Heterologous protection against invasive Escherichia coli K1 disease in newborn rats by maternal immunization with purified mannose-sensitive pili.

Heterologous protection against Escherichia coli K1 bacteremia with antibody to purified mannose-sensitive (MS) pili was demonstrated in a neonatal rat model. The serological relatedness of purified MS pili from 17 E. coli K1 clinical isolates was examined by an enzyme-linked immunosorbent assay. Five pilus serogroups were identified, with the pili in each group showing 50% or greater cross-reactivity with the typing serum of the group. The MS pili from 12 of 17 (70%) strains belonged to just two serogroups. Pregnant Sprague-Dawley rats (dams) were immunized with purified pili, and their newborns (pups) were challenged with heterologous E. coli. Bacteremia was significantly reduced when the pili used for immunization were from the same serogroup as the pili expressed by the challenge bacteria. Thus, immunization with C94 pili and challenge with E03 (71% cross-reactivity) or E04 (50% cross-reactivity) resulted in bacteremia rates of 12 of 17 (17%) versus 51 of 79 (65%) in controls and 0 of 75 (0%) versus 28 of 70 (40%) in controls, respectively (P less than 0.001 for each comparison). With lower cross-reactivity, less protection was observed (P less than 0.05 for 22 to 37% pilus serological relatedness). No protection was seen in pups suckled by dams immunized with MS pili having only 5% serological relatedness to the pili on the challenge strain.