What is the major characteristic of Enterobacter cloacae among Enterobacteriaceae?

• A. Non-fermenting
• B. Indole positive
• C. Lactose fermenting
• D. Oxidase positive

Answer: (C)

Enterobacter cloacae is characterized by its ability to ferment lactose, which is a key feature that helps to differentiate it from some other members of the Enterobacteriaceae family. This fermentation results in the production of acid and gas, which can often be detected on specific media, such as MacConkey agar, where colonies appear pink due to acid production.

In general, Enterobacteria are known for their fermentative capabilities, but lactose fermentation specifically is a prominent trait that helps identify Enterobacter cloacae among various Enterobacteriaceae. This characteristic is particularly significant when distinguishing it from non-lactose fermenters, which would not produce acid and gas in the same conditions.

Furthermore, while other characteristics such as being indole positive or oxidase positive can be relevant to certain bacteria within the Enterobacteriaceae family, they do not apply universally to Enterobacter cloacae. Therefore, the ability to ferment lactose serves as a defining characteristic of this organism within its family.