Surface co-expression of Vibrio cholerae and Salmonella typhi O-antigens on Ty21a clone EX210.
In an attempt to construct a bivalent, live, oral cholera-typhoid vaccine, genes specifying the biosynthesis of Vibrio cholerae O-antigen have been transferred into a modified version of the attenuated, oral typhoid vaccine strain Salmonella typhi Ty21a. The present report investigates the production of V. cholerae and S. typhi O-antigens by one such clone, EX210. When cultured without galactose supplementation EX210 produces surface O-antigen of V. cholerae type, as detected by haemagglutination-inhibition and bactericidal assays, and by immuno-electron microscopy. However, the protective efficacy of Ty21a depends upon growth in the presence of exogenous galactose and under these conditions only S. typhi O-antigen is detectable on the surface of EX210. Subsequent experiments revealed that the proportion of polysaccharide of S. typhi type is dependent upon the level of galactose supplementation, and identified a limiting sugar concentration which results in surface co-expression of both O-antigens. Visualization of the two polysaccharides on silver-stained polyacrylamide gels indicates that S. typhi O-antigen subunits are polymerized into longer sidechains, suggesting that at higher galactose concentrations their predominance results in a masking of the shorter V. cholerae O-antigen.
Enterovax Limited, Department of Microbiology and Immunology, University of Adelaide, South Australia.
S R
SR
Attridge
D
D
Daniels
J K
JK
Morona
R
R
Morona
D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D000954:Antigens, Surface / Q000276:immunology*; D002999:Clone Cells / Q000276:immunology; D005690:Galactose / Q000494:pharmacology; D006168:Guinea Pigs; D008070:Lipopolysaccharides / Q000302:isolation & purification; D019081:O Antigens; D012485:Salmonella typhi / Q000187:drug effects / Q000254:growth & development / Q000276:immunology* / Q000648:ultrastructure; D014734:Vibrio cholerae / Q000187:drug effects / Q000254:growth & development / Q000276:immunology* / Q000648:ultrastructure
D000942:Antigens, Bacterial; D000954:Antigens, Surface; D008070:Lipopolysaccharides; D019081:O Antigens; D005690:Galactose