The medium used to determine oxidative or fermentative metabolism is which?

The medium used to determine oxidative or fermentative metabolism is which?

• A. CTA medium
• B. OF medium
• C. HE medium
• D. XLD medium

Answer: (B)

The key idea is distinguishing how bacteria metabolize carbohydrates—whether they rely on oxidative (aerobic) processes or on fermentation. OF medium does this by using two tubes with a carbohydrate substrate and an indicator: one tube is sealed with oil to create an anaerobic environment, the other remains open to air. If the organism ferments the sugar, acid is produced in both tubes, so both turn yellow. If it only oxidizes the sugar, acid appears only in the open tube, while the oil-sealed tube stays unacidified. If it doesn’t metabolize the sugar, there’s little or no color change in either tube. That specificity is why OF medium is used to determine oxidative versus fermentative metabolism. The other media listed are used for different tests (such as general enteric differentiation or specific sugar fermentations) and do not directly distinguish oxidative from fermentative pathways.

The key idea is distinguishing how bacteria metabolize carbohydrates—whether they rely on oxidative (aerobic) processes or on fermentation. OF medium does this by using two tubes with a carbohydrate substrate and an indicator: one tube is sealed with oil to create an anaerobic environment, the other remains open to air. If the organism ferments the sugar, acid is produced in both tubes, so both turn yellow. If it only oxidizes the sugar, acid appears only in the open tube, while the oil-sealed tube stays unacidified. If it doesn’t metabolize the sugar, there’s little or no color change in either tube. That specificity is why OF medium is used to determine oxidative versus fermentative metabolism. The other media listed are used for different tests (such as general enteric differentiation or specific sugar fermentations) and do not directly distinguish oxidative from fermentative pathways.