Molecular characterization of Salmonella enterica Serotype Typhi isolates by pulsed-field gel electrophoresis in Hong Kong, 2000-2004.
OBJECTIVE
To study Salmonella enterica serotype Typhi by pulsed-field gel electrophoresis in Hong Kong.


METHODS
One hundred thirty four isolates of Salmonella enterica serotype Typhi collected from 17 public hospitals and clinics in Hong Kong from 2000 to 2004 were studied in relation to epidemiological and clinical events. Isolates originated from 80 patients, with 29 patients providing multiple isolates. Susceptibility to six antibiotics was tested: ampicillin, trimethoprim-sulfamethoxazole, tetracycline, chloramphenicol, nalidixic acid, and ciprofloxacin. Strains were further subtyped by pulsed-field gel electrophoresis (PFGE) by separating XbaI-restricted genomic DNA of isolates. PFGE patterns that were shared between strains were further examined using restriction enzyme BlnI.


RESULTS
Of 134 S. Typhi isolates, 29 (21.6%) were resistant to at least one and up to five of the antibiotics tested. Using restriction fragments between 20 and 700 kb for analysis, the number of fragments generated by XbaI ranged from 14 to 20. Sixty-six distinct subtypes were identified in the first isolates of all 80 patients (epidemiologically unrelated) with a Simpson index of 0.993, indicating a high degree of diversity among these S. Typhi isolates. Multidrug-resistant and travel-associated S. Typhi appeared to cluster more closely than the rest of strains. Further analysis of PFGE patterns investigated the temporal relationships between the 83 strains collected from the 29 patients who gave multiple isolates.


CONCLUSIONS
Dual infections or variants of the same isolates in the same patient occurred during the course of follow-up. These findings imply that PFGE data could be a valuable tool in predicting relapse, evaluating new antimicrobial drugs, and controlling the spread of typhoid disease. A regional, as well as global, typhoid bacillus fingerprint database should be set up to improve epidemiological investigations, as clinical cases easily move across national boundaries.
Kam
Kai Man
KM
Division of Microbiology, Public Health Laboratory Service, Centre for Health Protection, Department of Health, Hong Kong, China. kmkam@dh.gov.hk
Luey
Kit Yee
KY
Chiu
Agatha Wai Huen
AW
Law
Choi Ping
CP
Leung
Susanna Fung Sim
SF
D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000032:analysis*; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods*; D005260:Female; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D010802:Phylogeny; D012150:Polymorphism, Restriction Fragment Length; D011634:Public Health; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology*; D012485:Salmonella typhi / Q000145:classification / Q000187:drug effects / Q000235:genetics; D014195:Travel
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial