Kligler iron agar (KIA) differs from triple-sugar iron agar (TSI) in the:

• A. Ratio of lactose to glucose
• B. Ability to detect H2S production
• C. Use of sucrose in the medium
• D. Color reaction denoting production of acid

Answer: (C)

Kligler iron agar (KIA) is designed specifically to assess the fermentation of glucose and lactose as well as the production of hydrogen sulfide (H2S). The key distinction that KIA has from triple-sugar iron agar (TSI) lies in its formulation regarding sugar content. KIA contains glucose and lactose, but it does not include sucrose. In contrast, TSI has glucose, lactose, and sucrose in its formulation.

The absence of sucrose in KIA is significant because it simplifies the test down to the two sugars that are mainly fermented by enteric bacteria—glucose and lactose. This makes KIA more focused when testing organisms that typically ferment these two carbohydrates and provides an essential differentiation point in identifying specific bacteria.

In summary, KIA's formulation without sucrose is the crucial factor that distinguishes it from TSI, making the option regarding the use of sucrose in the medium the correct choice.