Differentiation between human and ovine isolates of Bordetella parapertussis using pulsed-field gel electrophoresis

A novel multilocus variable-number tandem repeat analysis for Bordetella parapertussis

Purpose. Human-adapted Bordetella parapertussis is one of the causative agents of whooping cough; however, there are currently no genotyping systems with high discriminatory power for this bacterial pathogen. We therefore aimed to develop a multilocus variable-number tandem repeat analysis (MLVA) for human-adapted B. parapertussis.Methodology. Four highly polymorphic variable number tandem repeat (VNTR) loci in the B. parapertussis genome were selected and amplified by multiplex PCR. MLVA was performed based on the number of tandem repeats at VNTR loci. The discriminatory power of MLVA was evaluated with three laboratory reference strains and 50 human isolates of B. parapertussis.Results. Multiplex PCR-based MLVA characterized 53 B. parapertussis reference strains and isolates into 25 MLVA types and the Simpson diversity index was 0.91 (95 % confidence interval, 0.86-0.97). The three reference strains exhibited different MLVA types. Thirty-one Japanese isolates, ten French isolates and three Taiwanese isolates belonged to fourteen, nine and three MLVA types, respectively. In contrast, all five Australian isolates belonged to the same type. Two Japanese isolates collected from patients with known epidemiological links had the same type.Conclusion. Our novel MLVA method has high discriminatory power for genotyping human B. parapertussis. Regarding this organism, this genotyping system is a promising tool for epidemiological surveillance and investigating outbreaks.

Rediscovering Pertussis

Pertussis, caused by Bordetella (B.) pertussis, a Gram-negative bacterium, is a highly contagious airway infection. Especially in infants, pertussis remains a major health concern. Acute infection with B. pertussis can cause severe illness characterized by severe respiratory failure, pulmonary hypertension, leucocytosis, and death. Over the past years, rising incidence rates of intensive care treatment in young infants were described. Due to several virulence factors (pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin, filamentous hemagglutinin, and lipooligosaccharide) that promote bacterial adhesion and invasion, B. pertussis creates a unique niche for colonization within the human respiratory tract. The resulting long-term infection is mainly caused by the ability of B. pertussis to interfere with the host's innate and adaptive immune system. Although pertussis is a vaccine-preventable disease, it has persisted in vaccinated populations. Epidemiological data reported a worldwide increase in pertussis incidence among children during the past years. Either acellular pertussis (aP) vaccines or whole-cell vaccines are worldwide used. Recent studies did not detect any differences according to pertussis incidence when comparing the different vaccines used. Most of the currently used aP vaccines protect against acute infections for a period of 6-8 years. The resurgence of pertussis may be due to the lack of herd immunity caused by missing booster immunizations among adolescents and adults, low vaccine coverages in some geographic areas, and genetic changes of different B. pertussis strains. Due to the rising incidence of pertussis, probable solution strategies are discussed. Cocooning strategies (vaccination of close contact persons) and immunizations during pregnancy appear to be an approach to reduce neonatal contagiousness. During the past years, studies focused on the pathway of the immune modulation done by B. pertussis to provide a basis for the identification of new therapeutic targets to enhance the host's immune response and to probably modulate certain virulence factors.

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.

Molecular evolution of the two-component system BvgAS involved in virulence regulation in Bordetella

The whooping cough agent Bordetella pertussis is closely related to Bordetella bronchiseptica, which is responsible for chronic respiratory infections in various mammals and is occasionally found in humans, and to Bordetella parapertussis, one lineage of which causes mild whooping cough in humans and the other ovine respiratory infections. All three species produce similar sets of virulence factors that are co-regulated by the two-component system BvgAS. We characterized the molecular diversity of BvgAS in Bordetella by sequencing the two genes from a large number of diverse isolates. The response regulator BvgA is virtually invariant, indicating strong functional constraints. In contrast, the multi-domain sensor kinase BvgS has evolved into two different types. The pertussis type is found in B. pertussis and in a lineage of essentially human-associated B. bronchiseptica, while the bronchiseptica type is associated with the majority of B. bronchiseptica and both ovine and human B. parapertussis. BvgS is monomorphic in B. pertussis, suggesting optimal adaptation or a recent population bottleneck. The degree of diversity of the bronchiseptica type BvgS is markedly different between domains, indicating distinct evolutionary pressures. Thus, absolute conservation of the putative solute-binding cavities of the two periplasmic Venus Fly Trap (VFT) domains suggests that common signals are perceived in all three species, while the external surfaces of these domains vary more extensively. Co-evolution of the surfaces of the two VFT domains in each type and domain swapping experiments indicate that signal transduction in the periplasmic region may be type-specific. The two distinct evolutionary solutions for BvgS confirm that B. pertussis has emerged from a specific B. bronchiseptica lineage. The invariant regions of BvgS point to essential parts for its molecular mechanism, while the variable regions may indicate adaptations to different lifestyles. The repertoire of BvgS sequences will pave the way for functional analyses of this prototypic system.

