page_title: Petrifilm
section_title: Comparisons between Petrifilm plates and standard methods
hierarchical_section_title: Petrifilm / Comparisons between Petrifilm plates and standard methods
caption_attribution_description: English: 3M Petrifilm E. coli/coliform plates. The plate on the left has been inoculated and incubated, whereas the plate on the right has been unused. Created and uploaded by Achiu31 18:39, 8 April 2007 (UTC)
context_page_description: The 3M Petrifilm plate is an all-in-one plating system made by the Food Safety Division of the 3M Company. They are heavily used in many microbiology-related industries and fields to culture various micro-organisms and are meant to be a more efficient method for detection and enumeration compared to conventional plating techniques. A majority of its use is for the testing of foodstuffs.
  Petrifilm plates are designed to be as accurate as conventional plating methods. Ingredients usually vary from plate to plate depending on what micro-organism is being cultured, but generally a Petrifilm comprises a cold-water-soluble gelling agent, nutrients, and indicators for activity and enumeration.
  A typical Petrifilm plate has a 10 cm × 7.5 cm bottom film which contains a foam barrier accommodating the plating surface, the plating surface itself, and a top film which encloses the sample within the Petrifilm. A 1 cm × 1 cm yellow grid is printed on the back of the plate to assist enumeration. A plastic “spreader” is also used to spread the inoculum evenly.
context_section_description: Petrifilm plates have become widely used because of their cost-effectiveness, simplicity, convenience, and ease of use.  For example, conventional plating would require preparing agar for pour plating, or using agar plates and vial inoculum loops for streak plating; but for Petrifilm plates, the agar is completely housed in a single unit so that only the sample has to be added, which saves time.
  For incubation, Petrifilm plates can be safely stacked and incubated just like Petri dishes.  Since they are paper thin, more plates can be stacked together than Petri dishes (although 3M recommends that Petrifilms be stacked no higher than 20).  
  For enumeration, Petrifilm plates can be used on any colony counter for enumeration just like a Petri dish.  Various enumeration experiments have shown very little or no variance between counts obtained through Petrifilm and standard agar counts.  In some cases, Petrifilms were more sensitive in detection than standard microbiology methods, other than the case that a higher sensitivity could possibly lead to an increased risk of false positive results.
caption: E. Coli/Coliform Petrifilms
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