Media

Question 1

What is MacConkey Agar used for and what is it made up of?

Answer 1

Used to isolate and differentiate enteric bacteria

contains
- Crystal Violet (inhibits gram-positive growth)
-Lactose
-Bile salts
- Neutral red (pH indicator

Question 2

MacConkey Agar separates enteric bacteria into 2 groups. What are they?

Answer 2

1) Coliform bacteria which ferment and appear pink
2)Dysentery, typhoid, and paratyphoid bacteria which do not ferment and appear tan/transparent

Question 3

Eosin-methylene Blue Agar, Also known as EMB agar and Levine agar
contain

Answer 3

Lactose and sucrose
Eosin dye
Methylene blue dye

Question 4

The dyes in EMB are impartial to what kind of bacteria? What color does non-fermenting bacteria appear and why? What color does fermenting bacteria appear and why?

Answer 4

• The dyes are partially inhibitory to gram-positive bacteria
• Non-fermenting bacteria appear Purple because the colonies are transparent
• Fermenting bacteria are Pink because they uptake eosin
• strong fermentors like e.coli becomes metallic green because they can uptake methylene blue and eosin

Question 5

What color does E.coli and other strong fermentors appear to be in the EMB Agar and why?

Answer 5

E. coli and other strong fermenters appear Metallic Green because they take up BOTH eosin and methylene blue and form a new compound

Question 6

What does enriched media contain? What is it usually made up of and what is it used for?

Answer 6

• Contains lots of nutrients that are not in normal nutrient agar

-Usually made by supplementing agar with blood, yeast, or plant-based material such as potatoes

• Used to isolate fastidious bacteria, or bacteria that are really stubborn and don’t like to grow under normal conditions

Question 7

Examples of enriched media include

Answer 7

Blood agar
Chocolate agar
Potato agar

Question 8

How is blood agar made? What does it demonstrate?

Answer 8

-Made by mixing animal blood (usually sheep blood) into nutrient agar
- Also demonstrates hemolytic properties of some microorganissms

Question 9

What are the different type of hemolysis in blood agar and explain each of them

Answer 9

-Gamma hemolysis means there is no lysis of red blood cells
-Alpha hemolysis is incomplete lysis of red blood cells
- Beta hemolysis is complete lysis of red blood cells.

Question 10

Explain chocolate media, what is made up of and used for

Answer 10

-Non-selective media
-Made using blood that has been heated to lyse the red blood cells
-Used for growth of fastidious pathogenic bacteria

Question 11

What are serial dilutions used for

Answer 11

Standard curves
Prepare a series of concentrations for an experiment
Estimate number of cells in a liquid culture

Question 12

What are serial dilutions?How is it done?

Answer 12

-Series of sequential dilutions that are performed to convert a dense solution into a more usable concentration.

-Done step by step, taking a bit from the previous dilution and putting it into fresh water or broth to further dilute it
Done for

Question 13

What is CFU?

Answer 13

Colony forming units

Question 14

What is the equation for CFU

Answer 14

𝑐𝑓𝑢 𝑝𝑒𝑟 𝑚𝑙=(# 𝑜𝑓 𝑐𝑜𝑙𝑜𝑛𝑖𝑒𝑠 𝑜𝑛 𝑝𝑙𝑎𝑡𝑒) / (# 𝑚𝑙 𝑝𝑙𝑎𝑡𝑒𝑑) 𝑥 𝐷𝑖𝑙𝑢𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