Immunogenic compositions

A hyper-blebbing Gram-negative bacterium which over-expresses a flippase wherein said flippase is (a) encoded by a sequence having 80% or greater sequence identity with SEQ ID NO:

• 1 or SEQ ID NO:3 and/or (b) comprises a sequence having 80% or greater sequence identity with SEQ ID NO:
• 2 or SEQ ID NO:4;
• and
• wherein said bacterium is genetically modified to produce a lipopolysaccharide (LPS) that has less toxicity than the toxicity of a corresponding wild-type LPS;
• and
• said over-expression results in the outer membrane vesicles (OMVs) or Generalised Modules for Membrane Antigens (GMMAs) spontaneously produced by said bacterium to be enriched for one or more lipoproteins when compared to OMVs or GMMAs produced by bacterium not over-expressing said flippase;
• and
• wherein the one or more enriched lipoprotein comprises lipoprotein selected from the group consisting of fHbp, NHBA, and NadA and variants thereof, and combinations thereof.