Have questions about which 3M™ Petrifilm™ Plates to use? We have answers. (Part 1 of 5)

Are you wondering which method you should use for powdered eggs or oat paste? Here are some questions food safety labs have asked, answered by our 3M global and U.S. technical specialists.

Question: Can rapid yeast and mold plates be used with powdered egg?

3M Petrifilm Rapid Yeast and Mold Count PlatesAnswer: Egg powder was one of the products tested for the NF VALIDATION  by AFNOR Certification for 3M™ Petrifilm™ Rapid Yeast and Mold Count Plate. 3M Petrifilm Rapid Yeast and Mold Count Plate is a great application for both low and high-water activity products as it has been validated and considered an alternative to both low and high-water activity reference methods.

Question: Are 3M™ Petrifilm™ Lactic Acid Bacteria Count Plates suitable for beverages? More precisely, for craft beer?

Answer: We do not have any certification or validation data specifically for beer. We have done some limited internal testing with membrane filters that shows positive results but additional testing needs to be conducted. We do know that there are some companies in the brewing industry using the 3M Petrifilm Lactic Acid Bacteria Count Plates, mostly for environmental swabs.

Question: What plates would you recommend for product water quality checks and also final packaged beer?

Answer: 3M™ Petrifilm™ Plates have only been validated for bottled water testing applications and it is possible that our 3M Petrifilm Plate methods may have some limitations in water testing. We continue to do some experiments to better understand how our 3M Petrifilm Lactic Acid Bacteria Count Plates can be used in the brewing industry but this will take some time as the organisms of concern in the brewing industry are very specific and there is need for differentiation between organisms.

Question: What E. coli/coliform plates are recommended for plating fruit juices, concentrates, purees? Are they the same as meat and seafood plates?

REC.tifAnswer: Either the 3M™ Petrifilm™ E. coli/Coliform Count Plate or the 3M™ Petrifilm™ Rapid E. coli/Coliform Count Plate can be used for fruit juices, concentrates and purees. Considering the low pH of these products, you may find using the 3M Petrifilm Rapid E. coli/Coliform Count Plate method a better fit for this application as the recommended pH range is > 5 and the amount of sample pH adjustment that would need to be done is minimal compared to the standard plate.

Question: Does 3M no longer recommend MRS broth on 3M™ Petrifilm™ Aerobic Count Plate for lactic acid bacteria?

Answer: Correct, the MRS broth method on 3M Petrifilm Aerobic  Count Plate is not our recommended method for lactic acid bacteria. We strongly encourage current users of this method to switch to the new method as we believe that the 3M Petrifilm Lactic Acid Bacteria Count Plate is an improvement on the previous method.

Question: Can Listeria environmental film be used for detecting Listeria in samples?

3M™ Petrifilm™ Environmental Listeria PlateAnswer: No. We do not advise that you use this plate for testing food. This plate was developed for testing environmental samples and was not optimized for food. In addition, this 3M Petrifilm Plate method does not have an enrichment step. Extremely low numbers of Listeria may not be detected in food samples (this is necessary for a “zero tolerance” regulatory environment such as the United States). The 3M™ Petrifilm™ Environmental Listeria Plate method has been validated for environmental samples that may contain residual cleaning chemicals and/or trace amounts of foods.

Question: Are there environmental Salmonella plates in works similar to the environmental Listeria plates?

Answer: At this time 3M Food Safety only offers qualitative Salmonella methods that require an enrichment. These methods can be used for environmental swabs.

Question: What Listeria plate do you use to stick to the surface?

Answer: We do not suggest using 3M Petrifilm Environmental Listeria Plate for direct contact or surface plating as that is not our method. For Listeria, which can create biofilms and have a strong adherence to surfaces, a sponge or swab sample is a better application. Additionally, using a sponge or swab allows for the method to be followed and allow for the resuscitation of Listeria cells that may be injured from cleaners/sanitizers or hostile elements in the environment.

Question: I need to do a Lactobacillus test in an oat paste. Would you recommend the use of 3M Petrifilm Lactic Acid Bacteria Count Plate?

3M™ Petrifilm™ Lactic Acid Bacteria Count PlateAnswer: The 3M Petrifilm Lactic Acid Bacteria Count Plate is a great method to enumerate the total number of lactic acid bacteria in a sample. While we haven’t specifically tested oat paste, we have tested a wide variety of products. We suggest conducting a side by side comparison with the 3M Petrifilm Lactic Acid Bacteria Count Plate method with either your current method or the reference method.

Question: Is lactic acid bacteria testing just another way to test for anaerobic bacteria in general?

Answer: The nutrients and selective agents in the plate formulation are specific for lactic acid bacteria. We have not conducted any testing to demonstrate the success of the recovery of all anaerobic bacteria.

Question: Can we use 3M Petrifilm Aerobic Count Plates for hand swabs?

Answer: 3M Petrifilm Plates cannot be used for clinical diagnosis and we do not recommend using them for hand swabs. In Latin America, there are some country governments that have approved 3M Petrifilm Plate use for hand swabs as the hands are considered part of the environment.

Question: Have you seen the widespread use of your lactic acid plates? How new are they?

Answer: Yes, we’ve received great feedback since we launched our 3M Petrifilm Lactic Acid Bacteria Count Plate in 2016. There are multiple types of food processors and beverage manufacturers using this method for in-process, shelf-life testing and even environmental monitoring.

Question: Are the rapid 3M Petrifilm Plates for assuming results before full incubation or can you confirm these results beforehand?

Answer: Only the 3M™ Petrifilm™ Rapid Coliform Count Plate provides a presumptive result before the full incubation. The 3M Petrifilm Rapid Yeast and Mold Count Plate, 3M Petrifilm Rapid Aerobic Count Plate, and the 3M Petrifilm Rapid E. coli/Coliform Count Plate all provide final results at the validated and verified full incubation time.

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