Characterization of new resistance plasmids belonging to incompatibility group IncQ.

New IncQ R plasmids, pIE639 and pIE723, are characterized and compared to the prototype IncQ plasmid RSF1010. Additional resistance determinants not common on other R plasmids are located on small stretches of DNA interspacing essential regions at different positions in an otherwise unchanged core of IncQ plasmid DNA. The contribution of IncQ plasmids to resistance evolution in bacteria is discussed.