A native plasmid of Pasteurella haemolytica serotype A1: DNA sequence analysis and investigation of its potential as a vector.

The complete nucleotide sequence of a 4.3 kilobase pair plasmid, pAB2, isolated from a bovine strain of Pasteurella haemolytica serotype A1, was determined. It encodes a Rob-1 type beta-lactamase and a region with homology to the mobilisation (mob) region of the Escherichia coli plasmid, ColE1. An insertion mutant of pAB2 (pTC2/81) carrying a copy of Tn5 was transferred to E coli K12 by conjugation. Subsequently pTC2/81 could be transferred by transformation to E coli HB101, but not to P haemolytica serotypes A1 or A2. However, a derivative of this construct containing only a fragment of the Tn5 insertion sequence was able to transform P haemolytica. A further construct containing a fragment of the P haemolytica A1 leucotoxin A gene, was similarly restricted to transforming E coli. These results demonstrate that the pAB2 plasmid is capable of acting as an E coli/P haemolytica shuttle vector. However, the nature of the cloned DNA sequences are important to transformation.