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. MATERIALS AND 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. CONCLUSION: 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.

Molecular subtyping of Vibrio cholerae O1 and O139 by pulsed-field gel electrophoresis in Hong Kong: correlation with epidemiological events from 1994 to 2002.

Two hundred twenty isolates of Vibrio cholerae O1 and O139 collected from 1994 to 2002 in Hong Kong were analyzed by pulsed-field gel electrophoresis (PFGE). Chromosomal DNAs from all V. cholerae isolates in agarose plugs were digested with the restriction enzyme NotI, resulting in 20 to 27 bands. Sixty distinctive PFGE patterns in the range of 10 to 300 kb were noted among 213 isolates typeable by PFGE. By comparing the common PFGE patterns obtained from four well-defined outbreaks of V. cholerae O1 and O139 with those obtained from other, epidemiologically unrelated isolates during the study period, indistinguishable and similar PFGE patterns were identified, indicating their close relatedness, in agreement with the results of epidemiological investigations. Heterogeneous PFGE patterns (with four to six banding differences), however, were identified among strains that were imported from other parts of Asia, including Indonesia, India, and Pakistan. Correlations with epidemiological information further support the usefulness of PFGE as an epidemiological tool in laboratory investigations of suspected outbreaks. Standardization of PFGE methodology will allow international comparison of fingerprint patterns and will form the basis of a laboratory network for tracking V. cholerae.