|Description:||This image depicts two test tubes that contained triple sugar iron (TSI) growth media, and which had been inoculated on the left with an organism whose metabolic activity required no fermentative reaction, and an organism on the right, which required the fermentation of sugars to grow and thrive. The medium in either tube was exposed to environmental oxygen, otherwise known as an aerobic atmosphere.|
With TSI growth medium, the lack of any fermentative metabolism allowed the color of the medium to remain a bright red, while the breakdown of glucose, along with either the sucrose, or lactose component of the right tube, imparted a color change to more of a yellowish hue. With fermentation comes a change in the pH of the TSI medium to a more acidic environment, which in turn affected the color indicator present, changing the color from red to yellow.
”TSI Agar (Triple Sugar Iron Agar) is a differential medium for Gram-negative enteric organisms on the basis of their ability to ferment dextrose, lactose and sucrose and to produce sulfides.” (See link below)