Molecular Analysis of Shigella dysenteriae Type 1 Strains by Using Pulsed-Field Gel Electrophoresis

Abstract

Objective: Determine the use of pulsed-field gel electrophoresis (PFGE) in molecu [ar typing of Shigella dysenteriae type 1 strains from sporadic outbreaks and epidemic periods from different geographical location of the world. Methodology: Genomic DNA of 5. dysenteriae type 1 strains was analyzed using PFGE. The use of PFGE in a Not-I-digested DNA fragments clearly distinguished isolates involved in the epidemic from the non-epidemic strains. Genomic DNA was digested by Not-I restriction enzyme and the fragments separated using the contour-clamped homogenous electric field method on a CHEF-DRII system on 1 % agarose. Results: One hundred thirteen isolates of S. dysenteriae type 1(18 from epidemic and 95 from sporadic outbreaks) were typed by the PFGE method. These isolates were classified into 8 PFGE type A to H, comprising 1 to 22 patterns, and 25 patterns were identified in total. The major groups consisted of A and B. Type A was predominantly detected (in 51 of 56 strains) among the strains isolated in Bangladesh, while type B was rare (in 2 of 56 strains) and isolated only from Rangpur during the epidemic period in 1984. Among the very recent isolates (1995-1997) in Bangladesh, there were no type A pattern 2 isolates. This pattern was present among the epidemic strains isolated in Rangpur and in the Hooghly district of West Bengal, in 1984. Conclusion: The results of the analysis suggest that a clonal relationship existed between these strains during the epidemic period in Bangladesh and West Bengal in 1984. Thus, the PFGE technique could be used as an epidemiologic tool for identifying epidemic-associated strains as well as for molecular subtyping of epidemiologically unrelated strains