Distribution of plasmid maintenance regions among IncFIV plasmids.

The distribution of the IncFI basic replicons among IncFIV plasmids was assessed by DNA hybridization. In addition these and 20 other plasmids from 16 incompatibility groups were screened for the presence of IncIV, an incompatibility determinant recently found on the IncFIV plasmid R124. The IncIV determinant was found commonly but not universally among the IncFIV plasmids. It was also detected on the IncFI reference plasmid R386 and plasmids from IncB, IncI alpha and IncI gamma. The frequency and distribution of IncFI replicons among the IncFIV plasmids is similar to that observed in other F groups. The similarity of the IncFIV plasmids to plasmids of the other IncF groups and the failure to find replicons unique to IncFIV plasmids indicates that their division into a separate incompatibility group is not justified.