Final answer:
MacConkey agar helps differentiate lactose fermenters, identified by hot pink colonies, while EMB agar distinguishes them by metallic green or deep purple colonies.
Step-by-step explanation:
The differential medium that serves as both a determiner of carbohydrate fermentation patterns and gas production is MacConkey agar. This medium contains lactose and a pH indicator, which help in differentiating lactose fermenters from non-fermenters based on color changes. Lactose fermenters will produce acid, turning the medium and colonies hot pink, which is an indication of acid production from fermentation.
Another differential medium, EMB agar (Eosin Methylene Blue agar), helps distinguish lactose fermenters, which produce characteristic metallic green or deep purple colonies, from non-lactose fermenters that result in colorless colonies. Additionally, mannitol fermentation and gas production in various media can help separate strains such as E. coli O157:H7, which cannot ferment sorbitol, from other E. coli strains.