THE PROCEDURES:
1
st Session
1. Have a lab partner obtain a throat swab from a single
member of the group. Have the subject tilt their head
back. Use a tongue depressor to push the tongue
down so a sterile swab can be used to obtain a sample
from the back of the throat (pharynx). Avoid swabbing
the cheeks, tongue or teeth.
2. Cover one half of a blood agar plate with the swab
then use a sterile loop to streak a portion of the swab
onto the other half of the plate. The procedure is
identical to a streak plate procedure, with the
exception of using a cotton swab for the first section and then switching over to the
inoculating loop.
3. Incubate at 37 C in a candle jar.
2
nd Session
1. Pick a colony that shows complete clearing (-hemolysis) or partial clearing or
“greening” ( hemolysis). A beta hemolytic is preferred, if you have one.
2. Use the sectional isolation streak technique on a CNA plate. This will help to ensure
that your isolated colonies are really Streptococci and free of contaminants. BE SURE
TO PICK 1 COLONY ONLY FOR A PURE CULTURE.
3. Incubate at 37 C in a candle jar.
3
rd Session
1. Check the streaked culture by gram staining a single colony, looking for chains of
gram-positive cocci and no other types of cells.
2. Depending on whether or not you have a -hemolytic streptococci or hemolytic
streptococci perform the following tests.
3. Using a sterile swab, streak a blood agar plate completely with the organism USING
THE ZIG-ZAG STREAK TECHNIQUE, covering the entire plate.
If your isolate is -hemolytic: Place a Bacitracin (A) disk and an SXT disk on the
inoculated blood agar plate.
If your isolate is α-hemolytic: Place an Optochin disk and an SXT disk on the
inoculated blood agar plate.
4. Inoculate the surface of a bile esculin slant and a tube of 6.5% sodium chloride broth.
5. Incubate at 37 C in a candle jar.
3
4
th Session
1. Salt resistance in the 6.5% NaCl broth is determined