Exercise 11 - Differential plates

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.

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?