EMB agar is used in water quality tests to distinguish coliforms and fecal coliforms that signal possible pathogenic microorganism contamination in water samples.

What is an EMB plate differential for?

Eosin methylene blue agar (EMB) is a selective and differential medium used to isolate fecal coliforms. Eosin Y and methylene blue are pH indicator dyes which combine to form a dark purple precipitate at low pH; they also serve to inhibit the growth of most Gram positive organisms.

What grows on a EMB plate?

Some gram-positive bacteria, such as enterococci, staphylococci, and yeast will grow on this medium and usually form pinpoint colonies. Non-pathogenic, non-lactose-fermenting organisms will also grow on this medium.

How do you read an EMB plate?

EMB contents

Strong acidity produces a deep purple colony with a green metallic sheen, whereas less acidity may produce a brown-pink coloration of colony. Nonlactose fermenters appear as translucent or pink. Colonies of lactose fermenters will appear very dark purple, or have dark purple centers.

What type of bacteria does EMB inhibit?

EMB is a differential microbiological medium, which slightly inhibits the growth of Gram-positive bacteria and provides a color indicator distinguishing between organisms that ferment lactose (e.g., E. coli) and those that do not (e.g., Salmonella, Shigella).

What is the application of EMB agar?

Applications. EMB agar is a selective culture medium for Gram-negative bacteria. It is primarily used for isolation and differentiation of lactose fermenting (forms coloured colonies) and non-lactose fermenting (form colourless colonies) enteric bacilli.

How can you distinguish between E. coli and E Aerogenes on EMB?

Escherichia coli colonies produce a green, metallic sheen. Enterobacter aerogenes colonies are a pink/buff color with darker centers.

What color is E. coli on an EMB plate?

Typical E. coli colonies are small and pink on EMB agar with a green metallic sheen.

What are lactose fermenting bacteria?

Lactose fermenting species will grow pink colonies. Lactose fermentation will produce acidic byproducts that lower the pH, and this turns the pH indicator to pink. Example of Lac positive species: Escherichia coli, Enterobacteria, Klebsiella.

Is E. coli lactose fermenting?

E. coli are facultative anaerobic, Gram-negative bacilli that will ferment lactose to produce hydrogen sulfide.

Is E. coli a coliform?

E. coli is a sub-group of fecal coliform. When a water sample is sent to a lab, it is tested for total coliform. If total coliform is present, the sample will also be tested for either fecal coliform or E.