Analysis of Bordetella pertussis isolates collected in Japan before and after introduction of acellular pertussis vaccines

Single Amino Acid Polymorphisms of Pertussis Toxin Subunit S2 (PtxB) Affect Protein Function

Whooping cough due to Bordetella pertussis is increasing in incidence, in part due to accumulation of mutations which increase bacterial fitness in highly vaccinated populations. Polymorphisms in the pertussis toxin, ptxA and ptxB genes, and the pertactin, prn genes of clinical isolates of Bordetella pertussis collected in Cincinnati from 1989 through 2005 were examined. While the ptxA and prn genotypes were variable, all 48 strains had the ptxB2 genotype; ptxB1 encodes glycine at amino acid 18 of the S2 subunit of pertussis toxin, while ptxB2 encodes serine. We investigated antigenic and functional differences of PtxB1 and PtxB2. The S2 protein was not very immunogenic. Only a few vaccinated or individuals infected with B. pertussis developed antibody responses to the S2 subunit, and these sera recognized both polymorphic forms equally well. Amino acid 18 of S2 is in a glycan binding domain, and the PtxB forms displayed differences in receptor recognition and toxicity. PtxB1 bound better to the glycoprotein, fetuin, and Jurkat T cells in vitro, but the two forms were equally effective at promoting CHO cell clustering. To investigate in vivo activity of Ptx, one μg of Ptx was administered to DDY mice and blood was collected on 4 days after injection. PtxB2 was more effective at promoting lymphocytosis in mice.

Identification of linear B epitopes of pertactin of Bordetella pertussis induced by immunization with whole and acellular vaccine

Pertussis is a serious infectious disease of the respiratory tract caused by the gram-negative bacteria Bordetella pertussis. There has been a reemergence of this disease within the population of several countries that have well established vaccination programs. Analyzes of clinical isolates suggest an antigenic divergence between the vaccine-based strains to the circulating strains. Although antibodies against P.69 are involved in the observed protective immunity, the sequences recognized as antigenic determinants in P.133, the precursor for P.69, P.3.4 and P.30, have not be determined. Here, the precise mapping of linear B-cell epitopes within the predicted P.133 pertactin sequences was accomplished using the SPOT-synthesis of peptide arrays onto cellulose membranes and screening with murine sera generated by vaccination with either the Pertussis cellular (miPc) or Pertussis acellular (miPa) vaccine. A total of 23 major epitopes were identified by sera from miPc vaccinated mice, while thirteen were identified by sera from miPa vaccinated mice. Of these epitopes, 12 epitopes were specifically identified by antibodies produced in response to the miPc vaccine and two were specific to the miPa vaccine. These epitopes were distributed throughout the pertactin sequence but a significant number were concentrated to the P.30 Prn segment. An analysis of the epitope correlation homologies indicated that the variations from the observed mutations in pertactin would not constitute a problem using these vaccines. In addition, the mapping of epitopes demonstrated a higher number of linear B-cell epitopes immunized with the Pc vaccine than the Pa vaccine.

Are vaccination programs and isolate polymorphism linked to pertussis re-emergence?

Whooping cough remains an endemic disease, and the re-emergence of pertussis in older children and adolescents has been reported in several countries, despite high vaccine coverage. Polymorphism of Bordetella pertussis has been observed over time, and some characteristics of pertussis isolates have gradually diverged from the vaccine strains. The present review summarizes the current knowledge on B. pertussis variability in countries with different vaccination programs and discusses its potential impact on the recently observed increased incidence of whooping cough. No direct association between B. pertussis isolate variability and vaccination programs has been observed to date, except for shifts from fimbriae Fim2 to Fim3. More likely explanations for the re-emergence of pertussis include the change in the epidemiology and transmission patterns of pertussis in highly vaccinated populations, and a shift of disease from young children to adolescents and adults due to waning protective immunity.

Effect of vaccination on Bordetella pertussis strains, China

Strains in China may differ from those in countries that have long histories of high vaccination coverage.

