Frequently Asked Questions - Petrifilm®
October 18, 2023

Neogen® Petrifilm® Medium Frequently Asked Questions
By Process: Preparation | Inoculation | Culture | Measurement | Cleaning Up | Storage
By Product: AC | RAC | CC | EC | EB | LAB | YM | RYM | STX | SALX | AQUA
Neogen® Petrifilm® Plate Reader Advanced Frequently Asked Questions
By Process: Preparation | Measurement | Data | Maintenance
Petrifilm Medium Frequently Asked Questions
Preparation
What type of diluent should I use for Petrifilm medium?
Examples include physiological saline, 0.1% peptone water, phosphate buffer, and phosphate buffered saline. For other information, please refer to the instruction manual for each product.【Note】
Do not use buffers containing citrate, bisulfite, or thiosulfate as they may inhibit bacterial growth.
Inoculation
Is there a way to test samples with low pH without adjusting the pH?
Basically, we recommend that you adjust the pH of the sample solution to the appropriate pH for each plate by referring to the materials at the URL below. Alternatively, increasing the dilution factor further or diluting with a strongly buffered diluent (e.g. BPW) may yield appropriate results without adjusting the pH with e.g. NaOH. In this case, we recommend that you verify it once.The appropriate pH of the sample solution varies depending on the type of Petrifilm medium.
Please tell me about the difference in how to remove the upper film of Petrifilm Viable Bacteria Count Plate (AC Plate) and Petrifilm Coliform Count Plate (CC Plate).
For Petrifilm Viable Bacterial Count Plate (AC Plate), remove your hand from the top film and let the film fall naturally.For Petrifilm coliform count plates (CC plates), slowly lower the plate while holding the top film, being careful not to introduce air bubbles.
What food ingredients inhibit the growth of microorganisms? In that case, how should I deal with it?
In the case of raw garlic, raw ginger, raw onions, spices, matcha powder, coffee, highly concentrated sugar or salt, etc., the 10x sample solution will collect microorganisms due to the bacteriostatic action of the sample components, as with other agar medigrowth may be inhibited and colony formation may not be observed even on Petrifilm medium. In this case, try running the test at a higher dilution rate, such as by creating a 20x or 100x sample solution.Culture
After inoculating Petrifilm medium, can it be refrigerated until culturing?
We do not recommend refrigeration after inoculation and before culturing. After inoculation, start culturing immediately, and if you cannot measure it after culturing, store it in a sealed container and freeze it (recommended temperature: -15°C or less) and measure it within one week.Can I refrigerate Petrifilm Medium after incubation for the specified time if I am testing on a weekend?
To avoid changing the condition of the plate, we recommend freezing it at -15°C or below instead of refrigerating it (4°C). However, the Petrifilm Staphylococcus aureus measurement plate (STX plate) after inserting the Petrifilm Staphylococcus aureus measurement disk (STX disk), the Petrifilm Salmonella spp. measurement disk (SALX) After inserting the Petrifilm Salmonella bacteria measurement plate (SALX plate), do not store it after culturing and evaluate it immediately.Measurement/Judgement
Can I collect bacteria from Petrifilm medium? How can I do it again?
You can use fishing bacteria. Peel off the upper film, lightly touch the center of the colony you want to catch with a platinum wire or platinum loop, and transfer it to a non-discrimination medium.What is the minimum magnification when viewing mold under a microscope?
Most molds can be observed at 200 to 400 times magnification.How do I calculate the estimated number of colonies on Petrifilm Medium?
If the number exceeds the appropriate measurement range for each plate, you can calculate the estimated number of bacteria by counting the colonies in one section and multiplying the number of sections into which the plate is divided. After counting multiple compartments, you can calculate the estimated number of bacteria more accurately by averaging the number of bacteria in one compartment.What causes colonies to cluster around the edges of Petrifilm media?
If there are too many microorganisms on the plate (TNTC), the microorganisms may form colonies around the inoculated area or on the edges of the plate, so please dilute the solution further.When I cultured the Petrifilm Viable Bacteria Counting Plate (AC Plate) for more than 48 hours, the number of colonies increased. Does this also count?
