Triple Sugar Iron Agar (TSI 1)
The purpose of this test is to determine whether organisms can ferment glucose, sucrose and/or lactose, with or without production of gas. The ability of the organism to produce hydrogen sulphide from thiosulphate in an acid environment is also tested. Typically used to help differentiate between groups, genera and species among Enterobacteriaceae. Fermentation of glucose alone will show as a yellow colour in the butt of the medium, fermentation of sucrose and/or lactose will cause both butt and slant to be yellow. Production of hydrogen sulphide leads to blackening. Results are given as slant/butt/gas production/hydrogen sulphide production. 1. Uninoculated medium. 2. Acid/acid/gas: Klebiella. 3. Acid/acid: Yersinia enteocolitica (18 hours). 4. Acid/acid: Yersinia enteocolitica. After 48 hours the slant of the medium appears slightly red because the bacterium produces only a small amount of acid which is oxidised from the surface of the agar. 5. Acid/acid/gas/hydrogen sulphide: Citrobacter. Citrobacter may also produce an Alkaline/acid/gas/hydrogen sulphide reaction which is like that of Salmonella, but the degree of blackening is less. The gas produced is not visible in this picture. 6. Acid/acid/hydrogen sulphide: Erysipelothrix rhusiopathiae, which only weakly ferments lactose.
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