Whole-cell pertussis vaccine was introduced in China in the early 1960s. We used standard typing methods to compare 96 Bordetella pertussis isolates collected before and after introduction of vaccination, during 1953–2005. The following vaccine-type alleles of the pertussis toxin (ptx) gene were characteristic for all prevaccination strains: ptxA2, ptxA3, and ptxA4. The shift to ptxA1 occurred since 1963. All isolates collected since 1983 contained ptxA1. Pertactin (prn) allele 1, prn1, was predominant, although prn2 and prn3 have been detected since 2000. Serotypes fimbriae (Fim) 2 and Fim2,3 were found in all isolates collected before 1986. During 1997–2005, Fim3 became prevalent. Although changes in electrophoresis profiles over time were observed, the predominant profiles during 1997–2005 resembled those during the prevaccine era and those found in Europe before the 1990s. B. pertussis strains in China may differ from those in countries that have a long history of high vaccine coverage.

Synergic effect of genotype changes in pertussis toxin and pertactin on adaptation to an acellular pertussis vaccine in the murine intranasal challenge model

The Bordetella pertussis pertussis toxin and pertactin (Prn) are protective antigens and are contained in acellular pertussis vaccines. Polymorphisms in the A subunit of pertussis toxin (PtxA) and pertactin have been proposed to mediate vaccine resistance and contribute to pertussis reemergence. To test this hypothesis, previous studies compared clinical isolates expressing different alleles for the proteins. However, other virulence factors or virulence factor expression levels also may vary, confounding the analysis. To overcome these limitations, we constructed isogenic mutants of B. pertussis Tohama expressing the alleles ptxA1 or ptxA2 and prn1 or prn2 and compared the efficacies of an acellular pertussis vaccine against the mutants in a mouse model. While the vaccine was effective against all of the B. pertussis strains regardless of the allele expression pattern, the strain expressing ptxA1 and prn2 displayed a survival advantage over the other strains. These results suggest that an allele shift to the ptxA1 prn2 genotype may play a role in the emergence of pertussis in vaccinated populations.

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 effectiveness of vaccination with whole-cell pertussis vaccine by age group in Poland 1996–2001

Recurrence of pertussis in highly vaccinated populations has been observed in many countries. Two mechanisms have been proposed to explain it: a shift in incidence towards older age groups in which the protective effect of vaccination is diminished; and vaccine-induced changes in genomic and immunological characteristics of circulating strains of Bordetella pertussis, which become different from vaccine strains, thereby reducing vaccine efficacy. Marked increase in the incidence of pertussis has been observed in Poland since 1997, following a decade of stability at a low level. As previously shown, the immunization calendar in Poland does not ensure sufficient protection among children older than 9 y. The decrease in the protective effect becomes noticeable after the age of 5. In this paper we examine changes in the effectiveness of pertussis vaccination in 4 age groups during 1996-2001, using surveillance data. We find that over that period a decrease occurred in the reported effectiveness (in children aged 2 to 5 y, from 97.3% in 1996 to 73.5% in 2001 and in 6 to 9 y-olds, from 84.3%, to 68.8%). We also discuss an alternative hypothesis that the above findings are due to selection or measurement bias resulting from incomplete reporting or imperfect diagnostic procedures.

Antibody responses to defined regions of the Bordetella pertussis virulence factor pertactin

Although vaccines against Bordetella pertussis, the causative agent of whooping cough, have been in use for over 50 y, the disease has remained endemic and is still a public health problem in many countries. It has been shown that antibody titres against pertactin, which is 1 of the exposed virulence factors of pertussis, correlate with protection and pertactin is now 1 of the components of most acellular pertussis vaccines. However, little is known about the structure and location of protective epitopes on pertactin. Here we set out to investigate the antibody response using naturally occurring pertactin variants and deletion derivates. We found the N-terminus of pertactin to be immunodominant in both rabbits and humans. In contrast to vaccinated rabbits, we could not detect pertactin type-specific antibodies in human sera. In conclusion, these results show for the first time to which defined regions of the pertactin molecule antibody responses are induced. It also suggests that the amount of pertactin type-specific antibodies will not be very large and that the variation in pertactin probably will not constitute a problem in highly immune individuals.

