Protective capacity of antibodies to outer-membrane components of Escherichia coli in a systemic mouse peritonitis model.

Antibody-mediated protection was studied in an experimental murine model of peritonitis-septicaemia with Escherichia coli O18:K1. Protection from lethal intraperitoneal challenge was achieved by passive immunisation with horse anti-K1 capsular antiserum (H46) or rabbit antiserum to the homologous O18 antigen. The maximum increase in LD50 achieved with anti-K1 and anti-O18 antibodies was 10- and 5-fold, respectively. The protective capacity of the anti-O serum was found to be in the IgG fraction. Rabbits were also immunised with various semi-purified or purified outer-membrane-protein preparations (porins and OmpA protein) from rough E. coli or Salmonella strains or with whole E. coli J5 bacteria. Although this immunisation resulted in high antibody titres to homologous and, to a lesser extent, also to heterologous antigens, none of the antisera protected against challenge with the capsulate E. coli O18:K1 bacteria.