A vaccine for use in the treatment or prevention of Gram-negative bacterial infection or disease comprising: a first antigen which is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognises an outer membrane protein of at least a first Gram-negative bacterial strain, wherein said outer membrane protein is involved in uptake of extracellular zinc, wherein said first antigen comprises: a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 1, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 1, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of SEQ ID No. 1, and a second antigen, wherein said second antigen comprises: a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 50; optionally wherein said second antigen is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID NO. 50, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 50, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of the sequence of SEQ ID No. 50, and wherein said immunogenic fragment is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID No. 50, wherein said vaccine comprises a bacterial outer membrane vesicle preparation comprising said first antigen, optionally wherein expression of said first antigen is up-regulated in said outer membrane vesicle preparation. a first antigen which is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognises an outer membrane protein of at least a first Gram-negative bacterial strain, wherein said outer membrane protein is involved in uptake of extracellular zinc, wherein said first antigen comprises: a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 1, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 1, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of SEQ ID No. 1, and a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 1, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 1, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of SEQ ID No. 1, and a second antigen, wherein said second antigen comprises: a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 50; optionally wherein said second antigen is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID NO. 50, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 50, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of the sequence of SEQ ID No. 50, and wherein said immunogenic fragment is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID No. 50, wherein said vaccine comprises a bacterial outer membrane vesicle preparation comprising said first antigen, optionally wherein expression of said first antigen is up-regulated in said outer membrane vesicle preparation. a. a polypeptide having at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99% or at least 100% identity to the amino acid sequence of SEQ ID No. 50; optionally wherein said second antigen is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID NO. 50, or b. a polypeptide comprising an immunogenic fragment of the sequence of SEQ ID No. 50, wherein said immunogenic fragment consists of an amino acid sequence having 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 30, 40, 50 or more contiguous amino acids of the sequence of SEQ ID No. 50, and wherein said immunogenic fragment is capable of raising an immune response, if necessary when coupled to a carrier protein, which immune response recognizes the amino acid sequence of SEQ ID No. 50,