at the air-liquid interface (ALI). B. pertussis adhesion to the apical surface of polarized pseudostratified VA10 cell layers provoked a disruption of tight junctions and caused a drop in transepithelial electrical resistance (TEER). The reduction of TEER depended on the capacity of the secreted CyaA toxin to elicit cAMP signaling in epithelial cells through its adenylyl cyclase enzyme activity. Both purified CyaA and cAMP-signaling drugs triggered a decrease in the TEER of VA10 cell layers. Toxin-produced cAMP signaling caused actin cytoskeleton rearrangement and induced mucin 5AC production and interleukin-6 (IL-6) secretion, while it inhibited the IL-17A-induced secretion of the IL-8 chemokine and of the antimicrobial peptide beta-defensin 2. These results indicate that CyaA toxin activity compromises the barrier and innate immune functions of Bordetella-infected airway epithelia.

Characterization of a Bvg-regulated fatty acid methyl-transferase in Bordetella pertussis

The whooping cough agent Bordetella pertussis controls the expression of its large virulence regulon in a coordinated manner through the two-component signal transduction system BvgAS. In addition to the genes coding for bona fide virulence factors, the Bvg regulon comprises genes of unknown function. In this work, we characterized a new Bvg-activated gene called BP2936. Homologs of BP2936 are found in other pathogenic Bordetellae and in several other species, including plant pathogens and environmental bacteria. We showed that the gene product of BP2936 is a membrane-associated methyl-transferase of free fatty acids. We thus propose to name it FmtB, for fatty acid methyl-transferase of Bordetella. The role of this protein was tested in cellular and animal models of infection, but the loss of BP2936 did not appear to affect host-pathogen interactions in those assays. The high level of conservation of BP2936 among B. pertussis isolates nevertheless argues that it probably plays a role in the life cycle of this pathogen.

[Insertional Inactivation of Virulence Operon in Population of Persistent Bordetella pertussis Bacteria]

Avirulent B. pertussis bacteria containing IS elements in the bvgAS operon were detected during the study of whooping cough patients and bacilli carriers. The present work is devoted to the study of the accumulation dynamics and the mechanisms of generation of persistent forms of the B. pertussis bacteria in lower monkeys as the most adequate model for extrapolation ofthe experiment results to humans. By means of the real-time PCR method, it was established that the B. pertussis bacteria lived more than three months in the upper respiratory tract after a single intranasal monkey infection; the period was reduced to 14-28 days during repeated infection. An increase in the portion of B. pertussis Bvg mutants in the population to tens of percent from the total number of registered bacteria was registered. The experimental confirmation ofthe development and accumulation of avirulent B. pertussis Bvg mutants during the development of the infectious process was obtained. Further study of the composition of the B. pertussis persistent bacteria population at different stages of the disease will make it possible to formulate new approaches to the whooping cough diagnostics and prevention and creation of fundamentally new drugs.

Association of Vitamin D Receptor Polymorphism with Susceptibility to Symptomatic Pertussis

Pertussis, caused by infection with the gram negative B. pertussis bacterium, is a serious respiratory illness that can last for months. While B. pertussis infection rates are estimated between 1-10% in the general population, notifications of symptomatic pertussis only comprise 0.01-0.1% indicating that most individuals clear B. pertussis infections without developing (severe) clinical symptoms. In this study we investigated whether genetic risk factors are involved in the development of symptomatic pertussis upon B. pertussis infection. Single-nucleotide polymorphisms (SNPs) in candidate genes, MBL2, IL17A, TNFα, VDR, and IL10 were genotyped in a unique Dutch cohort of symptomatic clinically confirmed (ex-)pertussis patients and in a Dutch population cohort. Of the seven investigated SNPs in five genes, a polymorphism in the Vitamin D receptor (VDR) gene (rs10735810) was associated with pertussis. The VDR major allele and its homozygous genotype were more present in the symptomatic pertussis patient cohort compared to the control population cohort. Interestingly, the VDR major allele correlated also with the duration of reported pertussis symptoms. Vitamin D3 (VD3) and VDR are important regulators of immune activation. Altogether, these findings suggest that polymorphisms in the VDR gene may affect immune activation and the clinical outcome of B. pertussis infection.

