How is growth with green metallic sheen truly a coliform bacterium?

Growth with a green metallic sheen on selective media, such as Eosin Methylene Blue (EMB) agar, typically indicates the presence of coliform bacteria, specifically Escherichia coli (E. coli). This characteristic sheen arises from the fermentation of lactose, producing acid that interacts with the dyes in the agar. E. coli is a common indicator of fecal contamination, making its identification crucial in assessing water and food safety. Thus, the green metallic sheen serves as a visual cue for the presence of coliforms, confirming their growth.