Microbiology Lab Media

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Questions and Answers

What is the purpose of the inhibitory substance in selective media?

To inhibit the growth of unwanted bacteria (correct)
To change the color of the media
To promote the growth of all bacteria
To create an acidic environment

What is the characteristic of differential media?

They are used to promote the growth of all bacteria
They contain an inhibitory substance to prevent bacterial growth
They contain an indicator that changes color when bacteria grow (correct)
They are used to create an acidic environment

Which of the following is an example of selective media?

Blood agar
MacConkey agar
Nutrient agar
Thayer Martin agar (correct)

What is the purpose of the acidic environment in some media?

To inhibit the growth of unwanted bacteria (C) Signup and view all the answers

Which of the following is an example of differential media?

Levinstein-Jensen medium (B) Signup and view all the answers

What is the purpose of blood agar?

To encourage the growth of bacteria (C) Signup and view all the answers

What type of bacteria can grow on blood agar?

Fastidious bacteria that may not grow on other media (C) Signup and view all the answers

What is a characteristic of interactive media?

They contain a pH indicator that changes color when bacteria grow (D) Signup and view all the answers

What is an example of an interactive medium?

Blood agar (C) Signup and view all the answers

What is the main difference between blood agar and other media?

It is enriched to support the growth of fastidious bacteria (A) Signup and view all the answers

What is the number of types of blood agar classified based on the hemolytic activity of bacteria?

Three (A) Signup and view all the answers

What is the type of hemolysis where the bacterial colony is surrounded by a clear zone?

Beta hemolysis (B) Signup and view all the answers

What is the characteristic of beta hemolysis?

Complete hemolysis (A) Signup and view all the answers

Which type of hemolysis is associated with the destruction of red blood cells?

Beta hemolysis (B) Signup and view all the answers

What is the classification of blood agar based on?

Hemolytic activity of bacteria (B) Signup and view all the answers

What is the main purpose of Mannitol Salt Agar?

To determine if the bacteria is halophilic and can ferment mannitol (C) Signup and view all the answers

What happens to the medium when Staphylococcus aureus ferments mannitol?

The medium turns yellow (B) Signup and view all the answers

What characteristic of Staphylococcus aureus is detected by Mannitol Salt Agar?

Its halophilicity and ability to ferment mannitol (A) Signup and view all the answers

What type of bacteria is Staphylococcus aureus?

Halophilic and mannitol-fermenting (B) Signup and view all the answers

Why is Mannitol Salt Agar used in the detection of Staphylococcus aureus?

Because it can detect the bacteria's halophilicity and ability to ferment mannitol (D) Signup and view all the answers

What is the main function of EMB agar?

To inhibit the growth of most Gram-negative bacteria (B) Signup and view all the answers

What is the primary role of methylene blue in EMB agar?

To indicate the pH level of the medium (B) Signup and view all the answers

What is the characteristic of EMB agar that makes it differential?

It indicates the acidity of the medium through a color change (C) Signup and view all the answers

What is the result of E. coli growth on EMB agar?

A green, metallic sheen (A) Signup and view all the answers

What type of bacteria is EMB agar primarily used to isolate?

Anaerobic bacteria (A) Signup and view all the answers

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Study Notes

Microbiology Media

Differential media contain an indicator that changes color when bacteria grow, e.g. Blood agar, MacConkey agar.
Blood agar is an enriched, bacterial growth medium that encourages bacterial growth, especially for Streptococcus that may not grow normally in other media.

Types of Blood Agar

Can be classified into three types based on hemolysis activity:
Alpha (α) hemolysis (partial hemolysis)
Beta (β) hemolysis (complete hemolysis), e.g. Staphylococcus aureus, which ferments mannitol and turns the medium yellow.
Gamma (γ) hemolysis (no hemolysis)

Mannitol Salt Agar (MSA)

Used to determine if bacteria are halophilic (salt-loving) and can ferment mannitol.
Staphylococcus aureus ferments mannitol and turns the medium yellow.

Eosin Methylene Blue (EMB) Agar

A selective and differential medium used to isolate coliform bacteria.
Inhibits the growth of most Gram-positive bacteria.
The methylene blue indicator shows the degree of acidity.
If bacteria produce strong acid, such as E. coli, it leads to a greenish metallic color.