[The status of pertussis infection and molecular epidemiological characteristics of pertussis in Tianjin, 2013]

OBJECTIVE

To understand the status of pertussis infection and characteristics of molecular epidemiology of pertussis in 2013 in Tianjin.

METHODS

Totally, 181 suspected pertussis cases were selected and their nasopharyngeal swabs and serum were sampled at the Disease Monitoring Settings in Tianjin. Real-time PCR was used to detect Bordetella pertussis double target genes and enzyme linked immune-sorbent assay (ELISA) method was used to detect the specific pertussis toxin IgG (PT-IgG) antibody. Fimbriae 2 (FIM2) and Fimbriae 3 (FIM3) genes of pertussis was amplified by PCR for sequencing, from 30 pertussis DNA positive samples.

RESULTS

The positive rate of Real-time PCR was 68.24% in 148 cases and the positive rate of PT-IgG antibody was 55.56% in 108 cases. Among 101 cases that nucleic acid were positive, the median duration of disease was 11 days. Among the PT-IgG Positive cases (60 cases), the median duration of disease was 21 days. In cases under 1 year old, the Real-time PCR testing positive rate was 84.28%. Positive rates among other age groups, the differences were statistically significant. Nucleotide homologies of FIM2 and FIM3 genes from 30 pertussis strains were 99.6%-100.0%, while it was 99% when compared to both international standard Tohama strain and Chinese vaccine strain.

CONCLUSION

Detection of pertussis by Real-time PCR from clinical nasopharyngeal swab sample was quick and sensitive for the diagnosis. Bordetella pertussis epidemic strains in Tianjin area appeared close relation with both the international standards and China vaccine strains.

Diagnosis of pertussis: a historical review and recent developments

The accurate and timely diagnosis of pertussis continues to be challenging. The widespread use of pertussis vaccines has dramatically altered the epidemiology and clinical presentation of pertussis disease, such that many cases do not present with the hallmark symptoms, such as inspiratory whoop, post-tussive vomiting and paroxysmal cough. A variety of laboratory tools are available to aid in the diagnosis of pertussis, including culture, direct fluorescent antibody testing, PCR, and paired and single serology techniques. This article reviews the strengths and limitations, including the sensitivity and specificity, of each of these diagnostic tools.

[The kit of reagents for polymerase chain reaction diagnostic of infections caused by B. pertussis, B. parapertussis and B. bronchiseptica]

The effective treatment of whooping cough directly depends of early diagnostics. The polymerase chain reaction diagnostic is the most perspective diagnostic technique. The kit of reagents is developed to diagnose whooping cough, parapertussis and bronchosepticosis with polymerase chain reaction. The evaluation of its analytical characteristics was carried out. The sensitivity made 1 x 103 of genome equivalents per 1 ml of sample (the sorption technique of DNA extraction was applied) and 5 x 102 of genome equivalents per 1 ml (the precipitation technique of DNA extraction was used). The specificity of test in the framework of analyzed panel of strains and isolates of microorganisms made 100%. The diagnostic sensitivity of analysis exceeded the sensitivity of bacteriological analysis up to 20 times. The application of this kit of reagents permits to detect and to differentiate DNA of agent of whooping cough, parapertussis during one working day already at the beginning of catarrhal period of disease and up to 18th day from the moment of cough appearance. In perspective, this process creates an opportunity to apply timely the specific therapy. The specter of agents of acute respiratory diseases brining on acute prolonged cough in children who were directed to bacteriological analysis to confirm whooping cough is investigated.

[Accumulation of the bvg- Bordetella pertussis a virulent mutants in the process of experimental whooping cough in mice]

The duration of the persistence and dynamics of accumulation of insertion bvg- Bordetella pertussis mutants were studied in lungs of laboratory mice after intranasal and intravenous challenge by virulent bacteria of the causative agent of whooping cough. The capability of the virulent B. pertussis bacteria to long-term persistence in the body of mice was tested. Using the real-time PCR approximately hundred genome equivalents of the B. pertussis DNA were detected in lungs of mice in two months after infection regardless of the way of challenge. Using the bacterial test bacteria were identified during only four weeks after challenge. Bvg- B. pertussis avirulent mutants were accumulated for the infection time. The percentage of the avirulent bacteria in the B. pertussis population reached 50% in 7-9 weeks after challenge. The obtained results show that the laboratory mice can be used for study of the B. pertussis insertion mutant formation dynamics in vivo and confirm the hypothesis about insertional bvg- B. pertussis virulent mutants accumulation during development of pertussis infection in human.

