FAQ｜MC-Media Pad for Microbial Testing

Frequently asked questions are summarized as a Q&A collection.

Addition of sample solution, Culture (Food inspection)

Wrinkles appear on the surface when the sample solution is added, but does it affect the detection?

It does not affect the detection. Please do not smooth the wrinkles with your fingertips. The generated wrinkles disappear (almost) during culture.

When the cover is closed, there is a gap without perfect contact.

When opening the cover film, open it diagonally and pull it to close it to make sure it closes easily. If necessary, trace the area around the culture medium part with your fingertips to expel the air. Small gaps do not affect the detection.

How many sheets can be stacked?

It is possible up to about 50 sheets (range that does not fall). Use of a rack is convenient.

Spreading colonies and shooting star-shaped colonies were detected.

If they are consecutive, please count as one. In particular, highly motile and fast-growing bacteria show such a shape. For details, please refer to the color sample in the general catalog.

The surface of the medium is dry and there are no colonies.

This medium is designed for testing 1mL samples, and it is possible that the added amount of sample solution is small. It is also possible that it has dried during the culture, so it is recommended to ensure that the cover film is closed after inoculating 1 mL sample.

Is it necessary to culture immediately after adding the sample solution?

It is preferable to culture immediately.

Sample solution

What is an unsuitable sample solution?

1. Samples with high salt concentration. In the case of such specimens, the salt concentration in the medium is high, which affects growth.
2. Colored samples of soy sauce, sauce, coffee, etc. In this case, the culture medium itself is colored, making it difficult to see colored colonies.
3. Extreme pH samples such as beverages. In this case, there is growth inhibition due to mismatch pH level.

In this case, dilute it with a buffer such as phosphate buffer or neutralize the pH of the sample and adjust the pH to 7.

When testing foods with strong antibacterial properties (ex. garlic powder)?

When testing a sample with strong antibacterial properties, it is necessary to dilute the sample about 1000 times before testing, as it is difficult to detect bacteria.

All over the surface of CC, EC, “For Coliforms” group”, “For E. coli and Coliforms” or SA (Staphylococcus aureus) sheet was colored.

Colors due to enzymes derived from samples may be seen in meat and raw vegetables. Since it is lightly colored on one side, it can be distinguished from the color developed by microorganisms.

Is it possible to test even if there are food residues in the sample?

If MC-Media Pad is inoculated with food residue, it may be mistaken for a colony. Use a stomacher bag with a filter or test the supernatant.

Is it possible to inspect creamy (food) samples?

Suspend in a diluent and test.

Is it possible to test with cosmetics?

Since cosmetics generally contain antibacterial substances, it is recommended to dilute with a cosmetic diluent (LP diluent / polysorbate 80 etc.) before testing.

If the sample is a liquid, can I add it directly?

It is no problem except for samples with high viscosity and dark color (soy sauce, sauce, etc.).

Is it possible to inspect milk?

Yes. It is possible.

Is it possible to inspect oil or products with high oil content?

As with cosmetics, we recommend suspending with a diluent containing a surfactant such as LP diluent/Polysorbate 80.

Is it possible to inspect frozen desserts such as ice cream?

Yes. It is possible.

Do I have to use the membrane filter method to test liquid samples?

The detection sensitivity of this medium is 1 cfu/mL or more. For example, the membrane filter method is recommended when detecting bacteria in 1 cfu/100 mL. In this case, the filtered membrane filter can be cultivated by placing it on the sheet medium to which 1 mL of sterilized water has been added in advance.

Others

What is the storage temperature?

Store in the refrigerator at 2 to 15 ℃, away from light. After opening the aluminum bag, seal it tightly and store in the refrigerator at 2-15 ℃ and use within one month. Although MC-Media Pad is a dry medium, it is not completely dry, so even for short-term storage, keep it refrigerated. Please do not use any products that show discoloration.

I have stored it frozen but can it still be used?

Not recommended.

What should I describe the test method/use medium when I report the test externally?

It is recommended to report as the dry medium method, sheet medium method, etc.

There were differences in the test results when compared to other media.

The nutrient composition and the background of the nutrients may differ between agar media as well.

The cover film may be hard and difficult to open.

It may be difficult to open immediately after taking it out from the refrigerator, so please return it to room temperature before use.

When inspecting food materials, at what timing should the inspection be performed after manufacturing?

・In the case of shipping inspection, please inspect immediately after manufacturing.
・When confirming storage stability, please inspect at the expiration date.

ACplus (R-AC) / For aerobic count

What are the microorganisms for general viable bacteria that are difficult to detect?

It has been experimentally found that the following microorganisms are difficult to detect.
・Many lactic acid bacteria (decrease in color development due to acid production / TTC reduction efficiency)
・Gram-positive cocci such as certain Micrococcus bacteria (because they are sensitive to TTC)
・Some Pseudomonas bacteria and the number of bacteria, When the number is high (10⁶ cfu/plate or more), the color may become faint or independent colonies may not be identified.

What microorganisms are difficult to detect with ACplus (R-AC)?

It has been experimentally found that the following microorganisms are difficult to detect. ・Many lactic acid bacteria and psychrophilic bacteria (because they grow slowly originally and prefer temperatures lower than normal culture temperature) If the number of growing bacteria is large (10⁶ cfu/plate or more), it may not be possible to identify independent colonies.

