Triple Sugar Iron Agar

 

Use: Triple Sugar Iron Agar is an agar medium used as a differential medium for the presumptive identification of enteric bacteria.

Description: Selected colonies are transferred from the primary plating medium to tubes of Triple Sugar Iron Agar using a straight bacteriological wire, stabbing the butt of the tube and streaking the slanted portion of the medium. Inoculated tubes are incubated, and pH reactions, gas formation, and hydrogen sulfide production are noted. Other biochemical or serological tests are performed as required to determine the identification. The medium contains no growth inhibitors and most organisms grow, including gram-positive organisms and yeasts. Phenol red indicates fermentation of the carbohydrates by the production of a yellow color (acid reaction); lack of fermentation is indicated by a red color butt of the tube. Formation of hydrogen sulfide is detected by the ferrous ammonium sulfate and sodium thisulfate present in the medium, producing a blackening in the middle and upper portion of the slant. Gas formation is indicated by the presence of bubbles or cracks in the medium.

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