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Concept
Shiga toxin
Summary
Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome of lambdoid prophages. The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. Shiga-like toxin (SLT) is a historical term for similar or identical toxins produced by Escherichia coli. The most common sources for Shiga toxin are the bacteria S. dysenteriae and some serotypes of Escherichia coli (STEC), which includes serotypes O157:H7, and O104:H4.
Microbiologists use many terms to describe Shiga toxin and differentiate more than one unique form. Many of these terms are used interchangeably.
Shiga toxin type 1 and type 2 (Stx-1 and 2) are the Shiga toxins produced by some E. coli strains. Stx-1 is identical to Stx of Shigella spp. or differs by only one amino acid. Stx-2 shares 56% sequence identity with Stx-1.
Cytotoxins – an archaic denotation for Stx – is used in a broad sense.
Verocytotoxins/verotoxins – a seldom-used term for Stx – is from the hypersensitivity of Vero cells to Stx.
The term Shiga-like toxins is another antiquated term which arose prior to the understanding that Shiga and Shiga-like toxins were identical.
The toxin is named after Kiyoshi Shiga, who discovered S. dysenteriae in 1897. In 1977, researchers in Ottawa, Ontario discovered the Shiga toxin normally produced by Shigella dysenteriae in a line of E. coli. The E. coli version of the toxin was named "verotoxin" because of its ability to kill Vero cells (African green monkey kidney cells) in culture. Shortly after, the verotoxin was referred to as Shiga-like toxin because of its similarities to Shiga toxin.
It has been suggested by some researchers that the gene coding for Shiga-like toxin comes from a toxin-converting lambdoid bacteriophage, such as H-19B or 933W, inserted into the bacteria's chromosome via transduction. Phylogenetic studies of the diversity of E. coli suggest that it may have been relatively easy for Shiga toxin to transduce into certain strains of E.
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