title: Antibiotic susceptibility pattern and the indicator of decreased ciprofloxacin susceptibility of Salmonella enterica serovar Typhi isolated from Dhulikhel Hospital, Nepal.
abstract: Monitoring the antibiotic susceptibility pattern of Salmonella enterica serovar Typhi  (S. Typhi) is important for efficiently managing cases of typhoid fever. In this study,  the antimicrobial susceptibility patterns of 114 S. Typhi isolates, which were collected from  a university hospital in Nepal during July 2009-December 2010, were investigated by disc  diffusion assays. All of the S. Typhi isolates were sensitive to amoxycillin-clavulanic acid.  More than 95% of the isolates were sensitive to chloramphenicol, ceftazidime, ceftriaxone, and  cotrimoxazole. In addition, 1.7% of the studied isolates showed multiple drug resistance  patterns. Of the 40 S. Typhi isolates, 32 strains (80%) showed nalidixic acid (NA) resistance  with decreased susceptibility to ciprofloxacin (CIP). Importantly, we found the simultaneous  presence of NA resistance and decreased susceptibility to CIP, suggesting that the resistance  to NA is a reliable indicator of decreased CIP susceptibility (sensitivity, 97.5%; specificity,  100.0%). Furthermore, the sequencing of NA-resistant S. Typhi isolates showed a predominant  amino acid alteration in the quinolone resistance-determining region (QRDR) of gyrA gene at  position 83 from Ser→Phe. Two isolates with resistance to both CIP and NA had a  double-mutation (Ser83→Phe and Asp87→Asn) in the QRDR of the gyrA gene, of which one had an  additional amino acid mutation (Ser80→Ilu) in the QRDR of the parC gene.
authors.affiliation: Department of Immunology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
authors.forename: Dhruba
authors.initials: D
authors.lastname: Acharya
authors.forename: Suwanna
authors.initials: S
authors.lastname: Trakulsomboon
authors.forename: Surendra Kumar
authors.initials: SK
authors.lastname: Madhup
authors.forename: Sunee
authors.initials: S
authors.lastname: Korbsrisate
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006785:Hospitals, University; D006801:Humans; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology; D009390:Nepal / Q000453:epidemiology; D016133:Polymerase Chain Reaction; D012485:Salmonella typhi / Q000187:drug effects* / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D014435:Typhoid Fever / Q000453:epidemiology* / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D027081:DNA Gyrase