Identification, Characterization, and Distribution of a Shiga Toxin 1 Gene Variant ( stx _1c ) in Escherichia coli Strains Isolated from Humans

Abstract

By using sequence analysis of Shiga toxin 1 (Stx 1) genes from human and ovine Stx-producing Escherichia coli (STEC) strains, we identified an Stx1 variant in STEC of human origin that was identical to the Stx1 variant from ovine STEC, but demonstrated only 97.1 and 96.6% amino acid sequence identity in its A and B subunits, respectively, to the Stx1 encoded by bacteriophage 933J. We designated this variant "Stx1c" and developed stxB 1 restriction fragment length polymorphism and stx 1c -specific PCR strategies to determine the frequency and distribution of stx 1c among 212 STEC strains isolated from humans. During the past 20 years, Shiga toxin (Stx)-producing Escherichia coli (STEC) have emerged as important causes of diarrhea and the hemolytic-uremic syndrome (HUS) throughout the world (2,9,14,32,33). Stx are believed to be the cardinal virulence factors of STEC (20). Based on toxin neutralization assays (30) and sequence analysis of stx genes (11), two major toxin types, Stx1 and Stx2, have been assigned (11,20,30). Stx1 and Stx2 are not cross-neutralized by heterologous antisera in cell culture assays (30), and the structural genes encoding these toxins demonstrate approximately 55% overall nucleotide sequence identity (11). The Stx2 group has been shown to be highly heterogeneous, comprising, in addition to Stx2, several Stx2 variants that have been classified as Stx2c (29), Stx2d (24), Stx2e (34), and Stx2f (28). The substantial sequence heterogeneity observed between members of the Stx2 family (24,28,29,34) enabled the development of PCR techniques that differentiate stx 2 from its variants and identify the respective stx 2 alleles (7,24,28). This is of particular clinical importance, because STEC strains possessing different stx 2 variants appear to differ in their capacity to cause HUS (8). Information about the stx 2 allele of an infecting STEC strain has, therefore, considerable potential predictive value for the treating physician to assess the risk of HUS development in a patient that presents with STEC infection (8).In contrast to the Stx2 family, the Stx1 group appears to be more homogeneous. stx 1 genes carried in the genomes of bacteriophages H19B (6), H30 (18), and 933J (10) have identical nucleotide sequences (6, 10, 18) and differ by only three nucleotides in their A subunits, resulting in only one amino acid difference from the sequence of stx from Shigella dysenteriae type 1 (31). Paton et al. (21,22) reported three human STEC strains that possess slight variations in their stx 1 genes. Each of these stx 1 variants shared more than 99% nucleotide sequence identity with stx 1 from phage 933J and with stx from S. dysenteriae type 1 (21, 22). Stx1 encoded by these stx 1 variants differed by one and two amino acid residues in their A subunits from Stx of S. dysenteriae type 1 and from Stx1 encoded by phage 933, respectively, whereas their B subunits were identical to those of the latter two toxins (21,22). A considerably greater degree of sequence heterogeneity was observed in stx 1 genes of S...

Enterohaemorrhagic Escherichia coli: emerging issues on virulence and modes of transmission

“…The genetic information for the production of Stx1 and Stx2 is located in the genome of lambdoid prophages integrated in the STEC chromosome [110]. Whereas Stx1 shows only little sequence variations [189], several variants of Stx2 with altered antigenic or biological characteristics have been described. Such toxins have been termed Stx2c, Stx2d, Stx2e and Stx2f [110,147].…”

Association of Vt1C with Verotoxin-Producing Escherichia Coli from Goats and Sheep

“…1 Besides the eae gene, some VT types are associated with the virulence of VTEC for humans. 12 Based on toxin neutralization assays and sequence analysis of vt genes, 2 major toxin types, VT1 and VT2, have been described. The VT2 group has been shown to be highly heterogeneous.…”

stx2vha Is the Dominant Genotype of Shiga Toxin‐Producing Escherichia coli O157:H7 Isolated from Patients and Domestic Animals in Three Regions of China

“…Briefly, specimens were incubated with paramagnetic beads coated with anti-O157 specific antibody (Dynal Co., Ltd., Denmark), followed by culture on sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC). All sorbitol-negative colonies were tested for the presence of O157 antigen, and confirmed using the PCR method for virulence genes stx1, stx2, EHEChlyA, EHEC-eaeA, rfb O157 and fliC H7 (17,20,21,24).…”