Hemolysin plasmid coding for the virulence of a nephropathogenic Escherichia coli strain

The nephropathogenic Escherichia coli strain P673 was shown to harbor two plasmids with molecular sizes of 70 and 41 megadaltons, respectively. The 70-megadalton plasmid, pCW1, coded for tetracycline resistance, whereas hemolysin production was coded by the 41-megadalton plasmid, pCW2. Plasmid pCW1 proved to be self-transmissible, in contrast to pCW2. Transfer of the hemolysin character was associated with the appearance of a 110-megadalton plasmid, pCW3. The incompatibility of pCW3 with both native plasmids and restriction enzyme analysis led to the conclusion that pCW3 is a cointegrate of pCW1 and pCW2, pCW2, carrying the hemolytic determinant, is involved in the nephropathogenic character of strain P673, because (i) elimination of pCW2 from P673 was associated with a loss of virulence and (ii) the nephropathogenicity of the avirulent mutant could be restored by reintroduction of pCW2 DNA as part of a cointegrate structure.