Bacterial growth with a metallic sheen is truly a coliform bacterium?

In the diversity and abundance of bacteria, we always have some uncertainty about the identity of an isolate. With this in mind, how can we be certain that growth with a metallic sheen is truly a coliform bacterium?

is growth with a green metallic sheen truly a coliform

To ascertain that this isolate is a coliform, consider the biology of the coliforms (which are Gram-negative intestinal microbes like E. coli and E. aerogenes). What this means is that the metabolism of these coliforms must be considered, and as you may know, coliforms are facultative anaerobes WHICH FERMENT LACTOSE, also producing acid and gas. This of course ultimately provides the basis for determining the total number of coliforms within a given sample (water usually, or soil) via m.Endo MF agar

MF-Endo agar medium contains a fuschin sulfate indicator and therefore selectively recognizes the presence of fermenting microbes where lactose fermenting colonies and the surrounding medium appear red, non-fermenters are colorless and do not alter the color of the surround. Further, the fermenting coliforms that can grow on the media produce dark center, nucleated colonies, indicated by a gold metallic sheen. E. coli appear small and possess this sheen, where E. aerogenes tend to be larger and lack the sheen. Thus, the MF-Endo medium is also considered differential

So basically, to ascertain that you have Gram-negative coliform bacteria, utilize MF-Endo agar, which is designed to test for the biological properties of such bacterium. Also, realize that the gold metallic sheen produced only by coliforms..there are no other microorganisms other than the intestinal microbes aforementioned that produce the sheen.