Prepared Media Plates and Colony Counting for entry level microbiologists. Learn what to look for when differentiating between colonies. How colonies are counted along with what happens when you have bacterial overcrowding on prepared media plates.

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

2. Why are we Counting Colonies on a
Prepared Media Plate?
 In microbiology, a colony is a body that is formed from
millions of individual bacteria of the same type, or strain.
 Once a prepared media plated is inoculated, each
individual bacteria should grow into a colony of the same
kind.
 Bacteria colonies are almost
always visible to the naked eye.
 Some prepared media plates have
special chromogens in the agar
that highlight target bacteria. E. coli highlighted in magenta using
Modified m-TEC.

3. Prepared Media Plates and Colony
Morphology
 Colony morphology refers to the shape, texture, size,
color, odor, and other factors of a bacteria colony.
 Knowing the different colony morphology of bacteria
is one of the keys for the analysts in determining what
type of bacteria they are looking at.
 For example, fecal Coliform bacteria,
using an m-FC media, (SM9222d),
will appear dark blue
as in the example here…

4. Overcrowding of Prepared Media
Plates
 Overcrowding, or overpopulating, can cause some
problems when culturing microbes.
 Since each colony is growing at an alarming rate, they
consume all of the food as it is encountered on the
plate.
 If colonies start to grow into each other or overlap,
then there may be too much competition and colony
morphologies as well as recovery rates may vary.

5. Hey- You’re in my Space!
 Too many bacteria colonies on a prepared media plate
can cause an inhibitory response.
 Waste from colonies as well as competition for food
and space can reduce the overall colony count on a
plate.
 Also, if bacteria growth is too dense with overlapping
colonies, it may be difficult to get accurate counts.
 Fortunately, there are tools available to help us with
colony counting.

6. Darkfield Colony Counters
 Let’s take a look at some instruments that help us with
focus and differentiation when counting colonies.
 First – there’s the Darkfield Colony Counter
as seen here…
Some, like this fancy
instrument, will count
count colonies for you!

7. You’ve got to be “Gridding” me!
 Yeah, that’s right – membrane filters have a grid on
them to help you count.
 You can even count squares down, then over like an “L”,
and then multiply to get a pretty good estimate of the
colonies on the plate.
These filters catch the
bacteria, and fit right in the prepared media plate.

8. We hope you have enjoyed this
short presentation!
 Thanks for viewing our show – we hope it has helped
you better understand prepared media plates and
colony counting.
 For more information on Prepared Media Plates,
please visit…
http://www.aquaplates.com