Nonfermenters produce what reaction in triple sugar iron agar (TSIA)?

Nonfermenters are a group of bacteria that do not ferment sugars to produce acid and gas, which is typically indicated by the reaction observed in triple sugar iron agar (TSIA). In TSIA, the medium contains three sugars (glucose, lactose, and sucrose) as well as phenol red, a pH indicator.

When nonfermenters are inoculated into TSIA, they do not utilize the sugars present for fermentation. This leads to an alkaline result, as they often utilize peptones in the medium instead, resulting in the production of ammonia. This process raises the pH of the medium, causing the slant to turn alkaline, which is represented by a red color. The butt may remain neutral or alkaline because nonfermenters do not produce acid from the sugars, leading to no color change in that area.

Thus, the correct reaction of nonfermenters in TSIA is characterized by an alkaline slant and an alkaline or neutral butt, correlating with their metabolic capability of utilizing other sources rather than fermenting the sugars present in the agar.