[Characteristics of Bordetelia pertussis strains isolated from pertussis patients in Moscow by using multilocus sequencing]

AIM

Genotyping of B. pertussis strains isolated from pertussis patients in Moscow.

MATERIALS AND METHODS

53 strains of B. pertussis isolated from pertussis patients in Moscow in 2007 - 2010 as well as 3 vaccine strains currently used in Russia for the production of DTP vaccine were studied by multilocus sequencing (MLST) based on allele combinations of ptxA, ptxC and tcfA genes.

RESULTS

A genetic characteristic of B. pertussis strains isolated from pertussis patients in Moscow by using MLST is presented. Allele profile analysis of the studied B. pertussis strains was performed, 4 sequence types (ST) were identified--ST1, ST2, ST3 and ST5, most of the circulating strains (86.7%) were shown to belong to ST5, equal percentage of cases (5.7%)--to ST2 and ST3, and 1.9%--to ST1, while 2 vaccine production strains belong to ST2 and 1 - to ST1.

CONCLUSION

Clonal structure of contemporary Moscow strains was shown to be different from strain structure used for the production of DTP vaccine.

Bordetella pertussis and vaccination: the persistence of a genetically monomorphic pathogen

Before childhood vaccination was introduced in the 1950s, pertussis or whooping cough was a major cause of infant death worldwide. Widespread vaccination of children was successful in significantly reducing morbidity and mortality. However, despite vaccination, pertussis has persisted and, in the 1990s, resurged in a number of countries with highly vaccinated populations. Indeed, pertussis has become the most prevalent vaccine-preventable disease in developed countries with estimated infection frequencies of 1-6%. Recently vaccinated children are well protected against pertussis disease and its increase is mainly seen in adolescents and adults in which disease symptoms are often mild. The etiologic agent of pertussis, Bordetella pertussis, is extremely monomorphic and its ability to persist in the face of intensive vaccination is intriguing. Numerous studies have shown that B. pertussis populations changed after the introduction of vaccination suggesting adaptation. These adaptations did not involve the acquisition of novel genes but small genetic changes, mainly SNPs, and occurred in successive steps in a period of 40 years. The earliest adaptations resulted in antigenic divergence with vaccine strains. More recently, strains emerged with increased pertussis toxin (Ptx) production. Here I argue that the resurgence of pertussis is the compound effect of pathogen adaptation and waning immunity. I propose that the removal by vaccination of naïve infants as the major source for transmission was the crucial event which has driven the changes in B. pertussis populations. This has selected for strains which are more efficiently transmitted by primed hosts in which immunity has waned. The adaptation of B. pertussis to primed hosts involved delaying an effective immune response by antigenic divergence with vaccine strains and by increasing immune suppression through higher levels of Ptx production. Higher levels of Ptx may also benefit transmission by enhancing clinical symptoms. The study of B. pertussis populations has not only increased our understanding of pathogen evolution, but also suggests way to improve pertussis vaccines, underlining the public health significance of population-based studies of pathogens.

The re-emergence of pertussis: implications for diagnosis and surveillance

Pertussis, or whooping cough, a highly contagious disease caused by Bordetella pertussis, is making a comeback globally and nationally in spite of reasonable vaccination coverage. This paper provides an update on laboratory testing methods that assist the confirmation of clinical disease and investigation of outbreaks. Laboratory confirmation of the diagnosis by polymerase chain reaction or serology should be attempted, especially when atypical pertussis is suspected clinically. Genetic and antigenic variations in virulence factors of strains circulating in the population should also be monitored.

Comparative gene expression profiling in two congenic mouse strains following Bordetella pertussis infection

BACKGROUND

Susceptibility to Bordetella pertussis infection varies widely. These differences can partly be explained by genetic host factors. HcB-28 mice are more resistant to B. pertussis infection than C3H mice, which could partially be ascribed to the B. pertussis susceptibility locus-1 (Bps1) on chromosome 12. The presence of C57BL/10 genome on this locus instead of C3H genome resulted in a decreased number of bacteria in the lung. To further elucidate the role of host genetic factors, in particular in the Bps1 locus, in B. pertussis infection, and to identify candidate genes within in this region, we compared expression profiles in the lungs of the C3H and HcB-28 mouse strains following B. pertussis inoculation. Twelve and a half percent of the genomes of these mice are from a different genetic background.

