EXERCISE 6

 

Bacteria Indigenous to the Human Body

 

 

Supplies Required : 6 blood agar plates, 2 mannitol salt agar plates, 4 blood agar deeps, 2 tubes Staphylococcus medium 110, 6 sterile swabs, tongue depressor; culture of a beta hemolytic Streptococcus

 

Protocol:

 

This exercise will be begun by the instructors before the workshop. The protocol is included here so you will know what the procedure was.

 

Before workshop:

 

1.        Blood agar plates and medium 110 tube are labeled with the usual information. The throat, nose, or ear is swabbed and the swab rubbed thoroughly in one section of a blood agar plate. From this area the plate is streaked for isolated colonies. The loop is stabbed into the agar to allow for subsurface growth, which facilitates the production of some hemolysis.

The plates are labeled with the area swabbed. Plates are incubated for 24 hours at 37oC.

 

2.        Another sterile swab is used to thoroughly swab skin, scalp, or nasal region. The cotton portion and part of the wooden stick is placed directly into a tube of medium 110. It will help if the skin is pinched in the area to be swabbed in order to open up the pores and release "buried" bacterial cells. The broths are incubated at 37^o.

 

3.         The Streptococcus is streaked to a blood agar plate and stabbed into blood agar deeps. The plates and deeps are incubated at 37^o.

 

Period 1:

 

1.        Look for zones of hemolysis on the blood agar plates. If there is time make a Gram stain from a beta-hemolytic colony if one is present. What is the morphology and Gram reaction of the beta-hemolytic isolate?

 

2.        The tube of medium110 should be turbid by now. Aseptically remove a loopful of broth culture and streak a plate of mannitol salt agar for isolation. Incubate at 37oC.

After 24 hours the plates will be refrigerated.

 

3.         Examine the blood agar plates and deeps for hemolysis.

 

Period 2:

 

Observe your mannitol salt plate for colonies. Has the phenol red dye changed to yellow around

any of the colonies? Perhaps the whole plate or large portions will have turned yellow. If there is

time perform a Gram stain of a typical colony from the yellow or reddish portion of the plate.

What is the morphology as adjudged from your Gram stain? Did any plates contain S. aureus?