Comparison of serological and real-time PCR assays to diagnose Bordetella pertussis infection in 2007

Bacterial culture for diagnosing pertussis infection has high specificity but poor sensitivity and is slow. Highly sensitive real-time PCR assays and single-serum pertussis serology have been developed to overcome these limitations, but there are few data available on the relative sensitivities and specificities of such assays for pertussis diagnosis. Using data on 195 participants (>or=7 years old) from an epidemiological study, we assessed the sensitivity, specificity, and performance (Youden index) for pertussis diagnosis of the pertussis toxin enzyme-linked immunosorbent assay (using single and paired serology) and of real-time PCR assays (using the IS481 and ptxA-Pr targets). All available diagnostic information (clinical and laboratory) was pooled to serve as the gold standard. Single serology was the most efficient diagnostic test (Youden index, 0.57 to 0.58), with relatively high sensitivity (>64%) and high specificity (>90%), independent of the cutoff level. IS481 PCR performance was superior to that of ptxA-Pr PCR, and it was the second-most-efficient tool (Youden index, 0.30). Performing both ptxA-Pr and IS481 PCRs did not improve diagnostic performance. The greatest test efficiency (Youden index, 0.69 to 0.74) was achieved when single-serum serology was used in combination with IS481 or ptxA-Pr PCR or paired serology. Combining single serology with one PCR or paired serology increased the sensitivity with an associated limited decrease in specificity. The most specific tests for diagnosis of pertussis were single serology and ptxA-Pr PCR, and the most sensitive diagnostic tool was the combination of IS481 PCR with single serology.

Antigenic variation in Bordetella pertussis isolates recovered from adults and children in Japan

Recently, the incidence of reported pertussis cases of adults has dramatically increased in Japan. In the present study, we analyzed seven Bordetella pertussis isolates recovered from adults in Japan using pulsed-field gel electrophoresis (PFGE) and sequencing of their antigenic and virulence-associated proteins, compared with those from children. PFGE analysis demonstrated that the adult strains were closely related to the child strains (78-100% genetic similarity). On the other hand, the genotyping revealed that 71% (5/7) of the adult strains and 47% (25/53) of the child strains had the same combination of antigenic/virulence-associated allelic variants (ptxS1B/prn1/fim2-1/fim3A/fhaB1/tcfA2) as the Japanese vaccine strain Tohama, respectively. In comparison to the child strains, there was no apparent antigenic and genetic shift in the adult strains. Our result suggests that (i) there is no B. pertussis circulating strain specific to adults and (ii) the antigenic/virulence-associated proteins are unrelated to the rise in adult pertussis incidence in Japan.

The role of peptide loops of the Bordetella pertussis protein P.69 pertactin in antibody recognition

Bordetella pertussis, the etiological agent of whooping cough, is re-emerging in several countries with a traditionally high vaccine uptake. In these B. pertussis strains, polymorphisms were found in several proteins, including P.69 pertactin (P.69 Prn). P.69 Prn, an adhesin, contains two variable regions which are composed of repeats, one of which flanks the receptor binding site. Antibody titers against P.69 Prn correlate with protection and P.69 Prn is one of the components of acellular pertussis vaccines. Nevertheless, little is known about the structure and location of P.69 Prn epitopes. We used a three pronged approach to identify discontinuous epitopes that are recognized by mouse monoclonal antibodies, i.e. site-directed mutagenesis, deletion mapping and competition assays. Site-directed mutagenesis was focused on regions of P.69 Prn predicted to form loops according to the crystal structure. In this report we describe the location of several discontinuous epitopes that are also recognized by human antibodies. Our results reveal an important role of the N-terminus in immune recognition. We provide data for an indirect role of loops in immune evasion by masking of epitopes. We propose that the repeat regions have evolved to allow rapid antigenic variation to deflect the immune response from the functional domain of P.69 Prn. The results presented here provide a better understanding of the structure and function of variable loops and their role in the persistence of pathogens in immunologically primed populations.

