title: Prevalence and genetic analysis of phenotypically Vi- negative Salmonella typhi isolates in children from Kathmandu, Nepal.
abstract: The Vi capsular polysaccharide (ViPS) protects Salmonella enterica subspecies enterica serotype Typhi (S.Typhi) in vivo by multiple mechanisms. Recent microbiological reports from typhoid endemic countries suggest that acapsulate S.Typhi may occur in nature and contribute to clinical typhoid fever that is indistinguishable from disease caused by capsulate strains. The prevalence and genetic basis of ViPS-negative S.Typhi isolates in children from Kathmandu, Nepal, were tested in 68 isolates. Although 5.9% of isolates tested negative for capsular expression by slide agglutination tests, a novel multiplex PCR assay and individual PCR analyses demonstrated the presence of all 14 genes responsible for the synthesis, transportation and regulation of the ViPS. These data suggest that phenotypically acapsulate S.Typhi may not have a genetic basis for the same.
authors.affiliation: Oxford Vaccine Group, Department of Pediatrics, University of Oxford, Oxford, Oxfordshire, OX3 7LE, UK. apulickal@wihri.org
authors.forename: Anoop S
authors.initials: AS
authors.lastname: Pulickal
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Callaghan
authors.forename: Dominic F
authors.initials: DF
authors.lastname: Kelly
authors.forename: Mitu
authors.initials: M
authors.lastname: Maskey
authors.forename: Sandeep
authors.initials: S
authors.lastname: Mahat
authors.forename: Mainga
authors.initials: M
authors.lastname: Hamaluba
authors.forename: Sabina
authors.initials: S
authors.lastname: Dongol
authors.forename: Neelam
authors.initials: N
authors.lastname: Adhikari
authors.forename: Stephen
authors.initials: S
authors.lastname: Thorson
authors.forename: Buddha
authors.initials: B
authors.lastname: Basynat
authors.forename: David R
authors.initials: DR
authors.lastname: Murdoch
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Farrar
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pollard
mesh_terms: D002648:Child; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D006801:Humans; D007223:Infant; D009154:Mutation; D009390:Nepal / Q000453:epidemiology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D015995:Prevalence; D012485:Salmonella typhi / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification*; D014435:Typhoid Fever / Q000097:blood / Q000453:epidemiology* / Q000382:microbiology
chemical_list: D011135:Polysaccharides, Bacterial; C054154:capsular polysaccharide, Salmonella
keywords: Kathmandu; Nepal; Vi; acapsulate; polysaccharide; salmonella; typhi; typhoid