Salmonella enterica Serovar Typhi Lipopolysaccharide O-Antigen Modification Impact on Serum Resistance and Antibody Recognition.


Type
Article
Change log
Authors
Heiss, Christian 
Black, Ian 
Donohue, Nicholas 
Brown, Naj 
Abstract

Salmonella enterica serovar Typhi is a human-restricted Gram-negative bacterial pathogen responsible for causing an estimated 27 million cases of typhoid fever annually, leading to 217,000 deaths, and current vaccines do not offer full protection. The O-antigen side chain of the lipopolysaccharide is an immunodominant antigen, can define host-pathogen interactions, and is under consideration as a vaccine target for some Gram-negative species. The composition of the O-antigen can be modified by the activity of glycosyltransferase (gtr) operons acquired by horizontal gene transfer. Here we investigate the role of two gtr operons that we identified in the S Typhi genome. Strains were engineered to express specific gtr operons. Full chemical analysis of the O-antigens of these strains identified gtr-dependent glucosylation and acetylation. The glucosylated form of the O-antigen mediated enhanced survival in human serum and decreased complement binding. A single nucleotide deviation from an epigenetic phase variation signature sequence rendered the expression of this glucosylating gtr operon uniform in the population. In contrast, the expression of the acetylating gtrC gene is controlled by epigenetic phase variation. Acetylation did not affect serum survival, but phase variation can be an immune evasion mechanism, and thus, this modification may contribute to persistence in a host. In murine immunization studies, both O-antigen modifications were generally immunodominant. Our results emphasize that natural O-antigen modifications should be taken into consideration when assessing responses to vaccines, especially O-antigen-based vaccines, and that the Salmonellagtr repertoire may confound the protective efficacy of broad-ranging Salmonella lipopolysaccharide conjugate vaccines.

Description
Keywords
O-antigen, Salmonella enterica, lipopolysaccharide, phase variation, serum resistance, Animals, Antibodies, Bacterial, Bacterial Proteins, Base Sequence, Disease Models, Animal, Female, Gene Expression Regulation, Bacterial, Humans, Immune Sera, Immunization, Methylation, Mice, O Antigens, Operon, Salmonella typhi, Typhoid Fever
Journal Title
Infect Immun
Conference Name
Journal ISSN
0019-9567
1098-5522
Volume Title
85
Publisher
American Society for Microbiology