As an example, the general viable bacterial count generally refers to the number of mesophilic aerobic bacteria grown in a standard agar medium under aerobic conditions at 35±1°C for 48±3 hours. I am. In this way, the general number of viable bacteria is defined depending on the conditions, so please measure the number of bacteria after culturing for a specified period of time.Is there a way to easily judge dark-colored samples without diluting them?
- Illuminate the plate with a backlight to increase the contrast of the colonies and make them easier to see.
- For Petrifilm Viable Bacteria Count Plate (AC Plate), try spreading it thinly using a spreader for Petrifilm Mold/Yeast Measurement Plate (YM Plate).
- It may be easier to see by passing it through a filter bag without diluting it.
- If the sample particles are large enough to pass through the stoma filter, leave the sample for about 3 minutes and collect the supernatant.
- Use the longest culture time among the recommended culture times to make the colony as large as possible and make it easier to see.
We recommend that you try the above measures and dilute it further if it is difficult to judge.
What are the criteria for the appropriate measurement range for Petrifilm medium?
The appropriate measurement range for Petrifilm media (and other common media) is established as a guideline to obtain values that are closer to the truth when performing statistical processing.Historical values for general culture media are listed in the ISO law, FDA BAM law, food hygiene inspection guidelines, etc. In the case of Petrifilm media, optimal values are individually set at the time of certification.
I have a colony growing on a foam dam in Petrifilm medium. Is this colony also subject to measurement?
Colonies above foam dams are not subject to measurement. This is because there may not be enough nutritional and selective ingredients on the foam dam. Even when obtaining third-party certification, we confirmed the validity of the colonies on these foam dams without measuring them.Cleaning Up
How do I dispose of Petrifilm medium?
Regardless of the presence or absence of bacteria, please be sure to sterilize the product using an autoclave (high-pressure steam sterilizer) before disposing of it. If there are regulations regarding disposal, please follow them.Storage
How should I store the pouch after opening it?
Store at room temperature or freeze as it dislikes moisture.Fold the opening of the bag and tape or clip it closed. Store in an airtight container at room temperature (below 25 degrees Celsius, relative humidity below 50%) or in an air-conditioned room, and use within one month after opening.
If the test room is above 25°C, the relative humidity is above 50%, and there is no air conditioning, freezing is recommended. Close the bag with tape and place it in an airtight container. Use the product within the shelf life indicated on the bag. Do not use the automatic defrost device on your freezer.
If the plate is stored in the refrigerator before opening, or if it is sealed and frozen after opening, to prevent condensation due to sudden temperature changes, please let the plate return to room temperature before removing the plate.
Petrifilm Staphylococcus aureus measurement disk (STX disk) should be used within 6 months after opening if stored under the above room temperature storage conditions. Also, if frozen, please use it within the expiry date.
Regarding storage methods, why should I not refrigerate the pouch after opening it?
In general, refrigerators have higher humidity than freezers, and refrigerators are prone to condensation due to large temperature fluctuations, so a more reliable method is to use a sealed freezer without an automatic defrost function. We recommend storing at room temperature below 25°C and humidity below 50%.Also, condensation due to temperature changes when taking the plate out of the freezer can be a problem, so please let it return to room temperature in a sealed state before taking the plate out.
In addition, repeated freezing and thawing may have a similar effect, so if you are planning to use a small number of plates in multiple batches, it is recommended that you seal the portions in advance, protect them from light, and store them frozen. It is recommended.
By Product
AC
Can yeast grow on Petrifilm viable count plates (AC plates)?
Fast-growing yeast may grow on Petrifilm Viable Count Plates (AC Plates), but culture conditions of 48 hours at 35°C are not optimal for yeast growth. For fungal measurements, we recommend using Petrifilm for fungal measurements, such as the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and the Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate).If I inoculate a raw meat or vegetable sample onto a Petrifilm viable count plate (AC plate), will the live cells in the sample react with the TTC indicator and stain red?
No, it won't stain. Food residues also appear on the plate in irregular shapes and are usually easily distinguished from bacterial colonies.Why are all colonies stained red on the Petrifilm Viable Count Plates (AC Plates)?
In Petrifilm Viable Count Plates (AC Plates), bacterial colonies are stained red by the TTC indicator in the culture medium.What is the indicator for the Petrifilm viable count plate (AC plate)?