Is it possibility that a part of the medium part is greatly colored?

A very rare type of molds can cause a large portion of the medium to become highly colored. Please judge one block of the colored part as one colony.

After culturing for more than 48 hours, the number of bacteria increased.

It is recommended to keep the culture time because the aerobic plate count is defined as the plate count obtained when cultured at 35°C for 48 hours under aerobic conditions.

Is there any mold for general viable bacteria?

Molds and yeasts also grow for general viable bacteria. It is generally defined that molds and yeasts are also counted as aerobic plate count.

Coliforms related

What are the features “For Coliforms”?

The highly sensitive X-gal method is used for the detection principle. This difference in principle provides higher sensitivity than desoxycholate agar medium widely used in Japan.

Color spots are confirmed (increased number) over the second day.

In addition to coliform group, there are bacteria with β-galactosidase activity. Although the growth of these bacteria is suppressed, color may develop over time. Please keep the culture time.

Colored on all over the surface of sheet “For Coliforms, “For E. coli/Coliforms”.

Raw liver, shellfish such as oysters, dairy products, yogurt, lactic acid beverages, etc. may show color due to the enzyme derived from the sample. In such cases, it is necessary to further dilute the sample to reduce the effects of food-derived enzymes.

What if you want to test a powder or granular material as a sample?

In the case of a sample with a large amount of suspended solids, using a stomacher bag with a filter can reduce the amount of sample brought into the medium.

Detection was low in samples with high sugar content.

In samples that contain a lot of sugars such as glucose, the detection efficiency of the chromogenic enzyme substrate may be reduced. For this reason, we recommend diluting and testing samples that contain high concentrations of saccharides.

Is it possible to detect enterohemorrhagic Escherichia coli O157 etc.?

Enterohemorrhagic E. coli is coliform, so it is detected as coliform group in CC and “For Coliforms”, and as coliform group in EC, “For E. coli/Coliforms ”. However, since O157 does not have gluconitase, it is detected as coliform group in EC, “For E. coli/Coliforms”. Also, serotypes cannot be distinguished with MC-Media Pad.

YM（For fungi）

Is it possible to distinguish between mold and yeast for fungi?

Molds tend to form colonies that spread in the concentric circle shape, and yeasts form round colonies of about 1 to 2 mm, similar to bacteria.

Is all mold and yeast detected in 48-72 hours?

It has been confirmed that it has a high correlation with the ISO21527-1 method when cultured for 48 hours or 72 hours. However, there are many types of molds and yeasts, and it may take a long time for this medium to grow, especially for xerophilic molds and heat-resistant yeasts.

When used, the medium surface appears light pink.

The surface color of this product is white to pale pink. Therefore, the quality may not be affected even if it may appear slightly pink when used.

What kind of color is there other than red?

In the case of mold, spores may form, and the color tone of the coloring agent in the medium and the color of the spores may appear to be mixed. Also, in the case of yeast, pigments may be produced, so the color tone of the color former may appear mixed with the pigment produced by yeast.

SA（For Staphylococcus aureus）

Can it be confirmed as Staphylococcus aureus?

Biochemical discrimination such as the coagulase test is recommended for confirmation of Staphylococcus aureus.

Are the black colonies Staphylococcus aureus?

Not Staphylococcus aureus.

For salmonella

Is it possible to directly inspect Salmonella?

Detection may be possible if the number of Salmonella contaminating bacteria is high, but it is generally recommended to use an enrichment culture solution for testing.

Can I use “For Salmonella” for “For Coliforms”?

Not intended to detect coliform group. Please use the medium that suits your purpose.

Disposal method

How to dispose after use?

After use, sterilize by high pressure steam sterilization (autoclave) etc., and then discard.

Is chlorine sterilization acceptable?

It is not recommended because it requires a high concentration of hypochlorous acid and the bactericidal effect decreases quickly.

Direct wipe or stamp inspection

The liquid overflowed...

For wiping test, add 1 ml of sterilized physiological saline and absorb it completely before use. Since the medium components may remain on the wiped area, it is recommended to clean it with alcohol.

Is it possible to stamp directly on the ingredients?

We do not recommend it as it is possible that medium components may remain in the food.

Do I have to add sterile water 15 minutes before use?

Must be added 15 minutes before use. It can be stored for 2 weeks after addition, so it can be made and stored.

What should I do when directly wiping a place with foreign matter?

Please avoid foreign matter as much as possible and perform a wipe inspection. If it is still difficult, we recommend using a cotton swab for inspection.

Is it possible to inspect in a remote area without an incubator?

When used for quality control such as environmental inspection, culturing is not a problem, but we recommend culturing as soon as possible.

Judgment

What is the detection limit?

In principle, it is 1 cfu/mL or more.

How many colonies can I count?

Generally, it is necessary to measure 30 to 300 plates/plate, but it is convenient to use grid lines when 300 or more plates have grown.

How to express when it is innumerable?

Although it is usually TNTC (too numerous to count), it is recommended to perform further dilution test for more accurate test.

Why is it tendency to be detected the amount more than the pour method of agar plate?

Since there is no effect of heat on microorganisms as in the pour method, the number of bacteria may be higher in the sheet medium.