RESULTS

Upon B. pertussis inoculation 2,353 genes were differentially expressed in the lungs of both mouse strains. Two hundred and six genes were differentially expressed between the two mouse strains, but, remarkably, none of these were up- or down-regulated upon B. pertussis infection. Of these 206 genes, 17 were located in the Bps1 region. Eight of these genes, which showed a strong difference in gene expression between the two mouse strains, map to the immunoglobulin heavy chain complex (Igh).

CONCLUSION

Gene expression changes upon B. pertussis infection are highly identical between the two mouse strains despite the differences in the course of B. pertussis infection. Because the genes that were differentially regulated between the mouse strains only showed differences in expression before infection, it appears likely that such intrinsic differences in gene regulation are involved in determining differences in susceptibility to B. pertussis infection. Alternatively, such genetic differences in susceptibility may be explained by genes that are not differentially regulated between these two mouse strains. Genes in the Igh complex, among which Igh-1a/b, are likely candidates to explain differences in susceptibility to B. pertussis. Thus, by microarray analysis we significantly reduced the number of candidate susceptibility genes within the Bps1 locus. Further work should establish the role of the Igh complex in B. pertussis infection.

Bordetella pertussis PCR positivity, following onset of illness in children under 5 years of age

Bordetella pertussis is a significant cause of respiratory illness and an ongoing public health problem. Pertussis polymerase chain reaction (PCR) testing has been widely utilised since 2001, especially in infants. Uncertainty exists as to how long PCR remains positive following symptom onset. Further information on the time frame for pertussis PCR testing would assist diagnosis, epidemiological research and disease control. The Brisbane Southside Population Health Unit (BSPHU) conducted a retrospective analysis of enhanced surveillance data from pertussis notifications between January 2001 and December 2005, in children less than 5 years of age, in the BSPHU reporting area with the aim to determine the possible range of duration of Bordetella pertussis PCR, from symptom onset for this age group. Of 1,826 pertussis notifications to BSPHU between January 2001 and December 2005, 155 (8.5%) were children under 5 years of age, with 115 pertussis PCR positive results. Analysis indicated a range of PCR positivity from day one to day 31 from the onset of catarrhal symptoms with most (84%) being within 21 days from onset of catarrhal symptoms. The range of PCR positivity following onset of paroxysmal cough was from day one to day 38 with most (89%) being within 14 days from the onset of paroxysmal cough. This review of pertussis PCR data in young children showed that PCR positive results generally mirrored the understood length of infectivity with regard to both catarrhal symptoms and paroxysmal cough; namely that PCR positive results were obtained at least 21 days following onset of catarrhal symptoms and at least 14 days following onset of paroxysmal cough.

Lung response to Bordetella pertussis infection in mice identified by gene-expression profiling

Host genetics determines the course of Bordetella pertussis infection in mice. Previously, we found four loci, Tlr4 and three novel loci, designated Bps 1–3, that are involved in the control of B. pertussis infection. The purpose of the present study was to identify candidate genes that could explain genetic differences in the course of B. pertussis infection, assuming that such genes are differentially regulated upon infection. We, therefore, studied the course of mRNA expression in the lungs after B. pertussis infection. Of the 22,000 genes investigated, 1,841 were significantly differentially expressed with 1,182 genes upregulated and 659 genes downregulated. Upregulated genes were involved in immune-related processes, such as the acute-phase response, antigen presentation, cytokine production, inflammation, and apoptosis, while downregulated genes were mainly involved in nonimmune processes, such as development and muscle contraction. Pathway analysis revealed the involvement of granulocyte function, toll-like receptor signaling pathway, and apoptosis. Nine of the differentially expressed genes were located in Bps-1, 13 were located in Bps-2, and 62 were located in Bps-3. We conclude that B. pertussis infection induces a wide and complex response, which appears to be partly specific for B. pertussis and partly nonspecific. We envisage that these data will be helpful in identifying polymorphic genes that affect the susceptibility and course of B. pertussis infection in humans.

