Differences in the genomic content of Bordetella pertussis isolates before and after introduction of pertussis vaccines in four European countries.

Resurgence of pertussis has been observed in many countries with high vaccination coverage and clonal expansion of certain Bordetella pertussis strains has been associated with recent epidemics in Europe. It is known that vaccinations have selected strains which are different from those used for vaccine production. However, little is known about the differences in genomic content of strains circulating before the vaccination was introduced. In this study, we compared the genomes of 39 vaccine strains and old clinical isolates (isolated 1941-1984) collected from Finland (n = 5), Poland (n = 14), Serbia (n = 10) and the UK (n = 10). The analysis included genotyping, pulsed-field gel electrophoresis (PFGE) and comparative genomic hybridisation (CGH). Compared to the strain Tohama I, the European isolates analyzed have lost three major regions of difference (RD3, 5 and 29). However, difference in frequency of the absent RDs 3 (BP0910A-BP0934), 5 (BP1135-BP1141) or 29 (BP1225) was observed among isolates from the four countries. Of the isolates with absent RD5, half had also a duplicated region in the genome. All four RDs (RD22 (BB0535-BB0541), 23 (BB0916-BB0921), 24 (BB1140-BB1158) and 26 (BB4880-BB4888)) absent in Tohama I were present in majority of the tested isolates. Results obtained from PFGE analysis correlated well with those of CGH. Recently a novel pertussis toxin promoter allele (ptxP3) was described. Isolates with ptxP3 have replaced resident ptxP1 isolates in the countries where this was investigated. When the recent isolates, collected in 2000-2004, selected from the four countries were examined, the ptxP3 allele was found in all countries except Poland. Our result indicates that at least three clusters of B. pertussis circulated in Europe in pre- and early vaccine era and their genomes were distinct from that of the reference strain Tohama I. Although progressive gene loss occurs in B. pertussis population with time, difference in frequency of the lost genes were observed among isolates from the four countries. The observed differences in genomic content might be vaccine-driven.