Infection with Bordetella parapertussis but not Bordetella pertussis causes pertussis-like disease in older pigs

The 3 major Bordetella species--namely, B. pertussis, B. parapertussis, and B. bronchiseptica--can be distinguished by their different host ranges. B. bronchiseptica infects a wide range of mammals (including humans), whereas B. pertussis infects only humans and, under experimental conditions, mice and pigs. In contrast, B. parapertussis, also a causative agent of pertussis, displays a unique host specificity with 2 subgroups, one infecting only humans and the other infecting only sheep. Here, we show that both strains of B. parapertussis also infect older piglets when delivered intrapulmonarily. Infected piglets displayed mild fever and respiratory symptoms, such as coughing and breathing difficulties. Importantly, transmission was observed between infected and noninfected piglets. In tracheal organ cultures, adherence to ciliated epithelial cells was observed. Furthermore, both strains of B. parapertussis displayed higher resistance than B. pertussis to neutralization by porcine beta-defensin 1 in the respiratory tract, which has been demonstrated to be associated with protection against B. pertussis disease in older pigs. The development of this new model will assist us in better understanding the pathogenesis of this disease and in the development of more-effective vaccines against pertussis.

IEIIS Meeting minireview: Bordetella evolution: lipid A and Toll-like receptor 4

The evolution of Bordetella pertussis and Bordetella parapertussis from Bordetella bronchiseptica involved changes in host range and pathogenicity. Recent data suggest that the human-adapted Bordetella modified their interaction with host immune systems to effect these changes and that decreased stimulation of Toll-like receptor 4 (TLR4) by lipid A is central to this. We discuss Bordetella lipid A structure and genetics within the context of evolution and host immunity.

Genomic features of Bordetella parapertussis clades with distinct host species specificity

BACKGROUND

The respiratory pathogen Bordetella parapertussis is a valuable model in which to study the complex phenotype of host specificity because of its unique two-species host range. One subset of strains, including the sequenced representative, causes whooping cough in humans, while other strains infect only sheep. The disease process in sheep is not well understood, nor are the genetic and transcriptional differences that might provide the basis for host specificity among ovine and human strains.

RESULTS

We found 40 previously unknown genomic regions in an ovine strain of B. parapertussis using subtractive hybridization, including unique lipopolysaccharide genes. A microarray survey of the gene contents of 71 human and ovine strains revealed further differences, with 47 regions of difference distinguishing the host-restricted subgroups. In addition, sheep and human strains displayed distinct whole-genome transcript abundance profiles. We developed an animal model in which sheep were inoculated with a sheep strain, human strain, or mixture of the two. We found that the ovine strain persisted in the nasal cavity for 12 to 14 days, while the human strain colonized at lower levels and was no longer detected by 7 days post-inoculation. The ovine strain induced less granulocyte infiltration of the nasal mucosa.

CONCLUSION

Several factors may play a role in determining host range of B. parapertussis. Human- and ovine-associated strains have differences in content and sequence of genes encoding proteins that mediate host-pathogen contact, such as lipopolysaccharide and fimbriae, as well as variation in regulation of toxins, type III secretion genes, and other virulence-associated genes.

Domestic animals as carriers of Bordetella species in Senegal

Despite intense efforts to maintain a high level of vaccine coverage against human whooping cough, rural senegalese areas are still endemic for Bordetella pertussis. One explanation being the potential existence of animal reservoirs, the objective of this work was to precise the carriage by domestic animals of bacteria belonging to the genus Bordetella in Senegal. Bacteriological samples (swabs and aspirates) were obtained from various domestic animals living in different parts of the country. No B. pertussis nor B. parapertussis were isolated. However, for the first time to our knowledge, B. bronchiseptica was identified from small ruminants located in Africa. The positive animals were two goats and two sheep from Dakar slaughterhouse together with a goat living in a rural compound. The fact that it was identified in goats and sheep underlines the potential zoonotic of that bacterial species in countries where small ruminants are of economical and cultural relevance.