[Application of DNA microcarriers for evaluation of mice splenocytes genes expression after immunization with pertussis vaccines and challenged with different B. pertussis strains]

The study aimed at identification of splenocytes genes expression induced after immunization with whole-cell or acellular pertussis vaccines and subsequent challenge with B. pertussis strains of different ptxS1/prn genes alleles in correlation with differences in bacteria elimination from the lung tissue. Investigations were performed using DNA microcarriers. Analysis of genes expression generated through B. pertussis challenge on DNA microcarriers confirmed the role of specific B. pertussis virulence factors in differences of induced transcription response in the host. Level of differences in splenocytes transcriptional response of mice immunized with whole-cell pertussis vaccine was higher than that found in animals immunized with acellular pertussis vaccine. Level of genes expression change induced with B. pertussis 2316 strain was as much as twice higher than that found after challenge with B. pertussis 629 strain. Levels of gene expression change during challenge with B. pertussis 629 and 2316 strains were similar after immunization with acellular pertussis vaccine. Differences of transcriptional response induced with B. pertussis 2316 strain were associated with induction of immunological response, activation of inflammatory mediators, as well as with synthesis of heat shock proteins. Further studies performed with DNA microcarriers on sufficient number of B. pertussis strains might confirm this initial screening of genes identification involved in activation and repression of basic regulatory pathways after challenge with B. pertussis strains variant's for statistical evaluation of functional differences detected in presented study.

Host genetics of Bordetella pertussis infection in mice: significance of Toll-like receptor 4 in genetic susceptibility and pathobiology

The susceptibility to and the severity of Bordetella pertussis infections in infants and children varies widely, suggesting that genetic differences between individuals influence the course of infection. We have previously identified three novel loci that influence the severity of whooping cough by using recombinant congenic strains of mice: Bordetella pertussis susceptibility loci 1, 2, and 3 (Bps1, -2, and -3). Because these loci could not account for all genetic differences between mice, we extended our search for additional susceptibility loci. We therefore screened 11 inbred strains of mice for susceptibility to a pertussis infection after intranasal infection. Susceptibility was defined by the number of bacteria in the lungs, being indicative of the effect between the clearance and replication of bacteria. The most resistant (A/J) and the most susceptible (C3H/HeJ) strains were selected for further genetic and phenotypic characterization. The link between bacterial clearance and chromosomal location was investigated with 300 F2 mice, generated by crossing A/J and C3H/HeJ mice. We found a link between the delayed clearance of bacteria from the lung and a large part of chromosome 4 in F2 mice with a maximum log of the odds score of 33.6 at 65.4 Mb, which is the location of Tlr4. C3H/HeJ mice carry a functional mutation in the intracellular domain of Tlr4. This locus accounted for all detectable genetic differences between these strains. Compared to A/J mice, C3H/HeJ mice showed a delayed clearance of bacteria from the lung, a higher relative lung weight, and increased body weight loss. Splenocytes from infected C3H/HeJ mice produced almost no interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) upon ex vivo restimulation with B. pertussis compared to A/J mice and also showed a delayed gamma interferon (IFN-gamma) production. TNF-alpha expression in the lungs 3 days after infection was increased fivefold compared to uninfected controls in A/J mice and was not affected in C3H/HeJ mice. In conclusion, Tlr4 is a major host factor explaining the differences in the course of infection between these inbred strains of mice. Functional Tlr4 is essential for an efficient IL-1-beta, TNF-alpha, and IFN-gamma response; efficient clearance of bacteria from the lung; and reduced lung pathology.

Genetic control of Bordetella pertussis infection: identification of susceptibility loci using recombinant congenic strains of mice

