Learn about the difference between positive and sterile, or negative controls in micro. How to properly obtain a positive control organism for verification of bacteria cultures. Applies to USEPA 1603 - modified m-TEC, SM9222D - m-FC, and USEPA 1600 - MEI membrane filtration methods as well. Prepared media plates and laboratory controls.

1. The following presentation is by Scott J. Bradley, and…

2. Just what IS Quality Control?
 In the laboratory environment, we strive to control
many conditions, so that we may be able to measure
our intended result.
 When talking about prepared media plates, it means
analyzing at least a sterile control and a positive
control with every run.

3. Why do we need Quality Control?
 When we inoculate, or plant microbes onto a petri
dish or prepared media plate, we want to make sure
that what we end up growing is the same bug we
planted originally, and we also want to know that we
can grow that particular microbe given the conditions
we used for incubation.
 A positive control is a known microbe (bacteria), that
comes from a certified source, such as the American
Type Culture Colony stock (ATCC).

4. You gotta keep control!
 A Sterile Control is a petri dish or prepared media plate
that is usually inoculated with a sterile blank, or sterile
dilution water, then analyzed for any signs of growth at
the end of the incubation period.
 We perform this procedure to assure we haven’t cross
contaminated our run.
 It is important to understand that any positive control
that doesn’t originate from a certified, known source,
is not a positive control. (including wastewater influent)

5. Other Factors to Consider…
 Prepared agar plates should be checked to make
sure that the pH is within the prescribed range for
that particular media.
 Glass Petri Dishes that are reused must
be made scrupulously clean before sterilization.
 Incubation temperatures should be continuously
monitored to assure no lapse in temperatures
have occurred overnight for instance.
 Technique of analysts in training must be monitored
carefully to avoid errors such as sterilizing
positive controls and inducing cross contamination.

6. What other factors must we control
for basic bacteria culturing?
 Growing target organisms, or specific types of bacteria usually involves a
petri dish or prepared media plate that has an agar that is specific to
growing that type of organism.
 Some other factors to be considered during incubation are,
pH, temperature, moisture/humidity, and aseptic technique.
 (careful methods used to prevent
cross-contamination of samples
or analyst).
meducation.net

7. Getting great results with your
prepared media plates!
 Remember the 5 P’s (or 6 like below!) proper
preparation prevents poor performance!
 Make sure you are using properly sterilized equipment
along with known control organisms and monitored
temperatures, and you’ll be a long way towards
assuring yourself of nice,
reliable, and consistent results
using petri dishes and prepared
media plates.

8. We hope you have enjoyed this short
presentation on Quality Control with
Prepared Media Plates and Petri Dishes!
 For more information on Prepared Media Plates,
please visit…
http://www.aquaplates.com