The Toxic Role of Alpha-haemolysin in the Pathogenesis of Experimental Escherichia coli Infection in Mice

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Abstract
Filtrates from strains of E. coli possessing plasmid-cloned hemolysin (Hly) genes and from strains possessing wild Hly plasmids were lethal for mice on i.v. inoculation; similar doses of preparations from derivatives of these strains in which the Hly genes had been rendered non-functional or which did not possess the wild plasmids were not. Live cultures of both kinds of Hly+ strain usually had a lower lethal dose for mice on i.p. inoculation than the corresponding Hly- forms. Mice that had been inoculated with Hly+ forms had shorter survival times and lower numbers of organisms in peritoneal washings, lungs and blood at point of death than mice that had been inoculated with the corresponding Hly- forms; this was also so for mice pre-treated with FeSO4, a procedure which rendered mice equally susceptible to the lethal effects of the Hly+ and Hly- forms of a strain. In FeSO4-treated mice the numbers of organisms in the tissues of those dying from infection with Hly+ organisms were no higher than they were at the same time after inoculation in others given the corresponding Hly- forms; before mice of the latter category died the numbers of organisms in their tissues increased greatly. The clinical and pathological signs exhibited by mice inoculated with Hly+ organisms, but not with Hly- organisms, resembled those exhibited by mice inoculated with bacteria-free hemolysin preparations. Thus, hemolysin evidently played a significant role in the pathogenesis of the disease produced by the Hly+ organisms by having a direct toxic action on the host.