Endonuclease fingerprinting of plasmids mediating gentamicin resistance in an outbreak of hospital infections.

Three plasmids which each determined the same extensive antibiotic resistance phenotype, including resistance to gentamicin, and which had been recovered from organisms involved in an outbreak of gentamicin-resistant infections in Melbourne hospitals in 1975--1976, were analysed by fingerprinting with the restriction endonucleases Eco RI, Hind III and Pst I, In each case the fingerprints for all three plasmids were identical, despite the fact that each plasmid originated in a different host species at different hospitals. This observation confirms our earlier hypothesis (Davey and Pittard, 1977) that the plasmids mediating gentamicin resistance in the outbreak were the closely related descendants of one ancestral (IncL) plasmid.