Chromosome- and plasmid-mediated gentamicin resistance in Staphylococcus aureus encoded by Tn4001

Department of Microbiology. Monash University, Clayton. Victoria 3168, Australia Correspondence and offprint requests should be sent to Dr R. A. Skurray. Received September 17, 1986 Accepted October 15, 1986 DNA sequences corresponding to the 4·7-kb gentamicin, tobramycin and kanamycin resistance (Gm r Tm r Km r ) transposon Tn4001 have been detected on a series of nine structurally-related plasmids that mediate this phenotype in Australian isolates of Staphylococcus aureus. Tn4001 sequences have also been demonstrated on the chromosomes of GmTm r Km r isolates that do not possess these plasmids, and the exhibited diversity of chromosomal sites occupied by this element implies that Tn4001 has transposed to the chromosome on numerous occasions in vivo. These results suggest that the rapid emergence of nosocomial Gm r Tm r Km r S. aureus in the early 1980s may have been the result of the transposition of Tn4001 from a chromosomal site to a readily disseminated plasmid. Present address: Department of Genetics, Monash University, Clayton, Victoria 3168, Australia. * Present address: Research Centre for Cancer and Transplantation, Department of Pathology, University of Melbourne, Parkville, Victoria 3052, Australia.