Susceptibility to and severity of Bordetella pertussis infection in infants and children vary widely. The spectrum of clinical symptoms ranges from subclinical infection to mild disease, severe whooping cough, and death. The aims of this study were to examine genetic susceptibilities of mice to B. pertussis and to identify genetic loci in the mouse genome that are involved in susceptibility to B. pertussis infection. For this purpose we screened two sets of recombinant congenic strains (RCS) of mice, HcB and CcS, for differences in the numbers of bacteria in the lung 7 days after inoculation. For both CcS and in HcB mice, a wide range in numbers of bacteria in the lung was found, suggesting that the course of infection is under multigenic control. From both RCS sets of mice, we selected one strain to identify possible susceptibility loci in F(2) hybrid mice. The degree of lung colonization 7 days postinoculation in these F(2) mice was evaluated in relation to genetic markers by linkage analysis. We found three novel loci that are involved in the control of B. pertussis infection. One locus, designated B. pertussis susceptibility locus 1 (Bps-1), was identified on chromosome 12. The presence of the C57BL/10 genome on this locus instead of the C3H genome significantly decreased the number of B. pertussis bacteria in the lung. Bps-1 has a dominant-positive effect on the clearance of B. pertussis from the lung. The function of most genes in this region is unknown. Two other loci, Bps-2 and Bps-3, showed genetic interaction and are located on chromosomes 5 and 11. We aim to identify the gene(s) in these regions which modify susceptibility to B. pertussis.

Evaluation of the role of the Bvg intermediate phase in Bordetella pertussis during experimental respiratory infection

The BvgAS system of Bordetella pertussis was traditionally considered to mediate a transition between two phenotypic phases (Bvg(+) and Bvg(-)) in response to environmental signals. We characterized a third state, the intermediate (Bvg(i)) phase, which can be induced by introducing a 1-bp substitution into bvgS (the bvgS-I1 mutation) or by growing B. pertussis under conditions intermediate between those leading to the Bvg(+) and Bvg(-) phases. Like B. bronchiseptica, B. pertussis displays in its Bvg(i) phase a characteristic colony morphology and hemolytic activity and expresses a Bvg(i)-phase-specific polypeptide called BipA, whose synthesis is regulated by bvgAS at the transcriptional level. Based on our results, we hypothesize that the Bvg(i) phase of B. pertussis may be involved in facilitating transmission between hosts. Thus, a B. pertussis mutant carrying the bvgS-I1 mutation (GMT1i) persisted at wild-type levels only in the upper murine respiratory tract. Interestingly, a bipA deletion derivative of GMT1i displayed a reduced ability to colonize the nasal cavity of mice compared with GMT1i. However, in experimental mixed infections GMT1i expressing the Bvg(i) phase could establish an initial colonization in the nose and trachea of mice as efficiently as GMT1, but the wild-type strain outcompeted GMT1i at a later time point at all sites of the respiratory tract, suggesting that the Bvg(i) phase does not serve as a phenotypic phase specialized in colonization. Finally, even though B. pertussis expresses in vitro the Bvg(i) phase at the human nasal temperature, anti-BipA antibodies were undetectable in a large collection of sera from pertussis patients.

[Routine use of gene amplification for pertussis diagnosis in children]

OBJECTIVES

The resurgence of whooping cough observed in France convinced us to develop a specific PCR assay to detect B. pertussis in nasopharyngeal secretions in parallel of the culture. The aim of our study was to show the value of the PCR in routine diagnosis.

MATERIAL AND METHODS

From November 1996 to August 2000, in two hospitals located in the Yvelines (France), the children consulting for a cough compatible with the diagnosis of whooping cough were included in this study. A questionnaire including clinical, biological and radiological items was completed for each one of these patients. A culture of Bordetella and a detection by PCR of B. pertussis were carried out on each nasopharyngeal aspirate. The diagnosis of whooping cough was retained if the detection was positive in PCR and/or culture.

RESULTS

Among the 215 investigated children with suspected cases of whooping cough, the diagnosis was positive for 45 (20.9%), of which 39 were less than one year old (median: three months). Sixteen (35.5,%) were positive at the same time for both the PCR and the culture, 26 (57.8%) for only PCR and three (6.7%) for only culture. The PCR was positive in 93.3% of the cases. The results were obtained with an average time of 48 hours. The culture was positive in 61.2% of the cases with an average time of six days. The monthly distribution of the cases of whooping cough was very inhomogeneous and of epidemic appearance. The majority of the cases was located between two periods: 42% between November 1996 and September 1997 and 40% between November 1999 and August 2000. Among the infected children, 15 were less than two months old and were not yet vaccinated; among the 24 others infants, a delay in the vaccine calendar was noted in 50% of the cases. Four children between six and 14 years old were correctly vaccinated. The evolution was favourable in all the children.

