t Lab Exercise by MikeJenny


                                                    MICROBIOLOGY LAB MANUAL

                                       Lab Exercise 20 - Throat Culture
                                       1. Describe the correct technique used for throat
                                       cultures and incubation.
                                       2. Correctly perform and interpret the results of a
                                       normal throat culture.
                                       3. Describe the normal bacterial flora of the throat.
                                       4. List the medical significance of the major pathogens
                                       found in the URT

The initial step in diagnosis of an infectious disease is usually culture or serological
analysis. If this step is not performed properly then any data collected from these tests are
useless. Titers quantitate the amount of circulating antibody present. The date that this
specimen is taken is of very importance because antibody titers will differ during prodromal,
acute, and convalescent stages. Evaluation of the timing and titer are essential in
determining whether the infection is active or simply antibodies from an old infection.
Collection of a specimen for culture is equally important. The following parameters are
1. Proper site (Not near the area but the specific location.)
2. Acceptable specimen (Not contaminated with extraneous material e.g. feces in urine.)
3. Proper labeling, including patient name, id. number, date and time.
4. Proper transport. (A special transport media may be required, or oxygen may need
5. Proper timing. (Prior to administration of antibiotics or antiseptics.)
        When culturing a throat you should bear in mind that this is probably an airborne
infection. Take the best precautions to assure the procedure does not expose you to the
agent causing their problem. Prepare the area with the
                                                               Author Lewis Tomalty Licensed for
materials you will need for the procedure.                     use, ASM MicrobeLibrary (linked to
MATERIALS:                                                     http://www.microbelibrary.org)
goggles          matches           EMB plate
gloves           candle            BAP plate
culturette       candle jar
1. Swab the glossopalantine arches on either side of the
uvula. Crush the ampule to release the transport media
that maintains the bacteria on the swab until they are put
on media.
2. Roll the swab in the area of the initial streak. Be sure
that all the sides of the swab contact the plate in quadrant
1 of the BAP and EMB plates.
3. Streak both plates for isolation.
4. Incubate the BAP plate in a CO2 jar. The pathogens we are looking for are capnogens
(preferring high CO2 content.) Light the candle, secure the lid, and watch the candle go out.

Place it in the 37C incubator.

5. Discard the tonque depressors and culturettes in the biohazard container.
                                                  MICROBIOLOGY LAB MANUAL

Lab Exercise 18            Throat Culture
Lab 2
Observe the plate for various colony types. Gram stain each of these different types.
Record below the 3 dominant colony types seen.

 Colony description     Gram stain            Probable organism     Notes

1.Match the following Gram stain and morphology with these normal flora of the URT.
___diphtheroids                        a. GNDC

___alpha streptococci                    b. GPC in chains

___Staph. epidermidis                    c. pleomorphic GPR

___ Neisseria sp.                        d. GPC in clusters

2. What is the best type of culture to take if pneumonia is suspected?

3. Describe the types of hemolysis observed on your culture. What is the significance?

4. Identify the type of hemolysis shown in the image below. What is the significance of this
                                                MICROBIOLOGY LAB MANUAL

kind of hemolysis when associated with catalase negative GPC in chains?

    Author Lewis Tomalty Licensed for
    use, ASM MicrobeLibrary (linked to

5. Assume that you have isolated an organism from a colony that appear GPC in the Gram
Stain. What simple test could you perform to distinguish quickly between staphylococci and
streptococci? Explain how this test works.

6. List the 2 pathogens of the URT (Upper Respiratory Tract).

7. List 2 pathogens of the LRT (Lower Respiratory Tract).

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