The indicator used in the Petrifilm viable count plate (AC plate) is a TTC indicator (2,3,5-triphenyltetrazolium chloride).Are there any types of bacteria that the Petrifilm Viable Bacteria Count Plate (AC Plate) is not suitable for?
Most bacteria appear as red colonies on Petrifilm Viable Count Plates (AC Plates), but some lactic acid bacteria and some micrococci can dehydrogenate by reacting with the TTC indicator. It does not have enzymes and may not be easily stained red. Also, as with standard agar media, there are some bacteria that are difficult to grow under the specified conditions.Can Pseudomonas be detected with the Petrifilm Viable Bacteria Count Plate (AC Plate)?
The genus Pseudomonas is considered to be the bacteria that normally appears on Petrifilm viable count plates (AC plates). Normally, growth is not particularly slow, but some species and strains prefer slightly lower temperatures, so it is possible that growth may be slowed down by the culture temperature.When I cultured the Petrifilm viable count plate (AC plate), it liquefied. Are there any countermeasures?
Petrifilm countermeasures include the following.- Increase the dilution factor
- Count once after 24 hours of culture.
We recommend checking once after 24 hours of culture, which is shorter than the normal culture time. - Replace the spreader with a YM plate spreader.
Liquefaction spreads from around the bacterial colony that causes the liquefaction. Therefore, by replacing the spreader with the spreader of the Petrifilm mold and yeast measurement plate (YM plate), which has a wider area than the spreader of the Petrifilm viable count plate (AC plate), the influence of liquefaction can be reduced. You can secure areas that are not affected by. - Change the culture temperature from 35°C to 32°C.
Normally, the culture temperature of Petrifilm viable bacteria count plate (AC plate) is 35±1°C, but by changing it to 32°C, the "enzyme produced by bacteria" that causes liquefaction can be suppressed. Makes it difficult to produce. - Change to Petrifilm rapid bacterial count plate (RAC plate)
Petrifilm Rapid Bacterial Count Plate (RAC Plate) is less susceptible to liquefaction than Petrifilm Viable Bacterial Count Plate (AC Plate) due to the improved culture medium components.
Even on a standard agar medium, which is commonly used to measure the number of viable bacteria, it is expected that the colonies of such bacteria will spread widely and will be difficult to count. Please try the above first.
When I use the spreader to spread the sample solution on the Petrifilm viable count plate (AC plate), it does not form a clean circle. Are there any problems with the inspection?
It doesn't matter if it's not a perfect circle. Since the number of colonies is measured per 1 mL of sample solution, there is no effect on the test. However, if the sample solution spills out, please measure again.When I inoculated the Petrifilm Viable Bacteria Count Plate (AC Plate) with a sample solution, it protruded from the bottom film. Will it affect the test?
Contamination may occur from the outside through the spilled liquid, which may affect the test results. It is also expected that the number of bacteria will decrease due to insufficient volume of sample solution.Q. Will mold grow on the Petrifilm viable count plate (AC plate)?
Generally, mold does not grow on Petrifilm Viable Bacterial Count Plates (AC Plates), but in rare cases mold may grow on them. However, since viable bacteria count is performed after 48 hours of culture, molds that grow slowly are generally rarely detected. For fungal measurements, we recommend using Petrifilm for fungal measurements, such as the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and the Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate).RAC
How is it possible to determine general viable bacteria in 24 hours using the Petrifilm Rapid Viable Count Plate (RAC Plate)?
By adding an indicator, it is now possible to visualize colonies that were previously difficult to identify with 24-hour culture. Therefore, judgment can be made within 24 hours.In the Petrifilm Rapid Viable Bacterial Count Plate (RAC plate), all red colonies and blue colonies are counted as general viable bacteria, and there is no identification of bacterial species by color. Why are there two colors?
IIn order to detect a variety of bacteria in 24 hours, the Petrifilm Rapid Viable Count Plate (RAC plate) uses multiple indicators in addition to the TTC indicator. Therefore, colonies stained with indicators other than TTC will appear as blue colonies.CC
Will Gram-positive bacteria grow on Petrifilm coliform count plates (CC plates)?
Petrifilm Coliform Counting Plates (CC Plates) are based on a modified VRB medium, which inhibits the growth of Gram-positive bacteria.After inoculating the sample onto the Petrifilm Coliform Count Plate (CC plate) and culturing it, the plate turned yellow. What is the cause?
