Abstract: The present invention relates to vaccines, in particular, to an attenuated gram-negative cell comprising the SPI2 gene locus, wherein at least one gene of the SPI2 locus is inactivated, wherein said inactivation results in an attenuation/reduction of virulence compared to the wild type of said cell, and to a carrier for the presentation of an antigen to a host, which carrier is said attenuated gram-negative cell, wherein said cell comprises at least one heterologous nucleic acid molecule comprising a nucleic acid sequence coding for said antigen, wherein said cell is capable of expressing said nucleic acid molecule or capable of causing the expression of said nucleic acid molecule in a target cell.

Abstract: A series of genes from Streptococcus pyogenes are shown to encode products which are implicated in virulence. The identification of these genes therefore allows attuated microorganisms to be produced. Furthermore, the genes or their encoded products can be used in the manufacture of vaccines for therapeutic application.

Abstract: The present invention is based on the identification of a series of virulence genes in E. coli K1, the products of which may be implicated in the pathogenicity of the organisms. The identification of the genes allows them, or their expressed products, to be used in a number of ways to treat infection.