Lab 19: Intro to Selective and Differential Media

Question 1

selective media contains?

Answer 1

contains one or more ingredients that suppress the growth of unwanted bacteria while encouraging growth of desired ones

Question 2

differential media?

Answer 2

distinguish between microorganisms based on color changes of the medium or the color of the colonies growing on its surface

Question 3

what kind of media is:
-7% NaCl Agar
-Fermentation Broth with Glucose
-Eosin Methylene Blue Agar (EMB)
-Mannitol Salt Agar (MSA)

Answer 3

-7% NaCl Agar is selective medium
-Fermentation Broth with Glucose is differential medium
-Eosin Methylene Blue Agar (EMB) is both
-Mannitol Salt Agar (MSA) is selective for Gram-positive cocci

Question 4

what is 7% NaCl Agar and its results?

Answer 4

-selective medium and the salt makes it selective for Gram-positive bacteria, especially cocci. Gram-negative can’t tolerate more than 1% or 2%
-E. coli = no growth
-Staphylococcus aureus = yes to growth
-Alcaligenes faecalis = varies

Question 5

what is Fermentation Broth with Glucose and its results?

Answer 5

differential medium. contains peptone, which serves as a source of protein, pH indicator, phenol red, and carbohydrate and tests for the ability to ferment glucose.
-red prior to inoculation
-fermentation = acidic byproducts = yellow
-no fermentation = alkaline byproducts = darker red
-orange = negative
-E. coli = yellow = fermentation
-S. aureus = yellow = fermentation
-A. faecalis = red = no fermentation

Question 6

what is Eosin Methylene Blue Agar (EMB) and its results?

Answer 6

-both selective and differential medium, selects for Gram-negative bacteria and differentiates lactose fermenters from lactose non-fermenters
-E. coli = black = lactose-positive/fermented
-S.aureus = colorless = lactose-negative/no fermentation
-A. faecalis = colorless = lactose-negative/no fermentation

Question 7

what is Mannitol Salt Agar (MSA) and its results?

Answer 7

selective for Gram-positive cocci. also differentiates pathogenic staphylococci from nonpathogenic species. contains 7% NaCl, carbohydrate mannitol, and phenol red (pH indicator)
-E. coli = red = nonpathogenic staphylococci or mannitol was not fermented
-S. aureus = yellow growth = pathogenic staphylococci/ fermented mannitol
-A. faecalis = red = nonpathogenic staphylococci or mannitol was not fermented

Question 8

enteric

Answer 8

bacteria that typically exist in the intestines of animals and humans

Question 9

coliform

Answer 9

organisms that are present in the environment and in the feces of all warm-blooded animals and humans

Question 10

chemically defined media

Answer 10

a growth medium suitable for the culture of microbes or animal cells of which all of the chemical component are known

Question 11

complex media

Answer 11

rich in nutrients that contain water soluble extracts of plants or animal tissue

Question 12

reducing media

Answer 12

added to the medium that would remove oxygen and the make reduced media