Lab 34: Throat Culture

Lab 34: Throat Culture 

1.  Pharynx=Throat= warm, moist environment that houses a mixed normal flora with organisms from both the upper respiratory and digestive tracts

-besides normal flora, the pharynx can also harbor potentially pathogenic bacteria

-these pathogens are kept in check by normal flora, but they can cause disease if they breach this barrier or      are transmitted to vulnerable individuals 

-In this lab, we take throat swabs from nasopharynx, which is the respiratory part of the pharynx (in the far back region of throat, behind uvula) 

2. Growth medium= sheep’s blood agar plates-contains 5% sheep’s blood, and is a differential medium agar which helps to categorize bacteria by hemolysis patterns -=how bacteria destroy RBCs (hemo- RBC; -lysis= burst)

ie. differential medium agar for hemolysis patterns

3. Hemolysins=toxins produced by colonies that cause either partial or dotal destruction of surrounding RBCs

4. We see Three Hemolysis Patterns:

1. Alpha (α) Hemolysis= partial clearing and greenish pigmentation around colonies

a. Alpha hemolytic bacteria:

1. are normal flora

2. MOST COMMON bacteria in throat

2. Beta (β) Hemolysis= complete lysis of RBC around colonies resulting in a clearing 

a. Beta hemolytic bacteria:

1. usually pathogens 

ex. Streptococcus pyogenes

      Staphylococcus aureus 

3. Gamma (ɣ) hemolysis= no clearing or surrounding ring, just dark colony with sheep’s blood agar surrounding it

a. Gamma hemolytic bacteria= normal fora 

Colonies on upper right are Alpha Hemolytic 

 

Mix of Alpha, Beta, and Gamma 

Mix of Alpha, Beta, and Gamma

Pure  Beta hemolytic bacteria

Pure Beta Hemolytic bacteria- notice the huge clearing