[Laboratory experiments with a polyvalent extract vaccine for oral immunization against E. coli enteritis].

Bacteria of E. coli causing enteritis can be extracted by EDTA-sodium. These extracts having lower dry weights result in better protective effects in contrast to sodium-deoxycholate extracts. The EDTA-sodium extracts can be concentrated, purified and sterile filtrated. Thus the production of polyvalent vaccines is possible. A direct relation exists between the effectiveness of the extracts and the virulence of the strains used for extraction. The more virulent the original strain the better is the protective effect of the vaccine produced by extraction of the original strain. The single components of the polyvalent vaccine show a certain improvement of their protective effects. For estimating the immunizing dose, it is necessary to consider the limiting dose. When exceeding this dose the protective effect or the vaccine does not further increase but remains constant of even decreases. The immunizing dose wanted must be greater than the ED50 but smaller than the limiting dose. Extremely high oral doses of vaccine result in symptoms of incompatibility in mice.