Distribution of insertion element IS1 in natural isolates of Escherichia coli.

Total DNAs from twelve natural isolates of Escherichia coli from animals and humans were examined by hybridization with a probe for IS1. Considerable variation in copy number was found. In the case of two strains isolated from the same individual, one strain contained no copies of IS1 and the other, much greater than 30. Evidence was also obtained for the existence of IS1-like elements (iso-IS1s) of greater than 15% sequence divergence relative to the IS1 from antibiotic resistance plasmid R100.