Blog Post #9

blood agar plates

Last week in lab Sammy and I tested our mystery microbe's hemolytic abilities. We did this by using blood agar plates containing general nutrients and 5% sheep blood. We used the T-streak method to inoculate S. aureus, S. epiderdimis, and our unknown microbe onto three separate plates. We then incubated the plates at 37 degrees Celcius and checked them at 24 and 48 hours to check for hemolysis. 

24 hours: left: unknown, top right: S. aureus,
bottom right: S. epididermis

Unknown after 24 hours of incubation

According to our lab handout there can be divided into three groups – alpha, beta, and gamma – based upon their hemolytic activity on blood agar. Beta (β) hemolysis is defined as complete or true lysis of red blood cells. Alpha (α) hemolysis is the reduction of the red blood cell hemoglobin to methemoglobin in the medium surrounding the colony. Gamma (γ) hemolysis indicates the lack of hemolysis. After 24 hours there is already significant growth on some of our plates. Our mystery microbe grew very quickly on the blood agar and is seems to fit the description of an alpha hemolytic bacteria. As you can see in the photos there is a clear dark discoloration surrounding the colonies on the plate.

Unknown after 48 hours

Plates after 48 hours

Bacteria are able to lyse red blood cells by producing enzymes called homolysins. Thers enzyemes function by destroying the outer membrane of a red blood cell. Some create pores in the membrane, weakening it, while other hydrolyze the phospholipid components of the cell's phospholipid bilayer. Hemolytic microbes are more virulent than non-hemolytic microbes because they destory iron-containing red blood cells that fight infection. This results in a reduced number of red blood cells in the body and therefore reduced oxygen transportation to the body which can be dangerous. I would not expect a typical soil microbe to be capable of hemolysis because most of them are not pathogenic. 

We've been attempting to identify our mystery microbe this semester by using a dichotomous key. This week we determined that our microbe is capable of alpha hemolysis.

1. Gram positive

2. Morphology, Rod Shaped (Bacilli)

3. Non-acid fast organism

4. Catalase positive 

5. Endospore positive

6. Motile

7. Nitrate reduction

8. Alpha hemolysis

The dichotomous key indicates that our microbe belongs to the genus Streptococcus! 

http://en.wikipedia.org/wiki/Hemolysin

http://en.wikipedia.org/wiki/Streptococcus