Extrachromosomal deoxyribonucleic acid in R factor-harboring Enterobacteriaceae

Abstract

Extrachromosomal deoxyribonucleic acid (DNA) from 24 different R factor-harboring Enterobacteriaceae was isolated and characterized by analytical ultracentrifugation and electron microscopy. The R factors represented 15 different patterns of transferable drug resistance found in enterobacteria from an enclosed geographic area. All of the strains contained extrachromosomal, circular DNA molecules within the range of 0.4 to 52 mum. More than one size class of circular DNA molecules was observed in the majority of the extrachromosomal DNA preparations. The buoyant density of the extrachromosomal DNA ranged from 1.700 to 1.720 g/cm3. The majority of the bacteria contained extrachromosomal DNAs of various densities. Three-fourths of the R factors were classified as fi+. The investigation illustrates the extensive variability in the physical characteristics of plasmid DNA from R factor-harboring strains.

Growth of Enterobacter cloacae in the presence of 25% sodium dodecyl sulfate

“…Thus, extreme detergent resistance may be characteristic of the genus Enterobacter and may be of considerable taxonomic significance. Strains of E. cloacae are known to harbor plasmids (11,16), but we have as yet no evidence whether or not this detergent resistance is plasmid mediated.…”