A footpad lesion test to demonstrate the pathogenicity of Escherichia coli strains

A virulence test based on the ability of E. coli strains to cause lesion in the footpads of mice was devised to demonstrate their pathogenicity. Virulence was expressed by a scale from 0 to 7 according to the importance of the lesions. Among 54 strains tested, those inducing death after intraperitoneal inoculation caused severe oedema or necrosis (score greater than 4) in footpads. Three other virulence tests (virulence measured in pregnant mice, in adult mice intraperitoneally challenged and in baby mice after oral inoculation) were used to study seven of the most characteristic strains. Good correlation was observed: strains pathogenic in the footpad lesion test were pathogenic in at least one of the other tests.