MAC

Dr. Spencer explains that we need a non-selective medium in this case. MacConkey is selective for Gram-negative bacteria due to the presence of bile salts and crystal violet, which inhibit Gram-positive bacteria. It is also differential for lactose fermentation, indicated by a color change. 

Website: https://microbiologyinfo.com/macconkey-agar-composition-principle-uses-preparation-and-colony-morphology/ 

While effective for identifying enteric (intestinal) bacteria and coliforms in foods, it is not suitable for detecting the presence of a broad range of bacterial species because it may not support the growth of Gram-positive or non-lactose fermenting bacteria. Let’s give it another go!