PHYSICAL CHARACTERIZATION OF 10-R PLASMIDS OBTAINED FROM AN OUTBREAK OF NOSOCOMIAL KLEBSIELLA-PNEUMONIAE INFECTIONS

Gentamicin resistance in K. pneumoniae involved in an outbreak at the Minneapolis Veterans Administration Hospital was due to a transmissible R plasmid. In addition to gentamicin, this plasmid conferred resistance to tobramycin, kanamycin, ampicillin, carbenicillin, cephalothin, chloramphenicol, and sulfathiazole. R plasmids which transferred this complex antibiogram were identified in several clinical isolates, including four different serotypes of K. pneumoniae, E.coli, Enterobacter cloacae, and Proteus morganii. The covalently closed circular form of all R plasmids isolated had a sedimentation coefficient of 76S to 77S, corresponding to a molecular weight of 58x106. The possibility that a single R plasmid was responsible for the dissemination of multiple drug resistance among all of these different clinical strains was examined by characterizing the plasmids by using EcoRI restriction endonuclease. The same 15 fragments were obtained from each of the 10 plasmids analyzed. Their molecular weights ranged from 4x105 to 11x106. It is concluded that each of the 10 plasmids present in the various clinical strains isolated from the hospital over a 7-mth period originated from a common source and that R plasmid transfer was important in their spread.