Serum bactericidal antibody titres of pooled murine sera against 4 target strains, following immunisation with recombinant OpaA and OpaD, and Opa-positive and Opa-negative OMVs.

Titres represent highest dilution at which there was 50% bacterial survival. Immunisation with recombinant Opa elicited bactericidal antibodies in mice if the same Opa variant was expressed by the target strain in the SBA assay, with a titre of 1∶256 in all cases. Immunisation with any of the OMVs elicited high levels of bactericidal antibodies in mice against all strains in the SBA assay, with titres between 1∶1024 and 1∶4096.