Exercise 16 - Basic Microbiology Media

Question 0

Selective media

Answer 0

Contains 1 or more agents that inhibit the growth (select against) certain bacteria; therefore encourages (selects for) others

Salt agar - TSA + 10% NaCL, Mannitol salt agar - MSA, MacConkey Agar - MAC

Question 1

General purpose media

Answer 1

Designed to grow a broad spectrum of bacteria

Trypticase Soy Agar - TSA

Question 2

Differential media

Answer 2

Designed to display visible difference amongst bacteria

Ex. Can they ferment or not, can they perform hemolysis or not

Mannitol salt agar - MSA, MacConkey Agar - MAC, Blood Agar - BA

Question 3

Enrichment media

Answer 3

Contain ingredients (vitamins, proteins) that certain fastidious require for growth

Blood Agar - BA

Question 4

Fastidious

Answer 4

Picky eater

Question 5

Salt agar - TSA + 10% NaCL:

Types of media

Selective or differential agents

Selects for (+) , against (-)

Answer 5

Selective

S: 10% NaCL

+ Halophile or Halotolerant
- NonHalophile or NonHalotolerant

Question 6

Trypticase Soy Agar - TSA:

Types of media

Answer 6

General purpose

Question 7

Mannitol Salt Agar - MSA:

Types of media

Selective or differential agents

Selects for (+) and against (-)

Differential outcome

Answer 7

Selective and differential

S: 7.5% NaCL
D: Mannitol (sugar) and Phenol Red

+ Halophile or Halotolerant
- NonHalophile or NonHalotolerant

Fermentation of Mannitol
+ yellow agar
- red agar (NC)

Question 8

MacConkey Agar - MAC:

Types of media

Selective or differential agents

Selects for (+) and against (-)

Differential outcome

Answer 8

Selective and differential

S: Bile Salts
D: Lactose and Neutral Red

+ Gram Negative Enterics
- Gram +

Fermentation of Lactose
+ red/pink colony
- white/opaque colony

Question 9

Blood Agar - BA:

Types of media

Selective or differential agents

Differential outcome

Answer 9

Differential and enrichment

D: Blood (hemoglobin)

Beta hemolysis (clear)(has alpha toxin) 
Alpha hemolysis (green) 
Gamma hemolysis (NC)

Question 10

MAC:

Differential agents:

Neutral red

Answer 10

If bacteria ferment Lactose, red/pink colonies (+)

Question 11

MSA:

Differential agents:

Phenol red

Answer 11

If bacteria ferment Mannitol, decreases pH; acids produced

Agar turns from red to yellow (acid)

Question 12

Three hemolysis patterns that can be observed in blood agar

Answer 12

Beta hemolysis “most” - agar will go from red to clear

Alpha (partial) - agar will go from red to green

Gamma hemolysis - (none) no color

Question 13

What is the reaction of staphylococcus aureus in 7.5% mannitol salt agar? And why?

Answer 13

Turns agar yellow

Because it is a Halophile that ferments mannitol

Question 14

What is the reaction of E. Coli in MAC? And why?

Answer 14

The E. Coli turns red/pink

Because it is a gram negative bacteria that ferments lactose

Question 15

What is the reaction of staphylococcus aureus in blood agar, and why?

Answer 15

Turns the agar from red to clear

Because it has alpha toxin, making it beta hemolysis

Question 16

What is the general shape of staphylococcus aureus and staphylococcus epidermis

Answer 16

Round (coccus)

Question 17

What is the general shape of E. Coli and salmonella entorica

Answer 17

Rods (bacillus)