background: salmonella enterica serovar typhi (s. typhi) the cause of the acute febrile disease typhoid fever is the major public health problem in developing countries. asymptomatic carriers are the main sources of typhoid. the aim of this study was to investigate methods for isolation and identification of s. typhi in asymptomatic carriers. materials and methods: two hundred stool samples wer...

the role of vi-capsular polysaccharide (vi-cps) in human immunity against infection caused by salmonella typhi is well known. the downstream process of purification generally causes depolymerization of vi-cps to a nonimmunogenic low molecular weight form. in the present study, a standard strain of sal. typhi ty6s was grown under submerge cultural conditions in a pilot-plant scale of 90 liter fe...

To the Editor—Field investigations in the People’s Republic of China to determine the protective efficacy of typhoid Vi polysaccharide vaccine (Vi vaccine) were done among students attending a middle school [1]. Vi vaccine was offered to students even during an outbreak of typhoid fever. The efficacy was 73% among those immunized before the outbreak and 71% among vaccine recipients during the o...

Salmonella enterica serovar Typhi expresses a capsule of Vi polysaccharide, while most Salmonella serovars, including S. Enteritidis and S. Typhimurium, do not. Both S. Typhi and S. Enteritidis express the lipopolysaccharide O:9 antigen, yet there is little evidence of cross-protection from anti-O:9 antibodies. Vaccines based on Vi polysaccharide have efficacy against typhoid fever, indicating ...

Salmonella typhi Vi typing phages were used to transduce temperature-sensitive (Ts) mutants of Salmonella typhi. Antibiotic resistance and Ts+ markers were transduced at high frequency (> 10(-4) per virulent phage). Several markers were cotransduced by phage Vi I, suggesting that it may be useful for mapping studies of the S. typhi genome.

Characterization of Salmonella enterica Serovar Typhi isolates for their Vi capsular polysaccharide antigen-related genetic sequences is desirable to define the role of isolates lacking such sequences in differential replication at unusual sites, including those coinfected with human immunodeficiency virus (HIV). Infection with Vi-negative strains might produce typhoid fever among those immuniz...

T cells are critical to immunity against pathogenic Salmonella including Salmonella Typhi which causes systemic infection, typhoid, in humans. The strategies that this pathogen employs to keep T-cell mediated immune responses in check during establishment of systemic infection are not completely understood. Here, we show that the virulence polysaccharide Vi, which distinguishes S. Typhi from lo...

The synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi (S. Typhi), is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some S. Typhi isolates exhibit over-expression of Vi polysaccharide, which masks clinical detection of LPS O-antigen. This variation in Vi polysaccharide and O-antigen ...

Strains of Salmonella typhi isolated from the blood of patients with typhoid fever invariably express a capsular polysaccharide, termed the Vi antigen. Vi antigen expression is controlled by two separate chromosomal loci, viaA and viaB. The viaA locus is commonly found in enteric bacteria. In contrast, the viaB locus appears to be specific to Vi-expressing strains of Salmonella and Citrobacter....