Association of virulence markers with animal pathogenicity of Escherichia coli in different models.

Employing chicken and several strains of mice, different routes (intraperitoneal, subcutaneous) of infections and isogenic pairs of strains, association of virulence markers with animal pathogenicity was studied in Escherichia coli. Mouse virulence of avian strains was less significant than the lethality for chicks of human strains. LD50 in various animals did not differ significantly. Strains with antigen K1 were more virulent for mice than their K1- derivatives. Loss of haemolysin (Hly), mannose resistant haemagglutinating capacity or antigen K5 less markedly decreased the virulence. As opposed to other virulence factors, increased virulence of K1+ strains could also be demonstrated in mouse sepsis assay based on bacterial counts in the liver. Loss of Hly alone did not influence the persistence in the liver, however, these strains killed less mice. Aerobactin acts together with other factors, it is not per se a virulence factor. In organotropic experiments 19 strains out of 36 belonging to serotypes O7:K1:H-, O18:K1:H-, O78:H- and spontaneously agglutinable K1+ cultures, caused ophthalmitis with purulent discharge, and 4 out of 22 strains that belonged to serotype O78:H- induced uncoordinated movement of mice. Because of its special organotropic affinity to the brain and as it caused two epidemics of meningitis among newborns in Hungary, serotype O78:H- has a special pathogenic property and differs from other O78 strains that were isolated in other countries.