The expression of alpha-hemolysin is a property frequently associated with Escherichia coli extraintestinal infections. We have examined the genetic basis for hemolysin expression by an E. coli strain isolated from a human urinary tract infection. The genes necessary for hemolysin synthesis were found to be chromosomal and to map near the ilv gene cluster. Isogenic hly+ and hly derivatives were also prepared and tested for virulence in the chicken embryo model system. Hemolysin was found to be necessary but not in itself sufficient for E. coli virulence in this in vitro model.