Certain Pseudomonas species and bacteria that alkalinize the culture medium may cause the pH indicator contained in the Petrifilm Coliform Counting Plates (CC Plates) to turn yellow to yellowish brown. There are some things that cause discoloration. When testing such samples, we recommend further dilution and retesting.Will Pseudomonas appear as colonies with air bubbles on Petrifilm Coliform Count Plate (CC plate)?
Due to their general properties, Pseudomonas bacteria do not appear as colonies accompanied by gas on Petrifilm Coliform Counting Plates (CC Plates).Regarding the evaluation of the Petrifilm Coliform Count Plate (CC plate), there are no colonies on the entire plate or on the edges, but the entire Petrifilm has a reddish-purple color. Is this TNTC?
In cases other than TNTC, the overall reddish-purple color may be strong due to the low pH of the sample solution. If the pH of the sample solution is low, we recommend adjusting the pH to 6.6-7.2 using the attached document and retesting. Please note that if the pH of the sample solution is too low, coliform bacteria may not be detected properlyMany colonies appeared on the desoxycholate agar medium, but bubbles appeared on the Petrifilm Coliform Counting Plate (CC Plate) and the Petrifilm E. coli and Coliform Counting Plate (EC Plate). We did not see many colonies with this. Why?
Desoxycholate agar medium generates not only coliform bacteria but also gram-negative bacteria other than coliform bacteriIt is difficult to determine which colonies are coliform bacteria from the culture results on desoxycholate agar medium. On the other hand, the Petrifilm Coliform Bacteria Counting Plate (CC Plate) and the Petrifilm E. coli and Coliform Bacteria Counting Plate (EC Plate) also contain grams of non-coliform bacteria, similar to the desoxycholate agar medium. Negative bacteria also grow, but coliform bacteria grow as colonies with air bubbles, so they can be distinguished from other Gram-negative bacteria on a single medium. Tests using desoxycholate agar alone may also count Gram-negative bacteria other than coliform bacteria. As a result, it seems that there are differences in the results.Can foods containing enzymes react with the Petrifilm Coliform Count Plate (CC plate)?
Petrifilm Coliform Bacteria Counting Plate (CC Plate) does not use a chromogenic enzyme substrate and identifies coliform bacteria using the selectivity of VRB medium and the capture of air bubbles by the film, making it suitable for use in foods. There is no effect of the enzymes contained in it.Petrifilm E. coli and Coliform Count measurement plates (EC plates) only use enzyme-substrate reactions to determine E. coli, so foods containing large amounts of enzymes may result in false positives. However, false positives are rare for common foods, and we have obtained AOAC OMA certification for all food categories.
When I inoculated the sample solution into the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), air bubbles were created. I did. Will it affect the test?
Judgment with Petrifilm Coliform Counting Plate (CC Plate) and Petrifilm E. coli and Coliform Counting Plate (EC Plate) is based on the presence of air bubbles associated with colonies. It will be.By marking air bubbles introduced during operation, you can distinguish them from air bubbles produced by coliform bacteria or E. coli after culturing.
When using the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), the gas produced by coliform bacteria in the medium area is much smaller than the gas produced by coliform bacteriMany bubbles were confirmed. Is this a characteristic of the non-measurable majority (TNTC)?
These minute bubbles are expected to be caused by water when the medium is hydrated.When you use a backlight to observe air bubbles on the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), you can see the following: You can check as follows.
Air bubbles produced by coliform bacteria ⇒ “Colorless” and transparent (air bubbles are present by displacing the medium)
Air bubbles derived from the medium ⇒ “Red” transparent (air bubbles exist in the medium)
EC
What exactly are the red and blue colonies without air bubbles on the Petrifilm E. coli and Coliform Count Plate (EC plate)?
Gram-negative bacteria other than Coliform bacteria (Gram-negative rods that break down lactose and produce acid and gas) under the Food Sanitation Act, and are classified as Enterobacteriaceae, mainly fall under this category.What is the indicator for the Petrifilm E. coli and Coliform Count Plate (EC plate)?
The following indicators are included.Red: TTC indicator (coliform bacteria)
Blue: 5-bromo-4-chloro-3-indolyl-D-glucuronide [BCIG] (E.coli among coliform bacteria)
If blue colonies (E. coli) with air bubbles appear on the Petrifilm E. coli and Coliform Count Plate (EC plate), do I need to catch them afterwards to confirm? Or?
