Hydrating 3M™ Petrifilm™ Plates

When preparing 3M™ Petrifilm™ for use in your environmental monitoring program there are different hydration methods to follow, depending on the test and the context in which it is used.

For air or direct contact procedures where Aerobic Count, Coliform Count, E.coli/Coliform Count, Rapid Coliform Count or Enterobacteriaceae Count Petrifilm™ are being used, hydrate plates with 1 mL of appropriate sterile diluent. Allow hydrated plates to remain closed for a minimum of 1 hour before use.  If using Staph Express Count Petrifilm™, hydrate plates with 1 mL of appropriate sterile diluent. Refrigerate hydrated plates for a minimum of 3 days before using.

For air testing using either Yeast and Mold Count or Rapid S. aureus Count Petrifilm™, hydrate plates with 1 mL of appropriate sterile diluent. Allow hydrated plates to remain closed for a minimum of 1 hour before use.

For direct contact methods only using Yeast and Mold Count Petrifilm™, hydrate plates with 1 mL of sterile letheen broth only. Place letheen inoculated plates into sealed bag and incubate at 30-37°C (86-99°F) for 24 hours. After incubation, store sealed bag of plates in refrigerator for a minimum of 4 hours to allow gel to solidify. Plates hydrated with letheen will have a mottled appearance.

If you prefer using the new Rapid Aerobic Count Petrifilm™ the hydration times are slightly longer for air or contact surface monitoring. Air sampling has a 24-hour minimum hydration period refrigerated. After hydration plates can be stored up to 7 days. Contact sampling has a 3-day minimum hydration period refrigerated. These plates may also be stored for 7 days after hydration.

Refer to relevant package insert for details and listing of appropriate diluents.

For storage purposes, place all hydrated Petrifilm™ in sealed pouch or plastic bag. Protect plates from light and refrigerate at 2-8°C (36-46°F). Hydrated Petrifilm™ Aerobic Count plates may be refrigerated up to 14 days, all other hydrated Petrifilm™ plates may be refrigerated up to 7 days.

Source: 3M