MOLECULAR CHARACTERIZATION OF 2 BORDETELLA-BRONCHISEPTICA STRAINS ISOLATED FROM CHILDREN WITH COUGHS

During a surveillance program associated with the Italian clinical tri al for the evaluation of new acellular pertussis vaccines, two bacteri al isolates were obtained in cultures of samples from immunocompetent infants who had episodes of cough. Both clinical isolates were identif ied as Bordetella bronchiseptica by biochemical criteria, although bot h strains agglutinated with antisera specific for Bordetella parapertu ssis, suggesting that the strains exhibited some characteristics of bo th B. bronchiseptica and B. parapertussis. Both children from whom the se strains were isolated exhibited an increase in serum antibody titer to pertussis toxin (PT), a protein that is produced by Bordetella per tussis but that is not thought to be produced by B. bronchiseptica. We therefore examined whether the clinical isolates were capable of prod ucing PT. Neither strain produced PT under laboratory conditions, alth ough both strains appeared to contain a portion of the pfx region that encodes the structural subunits of PT. In order to determine whether the ptx genes may encode functional proteins, we inserted an active pr omoter directly upstream of the ptx region of one of these strains. Bi ologically active PT was produced, suggesting that this strain contain s the genetic information necessary to encode an active PT molecule. S equence analysis of the ptx promoter region of both strains indicated that, while they shared homology with the B. bronchiseptica ATCC 4617 sequence, they contained certain sequence motifs that are characterist ic of B. parapertussis and certain motifs that are characteristic of B . pertussis. Taken together, these findings suggest that variant strai ns of B. bronchiseptica exist and might be capable of causing signific ant illness in humans.