Plasmids mediating resistance to gentamicin and other antibiotics in Enterobacteriaceae from four hospitals in Melbourne.

In twenty-nine gentamicin-resistant strains (mostly Klebsiella species) isolated from four Melbourne hospitals over a six month period, the genes for gentamicin resistance were carried on conjugative plasmids belonging to the rare incompatibility group L. These plasmids conferred resistance to gentamicin and sisomycin but not to amikacin or tobramycin, and were inferred to specify the enzyme aminoglycoside 3-N-acetyltransferase (AAC(3)I or GAT I). In addition, they specified resistance to a number of other antibiotics, including ampicillin and carbenicillin, chloramphenicol, kanamycin and neomycin, spectinomycin and streptomycin, sulphonamides and tetracyclines. Although they had a wide host range amongst the Enterobacteriaceae, none of these plasmids appeared able to transfer to Pseudomonas.