The Role of Alpha Haemolysin in the Virulence of Escherichia Coli for Mice

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Abstract
Transfer of an Hly plasmid determining production of .alpha.-hemolysin to a non-hemolytic strain of E. coli increased the virulence of the strain for mice. Injections of non-toxic amounts of .alpha.-hemolysin, phenylhydrazine, Hb, Fe or Mn salts simulated the effects of the Hly plasmid by stimulating bacterial growth. Active or passive immunization against .alpha.-hemolysin protected mice on challenge with hemolytic E. coli by inhibiting in-vivo proliferation of the strain. Protection was eliminated by administration of Fe salts at the time of challenge. The Hly plasmid probably acts as a virulence factor by enabling hemolytic strains of E. coli to obtain Fe for growth from the lysed erythrocytes of infected animals.