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

Abstract

To determine the value of gene markers for surveillance and to assess the genetic stability of potential acellular pertussis vaccine components, the sequence variation in ten virulence-related genes of Bordetella pertussis was investigated in strains isolated in the UK between 1920 and 2002. These genes encode: pertactin (prnA); pertussis toxin subunits S1 (ptxA) and S3 (ptxC); tracheal colonization factor (tcfA); bordetella autotransporter protein C (bapC); bordetella resistance to killing protein (brkA); fimbrial antigen 2 (fim2); outer-membrane protein Q (ompQ); virulence-activated gene 8 (vag8) and adenylate cyclase toxin (cyaA). The encoded proteins are either components of current acellular vaccines (ACVs), or potential virulence markers for B. pertussis. Three strains used in the pertussis UK whole-cell vaccine (WCV), strain Tohama-I used for production of ACV components and the type strain of B. pertussis (18323 T ) were also analysed. Several novel alleles were found. The UK isolates were assigned multi-locus sequence types (MLSTs) according to a previously described scheme for B. pertussis based on three of these genes (ptxA, ptxC and tcfA). Compared with isolates from other countries, the UK clinical strains showed a distinct distribution of MLSTs. Apart from one strain that was MLST-3, all other recent isolates (2000)(2001)(2002) were identified as MLST-5. These isolates differed from the three WCV strains, which were MLST-2 or MLST-3, the Tohama-I strain (MLST-2) and the type strain of B. pertussis (MLST-9). MLST-3 and MLST-5 differ only by a single synonymous mutation, but this method does indicate that currently circulating strains of B. pertussis are not identical to the vaccine types, and they may differ in other important characteristics. Two new MLSTs were identified amongst historical UK isolates. Sequence-based typing offers a convenient method of analysing and comparing populations of B. pertussis from different time periods and from different countries. The variation exhibited by prnA and fim2 suggests that they could be useful, additional epidemiological markers in such a typing scheme.

Analysis of Bordetella pertussis Populations in European Countries with Different Vaccination Policies

“…Previous studies have revealed very little polymorphism in B. pertussis surface proteins. (5,18,21,22,28,38). We focused on genes for proteins incorporated in the ACVs and which were shown to be polymorphic in previous studies: ptxC, ptxA, and prn.…”

Resurgence of pertussis calls for re-evaluation of pertussis animal models

“…The choice of covariates and end points are highly decisive for whether differences in pathogenicity between B. pertussis isolates can be demonstrated or not, and should be made carefully (Table 2). The most commonly used B. pertussis strains in animal models of infection, 18323, Wellcome 28 and Tohama I, are laboratory subcultured and attenuated strains, and hence genetically different from clinical isolates [37,114,119]. Since differences in genome sequences may affect the pathogenicity of B. pertussis in animals and humans, these laboratory strains are not representative for current B. pertussis strains.…”

“…However, the two key factors held responsible for the pertussis resurgence in vaccinated populations are, on the one hand, the appearance of new B. pertussis strain variants, and on the other hand, the gradual loss of vaccine-induced protective immunity in vaccinees, in an era of less circulation and natural boosting (Figure 1). The relative impact of these factors in the resurgence of pertussis is under investigation and may differ between subpopulations and countries [35][36][37][38].…”

Plasticity of fimbrial genotype and serotype within populations of Bordetella pertussis: analysis by paired flow cytometry and genome sequencing

“…B. pertussis expresses two serologically distinct fimbriae composed of either Fim2 or Fim3 subunits (22.5 and 22.0 kDa, respectively). Subtypes of Fim2 (fim2-1 and fim2-2) and Fim3 (fim3-1, fim3-2 and fim3-3) have also been described (Packard et al, 2004;Tsang et al, 2004). Both Fim2 and Fim3 subunits are assembled in a coil to produce long filaments on the surface of the bacteria (Heck et al, 1996).…”