MOLECULAR TYPING OF ENTEROHEMORRHAGIC ESCHERICHIA-COLI O157-H7 ISOLATES IN JAPAN BY USING PULSED-FIELD GEL-ELECTROPHORESIS

Pulsed-field gel electrophoresis (PFGE) was applied for molecular typi ng of 825 enterohemorrhagic Escherichia coli (EHEC) O157:H7 isolates, most of which were from 19 outbreaks and 608 sporadic cases in Japan, mainly in May to August 1996, By PFGE, the EHEC O157:H7 isolates were classified into six types (type I to V and ND [nondescript]) and UT un typeable isolates, Fifty isolates from seven outbreaks in May to June and 60 isolates from patients with sporadic cases of infection showed almost identical PFGE patterns which differed in only 1 of 22 DNA frag ments, They were classified into type I, Ninety-nine isolates from 10 other outbreaks and 156 isolates from patients in the Kinki area with sporadic cases of infection obtained in the early summer of 1996 showe d identical PFGE patterns, suggesting that they were derived from one huge outbreak. They were classified into type II. Type IV EHEC isolate s, which had only the stx2 gene, caused another outbreak in a primary school in June. EHEC isolates of two other types, types III and V, wer e not related to the outbreak but were isolated in several parts of Ja pan. ND EHEC isolates included a variety of patterns which could not b e classified into either of the types mentioned above, Twenty-five iso lates could not be analyzed due to degradation of their genomic DNAs a nd were represented as UT. These results indicate that EHEC O157:H7 st rains with various PFGE types have already spread to Japan and caused the multiple outbreaks and sporadic infections in Japan in the summer of 1996.