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Open Access Research article

Genetic Diversity of Salmonella enteric serovar Typhi and Paratyphi in Shenzhen, China from 2002 through 2007

Weiyuan Wu1, Hui Wang2*, Jian Lu3, Jinsong Wu1, Minjun Chen2, Yingchun Xu2 and Yuemei Lu1

Author Affiliations

1 Department of Laboratory Medicine, Shenzhen People's Hospital, Jinan University Second Clinical Medical College, Shenzhen (Guangdong), 518020, PR China

2 Department of Clinical Laboratory, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100730, PR China

3 Department of Infectious Disease, Shenzhen East Lake Hospital, Shenzhen (Guangdong), 518020, PR China

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BMC Microbiology 2010, 10:32  doi:10.1186/1471-2180-10-32

Published: 30 January 2010

Abstract

Background

Typhoid and paratyphoid fever are endemic in China. The objective of this investigation was to determine the molecular features of nalidixic acid-resistant Salmonella enteric serovar Typhi (S. typhi) and Paratyphi (S. paratyphi) from blood isolates in Shenzhen, China.

Results

Twenty-five S. typhi and 66 S. paratyphi were isolated from 91 bacteriemic patients between 2002 and 2007 at a hospital in Shenzhen, Southern China. Fifty-two percent (13/25) of S. typhi and 95.3% (61/64) of S. paratyphi A were resistant to nalidixic acid. Sixty-seven isolates of nalidixic acid-resistant Salmonella (NARS) showed decreased susceptibility to ciprofloxacin (MICs of 0.125-1 μg/mL). All 75 NARS isolates had a single substitution in the quinolone resistance-determining region (QRDR) of GyrA (Ser83→Phe/Pro/Tyr, or Asp87→Gly/Asn), and 90.7% of these isolates carried the substitution Ser83Phe in GyrA. No mutation was found in the QRDR of gyrB, parC, or parE. Plasmid mediated quinolone resistance genes including qnr and aac(6')-Ib-cr were not detected in any isolate. Twenty-two distinct pulsed field gel electrophoresis (PFGE) patterns were observed among S. typhi. Sixty-four isolates of S. paratyphi A belonged to one clone. Eighty-seven investigated inpatients were infected in the community. Six patients infected by S. paratyphi A had a travel history before infection.

Conclusions

Nalidixic acid-resistant S. typhi and S. paratyphi A blood isolates were highly prevalent in Shenzhen, China. PFGE showed the variable genetic diversity of nalidixic acid-resistant S. typhi and limited genetic diversity of nalidixic acid -resistant S. paratyphi A.