ML Differential and Selective Media Quiz

What selective media was used in the In The Clinic video to identify Staphylococcus aureus?

MSA

What is the definition of selective media?

Selective media incorporate chemical substances that inhibit the growth of one type of bacteria while permitting the growth of another.

What is the definition of differential media?

Differential media incorporate chemical compounds that produce characteristic changes in the appearance of the bacterial colonies.

What is the definition of enriched media?

Enriched media have been supplemented with highly nutritious materials for the purpose of cultivating fastidious organisms.

Which of the following associations is INCORRECT regarding selective media?

Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms

What is the purpose of adding phenol red to mannitol salt agar?

Phenol red permits the differentiation of bacteria based on their ability to ferment mannitol.

What is the purpose of adding eosin and methylene blue to eosin-methylene blue agar?

Eosin and methylene blue are dyes that precipitate on the surface of acid-producing colonies of enteric lactose fermenters, creating a metallic green sheen.

You observe a yellow zone surrounding growth on mannitol salt agar. What does this indicate about the organism?

The organism is able to ferment mannitol.

What is the purpose of adding salt to mannitol salt agar?

High concentrations of salt inhibit the growth of non-halophilic organisms but allow for the growth of bacteria from the genus Staphylococci.

You observe red (pink) colored colonies growing on MacConkey agar. What does this indicate about the organism?

The organism is able to ferment lactose.

Enriched blood agar permits the demonstration of the hemolytic properties of what group of microorganisms?

Streptococci

Which of the following describes an INCORRECT association regarding hemolytic activity?

Beta hemolysis; results in a greenish halo around the bacterial growth

You inoculate an organism onto blood agar and observe a clear zone surrounding the bacterial growth. What type of hemolysis is indicated by this observation?

Beta hemolysis

You observe colonies growing on EMB agar that are blue-black with a metallic green sheen. What species of bacteria is this likely to be?

E. coli

From the In The Clinic video, Mannitol Salt Agar (MSA) is selective because

It contains 7.5% NaCl which prevents the growth of most microorganisms but permits the growth of halophiles such as staphylococcus

From the In The Clinic video, Mannitol Salt Agar (MSA) is differential because

It contains the sugar mannitol and the ph indicator phenol red. Pathogenic staphylococcus like Staph aureus ferment mannitol as indicated by the yellow color.

In the In The Clinic video, what was found to be the cause of the patient's infection?

Methicillin sensitive strain of Staphylococcus aureus

From the In The Clinic video, a culture medium provides

None of the answers are correct

properly adjusted pH and levels of oxygen

sufficient moisture

All of the answers are correct

nutrients necessary to support growth of microorganisms

All of the answers are correct

In the In The Clinic video, what did the Gram staining of the sample from the patient show?

An abundance of purple-colored cocci suggestive of a Gram + staphylococcal infection

From the In The Clinic video, non-pathenogenic staphylococci like Staph epidermidis generally do not ferment mannitol and leave the medium red.

True