Escherichia coli CoIV plasmid pRK100: genetic organization, stability and conjugal transfer.

Uropathogenic Escherichia coli strains express chromosomal and plasmid-encoded virulence-associated factors such as specific adhesins, toxins and iron-uptake systems. A CoIV plasmid (pRK100) of a uropathogenic strain and its host KS533 were studied. The host strain encodes the K1 capsule, and P and S fimbriae, but neither haemolysin nor the cytotoxic-necrotic factor CNF1, indicating that this strain does not harbour a larger pathogenicity island. A restriction map of pRK100 was constructed on the basis of hybridization experiments and nucleotide sequencing. pRK100 harbours CoIV, the conserved replication region RepFIB, the aerobactin-uptake system, a RepFIC replicon and additionally Colla as well as transposon Tn5431. The location of the RepFIC replicon was similar to that in plasmid F. CoIV plasmids and F thus share a region spanning more than half the length of plasmid F. Even though their replication and transfer regions are homologous, CoIV plasmids are found only in E. coli strains. Among the four other species tested, conjugal transfer of pRK100 was demonstrated, with low frequency, only to Klebsiella pneumoniae, suggesting that a natural barrier effectively bars transfer. In vitro stability of the plasmid with integration into the chromosome to ensure maintenance in the presence of an incompatible plasmid was demonstrated.