A comparison of the DNA fragment patterns of the mouse-virulent challenge strains and clinical isolates of Bordetella pertussis.

The DNA fragment patterns of two mouse-virulent strains of Bordetella pertussis, commonly used in animal protection tests, were compared to those of clinical isolates. Strain W.18-323 and six variants were examined together with strain 353/Z and two variants. Chromosomal DNA was digested with the rare-cutting enzyme Xba I in order to produce relatively large fragments resolved by pulsed-field gel electrophoresis. The resulting DNA fragment patterns of strain 353/Z and those of its variants were indistinguishable from those of the commonest DNA type among clinical isolates. In contrast, strain W.18-323 and its variants showed a distinct genetic type, different from clinical isolates of B. pertussis, B. parapertussis or B. bronchiseptica. This finding, together with some phenotypic anomalies of this strain, raises doubts as to the suitability of W.18-323 as a challenge strain for assessing the efficacy of vaccines in the mouse model.