IS257-MEDIATED COINTEGRATION IN THE EVOLUTION OF A FAMILY OF STAPHYLOCOCCAL TRIMETHOPRIM RESISTANCE PLASMIDS

Analyses of the Staphylococcus epidermidis multiresistance plasmids pS K697 and pSK818 have revealed them to be closely related to the trimet hoprim resistance plasmid pSK639, also isolated from S. epidermidis. p SK697 and pSK818 were found to contain a cointegrated copy of a second plasmid related to the S. epidermidis multidrug antiseptic and disinf ectant resistance plasmid pSK108 and the S. aureus tetracycline resist ance plasmid pT181, respectively. In contrast to pSK639, both plasmids were found to contain a third copy of IS257, such that the integrated plasmids in both cases are flanked by a copy of this element. This or ganization and the presence of duplicated sequences at the extremities of the integrated plasmids implicate IS257 in the formation of these cointegrate plasmids. Sequence analysis of the IS257 elements from the se plasmids has provided insights into the probable mechanism of coint egration, viz., nonresolved replicative transposition of IS257.