Modified Tryptone Soya Broth (Dehydrated)

Selectively enrich and isolate Escherichia coli O157 from food or fecal samples with Thermo Scientific™ Oxoid™ Modified Tryptone Soya Broth (Dehydrated). The modifications to the original medium include an increase in the concentration of the buffer, dipotassium hydrogen phosphate and bile salts. The bile salts inhibit the growth of spore formers and enterococci but allow the growth of Escherichia coli O157.

E. coli form part of the commensal microbial flora of all animals, including humans. Most strains of coli are non-pathogenic and serve a useful function within the intestines by suppressing the growth of harmful bacteria. Some strains of E. coli are capable of causing gastroenteritis in humans, among them is E. coli serotype O157: H7, a rare variety which produces toxins that are closely related to the toxin produced by Shigella dysenteriae. This toxin causes a severe gastroenteritis in humans commonly referred to as hemorrhagic colitis.

Many selective broths have been formulated for the enrichment of Escherichia coli O157. Modified Tryptone Soy Broth is a nutritious, selective base which was devised by Doyle and Shoeni.¹ The broth was incubated for at 37°C for 24 hours in shaken flasks. Szabo and co-workers² also used Modified Tryptone Soy Broth and found incubation at 43°C with agitation gave better recovery rates from inoculated food samples.

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