Petrifilm® 3M

Aerobic Count Plates

To be used for total aerobic bacteria enumeration.


The Petrifilm Aerobic Count plate is a reliable, ready made medium system for enumerating total aerobic bacteria populations (1,2,3,4). Petrifilm Aerobic Count plates contain Standard Methods nutrients, a cold water soluble gelling agent and a tetrazolium indicator dye which facilitates colony enumeration.


Petrifilm Aerobic Count plates are not intended to be used for in vitro diagnostic use.

Storage and disposal:

Store sealed Petrifilm Aerobic Count plate foil pouches at or below 46F (8C). After opening, return unused plates to foil pouch. Seal foil pouch by folding and taping the open end. Store resealed foil pouches in a cool dry place. Use plates within one month after opening. Exposure of Petrifilm Aerobic Count plates to temperatures and/or humidities above 75F (24C) and 50% RH can affect the performance of the plates. Resealed foil pouches may be stored in freezer to protect plates from high temperatures and/or humidities. Do not use plates that show brown discoloration.

After use, Petrifilm Aerobic Count plates will contain viable bacteria. Handle and discard appropriately.

Directions for use:

1. Place the Petrifilm Aerobic Count plate on a flat surface.

2. Lift top film. Hold pipette perpendicular to the plate and carefully dispense 1 ml of sample onto the center of bottom film.

3. Release top film down onto sample.

4. Distribute sample evenly using a gentle downward pressure on the center of the (recessed side). Do not slide the spreader across the film. Remove spreader and leave plate undisturbed for ore minute to permit solidification of the gel.

5. Incubate plates in a horizontal position, with the clear side up in stacks not exceeding 20 plates. Follow current total plate count standards for incubation temperature. Temperatures above 37C are not recommended. Incubate plates 48 + 3 hr.

6. Petrifilm Aerobic Count plates can be counted on a standard colony counter. The reduction of the tetrazolium indicator dye will cause the colonies to become red. All red dots regardless of size or intensity should be counted as colonies.

The circular growth area is approximately 20 cm2. Estimates can be made on plates containing greater than 250 colonies by counting a representative number of squares and multiplying by the appropriate number to obtain an estimated count for the total 20 cm2 growth area. The presence of very high concentrations of colonies on me plates will cause the entire growth area to become red or pink in color; record results as "too numerous to count (TNTC). Occasionally, on overcrowded plates, the center may lack visible colonies but many small colonies will be seen on the edges. When this occurs, record results as TNTC. Some organisms can liquefy the gel, allowing them to spread out and obscure the presence of other colonies. If a liquifier interferes with counting, an estimated count should be made by counting the unaffected areas.

7. To isolate colonies for further identification, lift the top film and pick the colony from the gel.


1. Ginn, R.E., V.6. Packard, and T.L Fox. 1986. Enumeration of Total Bacteria and Coliforms in Milk by Dry Rehydratable Film Methods: Collaborative Study. J. Assoc. Off. Anal. Chem. 69 (3): 527-531.

2. McAllister, J.S., M.S. Ramos, and T.L. Fox. 1987. Evaluation of the 3M Dry Medium Culture Plate (Petrifilm TM) Method for Enumerating Bacteria in Processed Fluid Milk Samples. Dairy and Food Sanitation 7(12): 632-635.

3. McGoldrick, K.F., T.L Fox, and J.S. McAllister. 1986. Evaluation of a Dry Medium for Detecting Contamination on Surfaces. Food Technology 40 (4):77-80.

4. Smith, LB., T.L Fox, and F.F Busta. 1985. Comparison of a Dry Medium Culture Plate (Petrifilm TM Plates) Method to the Aerobic P late Count Method for Enumeration of Mesophilic Aerobic Colony-Forming Units in Fresh Ground Beef. J. Food Prot. 48 (12):1044-45.

Instructions for specific dairy and food product applications and environmental surface sampling procedures are available upon request by calling your local Petrifilm Account Representative or Petrifilm Technical Services: (800) 328-6553 outside of Minnesota: (612) 738-1258 inside of Minnesota.

Petrifilm - APC