Antibody response of patients infected with verocytotoxin-producing Escherichia coli to protein antigens encoded on the LEE locus

Sera from patients infected with verocytotoxin-producing Escherichia coli (VTEC) O157, from patients with antibodies to E. coli O157 lipopolysaccharide (LPS) and from healthy controls were examined for antibodies to proteins involved in expressing the attaching and effacing phenotype. After SDS-PAGE, purified recombinant intimin, EspA-filament structural protein, translocated protein EspB and three separate domains of the translocated intimin receptor (Tir) were tested for reaction with patients' sera by immunoblotting. An ELISA was also used to detect antibodies to intimin in sera from E. coli O157 LPS antibody-positive individuals. Seven of nine culture-positive patients and one control patient had antibodies to EspA. Five of these patients and two controls had serum antibodies to the intimin-binding region of Tir, whereas none of the sera contained antibodies binding to either of the intracellular domains of Tir. By immunoblotting, 10 of 14 culture-positive patients had antibodies to the conserved region of intimin, eight of whom were infected with E. coli O157 phage type 2. Thirty-six of 60 sera from culture-negative but E. coli O157 LPS antibody-positive patients had antibodies to intimin as determined by ELISA. The secreted proteins are expressed in vivo during infection and are considered as pathogenic markers. Antibodies to these proteins may form the basis of a serodiagnostic test for the detection of patients infected with VTEC which carry the locus for the enterocyte effacement pathogenicity island and provide an adjunct test to the established serological tests based on VTEC LPS.