Immunogenicity of an E. coli extract after oral or intraperitoneal administration: induction of antibodies against pathogenic bacterial strains

For the treatment of recurrent infections of the urinary tract, a bacterial extract (OM-89) consisting of immunostimulating components derived from 18 Escherichia coli strains is orally applied to patients. We investigated in a mouse model the immunogenicity of the bacterial extract after intraperitoneal or oral administration. After repeated administration of the extract, serum IgG and IgA responses against the E. coli strains used for the preparation of OM-89 were obtained. This antisera also recognized a number of bacterial strains isolated from patients with urinary tract and enterohemorrhagic E. coli infections, and bound to a variety of other pathogenic strains. Moreover, the supernatants of cell cultures prepared from the urogenital tract of mice immunized with OM-89 contained increased levels of strain specific and of total IgG and IgA. Our findings may contribute to explain the therapeutic effect of OM-89 demonstrated in clinical studies.