What ingredient in MacConkey makes it differential?
The selective ingredients are the bile salts and the dye, crystal violet which inhibit the growth of Gram-positive bacteria. The 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.
Why is MacConkey agar considered differential?
MacConkey agar is a selective and differentiating agar that only grows gram-negative bacterial species; it can further differentiate the gram-negative organisms based on their lactose metabolism.
How do we make MacConkey agar non differential medium?
Preparation of MacConkey Agar
- Suspend 49.53 grams of dehydrated medium in 1000 ml purified/distilled water.
- Heat to boiling to dissolve the medium completely.
- Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
- Cool to 45-50°C.
- Mix well before pouring into sterile Petri plates.
What ingredient makes blood agar differential and describe how it works?
The differential ingredient is lactose. Fermentation of this sugar results in a pH of less than 6.8 and causes the pH indicator, neutral red, to turn a bright pinky-red color. Thus organisms capable of lactose fermentation such as Escherichia coli, form bright pinky-red colonies (plate pictured on the left here).
How is MacConkey agar selective as well as differential?
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.
Does Enterobacter aerogenes grow on MacConkey agar?
On MacConkey agar, E. cloacae and E. aerogenes commonly appear as pink, lactose-fermenting, mucoid colonies similar in appearance to Klebsiella pneumoniae and K.
Which ingredient makes MSA selective?
Mannitol salt agar is selective due to the presence of 7.5% sodium chloride (NaCl).
Why is MacConkey agar selective as well as differential quizlet?
It isolates colonies. 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 mimics the human environment and provides additional nutrients that some bacteria need in order to grow.
Is MacConkey agar chemically defined?
Is MacConkey agar a defined or an undefined medium? Provide the reasoning behind your choice and explain why this formulation is desirable. It is undefined due to the pancreatic digests of gelatin and casein, peptic digest of animal tissue, and bile salts in the medium.
What makes the identified media selective and/or differential?
Selective media generally selects for the growth of a desired organism, stopping the growth of or altogether killing non-desired organisms. Differential media takes advantage of biochemical properties of target organisms, often leading to a visible change when growth of target organisms are present.
What makes MacConkey agar a selective and differential medium what group does it select how does it differentiate between species in the selected group?
MacConkey Agar (MAC) is a selective and differential medium designed to isolate and differentiate enterics based on their ability to ferment lactose. Bile salts and crystal violet inhibit the growth of Gram positive organisms. Lactose provides a source of fermentable carbohydrate, allowing for differentiation.
What makes MacConkey agar a selective and differential media?
Composition of MacConkey Agar Principle of MacConkey agar MacConkey agar contains four key ingredients (lactose, bile salts, crystal violet, and neutral red) that make it a selective and differential media.
How does carbon dioxide affect MacConkey agar plate?
The incubation of MacConkey agar plate makes it susceptible to an increase in carbon dioxide which can significantly affect the growth/reduction of some strains of Gram-negative bacilli. (2, 6, and 9) Why is MacConkey agar selective as well as a differential?
What kind of colonies are found in MacConkey agar?
Dry pink colonies of E. coli in MacConkey Agar Strongly lactose fermenting bacteria produce sufficient acid which causes precipitation of the bile salts around the growth. It appears as a pink halo surrounding colonies or areas of confluent growth.
How is MacConkey agar used in controlled swarming?
MacConkey Agar, CS (“Controlled Swarming”): MacConkey agar without Crystal Violet or Salt and MacConkey Agar without Salt is used to prevent the swarming of Proteus spp. Sorbitol MacConkey Agar: Sorbitol MacConkey agar is a variant of MacConkey agar, it contains sorbitol instead of lactose as fermentable sugar.