CAROLINA ® Teamed with Teachers 82-4010 3M™ Petrifilm™ Yeast and Mold Count Plates Instruction Manual
Description The 3M™ Petrifilm™ Yeast and Mold Count (YM) Plate is a ready-made culture medium system that contains nutrients supplemented with antibiotics, a cold-water-soluble gelling agent, and an indicator dye that makes colonies easier to see. Petrifilm plates are manufactured with a grid background to facilitate counting colonies.
Safety Petrifilm YM plates contain the antibiotics chloramphenicol and tetracycline to prevent bacterial growth. The hydrated medium should not come into contact with skin. Do not inoculate Petrifilm YM plates by touching them. After use, Petrifilm YM plate will contain viable yeast and mold colonies. Opening a used YM plate risks spreading spores. If allowed to sit for several days, molds can grow out of the plates and spread spores.
Figure 3 4. Release the top film. Allow it to drop onto the bottom film. Do not roll the top film down (fig. 4). Figure 4 5. Holding the YM spreader by the handle, place the spreader on the top film over the inoculum (fig. 5).
6. Gently apply pressure on the spreader to distribute the inoculum over a circular area. Do not twist or slide the spreader (fig. 6). Figure 6 7. Lift the spreader. Wait at least 1 minute for the gel to solidify (fig. 7). Figure 7 8. Incubate plates with the clear side up in stacks of up to 20 plates. Incubation time and temperature will vary according to the application and equipment available. 9. Colonies on Petrifilm plates can be counted on a standard colony counter or other light source (fig. 8).
10. Disinfect before disposal. To disinfect, fill a dishpan with 10–20% bleach and put on a pair of latex or other protective gloves. Immerse the taped Petrifilm plates in the solution, then open them. This procedure ensures that the organisms will be exposed to bleach, but minimizes the risk of spreading spores. Soak the plates in the bleach solution for at least 1 hour. Then, they can be placed in the trash.
Microscopic Differentiation To examine the organisms, lift the top film and pick the colony from the gel (fig. 10). Transfer the colony to a drop of water on a microscope slide, cover with a coverslip, and view under oil immersion (fig. 11). Look for ovalshaped budding yeast (fig. 12) and for mold—both its branching mycelium (fig. 13) and its germinating spores (fig. 14).
Figure 13 Figure 14 To order call: 1-800-334-5551 (US and Canada) 336-584-0381 (International) For technical help call: 1-800-227-1150 www.carolina.
