What is MacConkey and how is it prepared for microbial analysis?
What is MacConkey and how is it prepared for microbial analysis?
MacConkey Agar is a solid, selective and differential agar that only cultivates gram-negative bacterial species, it can further differentiate Gram-negative organisms based on their lactose metabolism: Lactose fermenters, colonies, turn red or pink on MacConkey agar. Non-fermenters do not change color.
What ingredients make MacConkey agar 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.
How do you make MacConkey broth?
Preparation Instructions Suspend 40.00 grams of MacConkey Broth in 1000 mls of distilled water. Heat to dissolve the medium completely. Distribute into tubes containing inverted Durham’s tubes and sterilize by autoclaving at 15 lbs. pressure (121°C) for 15 minutes.
What is the composition of MacConkey?
Key components of the MacConkey medium include crystal violet dye, bile salts, lactose, and neutral red (pH indicator). Crystal violet dye and bile salts halt the growth of gram-positive bacteria. This allows only gram-negative species to form colonies on MAC agar.
What grows best on MacConkey agar?
MacConkey’s is a selective medium that inhibits the growth of Gram-positive bacteria due to the presence of crystal violet and bile salts. Gram-negative bacteria grow well on MAC.
What ingredient makes MacConkey agar selective for gram-negative bacteria?
What ingredient(s) makes MacConkey agar selective for Gram-negative bacteria? Bile salts and crystal violet make MacConkey agar selective for gram-negative bacteria.
What is MacConkey broth made of?
MacConkey Broth is a modification of the medium developed by MacConkey which contained 0.5% sodium taurocholate and litmus as an indicator. 1 The presence of Oxgall replaces the sodium taurocholate to inhibit gram positive organisms.
What grows MacConkey broth?
Lactose-fermenting, Gram negative rods grow well in MacConkey Broth and produce acid, causing the medium to turn yellow after sufficient incubation time. Non-fermenting Gram negative organisms produce good growth but will not produce acid.
Why is MacConkey agar yellow?
Organisms unable to ferment lactose will form normal-colored (i.e., un-dyed) colonies. The medium will remain yellow. Examples of non-lactose fermenting bacteria are Salmonella, Proteus species, Yersinia, Pseudomonas aeruginosa and Shigella.
What is the principle of MacConkey agar?
Principle of MacConkey Agar Lactose monohydrate is the fermentable source of carbohydrates. The selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria. Sodium chloride maintains the osmotic balance in the medium.
Why is an indicator dye used in MacConkey agar?
Why is an indicator dye used in MacConkey agar? The indicator dye is used to show the lactose fermenting colonies that produce acidic compounds, lowering the pH of the media allowing the dye to work.
What are the uses and advantages of an agar plate?
Place the desired number of tubes in a rack and obtain an equal number of screw caps.
How to make the perfect agar plate?
How to Make the Perfect Agar Plate Every Time Make up the medium according to the recipe, then add the desired amount of agar (normally about 1% w/v) and stir. Autoclave for 25 minutes. Cool the medium-agar mix to 55°C. Add any antibiotics or supplements. Pour the plates. Allow the plates to set.
How do you prepare MacConkey agar?
Hydrate it according to directions
Why is MacConkey agar selective and differential?
Why is MacConkey agar selective as well as a differential? The MacConkey medium is identified as a selective and a differential medium. It is a selective medium in the sense that it inhibits the growth of gram-positive bacteria primarily because of the presence of bile salts and crystal violet in the medium.