Antigenic divergence between Bordetella pertussis clinical isolates from Moscow, Russia, and vaccine strains

We analyzed temporal changes in the frequencies of the ptxA, prn, fim2, and fim3 alleles in Bordetella pertussis strains isolated from pertussis patients in Moscow, Russia, from 1948 to 2004. The three strains used for the whole-cell vaccine harbored the alleles ptxA2, ptxA4, prn1, fim2-1, and fim3A. Vaccine-type alleles of ptxA (ptxA2 and ptxA4) were characteristic for all prevaccination strains and for 96% of the strains isolated in the 1960s and 1970s. At the beginning of the 1970s, ptxA2 and ptxA4 were replaced by the ptxA1 allele. In the 1980s and to the present, strains with ptxA1 were predominant in the B. pertussis population. All prevaccination strains harbored the prn1 allele, which corresponds to the vaccine-type allele. In subsequent years, the proportion of strains with the prn1 allele decreased and the proportion of prn3 and prn2 strains increased. From 2002 to 2004 strains with prn2 or prn3 were predominant in the B. pertussis population. The vaccine-type alleles fim2-1 and fim3A were found in all prevaccination strains and in 92% of the strains isolated from 1960 to 1989. The fim2-2 and fim3B alleles were first observed at the beginning of the 1980s. In subsequent years, these strains became predominant. Together with waning immunity, the antigenic divergence between vaccine strains and clinical isolates observed in the Moscow area may explain the persistence of pertussis, despite the high rates of vaccine coverage. The results demonstrate that the selection of B. pertussis strains for vaccine manufacturing must be based on a thorough study of the B. pertussis population.

Community-acquired pneumonia: paving the way towards new vaccination concepts

Despite the availability of antimicrobial agents and vaccines, community-acquired pneumonia remains a serious problem. Severe forms tend to occur in very young children and among the elderly, since their immune competence is eroded by immaturity and immune senescence, respectively. The main etiologic agents differ according to patient age and geographic area. Streptococcus pneumoniae, Haemophilus influenzae, respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV-3) are the most important pathogens in children, whereas influenza viruses are the leading cause of fatal pneumonia in the elderly. Effective vaccines are available against some of these organisms. However, there are still many agents against which vaccines are not available or the existent ones are suboptimal. To tackle this problem, empiric approaches are now being systematically replaced by rational vaccine design. This is facilitated by the growing knowledge in the fields of immunology, microbial pathogenesis and host response to infection, as well as by the availability of sophisticated strategies for antigen selection, potent immune modulators and efficient antigen delivery systems. Thus, a new generation of vaccines with improved safety and efficacy profiles compared to old and new agents is emerging. In this chapter, an overview is provided about currently available and new vaccination concepts.

Integrating life history and cross-immunity into the evolutionary dynamics of pathogens

Models for the diversity and evolution of pathogens have branched into two main directions: the adaptive dynamics of quantitative life-history traits (notably virulence) and the maintenance and invasion of multiple, antigenically diverse strains that interact with the host's immune memory. In a first attempt to reconcile these two approaches, we developed a simple modelling framework where two strains of pathogens, defined by a pair of life-history traits (infectious period and infectivity), interfere through a given level of cross-immunity. We used whooping cough as a potential example, but the framework proposed here could be applied to other acute infectious diseases. Specifically, we analysed the effects of these parameters on the invasion dynamics of one strain into a population, where the second strain is endemic. Whereas the deterministic version of the model converges towards stable coexistence of the two strains in most cases, stochastic simulations showed that transient epidemic dynamics can cause the extinction of either strain. Thus ecological dynamics, modulated by the immune parameters, eventually determine the adaptive value of different pathogen genotypes. We advocate an integrative view of pathogen dynamics at the crossroads of immunology, epidemiology and evolution, as a way towards efficient control of infectious diseases.