Blue colonies with air bubbles on Petrifilm E. coli and Coliform Count Plate (EC plate) have been confirmed by AOAC OMA to be E. coli. As an administrative inspection, it is not possible to show complete agreement with the fecal coliform bacteria in Japan's official method, but as a self-inspection for food business operators, Petrifilm E. coli and Coliform Count measurement plates EC There is no problem in determining that the blue colonies with air bubbles on the plate are E. coli.In a coliform test using Petrifilm E. coli and Coliform Count plates (EC plates), red colonies with no air bubbles were observed after 24-hour incubation, but cells with air bubbles formed after 48-hour incubation. There were red colonies, but could they be coliform bacteria?
A red colony with air bubbles after 48 hours of incubation is outside the definition of coliform bacteria, so a colony with air bubbles after 48 hours of incubation is a gram-negative bacterium other than coliform. Some bacteria produce gas when cultured for a long time, so it is reasonable to assume that such a species was detected.With Petrifilm E. coli and Coliform Count measurement plates (EC plates), the color of the plate may turn a little blue-black depending on the sample. Why is this?
The color of the Petrifilm E. coli and coliform count plate (EC plate) may be affected by the enzymes contained in the sample. This is true for visceral samples such as raw liver. Raw meat (muscle) usually has no effect. In such cases, we recommend that you dilute the solution further and test, depending on the number of bacteria.Many colonies appeared on the desoxycholate agar medium, but bubbles appeared on the Petrifilm Coliform Counting Plate (CC Plate) and the Petrifilm E. coli and Coliform Counting Plate (EC Plate). We did not see many colonies with this. Why?
Desoxycholate agar medium generates not only coliform bacteria but also gram-negative bacteria other than coliform bacteriIt is difficult to determine which colonies are coliform bacteria from the culture results on desoxycholate agar medium. On the other hand, the Petrifilm Coliform Bacteria Counting Plate (CC Plate) and the Petrifilm E. coli and Coliform Bacteria Counting Plate (EC Plate) also contain grams of non-coliform bacteria, similar to the desoxycholate agar medium. Negative bacteria also grow, but coliform bacteria grow as colonies with air bubbles, so they can be distinguished from other Gram-negative bacteria on a single medium. Tests using desoxycholate agar alone may also count Gram-negative bacteria other than coliform bacteria. As a result, it seems that there are differences in the results.Can foods containing enzymes react with the Petrifilm Coliform Count Plate (CC plate)?
Petrifilm Coliform Bacteria Counting Plate (CC Plate) does not use a chromogenic enzyme substrate and identifies coliform bacteria using the selectivity of VRB medium and the capture of air bubbles by the film, making it suitable for use in foods. There is no effect of the enzymes contained in it.Petrifilm E. coli and coliform count measurement plates (EC plates) only use enzyme-substrate reactions to determine E. coli, so foods containing large amounts of enzymes may result in false positives. However, false positives are rare for common foods, and we have obtained AOAC OMA certification for all food categories.
When I inoculated the sample solution into the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), air bubbles were created. I did. Will it affect the test?
Judgment with Petrifilm Coliform Counting Plate (CC Plate) and Petrifilm E. coli and Coliform Counting Plate (EC Plate) is based on the presence of air bubbles associated with colonies. It will be. By marking air bubbles introduced during operation, you can distinguish them from air bubbles produced by coliform bacteria or E. coli after culturing.When using the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), the gas produced by coliform bacteria in the medium area is much smaller than the gas produced by coliform bacteria. Many bubbles were confirmed. Is this a characteristic of the non-measurable majority (TNTC)?
These minute bubbles are expected to be caused by water when the medium is hydrated. When you use a backlight to observe air bubbles on the Petrifilm Coliform Counting Plate (CC Plate) or the Petrifilm E. coli and Coliform Counting Plate (EC Plate), you can see the following: You can check as follows. Air bubbles produced by coliform bacteria ⇒ “Colorless” and transparent (air bubbles are present by displacing the medium) Air bubbles derived from the medium ⇒ “Red” transparent (air bubbles exist in the medium)EB
Regarding the culture temperature of the Petrifilm Enterobacteriaceae Count Plate (EB plate), the instruction manual and catalog differ. What temperature is appropriate for culturing?
