Which organism is often confused with Salmonella biochemically?

• A. E. coli
• B. Citrobacter freundii
• C. Enterobacter cloacae
• D. Shigella dysenteriae

Answer: (B)

The organism that is often confused with Salmonella biochemically is Citrobacter freundii. This confusion arises because both Salmonella and Citrobacter freundii are members of the Enterobacteriaceae family and share several biochemical characteristics. For instance, they are both capable of fermenting glucose, producing gas, and they share similar patterns in tests such as urease activity and hydrogen sulfide production.

Citrobacter freundii can produce hydrogen sulfide (H2S) on triple sugar iron (TSI) agar, similar to Salmonella, which can mislead identifications in laboratory settings. Additionally, both organisms can be found in similar environments, such as the gastrointestinal tract, further complicating their differentiation without specific identification tests.

Other organisms listed do have biochemical similarities to Salmonella, but are generally more distinct in key biochemical tests, making them easier to differentiate. For example, E. coli has distinctive lactose fermentation properties that set it apart, Enterobacter cloacae is usually oxidase negative unlike some Salmonella strains, and Shigella dysenteriae has different fermentation profiles and is typically non-H2S producing. Thus, the biochemical similarity of Citrobacter freundii to Salmonella is the primary reason it is frequently confused with this