Streptococcus Identification

Question 1

What are the 3 types of hemolytic patterns on blood agar?

Answer 1

Beta - Complete lysis
Alpha - Partial lysis
Gamma - No lysis

Question 2

Give an example of each hemolytic pattern

Answer 2

Beta - St. pyogenes
Alpha - St. pneumoniae
Gamma - Enterococcus faecalis

Question 3

Is BEA differential, selective, or both?

Answer 3

Both

Question 4

What ingredients are in a BEA slant?

Answer 4

Bile salts, esculin, ferric ammonium citrate, and beef and gelatin extracts

Question 5

What is the selective ingredient in BEA?

Answer 5

Bile salts

Question 6

What is the differential ingredient in BEA?

Answer 6

Esculin

Question 7

What does a positive reaction to esculin hydrolysis look like? What does it mean?

Answer 7

Greater than 50% black precipitate. The organism is able to hydrolyze esculin.

Question 8

What reaction went forth for the 50% black precipitate to form in the BEA slant?

Answer 8

The organism produced glucose and esculetin.
The esculetin reacted with the ferric ammonium citrate producing the black precipitate

Question 9

What does a positive esculin reaction produce?

Answer 9

Glucose and esculetin

Question 10

What does a negative reaction to esculin hydrolysis look like?

Answer 10

less than 50% black precipitate

Question 11

What Strep species is positive for esculin hydrolysis?

Answer 11

E. faecalis

Question 12

What Strep species is negative for esculin hydrolysis?

Answer 12

St. pyogenes

Question 13

What is the only member of the Strep group that can grow on MSA plates?

Answer 13

Enterococcus faecalis