Plasmid pattern analysis of natural bacterial isolates and its epidemiological implication

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Abstract
SUMMARY: Natural isolates ofEscherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, andProvidencia stuartiiwere analysed to determine their plasmid content. This data allowed the identification of nosocomial strains ofK. pneumoniaeandP. stuartiiand helped in the differentiation of epidemic strains ofE. coli0111 andS. typhimurium. Phenotypically similar isolates ofS. typhimuriumcould be shown to be of independent origin using plasmid pattern analysis. The dissemination of a particular plasmid through different strains ofS. typhimuriumresulted in a simulation of a very widely distributed epidemic strain, because the plasmid interfered with the phage type of its host strain in addition to determining re sistance properties. Plasmid pattern analysis disclosed two independently existing but interacting epidemic processes: a bacterial ‘epidemic’ strain may become disseminated over a large territory and may predominate there for a long time; a single plasmid, however, may also become distributed through many different bacterial strains and may spread over a large territory. Plasmid pattern analysis provides a valuable and universal epidemiological laboratory method.