Bordetella pertussis: the intersection of genomics and pathobiology

There has been much recent concern over an increasing incidence of pertussis despite high levels of vaccine coverage of infants. Many reports have documented that much of the increased incidence is due to infection in adolescents and adults. This renewal of interest in pertussis comes at a time when the findings of the Bordetella genome project have led to a quantum leap forward in our understanding of the biology, evolution and pathogenesis of the bacterium responsible for the disease. The impact of this basic research on current clinical problems posed by B. pertussis infection is discussed.

Amplified fragment length polymorphism (AFLP) versus randomly amplified polymorphic DNA (RAPD) as new tools for inter- and intra-species differentiation within Bordetella

Automated amplified fragment length polymorphism (AFLP) and randomly amplified polymorphic DNA (RAPD) techniques with fluorescently labelled primers were used to track differences among isolates of the eight known species of the Bordetella genus. Eighty-one representative strains of these species from international and Polish bacterial collections were genotyped according to RAPD protocols using primer 1254 or 1247, and AFLP involving EcoRI/MseI or newly designed SpeI/ApaI restriction/ligation/amplification procedures. By comparing AFLP and RAPD data, it was concluded that the discriminatory power of AFLP is higher in comparison with RAPD for both intra- and inter-species differentiation of isolates of the Bordetella genus. The most precise level of inter-species discrimination and the highest level of intra-species discrimination of the Bordetella isolates of the eight species were observed in the AFLP EcoRI/MseI and SpeI/ApaI sets, respectively. Both techniques might provide alternative tools for the identification of Bordetella at the genomic species and strain levels, and thus may be valuable in human and veterinary diagnostics as well as in epidemiology. By applying the AFLP technique presented in this article, more precise data on the emergence of newly acquired and/or on expanded clones and transmission routes of isolates of the Bordetella genus in the human and animal environments might be obtained.

Ciliostasis is a key early event during colonization of canine tracheal tissue by Bordetella bronchiseptica

The primary site of infection for Bordetella bronchiseptica, Bordetella pertussis and Bordetella parapertussis is the ciliated respiratory epithelium. Previous studies have implicated adherence of bacteria to cilia, induction of mucus production, induction of ciliostasis and damage to the ciliated epithelium in Bordetella pathogenesis. This paper describes the use of an air-interface organ culture system using canine tracheal tissue infected with B. bronchiseptica to assess the temporal relationship between these pathologies. Ciliostasis occurs very early during the host tissue-pathogen interaction, before mucus production and obvious signs of epithelial damage occur. A B. bronchiseptica bvg mutant does not colonize the organ culture model, induce ciliostasis or cause damage to the epithelial cell layer, but it does induce similar amounts of mucus release as does infection by wild-type bacteria. The authors propose that ciliostasis is a key early event during the B. bronchiseptica-host tissue interaction that abrogates the muco-ciliary defences of the host tissue, renders it susceptible to colonization by the bacteria and allows subsequent damage to the epithelium. The organ culture model described offers a physiologically relevant tool with which to characterize the molecular basis for interactions between Bordetella and its primary site of infection, the ciliated respiratory epithelium.

Structural characterization of the O-chain polysaccharide isolated from Bordetella avium ATCC 5086: variation on a theme(1)

The O-chain polysaccharide (O-PS) of Bordetella avium was isolated from the lipopolysaccharide by mild acid hydrolysis to remove the lipid A, followed by hydrofluorolysis to remove the lipopolysaccharide core oligosaccharide leaving a residual O-PS for structural analysis. High resolution (1)H and (13)C NMR and MALDI studies showed the O-chain to be a polymer composed of 1,4-linked 2-acetamidino-3-[3-hydroxybutanamido]-2,3-dideoxy-beta-D-glucopyranosyluronic acid residues.

Comparative phenotypic analysis of the Bordetella parapertussis isolate chosen for genomic sequencing

The genomes of three closely related bordetellae are currently being sequenced, thus providing an opportunity for comparative genomic approaches driven by an understanding of the comparative biology of these three bacteria. Although the other strains being sequenced are well studied, the strain of Bordetella parapertussis chosen for sequencing is a recent human clinical isolate (strain 12822) that has yet to be characterized in detail. This investigation reports the first phenotypic characterization of this strain, which will likely become the prototype for this species in comparison with the prototype strains of B. pertussis (Tohama I), B. bronchiseptica (RB50), and other isolates of B. parapertussis. Multiple in vitro and in vivo assays distinguished each species. B. parapertussis was more similar to B. bronchiseptica than to B. pertussis in many assays, including in BvgS signaling characteristics, presence of urease activity, regulation of urease expression by BvgAS, virulence in the respiratory tracts of immunocompromised mice, induction of anti-Bordetella antibodies, and serum antimicrobial resistance. In other assays, B. parapertussis was distinct from all other species (in pigment production) or more similar to B. pertussis (by lack of motility and cytotoxicity to a macrophage-like cell line). These results begin to provide phenotypes that can be related to genetic differences identified in the genomic sequences of bordetellae.

