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12 Cards in this Set

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Describe Enterobacteria

1. Found in the human intestinal system but may also be found in soil, plants, and insects.

2. Can produce acid from glucose

3. Grows on McConkey agar

4. Gram-negative

What are the fermentable substrates (2 sugars) in EMB agar?

Lactose and Sucrose

Why do some bacteria produce a green metallic sheen on EMB agar?

Gram negative bacteria produce a green metallic sheen because it ferments lactose and produces acid. Acid acts as a dye by creating dark bacterial colonies with green sheen.

Name one organism that is part of the Enterobacteria family that produces a green metallic sheen on MacConkey agar.

E. Coli

What is the purpose of MacConkey agar?

It is used to isolate and differentiate enteric bacteria based on the ability to ferment lactose and inhibit gram positive bacteria.

How is MacConkey Agar similar to EMB agar?

1. They are both used to differentiate lactose fermenters from non lactose fermenters.

2. Both are selective for gram negative organisms.

3. Both inhibit growth of gram positive microorganisms

4. Both allow growth of the gram negative microorganisms

How is MacConkey agar different from EMB agar?

1. MacConkecy contains lactose

2. EMB contains both lactose and sucrose

3. MacConkey uses bile salt to inhibit gram positive bacteria growth.

4. EMB uses methylene blue and eosin to inhibit gram positive bacteria growht

What bacteria are selected for when using MacConkey agar?

Gram negative, enteric bacilli such as E. Coli, Coliforms, Proteus, Salmonella, and Staphylococcus.

What bacteria are differentiated among when using EMB agar?

Enteric bacteria such as E. Coli, Salmonella, and Proteus.

How does EMB agar differentiate microorganisms?

It differentiates them through color reactions when the bacteria are combined with the dyes in EMB agar.

Which type of agar inhibits gram positive bacteria growth with bile salts?


Which type of agar inhibits gram positive bacteria with methylene blue and eosin?