Immunization of mice with antibiotic treated Escherichia coli.

The hypothesis of a different immunogenicity between untreated and antibiotic-treated Escherichia coli was investigated in vivo. Groups of mice were injected weekly for eight weeks with formalin-killed E. coli ATCC 25922 either exposed or not to 0.1 x MIC of aztreonam. A group of mice injected with sterile saline only served as control. IgG production towards whole bacteria was clearly enhanced in the group immunized with antibiotic-treated E. coli as shown in ELISA assays. In the same group, the appearance of additional bands of reactivity in the region of major outer membrane proteins was observed in immunoblot experiments as well as an enhanced protection towards a challenge of 10 x LD50 of live E. coli. These findings seem to support the hypothesis that sub-MICs of antibiotics modify the bacterial surface influencing host-parasite relationships.