Plasmids related to RSF1010 from Bordetella bronchiseptica

Six out of 14 Bordetella bronchiseptica isolates from U.K. pigs each contained one plasmid, of 8.7-44 kb. All plasmid-containing isolates were sulfonamide resistant, and this property was shown to be plasmid-encoded. Five of the plasmids were related; two were indistinguishable from the broad-host-range plasmid, RSF1010. The other three, two of which appeared to be identical, were shown to have regions of homology with RSF1010. One of these regions encompassed the sulfonamide resistance determinant while the other contained oriV, which also determines plasmid incompatibility. None of the plasmids could be associated with virulence or phase variation, and it appears likely that they have been acquired in response to antibiotic pressure.