Carolina 3M Petrifilm Aerobic Count Plates - Manual (Page 7)

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2. Lift the spreader. Wait at least 2 hours for the gel to solidify (fig. 10).
Figure 10
3. Hydrated Aerobic Count plates can be stored in the refrigerator in a
sealed bag for up to 14 days before use.
4. To inoculate the medium, lift the top film. The circular gel area will adhere
to the top film (fig. 11). Hydrated Petrifilm can be used in many ways:
• Streak for isolated colonies with a
sterile loop, more gently and with
less pressure than you would a
standard plate. Tape the Petrifilm
plate to a flat surface in the open
position for streaking.
• Touch the circular gel area to a
surface of interest. This could be a
bench top, finger, doorknob, or
other smooth object.
• Sample the air by peeling back the
top film with the circular gel area
and taping the open Petrifilm plate
to a vertical surface, so that the gel area is exposed. After exposure
time has elapsed, take down the Petrifilm plate, close, and incubate.
Bacterial colonies on Petrifilm AC plates are red because of the indicator
dye in the medium. The red color helps to distinguish them from dust
particles or other environmental contaminants. Colonies may be isolated
for further study or to inoculate additional cultures (see Method A, step 10).
*Do not use diluents that contain citrate or sodium thiosulfate because they
can inhibit growth on the Petrifilm plate. These substances are not found in
common microbiological media such as Luria broth or nutrient broth.
Figure 11