Shiga toxin (Stx)-producing Escherichia coli (STEC) strains isolated from a seagull in Japan
were examined. A total of 50 faecal samples was collected on a harbour bank in Hokkaido,
Japan, in July 1998. Two different STEC strains, whose serotypes were O136[ratio ]H16 and
O153[ratio ]H− , were isolated from the same individual by PCR screening; both of them were
confirmed by ELISA and Vero cell cytotoxicity assay to be producing active Stx2 and Stx1,
respectively. They harboured large plasmids, but did not carry the haemolysin or eaeA genes of
STEC O157[ratio ]H7. Based on their plasmid profiles, antibiotic resistance patterns, pulsed-field gel
electrophoresis analysis (PFGE), and the stx genes sequences, the isolates were different.
Phylogenic analysis of the deduced Stx amino acid sequences demonstrated that the Stx toxins
of seagull-origin STEC were closely associated with those of the human-origin, but not those
of other animal-origin STEC. In addition, Stx2Φ-K7 phage purified from O136 STEC
resembled Stx2Φ-II from human-origin O157[ratio ]H7, and was able to convert non-toxigenic
E. coli to STEC. These results suggest that birds may be one of the important carriers in terms
of the distribution of STEC.