Analysis of Bordetella pertussis pertactin and pertussis toxin types from Queensland, Australia, 1999-2003

Background

In Australia two acellular Bordetella pertussis vaccines have replaced the use of a whole cell vaccine. Both of the licensed acellular vaccines contain the following three components; pertussis toxoid, pertussis filamentous haemagglutinin and the 69 kDa pertactin adhesin. One vaccine also contains pertussis fimbriae 2 and 3. Various researchers have postulated that herd immunity due to high levels of pertussis vaccination might be influencing the makeup of endemic B. pertussis populations by selective pressure for strains possessing variants of these genes, in particular the pertactin gene type. Some publications have suggested that B. pertussis variants may be contributing to a reduced efficacy of the existing vaccines and a concomitant re-emergence of pertussis within vaccinated populations. This study was conducted to survey the pertactin and pertussis toxin subunit 1 types from B. pertussis isolates in Queensland, Australia following the introduction of acellular vaccines.

Methods

Forty-six B. pertussis isolates recovered from Queensland patients between 1999 and 2003 were examined by both DNA sequencing and LightCycler™ real time PCR to determine their pertactin and pertussis toxin subunit 1 genotypes.

Results

Pertactin typing showed that 38 isolates possessed the prn1 allele, 3 possessed the prn2 allele and 5 possessed the prn3 allele. All forty-six isolates possessed the pertussis toxin ptxS1A genotype. Amongst the circulating B. pertussis population in Queensland, 82.5% of the recovered clinical isolates therefore possessed the prn1/ptxS1A genotype.

Conclusion

The results of this study compared to historical research on Queensland isolates suggest that B. pertussis pertactin and pertussis toxin variants are not becoming more prevalent in Queensland since the introduction of the acellular vaccines. Current prevalences of pertactin variants are significantly different to that described in a number of other countries with high vaccine coverage. Relative paucity of recovered isolates compared to notified infections, due primarily to non culture based pertussis diagnostics is however a confounding factor in the assessment of variant prevalence.

Comparison of acellular pertussis vaccines-induced immunity against infection due to Bordetella pertussis variant isolates in a mouse model

A significant increase in the incidence of pertussis in adolescents and adults has been observed in vaccinated populations. Concomitantly, emergence of novel pertussis toxin and pertactin types in circulating Bordetella pertussis isolates was noticed. In this study, immunity induced by acellular vaccines against infection due to isolates expressing different pertactin types and fimbriae was monitored in a mouse model. In accordance with previous studies, the effect of a bicomponent DTPa vaccine on bacterial clearance was lower when compared with tri- or pentavalent DTPa vaccines. Whatever the isolates used to infect mice, the tri- or pentavalent DTPa vaccines were both efficacious in inducing immunity that resulted in clearance of infection. These findings suggest that re-emergence of pertussis might not be related to emergence of isolates escaping vaccine protection. The present study reduces potential concerns about acellular vaccine efficacy, but frequent monitoring of protection and surveillance of the evolution of the B. pertussis population remains of particular importance.

Shifts of Bordetella pertussis variants in Sweden from 1970 to 2003, during three periods marked by different vaccination programs

The Swedish population of Bordetella pertussis strains was characterized from 1,247 isolates covering a whole-cell vaccine program up to 1979, a 17-year period without vaccination (1979 to 1996), and a period after the introduction of general vaccination among newborns with acellular pertussis vaccines (1997 to 2003). Strains were characterized by serotyping and genotyping of pertactin and ptxA and by means of pulsed-field gel electrophoresis (PFGE). With emphasis on vaccine-related markers, the vast majority of circulating strains were of nonvaccine type. There were shifts of serotype connected with shifts of vaccination program. Serotype Fim3 was most frequent during the periods with general vaccination schedules, whereas serotype Fim2 was predominant during the 17-year vaccine-free period. Pertactin 1 was predominant during the pertussis whole-cell (Pw) vaccine period but was thereafter replaced by prn2 and has not reappeared after the introduction of acellular pertussis (Pa) vaccines. ptxA (1) was predominant over all three decades. There was a significant difference in the distribution of serotypes between vaccinated and unvaccinated individuals, but not for pertactin. A few PFGE profiles were predominant over the years: BpSR25 (serotype Fim3 prn1/7) and BpSR18 (serotype Fim3 prn2) during the Pw period, BpSR1 (serotype Fim2 prn2) during the 17 years without general vaccination, and BpSR11 (serotype Fim3 prn2) after the reintroduction of general vaccination in 1996. Despite differences between the pertactin and toxin types of Pa vaccines and circulating strains, there is no evidence that there is a threat, i.e., the vaccination program so far has been effective against whooping cough, and there seems to be no impact on the effectiveness of the vaccination program from the bacterial polymorphism.

