This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Baker, S. Articles by Haque, A. Search for Related Content PubMed PubMed Citation Articles by Baker, S. Articles by Haque, A.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, September 2005, p. 4418-4425, Vol. 43, No. 9
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.9.4418-4425.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Detection of Vi-Negative Salmonella enterica Serovar Typhi in the Peripheral Blood of Patients with Typhoid Fever in the Faisalabad Region of Pakistan

Stephen Baker,^1* Yasra Sarwar,² Hafsa Aziz,² Asma Haque,² Aamir Ali,² Gordon Dougan,¹ John Wain,¹ and Abdul Haque²

The Wellcome Trust Sanger Institute, The Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, United Kingdom,¹ Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering, P.O. Box 577, Faisalabad, Pakistan²

Received 22 April 2005/ Returned for modification 13 June 2005/ Accepted 21 June 2005

The synthesis and transportation proteins of the Vi capsular polysaccharide of Salmonella enterica serovar Typhi (serovar Typhi) are encoded by the viaB operon, which resides on a 134-kb pathogenicity island known as SPI-7. In recent years, Vi-negative strains of serovar Typhi have been reported in regions where typhoid fever is endemic. However, because Vi negativity can arise during in vitro passage, the clinical significance of Vi-negative serovar Typhi is not clear. To investigate the loss of Vi expression at the genetic level, 60 stored strains of serovar Typhi from the Faisalabad region of Pakistan were analyzed by PCR for the presence of SPI-7 and two genes essential for Vi production: tviA and tviB. Nine of the sixty strains analyzed (15%) tested negative for both tviA and tviB; only two of these strains lacked SPI-7. In order to investigate whether this phenomenon occurred in vivo, blood samples from patients with the clinical symptoms of typhoid fever were also investigated. Of 48 blood samples tested, 42 tested positive by fliC PCR for serovar Typhi; 4 of these were negative for tviA and tviB. Three of these samples tested positive for SPI-7. These results demonstrate that viaB-negative, SPI-7-positive serovar Typhi is naturally occurring and can be detected by PCR in the peripheral blood of typhoid patients in this region. The method described here can be used to monitor the incidence of Vi-negative serovar Typhi in regions where the Vi vaccine is used.

---

* Corresponding author. Mailing address: Microbial Pathogenesis, The Sanger Institute, The Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, United Kingdom. Phone: 44 (0)1223-834244. Fax: 44 (0)1223-494919. E-mail: sgb{at}sanger.ac.uk.

---

Journal of Clinical Microbiology, September 2005, p. 4418-4425, Vol. 43, No. 9
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.9.4418-4425.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Le, T. A. H., Fabre, L., Roumagnac, P., Grimont, P. A. D., Scavizzi, M. R., Weill, F.-X. (2007). Clonal Expansion and Microevolution of Quinolone-Resistant Salmonella enterica Serotype Typhi in Vietnam from 1996 to 2004. J. Clin. Microbiol. 45: 3485-3492 [Abstract] [Full Text]  
• Tracz, D. M., Tabor, H., Jerome, M., Ng, L.-K., Gilmour, M. W. (2006). Genetic Determinants and Polymorphisms Specific for Human-Adapted Serovars of Salmonella enterica That Cause Enteric Fever.. J. Clin. Microbiol. 44: 2007-2018 [Abstract] [Full Text]