What reaction do nonfermenters produce in triple sugar iron (TSI) agar?

In the context of microbiology, particularly when using triple sugar iron (TSI) agar, nonfermenters are organisms that do not ferment glucose, sucrose, or lactose. As a result, they do not produce acids during the fermentation process. TSI agar is utilized to differentiate between various enteric bacteria based on their ability to ferment sugars and produce gas and hydrogen sulfide.

Nonfermenters typically result in an alkaline slant, which is indicated by a red color due to the production of amines from the degradation of peptides present in the medium, rather than from fermentation. The butt of the TSI tube may also remain alkaline or neutral because there is no acid production from sugar fermentation. This reaction is essential for identifying nonfermenting organisms, such as Pseudomonas species and other nonfermentative Gram-negative bacteria, as it provides critical data that guides further identification or testing.

The outcome of an alkaline slant and an alkaline or neutral butt is characteristic of nonfermenters, confirming their lack of sugar fermentation capability. This result helps distinguish them from fermenters, which would show different color reactions in the TSI agar due to acid production from sugar fermentation.