Selective & Differential Agar Media

What type of bacteria does MacConkey Agar select for?

Gram-negative bacteria

What inhibitory agents are in MacConkey Agar?

Bile salts and crystal violet

What is the differential agent in MacConkey Agar?

Lactose

What activity does MacConkey Agar test for?

Lactose fermentation to acid

What pH indicator is used in MacConkey Agar?

Neutral red

What color indicates lactose fermentation on MacConkey Agar?

Pink/red colonies

What color indicates non-lactose fermenters on MacConkey Agar?

Colorless/tan colonies

What type of bacteria does Columbia Blood Agar CNA select for?

Some Gram-positive bacteria

What inhibitory agents are in CNA agar?

Colistin and nalidixic acid

What is the differential agent in CNA agar?

Red blood cells (erythrocytes)

What activity does CNA agar test for?

Hemolysis (lysis of red blood cells)

What types of hemolysis can be observed on CNA agar?

Alpha, beta, and gamma hemolysis

What does alpha hemolysis mean?

Partial lysis of red blood cells

What does beta hemolysis mean?

Complete lysis of red blood cells

What does gamma hemolysis mean?

No lysis of red blood cells

What pH indicator is used in CNA agar?

None

What type of bacteria does Mannitol Salt Agar select for?

Salt-tolerant bacteria, especially Staphylococcus

What inhibitory agent is in MSA?

7.5% NaCl

What is the differential agent in MSA?

Mannitol

What activity does MSA test for?

Mannitol fermentation to acid

What pH indicator is used in MSA?

Phenol red

What color indicates mannitol fermentation on MSA?

Yellow colonies and agar

What type of bacteria does Bile Esculin Agar select for?

Enterococcus duran and some Gram-negative enteric bacteria

What inhibitory agent is in BEA?

Bile salts

What is the differential agent in BEA?

Esculin

What activity does BEA test for?

Esculin hydrolysis by esculinase

What indicator is used in BEA?

Ferric citrate

What result indicates a positive BEA test?

Blackening of the medium

What type of bacteria does Deoxycholate Agar select for?

Gram-negative enteric bacilli

What inhibitory agents are in DOC agar?

Deoxycholate and citrate salts

What are the differential agents in DOC agar?

Lactose and peptone (source of amino acids)

What activity does DOC agar test for?

Lactose fermentation to acid and amino acid metabolism to alkaline

What pH indicator is used in DOC agar?

Neutral red

What color indicates lactose fermentation on DOC agar?

Pink/red colonies (fecal coliforms)

What does NLF stand for on DOC agar?

Non-lactose fermenters

What color indicates non-lactose fermenters on DOC agar?

Colorless/tan colonies