Relaxed acyl chain specificity of Bordetella UDP-N-acetylglucosamine acyltransferases

Lipid A (endotoxin) is a major structural component of Gram-negative outer membranes. It also serves as the hydrophobic anchor of lipopolysaccharide and is a potent activator of the innate immune response. Lipid A molecules from the genus Bordetella are reported to exhibit unusual structural asymmetry with respect to the acyl chains at the 3- and 3'-positions. These acyl chains are attached by UDP-N-acetylglucosamine acyltransferase (LpxA). To determine the origin of the acyl variability, the single lpxA ortholog present in each of the genomes of Bordetella bronchiseptica (lpxA(Br)), Bordetella parapertussis (lpxA(Pa)), and Bordetella pertussis (lpxA(Pe)) was cloned and expressed in Escherichia coli. In contrast to all LpxA proteins studied to date, LpxA(Br) and LpxA(Pe) display relaxed acyl chain length specificity in vitro, utilizing C(10)OH-ACP, C(12)OH-ACP, and C(14)OH-ACP at similar rates. Furthermore, hybrid lipid A molecules synthesized at 42 degrees C by an E. coli lpxA mutant complemented with lpxA(Pe) contain C(10)OH, C(12)OH, and C(14)OH at both the 3- and 3'-positions, as determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In contrast, LpxA from B. parapertussis did not display relaxed specificity but was selective for C(10)OH-ACP. This study provides an enzymatic explanation for some of the unusual acyl chain variations found in Bordetella lipid A.

Adherence of ovine and human Bordetella parapertussis to continuous cell lines and ovine tracheal organ culture

The adherence of ovine and human isolates of Bordetella parapertussis to ovine and human continuous culture cell lines and to ovine tracheal organ culture was compared. Adherence to non-ciliated respiratory continuous culture cells did not reveal any host-specificity of the isolates. In contrast, adherence of ovine B. parapertussis strains to ciliated ovine tracheal organ culture was significantly greater than that of human strains. These results indicate that tracheal organ culture is a useful tool for studying host-specific adherence of B. parapertussis and suggest that adherence of B. parapertussis to ciliated epithelia is species-specific making it unlikely that the transfer of B. parapertussis between humans and sheep will result in an infection.

Genetic basis for lipopolysaccharide O-antigen biosynthesis in bordetellae

Bordetella bronchiseptica and Bordetella parapertussis express a surface polysaccharide, attached to a lipopolysaccharide, which has been called O antigen. This structure is absent from Bordetella pertussis. We report the identification of a large genetic locus in B. bronchiseptica and B. parapertussis that is required for O-antigen biosynthesis. The locus is replaced by an insertion sequence in B. pertussis, explaining the lack of O-antigen biosynthesis in this species. The DNA sequence of the B. bronchiseptica locus has been determined and the presence of 21 open reading frames has been revealed. We have ascribed putative functions to many of these open reading frames based on database searches. Mutations in the locus in B. bronchiseptica and B. parapertussis prevent O-antigen biosynthesis and provide tools for the study of the role of O antigen in infections caused by these bacteria.

Human but not ovine isolates of Bordetella parapertussis are highly clonal as determined by PCR-based RAPD fingerprinting

The DNA fingerprints of 170 human isolates and ten ovine isolates of Bordetella parapertussis were examined by arbitrarily-primed PCR/RAPD with 29 primers. Based on this technique, all the human isolates appear highly genetically homogeneous. The ovine isolates could be distinguished from human isolates and they showed diversity among themselves. Therefore, human isolates of B. parapertussis are a highly clonal group adapted to infect humans and they are distinct from polymorphic ovine isolates.

