Serotype conversion of a Shigella flexneri candidate vaccine strain via a novel site-specific chromosome-integration system.
Shigella flexneri SFL124 (serotype Y) is a promising live oral vaccine candidate, which has been shown to be safe and immunogenic in human volunteers. To change the serotype of this vaccine strain, we inserted a serotype conversion gene cluster into the chromosome of SFL124 by using a bacteriophage-based site-specific integration system. By cloning an integrase gene (int), an attachment site (attP) and a glucosyl transfer gene cluster from bacteriophage SfX into a suicide vector, and subsequently introducing this construct into S. flexneri SFL124, we obtained a S. flexneri strain (designated SFL1213) expressing the serotype X somatic antigen specificity. The strain retained other characteristics of the parent strain, such as colony shape, growth rate, and Congo red binding property. Stability test showed that the serotype X O-antigen specificity in SFL1213 was 100% stable after being cultured approximately 72 successive hours under non-selective condition. In a mouse pulmonary model, the recombinant strain elicited a significant level of humoral antibodies which recognized the lipopolysaccharide (LPS) of a wild-type S. flexneri serotype X strain. The site-specific insertion system will be useful when stable expression of a cloned single copy gene is desired in the chromosome of S. flexneri vaccine candidate, SFL124.
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Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australia.
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D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis; D000942:Antigens, Bacterial / Q000235:genetics; D001287:Attachment Sites, Microbiological / Q000235:genetics; D001428:Bacterial Vaccines / Q000235:genetics / Q000276:immunology*; D001435:Bacteriophages / Q000235:genetics; D002876:Chromosomes, Bacterial / Q000235:genetics; D005260:Female; D005798:Genes, Bacterial; D005821:Genetic Techniques; D005822:Genetic Vectors; D006801:Humans; D007114:Immunization; D019426:Integrases / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D005810:Multigene Family; D012703:Serotyping; D012763:Shigella flexneri / Q000145:classification* / Q000235:genetics / Q000276:immunology*
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001428:Bacterial Vaccines; D019426:Integrases