Common Plasmid Specifying Tobramycin Resistance Found in Two Enteric Bacteria Isolated from Burn Patients

Abstract

Tobramycin-resistant burn wound isolates of Klebsiella pneumoniae and Enterobacter cloacae , together with Escherichia coli K-12 transconjugants from these two strains, were examined for plasmid deoxyribonucleic acid (DNA). All the resistant strains contained a common, high-molecular-weight, covalently closed circular DNA plasmid that was absent in the tobramycin-susceptible E. coli recipient strain. The common plasmid residing in E. cloacae was designated pIE098, and that residing in K. pneumoniae was designated pIE099. Both plasmid species were found to have a molecular mass of approximately 60 × 10 6 daltons and a guanine-plus-cytosine content of 50 mol%. The DNA that was extracted from all of the tobramycin-resistant strains tested was able to hybridize to 86 to 100% with pIE098 and pIE099 [ 3 H]DNA generated by Eco RI to produce fragments of a size similar to those generated by Bam HI. This study illustrates the usefulness of simple screening methods for antibiotic resistance plasmids in a hospital epidemiological situation.