The instruction manual contains conditions based on certification, and the catalog contains practical examples, so there are differences in the notation. Correct results can be obtained under any conditions: 30°C, 35°C, 37°C. In addition, there is a tendency to use 37°C with emphasis on certification these days, so please select the culture temperature depending on the purpose of the test.LAB
Why is anaerobic culture not required for lactic acid bacteria testing using Petrifilm Lactic Acid Bacteria count plate (LAB plate)?
This is because the Petrifilm Lactic Acid Bacteria Count Plate (LAB Plate) is designed to create anaerobic conditions by itself. Films, foam dams, and oxygen scavengers in the medium reduce the oxygen available to microorganisms, resulting in anaerobic conditions.Why do I get colonies with air bubbles and colonies without air bubbles on the Petrifilm Lactic Acid Bacteria Counting Plate (LAB plate)?
This is because there are two types of lactic acid bacteria: homofermentative lactic acid bacteria that do not produce gas, and heterofermentative lactic acid bacteria that produce gas.YM
What is the coloring principle of Petrifilm Mold and Yeast Measurement Plate (YM Plate) and Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate)?
An enzyme called phosphatase exists in the cells of living organisms, and the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate) use this phosphatase. The indicator, which is activated in its presence, stains mold and yeast blue.I can't see any mold or yeast colonies, but the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and the Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate) are not showing up as a whole. It turned blue. Why?
The phosphatase reaction derived from the specimen is thought to be the cause. Depending on the strength of the reaction, they can be distinguished from mold/yeast colonies and can be measured, but by taking the following measures, you can reduce the coloration caused by the influence of the sample.- Inoculate with further diluted sample solution
- Let the sample solution stand still after homogenization for about 1 to 3 minutes, and then inoculate it with the supernatant.
- Observe the condition after 1 day of culture in advance
To confirm that it is not really mold or yeast, I would like to transfer the blue dots that have appeared to a different medium for inspection. Is there any better way?
It is possible to isolate and culture using standard methods. In the case of mold, we recommend that you thoroughly scrape off areas that are thought to be colonies.In the case of mold, it is usually scraped off using a hook-shaped platinum loop and separated on a potato dextrose agar medium.
RYM
What is the coloring principle of Petrifilm Mold and Yeast Measurement Plate (YM Plate) and Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate)?
An enzyme called phosphatase exists in the cells of living organisms, and the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate) use this phosphatase. The indicator, which is activated in its presence, stains mold and yeast blue.I can't see any mold or yeast colonies, but the Petrifilm Mold and Yeast Measurement Plate (YM Plate) and the Petrifilm Mold and Yeast Rapid Measurement Plate (RYM Plate) are not showing up as a whole. It turned blue. Why?
The phosphatase reaction derived from the specimen is thought to be the cause. Depending on the strength of the reaction, they can be distinguished from mold/yeast colonies and can be measured, but by taking the following measures, you can reduce the coloration caused by the influence of the sample.- Inoculate with further diluted sample solution
- Let the sample solution stand still after homogenization for about 1 to 3 minutes, and then inoculate it with the supernatant.
- Observe the condition after 1 day of culture in advance
To confirm that it is not really mold or yeast, I would like to transfer the blue dots that have appeared to a different medium for inspection. Is there any better way?
It is possible to isolate and culture using standard methods. In the case of mold, we recommend that you thoroughly scrape off areas that are thought to be colonies. In the case of mold, it is usually scraped off using a hook-shaped platinum loop and separated on a potato dextrose agar medium.STX
When using the Petrifilm Staphylococcus aureus measurement plate (STX plate), what should I do if I cannot insert the Petrifilm Staphylococcus aureus measurement disk (STX disk) immediately after culturing?
After culturing, Petrifilm Staphylococcus aureus measurement plates (STX plates) can be stored frozen (recommended: -15°C or below) for up to 1 week. This can be done by taking it out of the freezer, letting it thaw naturally, inserting the disk, and culturing it for the specified time.Are there any criteria for determining the strength of the pink zone that appears after inserting the Petrifilm Staphylococcus aureus measurement disc (STX disc) based on its size and color intensity (light pink, dark pink)?
