Acquisition by Escherichia coli of plasmid-borne beta-lactamases normally confined to Pseudomonas spp.

The β-lactamases determined by a number of Pseudomonas specific plasmids are quite distinct from the enzymes of the R factors of enteric bacteria (or by those freely transmissible between these groups). The genes determining these enzymes may be mobilized for transfer into Escherichia coli by a plasmid which transfers between the groups. In several cases the determinants have been incorporated into the mobilizing plasmid and we conclude that the Pseudomonas-specific plasmid was unable to replicate in E. coli; but in one case the determinant remains on a plasmid which replicates independently of the mobilizer, indicating that the limitation to Pseudomonas is a deficiency of intergeneric transferability. In all cases the β-lactamase genes function efficiently in the new host and the enzymes confer high levels of resistance to penicillins.