Epidemiology and Infection

Research Article

Genome fingerprinting of Salmonella typhi by pulsed-field gel electrophoresis for subtyping common phage types

S. Naira1, C. L. Poha1 c1, Y. S. Lima2, L. Taya2 and K. T. Goha3

a1 Department of Microbiology, Faculty of Medicine, National University of Singapore, Kent Ridge, Singapore 0511

a2 Enteric Bacteriology Laboratory, Department of Pathology, Singapore General Hospital and

a3 Quarantine and Epidemiology Department, Ministry of the Environment, Singapore


The genomic DNA of 39 strains of Salmonella typhi isolated from local residents and patients who had visited countries in the Asian region was analysed for restriction fragment length polymorphisms (RFLP). Pulsed-field gel electrophoretic (PFGE) analysis of Xba I- and Spe I-generated genomic restriction fragments established 22 PFGE types whereas phage typing differentiated the 39 isolates into 9 distinct phage types. This study showed that PFGE is more discriminatory than phage typing as it is capable of subtyping S. typhi strains of the same phage types. Genetic relatedness among the isolates was determined. Seven major clusters were identified at SABSof > 0–80 and the remaining 13 isolates were distributed into minor clusters which were related at SABS of less than O.80. In conclusion, PFGE analysis in conjunction with distance matrix analysis served as a useful tool for delineating common S. typhi phage types of diverse origins from different geographical localesand separated in time.

(Accepted July 12 1994)


c1 Author for correspondence.