Transfer of a pertussis toxin expression locus to isogenic bvg-positive and bvg-negative strains of Bordetella bronchiseptica using an in vivo technique

Bordetella pertussis is the causative agent of whooping cough, a contagious childhood respiratory disease. Increasing public concern over the safety of current whole-cell vaccines has led to decreased immunization rates and a subsequent increase in the incidence of the disease. The preparation of safer vaccines is at present concentrated on the production of detoxified virulence factors such as pertussis toxin (PT) for inclusion in acellular vaccine preparations. A permanently avirulent Bordetella bronchiseptica strain was previously engineered to constitutively produce PT.(1) An in vivo cloning technique, based on the principles of conjugal mating and chromosome transfer was employed to transfer the PT expression locus of this strain to virulent and avirulent strains of B. bronchiseptica. This transfer was confirmed by Southern hybridization. An analysis of PT secretion in isogenic virulent and avirulent strains of B. bronchiseptica revealed that the PT produced was cell-associated, and not secreted to the growth medium. This evidence suggests that B. bronchiseptica does not possess functional PT secretion (ptl) genes. Therefore, to achieve a PT expression and secretion system suitable for vaccine purposes in Bordetella bronchiseptica, functional ptl genes of B. pertussis are also required. (C) 1996 Academic Press Limited