Modified strain of salmonella enterica typhi

Abstract

The present invention relates to the modification of a live attenuated strain of Salmonella enterica serovar Typhi, wherein its natural surface-exposed polysaccharide and flagellin antigens may be converted to, or augmented by, those from other strains of Salmonella, including S. enterica serovars Paratyphi, Typhimurium and Enteritidis. The present invention also relates to modified strains of Salmonella enterica serovar Typhi being suitable for use as components of a vaccine for enteric fever and salmonellosis.

1 . A live attenuated strain of  Salmonella enterica  serovar  Typhi  wherein said strain is modified to express the lipopolysaccharide O2 O-antigens and the flagella proteins of  Salmonella enterica  serovar  Paratyphi A.    
     
     
         2 . The live attenuated strain of  claim 1 , wherein the modification of said strain includes where the native rfbE gene is inactivated. 
     
     
         3 . The live attenuated strain of  claim 1 , wherein the modification of said strain includes where the native rfbE gene is deleted. 
     
     
         4 . The live attenuated strain of  claim 1 , wherein the native rfbE gene is inactivated by the insertion of a spacer region of DNA, preferably wherein the spacer region of DNA is the cistron of the  Escherichia coli  gene wbdR. 
     
     
         5 . The live attenuated strain of  claim 1  wherein the resulting lipopolysaccharide O2 O-antigens are at least equivalent in length to the lipopolysaccharide O9 O-antigens of  Salmonella enterica  serovar  Typhi.    
     
     
         6 . The live attenuated strain of  claim 1 , wherein said strain has its native fliC gene substituted with the fliC gene of  Salmonella enterica  serovar  Paratyphi A , or wherein the substituted fliC gene is expressed in trans, such that the conferred serotype is altered from an Hd serotype to a Ha serotype. 
     
     
         7 . The live attenuated strain of  claim 1 , wherein said strain is modified to contain a functional fepE gene, such that long O-antige chains are generated, preferably wherein the O-antigen chains are 100 repeated units of the trisaccharide backbone in length and/or wherein said strain is further modified to constitutively express gtrC, or wherein the gtrC gene is expressed in trans, and/or wherein said strain is further modified to contain an additional copy of the tviA gene under the control of a phagosomally induced promoter. 
     
     
         8 . A vaccine comprising the live attenuated strain of  claim 1 , for use in enhancing immunogenicity against  Salmonella enterica  serovar  Paratyphi A  and for use in the treatment or prevention of enteric fever and  salmonellosis.    
     
     
         9 . The vaccine according to  claim 1 , wherein said strain is selected from the group consisting of ZH9, ZH9PA and a combination of ZH9 and ZH9PA. 
     
     
         10 . The vaccine according to  claim 9 , wherein the vaccine further comprises an additional live attenuated  Salmonella  strain. 
     
     
         11 . A live attenuated strain of  Salmonella enterica  serovar  Typhi  wherein said strain is modified to express the lipopolysaccharide O4 O-antigens and the flagella proteins of  Salmonella enterica  serovar  Paratyphi B  and  Salmonella enterica  serovar  Typhimurium.    
     
     
         12 . The live attenuated strain of  claim 11 , wherein the modification of said strain includes the replacement of the native rfbS gene with the rfbJ gene of  Salmonella enterica  serovar  Paratyphi B  and/or  Salmonella enterica  serovar  Typhimurium , or wherein the modification of said strain includes the inactivation of the native rfbS gene with the concurrent trans expression of the rfbJ gene of  Salmonella enterica  serovar  Paratyphi B  and/or  Salmonella enterica  serovar  Typhimurium.    
     
     
         13 . The live attenuated strain of  claim 11 , wherein said strain has its native fliC gene replaced with the fliC gene of  Salmonella enterica  serovar  Paratyphi B  and/or  Salmonella enterica  serovar  Typhimurium , or wherein the substituted fliC gene is expressed in trans, such that the conferred serotype is altered from an Hd serotype to a Hb and Hi serotype respectively. 
     
     
         14 . The live attenuated strain of  claim 11 , wherein the fljBA locus of  Salmonella enterica  serovar  Paratyphi B  and  Salmonella enterica  serovar  Typhimurium  are inserted into the chromosome of  Salmonella enterica  serovar  Typhi  or expressed in trans. 
     
     
         15 . The live attenuated strain of  claim 11 , wherein the hix sites flanking the native promoter of the fIjBA operon, or the hin recombinase gene, are modified to achieve constitutive expression. 
     
     
         16 . The live attenuated strain of  claim 11 , wherein the strain is further modified according to  claim 7 . 
     
     
         17 . A vaccine comprising the live attenuated strain of  claim 11 , for use in enhancing immunogenicity against  Salmonella enterica  serovar  Paratyphi B  and/or  Salmonella enterica  serovar  Typhimurium  and for use in the treatment or prevention of enteric fever and  salmonellosis.