Towards a vaccine candidate against Shigella dysenteriae 1: expression of the Shiga toxin B-subunit in an attenuated Shigella flexneri aroD carrier strain.

Shiga toxin is considered to be one of the main causes of severe side effects, such as the hemolytic uremic syndrome, of shigellosis. The genetic determinants for a fusion of its B-subunit (StxB), which mediates toxin binding to target cells, with the COOH-terminus of Escherichia coli hemolysin A (Stx'-'HlyA) has been combined with the determinants of the accessory translocator proteins HlyB and HlyD in a Notl cassette. This cassette has been integrated via a mini-transposon into a recombinant vaccine strain that expresses Shigella flexneri Y and Shigella dysenteriae 1 O-antigen lipopolysaccharides. Characterisation of the resulting strains showed that they maintain all the vaccine-relevant biological properties of the carrier and export efficiently the StxB'-'Hly A fusion peptide into the culture medium. Polyclonal antibodies raised against the StxB'-'HlyA fusion exhibited neutralizing activity in the HeLa cytotoxicity assay. The newly developed strains thus represent promising bivalent vaccine candidates against severe shigellosis caused by S. dysenteriae 1 and S. flexneri Y.