Summary: Transposon-insertion mutants were prepared from virulent field isolates of and Detailed restriction-enzyme mapping of the single sites of Tn insertion in two mutants (M51 and M173) of that showed diminished virulence in a mouse assay indicated that these sites were about 5 kbp apart on the approximately 70 kbp plasmid harboured by the isolate. A Tn-insertion mutant (M242) of that showed diminished virulence was also identified. A single copy of Tn was inserted into the approximately 90 kbp plasmid harboured by this isolate. Hybridization studies indicated that homology existed between the region encompassing the sites of Tn insertion in M51 and M173 and that encompassing the site of Tn insertion in M242. Restriction mapping indicated that the two regions were very similar and could even be identical and, if so, the Tn insertion in M242 could be mapped to a point 1·5 kbp from the Tn insertion in M51 and 6·5 kbp from that in M173. It appeared that the maximal extent of the putative similarity/identity was between 13 and 23 kbp. It is proposed that this stretch of high homology could represent a virulence sequence that has been conserved during the evolutionary divergence of the two serotypes.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error