Abstract
BackgroundTyphoid 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.ResultsTwenty-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.ConclusionsNalidixic 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.
Highlights
Typhoid and paratyphoid fever are endemic in China
In this study we investigated the molecular basis of resistance and the epidemiology of 25 S. typhi and 66 S. paratyphi blood isolates that were recovered from hospitalized patients in Shenzhen City, Southern China over 6-year period
DNA sequencing of both strands was performed by the direct sequencing method with an ABI Prism 3100 generic analyzer (Applied Biosystems, Foster City, CA), and the DNA sequences of the quinolone resistance-determining region (QRDR) of gyrA, gyrB, parC, and parE were compared with the DNA sequences of the QRDRs of S. typhi, S. paratyphi A, and S. paratyphi B (GenBank: NC_004631, NC_006511, NC_010102). b-lactamase genes were detected by Polymerase chain reaction (PCR) with primers specific for blaCTX-M, blaTEM, blaSHV, blaOXA among isolates resistant to ampicillin as described previously [11,12,13], and PCR products were sequenced as described above
Summary
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. Due to infection with Salmonella enteric serovar Typhi (S. typhi) and Paratyphi (S. paratyphi), are major global problems. Nalidixic acid-resistant (NAR) S. typhi and S. paratyphi are endemic to many Asian countries [1]. NAR isolates have reduced susceptibility to fluoroquinolones, which is associated with higher rates of morbidity and mortality, prolonged fever clearance time and increased need for retreatment [2]. Quinolone resistance in Salmonella is usually associated with mutations of the target site, DNA gyrase, most commonly in the quinolone resistance-determining region (QRDR) of the A subunit. Plasmid mediated quinolone resistance genes of qnr (qnrA, qnrB, qnrS, and qnrD) and aac(6’)-Ib-cr has
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