Nucleotide sequence homology to pertussis toxin gene in Bordetella bronchiseptica and Bordetella parapertussis.

Multiple strains of Bordetella parapertussis and B. bronchiseptica were examined for the presence of nucleotide sequences which hybridized with a cloned 4.5-kilobase (kb) fragment of B. pertussis DNA containing the genes responsible for pertussis toxin expression. All six B. parapertussis strains tested had nucleic acid sequences that hybridized with the cloned 4.5-kb fragment in Southern blot analyses. When the B. parapertussis DNA was digested with restriction endonuclease PstI, the pattern of hybridization was identical to that obtained with B. pertussis. Only five of the seven B. bronchiseptica strains tested had sequences that hybridized with the 4.5-kb fragment. Three of these B. bronchiseptica strains had a hybridization pattern identical to B. pertussis upon PstI digestion and Southern blot analyses. Two B. bronchiseptica strains were shown to lack a PstI cleavage site downstream from the region analogous to that coding for the pertussis toxin structural genes. Monoclonal antibody analyses were unable to detect pertussis toxin subunits S1 and S2 in Western blots with cellular material or culture supernatant from several B. bronchiseptica and B. parapertussis strains that possessed the DNA homologies. In addition, preliminary Northern hybridizations with RNA isolated from B. bronchiseptica and B. parapertussis strains suggested that the homologous regions were not transcribed. The data show that the gene coding for the toxic component of B. pertussis is common in other Bordetella species, though the gene probably is not expressed.