Final answer:
On EMB Agar, strong lactose fermenters show metallic green or deep purple colonies, moderate fermenters display pink or dark purple colonies, and non-fermenters produce colorless colonies.
Step-by-step explanation:
The distinction in the appearance of gram-negative bacterial colonies on EMB Agar is based on their ability to ferment lactose. Strong lactose fermenters will display colonies with a distinctive metallic green sheen or deep purple color. Moderate lactose fermenters produce pink or dark purple colonies without the metallic sheen, while non-lactose fermenters form colorless or transparent colonies due to the lack of lactose fermentation.
On EMB Agar, strong, moderate, and non-lactose fermenters can be distinguished by their colony appearance. Lactose fermenters will form metallic green or deep purple colonies on EMB Agar. These colonies have a distinctive color due to the fermentation of lactose, which produces acid that reacts with the eosin and methylene blue dyes in the agar. Non-lactose fermenters, on the other hand, will form colonies that are completely colorless on EMB Agar.