Dissemination of a gentamicin resistance plasmid in the microbial population of hospital patients.

The dissemination of a gentamicin resistant plasmid, originally found in strains of Klebsiella and termed pk181, into the microbial population of patients of the Orvieto Hospital was studied during 1982. Five hundred and seventy-four strains of Gram-negative bacilli were examined, transferable gentamicin resistance being revealed in five different bacterial species. The resistance was shown to be encoded by 81-megadalton plasmids in Escherichia coli and Enterobacter cloacae, and by 93-megadalton plasmids in Serratia marcescens and Pseudomonas spp. Restriction endonuclease digestion of plasmid DNA showed that the fragment patterns of the 81-megadalton plasmids from E. coli and enterobacter cloacae were identical to one another and to the pattern of plasmid pk181. The fragment patterns of the 93-megadalton plasmids from Serratia and Pseudomonas, on the contrary, differed substantially from those of the 81-megadalton plasmids.