Molecular typing of enterohemorrhagic Escherichia coli O157 : H7 isolated in Okayama Prefecture using pulsed field gel electrophoresis and random amplification of polymorphic DNA

Three outbreaks and many isolated cases of enterohemorrhagic Escherichia co li O157: H7 occurred in 1996 and 1997 in Okayama Prefecture, Japan. In an a ttempt to investigate the route of these infections, the strains isolated f rom the 3 outbreaks (total 33 strains) and 15 isolated cases (total 15 stra ins) were investigated using random amplification of polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE). In addition, 10 strains from an outbreak in Tojo Cho, Hiroshima Prefecture (June 1996), 2 strains from t he particular types of meat in Kochi Prefecture, and 42 strains isolated fr om bovine feces in a farm in Okayama Prefecture were also investigated in t he same manner. PFGE was much more useful than RAPD for molecular typing of the clinical isolates, in that it allowed us to classify them into 10 PFGE groups. We noted that the strains differed according to the time and place of the outbreaks (or isolated cases). This indicates that O157: H7 infecti ons in Okayama Prefecture were caused by different strains (although some c ases were aggravated by the same strains as were found in other areas). The isolates from bovine feces were classified into 5 groups by PFGE profiles, but none of them were identical to those of the clinical isolates.