Spontaneous reactivation of Shiga toxins in Escherichia coli O157:H7 cells caused by transposon excision.
IS1203v is an insertion sequence which has been found in inactivated Shiga toxin 2 genes (stx2) of Escherichia coli O157:H7. Using PCR amplification, we detected the wild-type stx2 genes in colonies of E. coli O157:H7 which possessed stx2 genes inactivated by insertion of IS1203v. This suggests that IS1203v is excised from the inactivated stx2 genes in E. coli O157:H7. We isolated the cells possessing the wild-type stx2 genes, and confirmed Stx2 productivities by reversed passive latex agglutination. We also analyzed the frequency of the appearance of the Stx2-producing cells using a quantitative PCR method. As a result, the frequency was 3.00 x 10(-6) with culturing for 24 h at 37 degrees C, and this increased to 8.83 x 10(-5) when E. coli O157:H7 possessing the inactivated stx2 genes was transformed by an expression plasmid harboring the IS1203v transposase. These results showed that some Stx2-nonproducing E. coli O157:H7 strains could be spontaneously changed into Stx2-producing cells.
Kusumoto
M
M
Tsuruga Institute of Biotechnology, Toyobo Co. Ltd., Tsuruga, Fukui 914-0047, Japan. masahiro_kusumoto@bio.tyobo.co.jp
Okitsu
T
T
Nishiya
Y
Y
Suzuki
R
R
Yamai
S
S
Kawamura
Y
Y