Vero Cytotoxins (Shiga-Like Toxins) of Escherichia coli
Shiga toxin produced by strains of Shigella dysenteriae type 1 and Vero cytotoxins (Shiga-like toxins) produced by strains of Escherichia coli belong to a family of related toxins. Two major forms of Vero cytotoxin (VT) are recognised. Polyclonal antiserum to Shiga toxin neutralises the activity of VT1 (SLTI) but not VT2 (SLTII). Strains of E. coli produce VT1 only, VT2 only or both toxins. Some strains of animal origin, but none as yet of human origin, also produce heat labile enterotoxin or heat stable enterotoxin. By definition, VT is detected by its cytotoxic effect on a monolayer of Vero cells grown in tissue culture, with serum neutralisation tests to determine which toxins are present1. For routine testing, bacteria are grown in a medium such as trypticase soy broth and the toxin present in filtered culture supernatants is assayed. Cell bound toxin can be released by polymixin treatment or sonication to obtain maximum yields. Production of VT1, but not VT2, is increased in an iron-depleted medium2. HeLa cells have also been used to test for VT, but this cell line can no longer be recommended as there are variant forms of VT2, termed VT2v, that have litle or no effect on HeLa cells although they are cytotoxic for Vero cells. The first variant toxin to be identified, produced by strains causing porcine (o)edema disease, has been termed VT2vp3 or VT2e4. VT2vh5 and VT2va6 are variant toxins from strains of human origin. All the VT2 forms are neutralised at least to some extent by polyclonal antisera raised against one of the other VT2 forms.
KeywordsVero Cell Hemolytic Uremic Syndrome Polyclonal Antiserum Haemolytic Uraemic Syndrome Shiga Toxin
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