Subtyping of Shiga toxin 2 variants in human-derived Shiga toxin-producing Escherichia coli strains isolated in Japan

Abstract

Shiga toxin 2 (Stx2) variants have been found to exhibit not only antigenic divergence, but also differences in toxicity for tissue culture cells and animals. To clarify whether all or just a subset of Stx2 variants are important for the virulence of Shiga toxin-producing Escherichia coli, we designed PCR primers to detect and type all reported variants. We classified them into four groups according to the nucleotide sequences of the Stx2 family; for example, group 1 (G1) contains VT2vha and group 2 (G2) contains VT2d-Ount. The 120 strains of Shiga toxin-producing E. coli used in this study were isolated from humans in Japan between 1986 and 1999. Among the four variant groups, the G1 gene only was detected in 23 of the 120 clinical strains (19.2%) and all belonged to the O157 serotype. G1 is considered the most important Stx2 variant group in terms of human pathogenicity. A multiplex PCR that can detect the stx1, stx2, and G1 genes was developed as a means of rapid and easy typing to better understand the roles of the different types of Stx.

First-Time Isolation and Characterization of a Bacteriophage Encoding the Shiga Toxin 2c Variant, Which Is Globally Spread in Strains of Escherichia coli O157

“…Subtyping of stx genes by PCR and endonuclease digestion of PCR products revealed that stx 2c or stx 2vha variant genes are frequently found in STEC O157 strains from different geographical origins (9,19,30,34,38,52). The stx 2c allele was most common among stx genes in STEC O157 strains that were isolated in Australia, Belgium, and Germany and is often present in combination with stx 1 or stx 2 genes (4,11,12,36).…”

“…Two major types of Shiga toxins called Stx1 and Stx2, whose genes show 58% identity on the DNA level, were found in STEC O157 strains (18). Further analysis revealed the presence of Stx2 variants called Stx2c or Stx2vha in some STEC O157 strains, and the nucleotide sequences of the corresponding stx genes were analyzed (18,30,32). Stx2 and its variants Stx2c and Stx2vha show Ͼ99% identity in the genes coding for the A subunit and ϳ96% identity in those coding for the B subunit of the toxin (18, 30).…”

“…Further analysis revealed the presence of Stx2 variants called Stx2c or Stx2vha in some STEC O157 strains, and the nucleotide sequences of the corresponding stx genes were analyzed (18,30,32). Stx2 and its variants Stx2c and Stx2vha show Ͼ99% identity in the genes coding for the A subunit and ϳ96% identity in those coding for the B subunit of the toxin (18,30). The nucleotide sequences of the B subunits of Stx2c (43) and Stx2vha (originally designated VTx2ha) (17) genes are identical, and the proteins were described as variants of the Stx2 toxin family.…”

Analysis of the Clonal Relationship of Shiga Toxin-Producing Escherichia coli Serogroup O165:H25 Isolated from Cattle

“…Stx2 is closely related to a family of Stx2 variants or alleles, which includes Stx2c (48), Stx2d (36), Stx2e (56), and Stx2f (47), although Stx2c and Stx2d are produced by STEC strains isolated from humans (36,38,43,44,48,50). Additional genetic variants of the stx 2 gene have been described (5,14,28,55). In contrast to STEC strains harboring stx 2 gene variants, however, STEC strains with the stx 2 genotype were significantly associated with HUS (17).…”

Characterization of the Escherichia coli O157:H7 Outbreak Strain Whose Shiga Toxin 2 Gene Is Inactivated by IS1203v Insertion

“…Detection of the stx 2 gene subtypes by PCR: The stx 2 gene subtypes, stx 2a , stx 2b , stx 2c , stx 2d , stx 2e , stx 2f , and stx 2g , were detected by PCR as described previously (15)(16)(17)(18)(19). Primers used are shown in Table 2.…”