Prepared and non-prepared petri dishes can be sterilized by several different methods. This short presentation takes a look at the different methods of plate sterilization, how they "do their thing," and which we're most likely to use in the lab.

1. The following presentation is by Scott J. Bradley
and…
Copyright 2013

2. In this video, I’m going to show you why…
You have some choices when it comes to…
Media Plate Sterilization
Methods!
 You’ll learn:
Several methods of media plate
Sterilization…
 How:
Each sterilization technique works –
and…
 Which method is commonly used in the
micro lab.
How’s that sound, OK? Great!
Let’s get started…

3. Why Sterilize Media Plates?
 Media plates are used in many different
industries and sciences to grow specific
types of bacteria.
 In order to be sure we are culturing, or
growing the type of “bug” we want, (our
target organism), we use specific types of
food, called agar.
 Also, to be sure we do not cross
contaminate our experiment, we
want to make sure that we start
with a sterile media plate.
 Sterility means the absence of all living
things!
Clker.com

4. What Methods are used to
Sterilize Media Plates?
First off: Gamma Radiation
 One of the most widely used means of
sterilizing media plates is by the use of
Gamma Radiation.
 A high energy photon is emitted from an
isotope source, (Cobalt 60), which in turn
creates an electron disruption
in products (ionization).
 If it is a living cell, this kind of
disruption will cause DNA and GAMMA RAY BLAST!
other structural damage to the cells.
 Photon induced molecular changes in
structure result in death, destruction, and
generally a really bad day for any receiving
organism!

5. Gamma Radiation
This type of sterilization is usually
reserved for larger processes,
but also for things like fruits!
Wanna build a Gamma Radiation
plant in your back yard for fun?
Here’s what they look like….
PS: You’re gonna need a really big Budget!

6. Second Up: Ethylene Oxide
 Ethylene Oxide – EO, or EtO, is a chemical
compound commonly used for sterilizing a
wide variety of items, including medical
instruments and
single use diagnostic tools.
 Sterilization occurs through
time, humidity, temperature,
and gas concentration.
 Disruption of organism reproduction is
caused by DNA destruction with the
Ethylene Oxide acting as an alkylating agent.
Lardbucket.org

7. OK …. so , why don’t we
use…Ethylene Oxide?
Certain items like some pharmaceuticals or
electronic components can’t take
high temperatures, or steam heat.
Let’s see, what else…oh yeah –
ethylene oxide is very poisonous, and…
you need lots of special precautions and
bells and whistles just to use it safely.1
1(Bells and Whistles You Say? OK – more specifically : Pure EtO gas has a
boiling point of 10.73 º C. at atmospheric pressure. Most of the time, it is mixed
with Nitrogen or CO2. This is an explosive condition that requires the Intrinsic
Safe material (ATEX) zoning, for security of staff and personnel as well as for
security of the gas mixing process itself.
So… there’s some good reasons not to use it for fun and sterilization!

8. And Number Three on
Our List:
Autoclaving to Sterilize
 Media plates can be sterilized via steam
autoclaving as long as they are made of glass
or autoclaveable plastic.
 Autoclaves kill organisms using steam heat
under pressure, over a certain period of time
based on the batch load.
 Autoclaves can be dangerous
to operate, and require a skilled
technician as in all of the
previously mentioned
sterilization methods. (photo courtesy of MedicalExo.com)
 Fifteen minutes at 15 PSI at 121 degrees C is a
common autoclave run configuration.

9. Are Your Media Plates
Really Sterile?
 How do know that your media plates are
sterile?
 When you run a batch of
samples, analysts will run
a positive control, and a
sterile control with each
batch, or set of samples.
 A positive control, is a plate that is run, or
analyzed after having been inoculated
with a certified and known bacteria, or
target microorganism.
 Usually in the US, we use bacteria strains
certified from the ATCC, or American
Type Culture Colony.
E. Coli on Modified m-TEC
c. Aquaplates, Prepared Media Plates

10. Sterile Controls in your
Runs
 A Sterile Control, is a plate that is
inoculated with sterile water or nothing,
and incubated along with the rest of the
batch to assure that the plates
themselves are not a causal agent in any
cross contamination issues that may
arise.
 No growth on a sterile
media plate.

11. And Number Four:
Groovy-UV: Ultraviolet Sterilization
 Although there are even more exotic
methods for sterilizing objects such as
media plates, the last topically relevant
method we shall talk about in this
presentation is UV, or ultraviolet
sterilization.
 UV produces some UV-C and short wave
emissions which wreak havoc with the
nucleic acids in the DNA and RNA of
organisms.
 Works great for disinfecting
residential water
systems as well.
(don’t look too closely – the light is
harmful to your eyes!) ; - )

12. Now…
…you know about some
Sterilization Techniques!
I hope this short presentation has been helpful
for you.
If you’d like more information of this type,
please feel free to visit us at:
http://www.aquaplates.com/report---pass-
your-dmrqa.html
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