Comparative sequence analysis of Bordetella bronchiseptica pertactin gene (prn) repeat region variants in swine vaccines and field isolates

The product of the Bordetella bronchiseptica pertactin gene, prn, has been implicated as an adhesin and a protective immunogen in swine. Recent studies demonstrate prn sequence heterogeneity in swine isolates and vaccine strains within and surrounding the region 1 amino acid repeat GGXXP(n) and the region 2 amino acid repeat PQP(n). However, only a few isolates have been evaluated. Allelic variation between vaccine strains and field isolates may affect vaccine efficacy, since region 2 is known to encode an immunodominant protective epitope. In the present study, the DNA and predicted amino acid sequences of the pertactin repeat regions from a collection of 81 recent swine field isolates and 5 vaccine strains from the United States were determined. Two region 1 variants and four region 2 variants, one of which has not been previously reported, were identified, comprising four pertactin types. Four vaccines are derived from strains with a region 1 variant identical to that found in the majority of field isolates. However, only two vaccines possess the most commonly identified sequence in region 2, while two others contain a variant found in only one other swine isolate. Ribotype analysis demonstrated that although vaccines containing the novel region 2 variant fall within the same major cluster as other common swine ribotypes, they are less closely related. No relationship was observed between pertactin type and ribotype.