Molecular subtyping of Shigella flexneri 3a isolates by plasmid profile analysis and pulsed-field gel electrophoresis

Twenty-two clinical isolates of Shigella flexneri 3a that were obtained from stool specimens from seven outbreaks of infection in northern Taiwan were subtyped and compared using plasmid profile analysis and pulsed-field gel electrophoresis (PFGE). Among 32 isolates, three distinct patterns were found by plasmid profile analysis and six by PFGE, with three different restriction enzymes, XbaI, SfiI, or NotI. Seven PFGE patterns were observed in a comparative analysis using a combination of these three enzymes. Isolates collected from the same outbreaks had the same PFGE combination patterns and were distinguishable from those obtained during other outbreaks. These findings suggest that PFGE may be the most powerful method of genotyping S. flexneri 3a in epidemiological studies.