An approach for modifying multiple types of bacteria to produce surface modifications that enhance the immunologic response when used as a vaccine. A series of plasmids (pYF, pYFC, pYFP, pSF, pSPF, and pSCF) may be used to transform bacteria which then produce surface-exposed ligands that bind to complement receptors on antigen presenting cells. When modified bacteria are used as a vaccine, the vaccine recipients produce significantly higher titers of specific antibodies and are better protected against challenges from the disease-causing bacteria.