Colonization factor antigens of enterotoxinogenic Escherichia coli : role in immunity and disease / Christina Åhrén.

Tese (doutor) - Groningen 1985

Enterotoxinogenic Escherichia coli (ETEC) is a major cause of diarrhoea in children in developing countries and in travellers. The bacteria cause disease through eleboration of one or two entorotoxins, ST and LT, of which only the latter is immunogenic. The present study was undertaken to investigate the immunogenicity of antigens which could be expected to elicit cross-protective immunity and interfer with different steps in the pathogenesis of ETEC infection, including bacterial colonization of the gut mucosa by means of fimbrial colonization factor antigens (CFAs) and toxin action. The aim was further to investigate the prevalence of such antigens on ETEC, and to evaluate their role in ETEC diasease. The ability of antisera against different E. coli antigens to decrease ETEC-induced fluid secretion was initially evaluated in rabbit ileas loops. Antibodies to LT protected against ETEC of different serotypes. Antiserum to homologous lipopolysaccharide (LPS) or to cross-reactive LPS structures had an additive protective effect on that of anti-LT, whereas antibodies to CFA/I or CFA/II had a much greater than additive effect on anti-LT, i.e. they cooperated synergistically for protection. The protective effect of an immunizing infection with bacteria expressing potentially protective antigens was evaluated in the RITARD model. This model allows studies of ETEC-induced diarrhoea in non-ligated rabbit intestine and also a more precise definition of the pathogenicity of ETEC strains with vaious virulence properties, e.g. different enterotoxins and CFAs. Previous infection with CFA/I=carrying, ST/LT-producing E. coli protected all animals reinfected with the same or an heterologous strain expressing CFA/I, ST and LT.When only one of the two antigens, CFA/I and LT, was shared by the ummunizing and heterologous rechallenge strains, partial protection was evident. The presence of CFAs, and entorotoxins on fresh, non-subcultured E. coli strains isolated from diarrhoea-sick and healthy individuals living in an ETEC-endemic area (Bangladesh) was studied. Methods suitable for epidemiological studies of CFAs and the effect of subculturing and storage of ETEC on their expression of ETEC isolates from patients with diarrhoea. All CFA-carrying strains were enteroxinogenic. Whereas the majority (93%) of the ST/LT strains carried CFAs, none of the LT only strains or any isolate from healthy persons possessed CFA/I or CFA/II. Agglutination tests with certain species of erythrocytes and/or absorbed CFA antisera did not identify CFA-positive strains with the same accuracy as immunodiffusion, whereas agglutination test using antisera against purified CFas appeared equally efficient as immunodiffusion. Transportation to Sweden and storage without subculturing did not alter the production of CFAs, whereas up to 80% of the initially CFA-positive strains no longer expressed these antigens after 5-10 subcultures. These studies suggest that antitoxic (anti-LT) and antibacterial (anti-CFA) immunity may cooperate for protection against experimental ETEC diarrhoea. In areas where CFAs are common on ETEC they may prove effective, alone or together with enterotoxin, in a future vaccine.