CONCLUSION

The PCR due to its sensitivity, its specificity and its rapidity offers to the clinician a powerful tool for the diagnosis of whooping cough. Nevertheless, the culture must be associated with the PCR, in order to follow the epidemiology and the sensitivity to antibiotics of B. pertussis.

Evaluation of an improved DNA probe for diagnosis of pertussis

A Bordetella pertussis specific subclone, pRZ61, of a Bordetella genus-specific clone, pB23, was evaluated on nasopharyngeal aspirates of 179 patients with suspected pertussis. Hybridization was performed directly after spotting or after 1-3 days of preculture of the nylon membranes on solid culture medium. A direct comparison of the two probes was obtained by reprobing with the subclone the same membranes that had been hybridized with the parent probe. pRZ61 detected 50% of the serologically defined cases of pertussis, that is, had the same sensitivity as standard culture. Specificity as compared with serology was close to 100%. The increasing sensitivity and the corresponding decreasing specificity after preculture noted for pB23 was not seen with the subclone. The study showed that the improved probe represents a rapid diagnostic method in pertussis.

Risk factors for community- and household-acquired pertussis during a large-scale outbreak in central Wisconsin

To identify risk factors associated with community- and household-acquired pertussis, we studied 61 households (HHs) with members with culture-positive illnesses and compared their characteristics with 58 neighborhood control-HHs and 62 randomly selected control-HHs. Case-HHs were more likely than either control group to have members 12-18 y of age (P less than .01); these individuals accounted for 34% of all primary cases. A history of exposure outside the home was the most important predictor of community-acquired infection (P less than .001), with adolescents being at higher risk than other age-groups (odds ratio, 3.2; P less than .001). After known exposure to a culture-positive case in the same HH, the risk of illness was unrelated to age; lengthy delays in initiating erythromycin therapy and prophylaxis were the only factors associated with secondary spread (P less than .01). The risk of pertussis may be related more to the likelihood of exposure than to age-related increases in susceptibility, and the risk can be reduced with appropriate use of erythromycin.

From whom do children catch pertussis?

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Heredity and infectious diseases: a twin study

A concordance study of 6 infectious diseases of childhood has been carried out in a sample of 656 twin pairs classified by sex and zygosity. A new approach is proposed to estimate the respective influence of heredity and of common environment. The estimates thus obtained range from 86% hereditary component in the case of measles to 100% environmental component in the case of scarlet fever.

Intrafamilial spread of pertussis

Intrafamilial spread of pertussis was evaluated in 21 families (97 individuals) of patients with whooping cough diagnosed by culture or by ELISA serology. During follow-up (average six months), an infectivity rate of 83% was established by an ELISA within these families. However, 46% of the secondary cases were asymptomatic. Most of the asymptomatic cases were in adults or vaccinated children. Unvaccinated infants had classic whooping cough and were exposed to pertussis by their vaccinated siblings or parents. The incidence of classic symptoms of pertussis decreased with age, and atypical pertussis was usually culture negative but rapidly diagnosed by measurement of the IgM- and IgA-class antibodies by ELISA.

[Spread of whooping cough among adults today]

Epidemiological surveys with the use of the clinical and bacteriological methods of examination were carried out in 107 foci of pertussis in families (283 adults), 25 foci in children's institutions (103 employees) and 1 focus in a surgical department for infants (29 adults). The infection was shown to be widely spread among adults at present: 23.7% in the surveyed families, 10% in children's institutions and 6.9% in the surgical department for infants. In the familiies, 26.2% of the adults were the first to fall ill with pertussis. no essential differences in the terms of the release of the infective agent, as well as in the course of the disease, in adults and in vaccinated children were found. Antiepidemic measures in respect to adult pertussis patients is proposed.

Further studies on the inheritance of responsiveness to pertussis HSF in mice

Inheritance of responsiveness to histamine-sensitizing factor of pertussis bacilli (HSF) was investigated in (C3H/HeJ times C57BL/6J)F1 hybrids, backcross progeny of this hybrid to C57BJ/6J parent (C3H/HeJ times DBA/2J)F1 hybrids, and in backcross progeny of this hybrid to DBA/2J parent. It was found that transmission is not by virtue of a single autosomal dominant gene, as has been postulated. Rather, inheritance of responsiveness to HSF is far more complex, probably involving polygenic transmission.