Question: What Ingredient Makes EMB Selective?

What is the purpose of EMB Agar?

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..

Is chocolate agar selective or differential?

Yellowing of chocolate agar was associated with alpha-hemolytic species of Streptococcus. The study demonstrated that reactions occurring on chocolate agar are useful in identifying gram-positive cocci. Chocolate agar, a differential medium for gram-positive cocci.

How do you make an EMB?

Preparation Instructions Suspend 36 grams of EMB Agar in 1000 mls of distilled water. Heat to dissolve the medium completely. Dispense and sterilize by autoclaving at 15 lbs. pressure (121 °C) for 15 minutes.

What Bacteria grows on EMB?

Some strains of Salmonella and Shigella may fail to grow on EMB Agar. 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 are EMB and MacConkey Agars different?

An example of a selective medium is MacConkey agar. It contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria. … EMB contains the dyes eosin and methylene blue that inhibit the growth of gram-positve bacteria.

What would growth on EMB and MacConkey Agars suggest?

By plating organisms in both EMB and MacConkey agars we would be able to detect gram-negative organisms, and more specifically E. coli from other enteric organisms.

Does Salmonella grow on EMB agar?

Only gram-negative bacteria grow on EMB agar. … Because Salmonella species do not ferment lactose or produce acid, their colonies appear grey on EMB agar.

What Bacteria grows on MacConkey Agar?

Altogether, MacConkey agar only grows gram-negative bacteria, and those bacteria will appear differently based on their lactose fermenting ability as well as the rate of fermentation and the presence of a capsule or not.

Do all bacteria have cell walls?

It is important to note that not all bacteria have a cell wall. Having said that though, it is also important to note that most bacteria (about 90%) have a cell wall and they typically have one of two types: a gram positive cell wall or a gram negative cell wall.

What makes EMB Agar selective?

Eosin Methylene Blue (or EMB) Agar is a Selective & Differential Medium. The selective and differential aspects are due to the dyes Eosin Y and Methylene Blue, and the sugars lactose and sucrose in the medium. It is Selective because it encourages some bacteria to grow while inhibiting others.

What ingredient makes EMB Agar differential?

lactoseThe differential ingredient is lactose. Fermentation of this sugar results in an acidic pH and causes the pH indicator, neutral red, to turn a bright pinky-red color.

How EMB media differentiate bacteria?

Eosin Methylene Blue (EMB) agar 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 does EMB stand for?

EMBAcronymDefinitionEMBEvery Man’s BattleEMBEndometrial BiopsyEMBEndomyocardial Biopsy (cardiology)EMBEmail Me Back39 more rows

What does EMB contain that allows E coli to be red or purple?

The selective/ inhibitory agents of EMB are the dyes eosin Y and methylene blue. Methylene blue inhibits the gram + bacteria (eosin to a lesser extent), while eosin changes color, to a dark purple, when the medium around the colony becomes acidic.

What kinds of organisms does EMB Agar differentiate?

EMB selects for Gram-negative organisms. what kinds of organisms does EMB agar differentiate? EMB differentiates from lactose fermentors and non-fermentors.