Molecular analysis of plasmids in epidemiologic investigation.

Abstract

The techniques themselves fall into two categories: indirect and direct techniques. Indirect techniques include agarose gel electrophoresis and restriction endonuclease analysis. Electrophoresis of plasmids in an agarose gel provides a fairly accurate estimate of the size of a plasmid molecule [3]. Re-. striction endonucleases are bacterial enzymes that cleave double-stranded DNA at specific recognition sites to generate a series of plasmid fragments [4]. The number and sizes of these fragments depend upon the number and location of specific recognition sites present in the plasmid molecule. If two plasmids are of the same size and yield identical patterns of fragments on restriction endonuclease analysis, especially if two or more restriction enzymes are used, they may be assumed to be identical or nearly so. Conversely, two plasmids of the same size may have entirely different base sequences; this can be recognized by the different fragment patterns generated by a restriction endonuclease. Finally, two plasmids may be quite different in size but possess one or more homologous regions of DNA; an intimation of this may be obtained by finding shared fragments on restriction endonuclease analysis. Direct techniques involve hybridization of DNA