Table of Contents
Eosin Methylene Blue Agar
Eosin Methylene Blue Agar (EMB agar) is used for isolation and identification of gram negative intestinal pathogens. It contains eosin and methylene blue that is utilized as an indicator and permits differentiation of organisms that ferments lactose and those who do not ferments. Media also consist of saccharose as some enterobacteria and coliform bacteria causes fermentation of saccharose more easily that fermentation of lactose.
In addition to that methylene blue also acts as a gram-positive bacteria inhibitor. E. coli contains a dark centre with a green metallic sheen, the pink Enterobacter aerogenes are mucoid and large. Some other microorganisms like Salmonella cannot ferment lactose and forms colonies that are not coloured. Thus we can say that this media is considered as differential based on lactose fermentation.
MacConkey Agar
This is another differential medium which is almost similar to EMB agar used for isolation and differentiation of gram negative bacteria and is differential based on lactose fermentation. It is mainly utilized for the detection of coliform bacteria and some enteric pathogens depending on their capability to ferment lactose. In this medium those bacteria that ferment lactose appears red to pink in colour whereas those who do not ferment lactose appear as transparent or colourless colonies.