After inserting the Petrifilm Staphylococcus aureus measurement disk (STX disk) and incubating for 1 to 3 hours, if a pink zone is visually confirmed, regardless of size or color intensity, coagulase is detected. Measures as positive Staphylococcus.On the Petrifilm Staphylococcus aureus measurement plate (STX plate), what kind of bacteria are the colonies other than reddish-purple?
Based on what we have confirmed so far, we can think of the following.- Black colonies: Staphylococcus epidermidis (common bacteria) or damaged Staphylococcus aureus
- Blue colonies: Bacillis spp.
- To determine whether black colonies are negative or positive, it is necessary to insert an STX disk and check whether or not they are coagulase-positive staphylococci.
The Petrifilm Staphylococcus aureus measurement plate (STX plate) is cultured for 24±2 hours, but is there any specific situation in which the determination may become incorrect due to long culture, such as when cultured for 48 hours? Please tell me specifically
By prolonging the culture time, there is a risk that false positives may occur, such as things that should not be positive becoming positive or colonies that would otherwise not be detected.To attach the Petrifilm Staphylococcus aureus measurement disc (STX disc), lift the top film of the Petrifilm Staphylococcus aureus measurement plate (STX plate) after culturing, and then remove the medium part. The gel was cracked and gel was partially attached to the upper and lower films. In this case, will inserting the Petrifilm Staphylococcus aureus measurement disk (STX disk) have any effect on the results?
There is no effect on the results.Since the Petrifilm Staphylococcus aureus measurement disc (STX disc) is coated with an indicator on both sides, the gel in the medium portion of the Petrifilm Staphylococcus aureus measurement plate (STX plate) may crack. Even if the gel is partially attached to the upper and lower films, it is possible to react with the indicator by bringing both gels into close contact with each other. In addition, regardless of whether the gel of the Petrifilm Staphylococcus aureus measurement plate (STX plate) is attached to the upper film or the lower film, the Petrifilm Staphylococcus aureus measurement disc (STX disc) can be inserted. There is no difference in visibility afterwards.
The pink halo may be difficult to see after using the Petrifilm Staphylococcus aureus measurement disc (STX disc). Is there a better way to make it easier to see?
The Petrifilm Staphylococcus aureus measurement plate (STX plate) with the Petrifilm Staphylococcus aureus measurement disk (STX disk) inserted should be illuminated from the front rather than the backlight, or the plate It is easier to judge by observing from different angles.In addition, if the culture time is less than 3 hours, extending the culture time to 3 hours will make the reaction clearer and easier to judge.
SALX
I do not have a precision balance to weigh out a small amount of Salmonella pre-enrichment supplement. How should I weigh it?
We recommend preparing an aqueous solution of Salmonella Pre-Enrichment Supplement. By weighing 0.1g and dissolving it in 40mL of sterile distilled water, you can prepare a supplement solution for 8 samples.Salmonella Pre-Enrichment Supplement does not fully hydrate. What should I do?
We recommend weighing it into a sterile spitz tube or sterile centrifuge tube, and mixing it with a test tube mixer to dissolve it.If there is a weekend, etc., the test may not be possible according to the protocol. In that case, is there any process that can be improved?
After culturing on Petrifilm Salmonella spp. assay plate (SALX plate) and marking a presumed positive colony, it can be stored at -20 to -10°C for up to 72 hours. If you are unable to check the disc on the same day, we can take care of it for you.After culturing, the culture solution was not suspended. Is it okay to conclude that the test is negative for Salmonella at this point?
Even if the culture solution is cloudy and does not appear, Salmonella bacteria may be present. Please do not judge by the turbidity of the culture solution, but rather by smearing it on a Petrifilm Salmonella spp. measurement plate (SALX plate).I don't know whether the sample is a highly contaminated sample or a low contaminated sample. How do I know?
In general, heat-processed products are considered to have low contaminant bacteria, and raw materials are considered to have high contaminant contaminants, but please judge the accuracy based on the results of a viable bacteria count test of the relevant sample.After autoclaving the pre-enrichment medium, the color of the medium was different depending on the bottle. What reasons can you think of?
