Exercise 6 Selective and Differential Media: Background / Ingridients
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41 Terms
What does EMB stand for?
Eosin Methylene Blue.
What type of medium is EMB agar?
Selective and differential.
What is EMB agar used for?
To differentiate lactose-fermenting Enterobacteriaceae from non-lactose-fermenting Enterobacteriaceae and inhibit Gram-positive/nonenteric bacteria.
What are the selective agents in EMB agar?
Eosin and methylene blue.
What is the differential agent in EMB agar?
Lactose.
What does growth on EMB agar indicate?
The organism is likely Gram-negative and enteric.
What does no growth on EMB agar indicate?
The organism is likely Gram-positive or nonenteric.
What do pink to black colonies on EMB indicate?
Lactose-fermenting Enterobacteriaceae (coliforms).
What do colorless colonies on EMB indicate?
Enterobacteriaceae that do not ferment lactose.
What are coliforms?
Lactose-fermenting Enterobacteriaceae.
What are non-coliform Enterobacteriaceae?
Enterobacteriaceae that do not ferment lactose.Is Mannitol Salt Agar (MSA) selective, differential, or both?
What is MSA used to identify?
Pathogenic species of Staphylococcus.
What is the selective agent in MSA?
7.5% sodium chloride (NaCl).
What does the high salt concentration in MSA inhibit?
Most Gram-negative bacteria, most Gram-positive bacilli, and Streptococcus.
Which groups commonly grow on MSA?
Staphylococcus and Micrococcus.
What is the differential agent in MSA?
Mannitol.
What does growth on MSA indicate?
The organism is likely Staphylococcus or Micrococcus.
What does no growth on MSA indicate?
The organism is likely Gram-negative, Gram-positive bacilli, or Streptococcus.
What happens when pathogenic Staphylococcus ferments mannitol?
Acid is produced and the medium changes from red to yellow.
What does a yellow medium around growth on MSA indicate?
Pathogenic Staphylococcus that ferments mannitol.
What does a red MSA medium indicate?
Nonpathogenic Staphylococcus or Micrococcus.What is Columbia CNA with 5% sheep blood used to identify?
Is CNA selective, differential, or both?
Both selective and differential.
What are the selective agents in CNA?
Colistin and nalidixic acid.
What do colistin and nalidixic acid inhibit?
Almost all Gram-negative bacteria.
What is the differential agent in CNA?
Sheep blood.
What does sheep blood detect on CNA?
Hemolysis.
What does growth on CNA indicate?
The organism is likely Gram-positive.
What does no growth on CNA indicate?
The organism is likely Gram-negative.What is TSA with 5% sheep blood also called?
What type of medium is blood agar?
Enriched and differential, but nonselective.
What is blood agar used for?
Routine culturing of clinical specimens.
What is the differential agent in blood agar?
Sheep blood.
What does blood agar differentiate?
Bacteria based on their ability to cause hemolysis.
Why is blood agar considered nonselective?
Almost everything might grow on it.What are the three types of hemolysis?
What is gamma hemolysis?
No hemolysis.
What does gamma hemolysis look like on blood agar?
No change around the colonies.
What is alpha hemolysis?
Partial hemolysis of red blood cells.
What does alpha hemolysis look like on blood agar?
A muddy green or greenish halo around the colonies.
What is beta hemolysis?
Complete hemolysis of red blood cells.
What does beta hemolysis look like on blood agar?
A clear zone around the colonies.
What does a muddy green halo indicate?
Alpha hemolysis.
What does a clear zone around colonies indicate?
Beta hemolysis.