Abstract
The hemolytic activity of wild-type strains of Escherichia coli was measured by a standardized method in liquid broth. The system also allowed us to investigate the influence of various Fe3+ concentrations in the cultures on the amount of secreted hemolysin. We found that the hemolysin secretion of all strains was clearly reduced after addition of FeCl3. However, the influence of additional iron chelators showed remarkable differences. The hemolytic activity of Hly plasmid-containing strains isolated in Berne significantly increased. Most of the strains with a chromosomal hemolysin determinant showed a similar effect, but to a lesser degree. Contrary to this, Hly plasmid-containing strains isolated in Essex and some strains with chromosomal hemolysin determinant were either not affected or even showed reduced hemolysin secretion after limitation of free iron ions in the broth. Our results suggest that hemolysin secretion in E. coli is related to the bacterial iron metabolism, and hemolysin secretion is differentially regulated among E. coli strains.