Experimental Escherichia coli O6 pyelonephritis in rabbits. Effect on O6 antibody quantity and avidity of prior immunization with E. coli O2 bacteria.

Haematogenous pyelonephritis was induced in rabbits using Escherichia coli 06:K13:H1 bacteria and the amounts and avidities of antibodies to the 06 antigen were analysed by the ammonium sulphate precipitation technique of Farr. In a group of six animals preimmunized with E. coli 02:K2ab:H1, five developed pyelonephritis and one pyelitis, as determined by histological examination. All aminals showed a considerable antibody response to E. coli 06 antigen during the infection. The animal with pyelitis gave a slightly smaller response than the others. The antibody avidity showed a pronounced variation. In a second group of six rabbits not preimmunized, five animals developed pyelonephritis. The titres of antibodies against E. coli 06 antigen increased during the infection inall of the six animals. However, the increase was significantly smaller than for the animals preimmunized with E. coli 02:K2ab:H1 (P smaller than 0.01). The pattern of the antibody avidities in this group was also heterogenous. The results are consistent with previous findings that exposure to serologically heterologous E. coli bacteria can enhance the development of the homologous antibody titres. This could be of relevance for serological diagnostic work as well as in the determination of the protective capacity of the antibody.