Quick Answer: Why Is MacConkey Agar Considered Both Differential And Selective?

Are MacConkey and EMB agar selective media differential media or both?

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.

MacConkey agar is also a differential medium.

Therefore, EMB is selective for gram-negatives..

Is EMB Agar selective or differential?

Selective for Gram negative Organisms Eosin–Methylene Blue (EMB) Agar is a differential medium for the detection of Gram negative enteric bacteria.

Is blood agar selective or differential?

Blood Agar This medium can be made selective by the addition of antibiotics. This medium is differential because: Blood Agar tests for the production of hemolysin which breaks down red blood cells.

What color is E coli on MacConkey Agar?

dark pinkPresumptive identification of E. coli was made based on its characteristic morphology colony on the selective medium MacConkey agar. Rapid lactose fermenting colonies of E. coli appear dry, donut shaped and dark pink in color and are surrounded with dark pink area of precipitated bile salts.

Why is MacConkey agar selective?

MacConkey Agar is Selective for Non-fastidious Gram-negative organisms. Therefore, MacConkey needed a way to limit this background of environmental flora and allow only his organisms of interest to grow. A medium that can perform this function is now known as a selective medium.

What are examples of selective media?

Examples of selective media include:Eosin methylene blue contains dyes that are toxic for Gram-positive bacteria. … YM (yeast extract, malt extract agar) has a low pH, deterring bacterial growth.MacConkey agar is for Gram-negative bacteria.Hektoen enteric agar is selective for Gram-negative bacteria.More items…

What is the purpose of differential media?

Differential media are used to differentiate closely related organisms or groups of organisms. Owing to the presence of certain dyes or chemicals in the media, the organisms will produce characteristic changes or growth patterns that are used for identification or differentiation.

What organisms are inhibited from growing on MSA?

It contains a high concentration (about 7.5–10%) of salt (NaCl), making it selective for most Gram-negative and some Gram-positive bacteria (Staphylococcus, Enterococcus and Micrococcaceae) since this level of salt is inhibitory to most other bacteria.

What bacteria does not grow on blood agar?

Blood agar is an enriched, bacterial growth medium. Fastidious organisms, such as streptococci, do not grow well on ordinary growth media. Blood agar is a type of growth medium (trypticase soy agar enriched with 5% sheep blood) that encourages the growth of bacteria, such as streptococci, that otherwise wouldn’t grow.

Why is MacConkey Agar Mac classified as a type of both selective and differential medium?

Why is MacConkey agar selective as well as differential? It’s selective to gram negative enteric bacteria because it contains bile salts, which inhibit most gram positive bacteria. It also contains lactose, which differentiates between gram negative lactose fermenter and gram negative non-fermenters.

What bacteria can grow on MacConkey Agar?

MacConkey agar is used for the isolation of gram-negative enteric bacteria. It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. It is used for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens.

Is peptone selective or differential?

Three peptone (protein) sources are included in the agar mix, and it is a type of supportive and selective and differential media used to help differentiate bacterial colonies based on their hemolysis patterns.

Why is MacConkey agar used for E coli?

Sorbitol MacConkey agar is a variant of traditional MacConkey agar used in the detection of E. coli O157:H7. … This is important because gut bacteria, such as Escherichia coli, can typically ferment lactose, while important gut pathogens, such as Salmonella enterica and most shigellas are unable to ferment lactose.

Which media is both selective and differential?

MacConkey agar is an example of a medium that is both differential and selective. The presence of bile salts, as well as crystal violet, within the media prevent gram-positive organisms from growing.

Why is EMB Agar both selective and differential?

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.

Is chocolate agar selective or differential?

Chocolate agar, a differential medium for gram-positive cocci.

What is an example of differential media?

Examples of differential media include: Blood agar (used in strep tests), which contains bovine heart blood that becomes transparent in the presence of hemolytic. … MacConkey (MCK), which is differential for lactose fermentationmannitol salt agar (MSA), which is differential for mannitol fermentation.