What characteristic does E. coli exhibit when grown on EMB agar?

What characteristic does E. coli exhibit when grown on EMB agar?

• A. It produces yellow colonies.
• B. It appears as colorless colonies.
• C. It produces green metallic sheen colonies.
• D. It produces purple colonies.

Answer: (C)

E. coli demonstrates a distinctive characteristic when grown on eosin methylene blue (EMB) agar, which is the production of green metallic sheen colonies. This reaction is due to the fermentation of lactose, a component of the agar, which leads to acid production. The acid causes a shift in the color of the dyes present in the medium, resulting in the formation of a green metallic sheen, particularly evident in vigorous lactose fermenters like E. coli. The presence of this sheen indicates a strong fermentation capability and is a key differentiating feature of E. coli, particularly from non-lactose fermenters or weaker fermenters within the Enterobacteriaceae family. This characteristic is useful for microbiologists in identifying and differentiating E. coli from other bacteria in clinical and environmental samples.

E. coli demonstrates a distinctive characteristic when grown on eosin methylene blue (EMB) agar, which is the production of green metallic sheen colonies. This reaction is due to the fermentation of lactose, a component of the agar, which leads to acid production. The acid causes a shift in the color of the dyes present in the medium, resulting in the formation of a green metallic sheen, particularly evident in vigorous lactose fermenters like E. coli.

The presence of this sheen indicates a strong fermentation capability and is a key differentiating feature of E. coli, particularly from non-lactose fermenters or weaker fermenters within the Enterobacteriaceae family. This characteristic is useful for microbiologists in identifying and differentiating E. coli from other bacteria in clinical and environmental samples.