What type of agar is used in the lactose lab?
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.
How does E coli appear on MacConkey agar?
Escherichia coli and other lactose ferments will produce yellow or orange colonies. Nonlactose fermenters including Shigella produce green colonies while Salmonella appears as black colonies due to production of hydrogen sulfide.
What are the characteristics of MacConkey agar?
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 ingredients MacConkey agar supplies carbon?
Which ingredients in MacConkey agar supplies carbon? Gelatin, casein (milk protein), animal tissue, lactose, and to some extent, bile salts are potential sources of carbon.
What is the composition of blood agar?
Blood agar is a type of growth medium with trypticase soy agar base enriched with 5% sheep blood. Beta hemolysis in sheep blood agar. Blood agar consists of a base containing a protein source (e.g. Tryptones), soybean protein digest, sodium chloride (NaCl), agar, and 5% sheep blood.
Does MacConkey agar contain lactose?
[2] MacConkey agar contains the essential nutrients required for microorganism growth. Additional key components include crystal violet dye, bile salts, lactose, and neutral red (a pH indicator). The lactose in the agar is a source of fermentation.
What type of media is MacConkey agar?
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.
What ingredients MacConkey agar supplies carbon and nitrogen?
It wouldn’t likely alter sensitivity because you would probably still be able to detect growth of organisms that “should” grow on it. Which ingredients in MacConkey agar supplies carbon? Gelatin, casein (milk protein), animal tissue, lactose, and to some extent, bile salts are potential sources of carbon.
What does MacConkey agar test for?
MacConkey agar is a selective and differential culture medium for bacteria. It is designed to selectively isolate Gram-negative and enteric (normally found in the intestinal tract) bacteria and differentiate them based on lactose fermentation.
What ingredients are in MacConkey agar that make it selective?
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.
What is the carbon source of MacConkey agar?
Lactose is a carbon source for energy. Sodium chloride supplies essential electrolytes and maintains osmotic equilibrium. Crystal violet and bile salts are selective agents which inhibit most gram-positive organisms.