Final answer:
Hektoen enteric agar differentiates enteric bacteria including pathogenic E. coli strains by their ability to ferment substances like sorbitol, with non-fermenting strains like E. coli O157:H7 producing colorless colonies.
Step-by-step explanation:
The Hektoen enteric agar is a specialized medium used for the isolation and differentiation of enteric pathogens from other Gram-negative bacteria. It allows for the identification of bacteria based on their ability to ferment lactose, sucrose, or salicin, producing acid and, thus, changing the color of the agar. For instance, pathogenic E. coli strains, such as E. coli O157:H7, which do not ferment sorbitol, will produce colorless colonies, whereas other lactose-fermenting organisms like typical E. coli strains will form colored colonies. Other differential tests, like the IMViC series, provide additional distinguishing characteristics among the Enterobacteriaceae family. Serological typing, PCR testing, and detection of specific genes like those for Shiga toxin and LEE (locus of enterocyte effacement) can help further identify and differentiate pathogenic strains.