Molecular and functional analysis of the lipopolysaccharide biosynthesis locus wlb from Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica

The Bordetella pertussis wlb locus (wlbpe, formerly bpl) is required for the biosynthesis of a trisaccharide that, when attached to the B. pertussis lipopolysaccharide (LPS) core (band B), generates band A LPS. The equivalent loci in Bordetella bronchiseptica (wlbbr) and Bordetella parapertussis (wlbpa) were identified and cloned. The wlbbr and wlbpa loci differ from wlbpe in that they lack the insertion sequence that defines the right-hand terminus of wlbpe. Deletion of 12 kb of DNA containing the whole wlb locus (delta wlb) by allelic exchange in each of the three bordetellae had no effect on band B biosynthesis, whereas band A biosynthesis was prevented in B. pertussis and B. bronchiseptica. In B. bronchiseptica and B. parapertussis, delta wlb mutants also lacked O-antigen. Reintroduction of the wlbpe or wlbbr loci on a shuttle vector into the three delta wlb mutants restored the wild-type LPS phenotype in the B. pertussis and B. bronchiseptica mutants. In the case of B. parapertussis, which normally does not synthesize an apparent band A structure, introduction of the wlbpe or wlbbr loci now enabled the generation of band A. This suggests that the attachment point for band A trisaccharide on the LPS core is present in B. parapertussis, and further suggests that the wild-type wlbpa locus is not fully functional. Introduction of the wlbpa locus into the delta wlbpe, delta wlbbr and delta wlbpa mutants had interesting consequences. The B. bronchiseptica and B. parapertussis recipients were now able to biosynthesize O-antigen, but no band A was generated. In the B. pertussis recipient, a truncated band A was expressed consistent with a mutation in the wlbH gene, but on Western blotting the expression of a small amount of full-length band A was also seen. Evidence that the wlbHpa protein is not fully functional was provided by the failure of the wlbpa locus to fully complement a B. pertussis wlbH (delta wlbHpe) mutant. This was supported by DNA sequence data showing that a single amino acid, conserved between homologous proteins from a range of bacteria, is altered in the B. parapertussis WlbH protein.

Bordetella parapertussis infection in children: epidemiology, clinical symptoms, and molecular characteristics of isolates

The clinical trial conducted in Italy to evaluate the efficacy of acellular pertussis vaccines provided an opportunity to estimate the frequency of clinical infections with Bordetella parapertussis and to compare the clinical characteristics of children suffering from Bordetella pertussis illness with those of children with B. parapertussis illness. This study dealt with 76 B. parapertussis infections diagnosed from a population of 15,601 children participating in the follow-up of suspected cases of pertussis. An overall incidence of 2.1 cases of laboratory-confirmed parapertussis per 1,000 person-years was observed. Children affected by B. parapertussis infections showed a less severe clinical picture both in the duration of symptoms and in the percentage of patients affected, even when compared with vaccinated children with pertussis. To characterize the isolated strains, we performed assays for susceptibility to erythromycin and sulfamethoxazole-trimethoprim, and we examined the genomic DNAs by pulsed-field gel electrophoresis. The results showed a high degree of genetic stability among B. parapertussis strains regardless of time of collection and geographical distribution.

Identification and cloning of waaF (rfaF) from Bordetella pertussis and use to generate mutants of Bordetella spp. with deep rough lipopolysaccharide

A DNA locus from Bordetella pertussis capable of reconstituting lipopolysaccharide (LPS) O-antigen biosynthesis in Salmonella typhimurium SL3789 (rfaF511) has been isolated, by using selection with the antibiotic novobiocin. DNA within the locus encodes a protein with amino acid sequence similarity to heptosyltransferase II, encoded by waaF (previously rfaF) in other gram-negative bacteria. Mutation of this gene in B. pertussis, Bordetella parapertussis, and Bordetella bronchiseptica by allelic exchange generated bacteria with deep rough LPS phenotypes consistent with the proposed function of the gene as an inner core heptosyltransferase. These are the first LPS mutants generated in B. parapertussis and B. bronchiseptica and the first deep rough mutants of any of the bordetellae.

Differentiation of human and animal strains of Streptococcus dysgalactiae by pulsed-field gel electrophoresis

The genetic diversity among 54 human isolates and 33 animal isolates belonging to the species Streptococcus dysgalactiae (20 alpha-haemolytic Streptococcus dysgalactiae, 23 Streptococcus equisimilis, 43 group G streptococci and one group L streptococcus) was evaluated by macrorestriction analysis of chromosomal DNA with SmaI and resolution by pulsed-field gel electrophoresis. This technique revealed a high degree of intraspecies polymorphism, leading to the differentiation of 80 distinct banding patterns, and identified the presence of two major clusters, one containing isolates of human origin and the other isolates of animal origin. These results suggest than human and animal isolates of S.dysgalactiae are genetically distinct, and support the recent proposal of the subspecies S. dysgalactiae subsp. equisimilis for human isolates. The heterogeneity revealed within isolates from the same host type indicates that pulsed-field gel electrophoresis is a powerful epidemiological tool for studying S. dysgalactiae infections.