Demonstration of a third incompatibility function on plasmids already incompatible with group P and group I plasmids

The addition of extra antibiotic resistance determinants to plasmids of a series previously shown to be incompatible in an atypical fashion with group I and group P plasmids, has enabled the existence of a third and major incompatibility function determined by these plasmids to be demonstrated. The in vitro construction of a plasmid consisting of the replication region of one of the plasmids, linked to the genes of the galactose operon, facilitated the identification of this third incompatibility function as similar to IncB plasmids.