The invention refers to an isolated antibody that specifically binds to O25b antigen of E. coli strains comprising at least an antibody heavy chain variable region (VH), which comprises any of the CDR1 to CDR3 sequences as listed in FIG. 1, and optionally further comprising an antibody light chain variable region (VL), which comprises any of the CDR4 to CDR6 sequences as listed in FIG. 1, or functionally active CDR variants of any of the forgoing CDR 1-6 sequences.