ROLE OF ADHESIVE FACTOR RABBIT-2 IN EXPERIMENTAL ENTEROPATHOGENIC ESCHERICHIA-COLI O103 DIARRHEA OF WEANED RABBIT

The Adhesive Factor/Rabbit 2 (AF/R2) is found in Escherichia coli stra ins of serovar O103:K-:H2 and rhamnose-negative biovars isolated from weaned rabbits with diarrhea. This adhesin allows the colonization of the distal parts of the digestive tract, a first step leading to sever e inflammatory diarrhea and death of the animals. In vitro, AF/R2 expr ession mediates diffuse adhesion of E. coli on HeLa cells, adhesion to ileal villi of newborn and weaned rabbits and the presence of a major 32 kDa subunit in bacterial surface extracts. In this work, we constr ucted Tn phoA mutants of the prototype strain B10 and selected an isog enic clone that did not express the AF/R2 32 kDa subunit when grown in permissive conditions in vitro. The pathogenicity of the wild type st rain and of the isogenic mutant was compared by oral inoculation to 35 -day-old weaned rabbits, The mutant showed impaired colonization and a highly significant loss of pathogenicity. However, the occurrence of residual weight losses, and of diarrheas and mortalities in some inocu lated rabbits suggest that pathogenicity of rabbit O103 enteropathogen ic like E. coli (EPEC-like) strains is due to multiple virulence facto rs and that other virulence traits remain to be found.