DIVERSITY OF STRUCTURES CARRYING THE HIGH-LEVEL GENTAMICIN RESISTANCEGENE (AAC6-APH2) IN ENTEROCOCCUS-FAECALIS STRAINS ISOLATED IN FRANCE

Of 24 high-level gentamicin-resistant clinical isolates of Enterococcu s faecalis, 20 carried gentamicin resistance (Gm(r)) plasmids. The pla smids ranged from 65.0 to 80.0 kb in size. Three of these plasmids wer e nonconjugative, and 17 transferred by conjugation to an E. faecalis recipient at low frequency (10(-5) to 10(-6) transconjugants per donor ). The remaining four strains had a nonconjugative chromosomal Gm(r) d eterminant. On the basis of restriction enzyme and DNA-DNA hybridizati on profiles, Tn4001-like alpha elements were located on the chromosome and three types of Tn4001-truncated structures, I, II, and III, were found to be carried by the Gm(r) plasmids. Structure I lacked IS256 in the right-hand flanking extremity of Tn4001. Structure II was the sam e as structure I except that it also had a partial deletion of IS256 i n the left-hand flanking extremity of Tn4001, Structure III lacked bot h the right- and left-hand flanking extremities of Tn4001. One of the wild-type strains carried the Gm(r) determinant both on the chromosome , as a Tn4001-like alpha element, and on a conjugative plasmid, as a T n4001-truncated type I structure.