If the powder is autoclaved without being dissolved, the color of the medium tends to become darker. Before autoclaving, we recommend dissolving the medium and sterilizing it so that no lumps of medium remain at the bottom of the bottle.I stored the Petrifilm Salmonella spp. assay plate (SALX plate) at room temperature after opening the aluminum pouch. Can it be used for testing?
After opening, please keep it tightly closed at -20°C to -10°C. If you have stored it at room temperature, we recommend that you refrain from using it.How should I protect the Petrifilm Salmonella spp. assay plate (SALX plate) from light after opening the aluminum pouch?
The easiest way is to cover it with a tray or aluminum foil to block light.What kind of equipment is used to smear the lines?
There are disposable 10μL plastic loops and platinum loops whose collection volume is adjusted to 10μL. A plastic loop is recommended as it is less likely to scrape the culture medium and can be applied more cleanly.Is there any trick to smearing the gel without scraping it?
It is easier to smear the Petrifilm Salmonella bacteria measurement plate (SALX plate) by lifting it with one hand. Place the platinum loop as flat as possible in the medium. Place the loop part parallel to the Petrifilm Salmonella spp. measurement plate (SALX plate), and apply the smear by quickly tracing the surface without applying force. If you are using a plastic loop, bend the loop slightly before use to make it easier to align it with the plate.Due to work circumstances, the incubation time for the plate after inserting the Petrifilm Salmonella Identification Disk (SALX Disc) is shorter or longer than 4 to 5 hours. Will it affect the test results?
We recommend culturing for 4-5 hours after inserting the Petrifilm Salmonella Verification Disk (SALX Disc), and certification has been obtained using this culture time. If it is too short, sufficient reaction time may not be secured, increasing the possibility of false negatives; if it is too long, reactions with bacteria other than Salmonella may begin, increasing the possibility of false positives.AQUA
What membrane filter is recommended for Petrifilm medium water quality testing plates?
There is no problem with a material with a pore size of 0.45μm and a diameter of 47mm, which is commonly used in food and beverages.I use a Petrifilm Water Coliform Count plate (AQCC plate) to measure coliform bacteria in mineral water. What is the difference between "Petrifilm Coliform Count Plate (CC plate)" and "Petrifilm Water Coliform Count Plate (AQCC plate)"?
Both the Petrifilm Coliform Counting Plate (CC Plate) and the Petrifilm Water Coliform Count Plate (AQCC Plate) have similar shapes, but they are different from what they are testing for (food in general). (Is it bottled water?) and the testing method (direct inoculation method or membrane filter method) are different. Products are optimized for each application and undergo individual validation and quality control. Please note that reference methods and samples used during validation are also different.Petrifilm Plate Reader Advanced Frequently Asked Questions
Preparation
Do I need a dedicated computer?
You can install the software if your computer has 1 GB or more of free disk space.How do I update my software?
Please see our Download Registration page.Measurement
Please tell me the types of plates that can be read.
It is possible to read AC plates, CC plates, EB plates, EC plates, RAC plates, RCC plates, REC plates, RYM plates, SEC plates, LAB plates, STX plates, and STX discs.Does the Petrifilm Plate Reader Advanced require a validation card?
Verification cards used in previous model plate readers are not required. When started, self-diagnosis is automatically performed and measurements can be taken immediately. You can also select "General Settings" from the software's "Settings" and perform "Image System Verification".Can I read frozen Petrifilm medium?
We have confirmed that the reading results will not be significantly affected if it is used for about a week. When reading frozen plates, we recommend allowing the plates to come to room temperature for at least 1 hour and inserting them on a dry surface before reading to avoid condensation effects and erroneous results.How accurate is the reading?
The reading accuracy is designed with the goal of achieving the same accuracy as visual judgment.Data
Where are the image files saved?
Select "General Settings" from "Settings" in the software, and check the location where the images will be saved under "Automatically save images".What is the size of the image file?
With automatic save settings, each image is approximately 1MB. Since it is stored on your computer, there is no time limit. If you turn off the automatic save setting, the data will be saved on the software for 3 days (72 hours).Can image files be extracted individually?
Yes, it is possible. After viewing plate images in the software's "Measurement" and "Results" sections, you can save them individually or copy them from the automatically saved location.Maintainence
Please tell me the cleaning method and frequency.
Wipe off any powder adhering to the device with a dry cloth before and after use. We recommend that you clean it every day.Cleaning Method