Distribution of msDNAs among serotypes of enteropathogenic Escherichia coli strains

A genetic element, called a retron, is present in certain Escherichia coli strains. It consists of genes for the production of a covalently linked DNA-RNA compound and a reverse transcriptase. The presence of a retron can be detected by testing for a satellite DNA band by polyacrylamide gel electrophoresis. This DNA band consists of the DNA portion of the DNA-RNA compound and is called msDNA (multicopy single-stranded DNA). In a survey of intestinal E. coli isolates we detected msDNAs in classical enteropathogenic (EPEC) strains and in strains with aggregative adherence to tissue-culture cells (AA), but not in enteroinvasive (EIEC) and enterotoxigenic (ETEC) strains. Among 76 EPEC strains belonging to 14 different serotypes, msDNA was found to be present in 7 serotypes. In total, five different types of msDNA were found, although within each serotype, the msDNAs were the same. These results suggest that different retrons are clonally inherited.