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

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

Antigenic divergence suggested by correlation between antigenic variation and pulsed-field gel electrophoresis profiles of Bordetella pertussis isolates in Japan

Antigenic divergence has been found between Bordetella pertussis vaccine strains and circulating strains in several countries. In the present study, we analyzed B. pertussis isolates collected in Japan from 1988 to 2001 using pulsed-field gel electrophoresis (PFGE) and sequencing of two virulence-associated proteins. The 107 isolates were classified into three major groups by PFGE analysis; 87 (81%) were type A, 19 (18%) were type B, and 1 (1%) was type C. Sequence analysis of the S1 subunit of pertussis toxin (ptxS1) and adhesion pertactin (prn) genes revealed the presence of two (ptxS1A and ptxS1B) and three (prn1, prn2, and prn3) variants, respectively, in the isolates. Among those isolates, 82 (95%) of the 87 type A strains and the type C strain had the same combination of ptxS1B and prn1 alleles (ptxS1B/prn1) as the Japanese vaccine strain. On the other hand, 17 (90%) of 19 type B strains had an allele (ptxS1A/prn2) distinct from that of the vaccine strain. A correlation was found between the antigenic variation and the PFGE profile in the isolates. In addition, the frequency of the type B strain was 0, 27, 0, 42, and 37% of the isolates in the periods 1988 to 1993, 1994 to 1995, 1996 to 1997, 1998 to 1999, and 2000 to 2001, respectively. In contrast, the number of reported pertussis-like and pertussis cases decreased gradually from 1991 on, suggesting that the antigenic divergence did not affect the efficacy of pertussis vaccination in Japan.

Sequence variation in pertussis S1 subunit toxin and pertussis genes in Bordetella pertussis strains used for the whole-cell pertussis vaccine produced in Poland since 1960: efficiency of the DTwP vaccine-induced immunity against currently circulating B. pertussis isolates

The present study indicates that the appearance of the B. pertussis harbouring prn2 gene allele variant (not found among clinical isolates before 1990s) may have been induced by long-term vaccination in Poland with DTP-composed vaccine strains presenting exclusively prn1. However, ptxS1A allele of pertussis toxin subunit S1 encoding gene, predominant in the currently isolated B. pertussis strains, has been found in vaccine strains used for whole-cell pertussis component (wP) production of DTP vaccine in 1960-1978. This outrules the possibility that the appearance of ptxSIA allele might be related to vaccine pressure driven by non-ptxS1A vaccine strains used for long-term immunization with wP. Intranasal challenge animal model testing the efficiency of the clearance of B. pertussis strains harbouring different ptxS1/prn allele gene combinations revealed that currently produced DTwP vaccine may not contain adequate B. pertussis vaccine strains, since isolates with gene variants different from those observed in vaccine strains were eliminated from the lungs of the immunized animals with lower efficiency.

Polymorphisms of the fimbria fim3 gene of Bordetella pertussis strains isolated in Canada

The fim genes which code for the fimbria protective antigens present in both the inactivated whole-cell and acellular vaccines were analyzed in 86 Canadian Bordetella pertussis isolates. At least one of the novel mutations identified was found to involve a surface epitope that has been mapped by serum antibodies from infected or vaccinated subjects.

Rapid typing of Bordetella pertussis pertussis toxin gene variants by LightCycler real-time PCR and fluorescence resonance energy transfer hybridization probe melting curve analysis

A LightCycler real-time PCR hybridization probe assay was developed for rapid typing of gene variants of the Bordetella pertussis virulence factor pertussis toxin. The assay correctly identified the ptxS1 alleles of all strains tested, comprising 57 Finnish clinical isolates and 2 vaccine strains. The method is simple, reliable, and suitable for large-scale screening of B. pertussis strains.

Multilocus sequence typing of Bordetella pertussis based on surface protein genes

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