Which characteristic differentiates E. coli from Shigella species?

Escherichia coli (E. coli) is characterized by its ability to ferment lactose, which is a key trait that sets it apart from Shigella species. The fermentation of lactose is evident in laboratory settings, especially on differential media such as MacConkey agar, where E. coli colonies appear pink due to acid production from lactose fermentation. This lactose fermentation capability is a reflection of the metabolic pathways active in E. coli, allowing it to utilize lactose as an energy source.

In contrast, Shigella species do not ferment lactose and are typically lactose-negative. This distinction is particularly critical in clinical microbiology as it aids in the identification and differentiation between these two genera of enteric bacteria. Identifying the ability to ferment lactose thus serves as a straightforward diagnostic characteristic in distinguishing E. coli from Shigella.

While other characteristics listed, such as hydrogen sulfide production, urease production, and mannitol fermentation, can provide insights into the metabolic profiles of different bacterial species, they do not serve as definitive differentiators between E. coli and Shigella in a clinical context. Therefore, the ability to ferment lactose is the most telling characteristic separating E. coli from Shigella species.