Exercise 5-25 Micro Lab: Blood Agar

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1

hemolysins

exotoxins produced by several species of gram positive cocci which are able to destroy red blood cells and hemoglobin - usually Streptococcus bacteria

2

Blood agar contains what?

5% sheep blood in a tryptic soy agar base

3

three major types of hemolysis

1. B-hemolysis
2. a-hemolysis
3. y-hemolysis

4

B-hemolysis (beta)

the complete destruction of RBCs and hemoglobin, results in a clearing of the medium around the colonies

5

a-hemolysis (alpha)

the partial destruction of RBCs and produces a greenish discoloration of the agar around the colonies

6

y-hemolysis (gamma)

is non-hemoylsis and appears as simple growth with no change to the medium

7

streptolysins

hemolysins produced by streptococci

8

streptolysins come in what two forms?

O and S

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Streptolysin O

is oxygen-labile and expresses maximal activity under anaerobic conditions

10

Streptolysin S

is oxygen stable but expresses itself optimally under anaerobic conditions as well

11

streak-stab technique

Blood agar is streaked for isolation and then stabbed with a loop. The stabs encourage streptolysin activity because of the reduced oxygen concentration of the subsurface environment. The easiest method.