Q&A

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

Storage

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?

It is not recommended to use for influence of culture performance.

Can it be exposed to sunlight or UV light?

The redox indicator reacts and colors the non-woven fabric. Store away from sunlight and UV.

Sample (food) preparation

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

Food residue may reduce visibility of the medium surface. Use a stomacher bag with a filter or test the supernatant.

Powder or granule 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.

Hard solid sample (ex. chocolate)

After crushing or cutting with a sterilized equipment, test as the same way as normal food.

Food with strong antibacterial properties (ex. garlic powder)?

Antibacterial inhibits growth of microorganisms, accurate test may be difficult. To decrease antibacterial effect, dilute the sample appropriately.

Creamy (food) sample

Suspend in a diluent and test.

Cosmetics

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

Oil or sample with high oil content

Suspending with a diluent containing a surfactant such as LP diluent/Polysorbate 80 is recommended.

Direct addition of liquid sample

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 frozen desserts such as ice cream?

Yes. It is possible.

Is the membrane filter method necessary for liquid sample test?

The detection sensitivity of this culture medium is 1 cfu/mL or more. For example, the membrane filter method is recommended when detecting bacteria in 1 cfu/100 mL. After 1mL of sterilized water is added to the MC-Media Pad, a filtered membrane is put on this culture medium.

What is an unsuitable sample solution?

1. High salt concentration samples may result in poor growth of microorganisms.
2. Colored samples such as soy sauce, sauce, coffee, etc., colonies may be difficult to count.
3. Extremely high or low pH of the sample may result in poor growth of microorganisms.
4. Food with strong antibacterial properties (ex. garlic powder) may inhibit growth of colony.
In these case, dilute it with a buffer such as phosphate buffer, or neutralize the pH of sample and adjust it to pH 7.0

When should food be tested after production?

・For the shipping inspection, test immediately after production.
・For the storage stability, test at the expiration date.

Method for use

The cover film was hard and difficult to open.

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

Wrinkles appeared on the surface when the sample solution is added.

It does not affect the detection. Do not smooth the wrinkles with your fingertips. The generated wrinkles will almost disappear during incubation.

When the cover was closed, gaps were observed.

Trace the area around the culture medium part with your fingertips to expel the air. Also, close the cover film with pulling it slightly, make it adhere more easily. 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.

Is it necessary to incubate immediately after adding of the sample solution?

It is preferable to incubate immediately.

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

It is recommended to incubate as soon as possible. When using selective media, it is recommended to verify in advance because different incubation times may affect the selection performance.

Count of colony

What is the detection limit?

In principle, it is 1 colony/plate or more.

How many colonies can be counted?

Although the upper limit is 300 colonies/plate, it varies depending on the grade. Check the instruction manual. If the upper limit is exceeded, dilute the samples and test. Grid lines can be used to calculate the approximate number of colonies.

How to express when it is innumerable?

It expressses usually TNTC (too numerous to count). Dilute the sample and test below the upper limit of detection.

Spreading colonies or shooting star-shaped colonies were detected.

Highly motile or fast-growing microorganisms show such colonies. If they are consecutive, count as one colony. For details, refer to the color sample of colony.

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

This medium is designed to perform with the addition of 1mL samples. It is possible that the added sample solution is small volume, and also possible that it has dried during the incubation. Be sure to add exactly 1 mL of sample and close the cover film. Addition of high viscosity sample, the same phenomenon may occur. In this case, dilution is recommended.

Unable to identify a single colony.

When many microorganisms are present (10⁴ CFU/mL or more), the colonies may overlap and identification will be difficult. In some case, too many microorganisms may lighten the colony color. Also depending on the substances in sample, the chromogenic agent may react and color the entire surface.

All over the surface of Acplus (R-AC) / For aerobic count or YM sheet was colored.

These media contain a redox indicator as a coloring agent. Exposure to sunlight or UV light causes coloration. If the sample contains substances that are easily oxidized, it will be colored.

All over the surface of CC, EC, SA or "For salmonella" sheet was colored.

These media contain chromogenic enzyme substrates. In the raw meat and raw vegetable, food-derived enzymes from these foods can make medium colored. Although the entire surface will be lightly colored, colonies can be distinguished. Further dilution of the sample is recommeded in case of uncountable. If the coloration occurs within 3 hours after the start of incubation, the influence of food-derived enzymes is suspected.

In the CC, EC, SA or "For salmonella", surroundings of food residues are colored and look like colonies.

Coloring due to food-derived enzymes may be visible in the colony. Use filtered stomacher bags and do not add food residues.

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

In the case of selective media, test results may differ due to differences in selection principles and combinations of selective agents. Even in the case of the same composition, differences in raw material backgrounds may cause differences in results.

It tended to be detected more than the agar medium with pour method.

In the MC-Media Pad, there is no effect of heat with pour agar, the number of microorganisms may be higher than agar.

The number of colonies was lower than on agar medium.

The sample in diluted 15-20 times with pour agar method, however the concentration of the sample solution remains the same in the MC-Media Pad. If the sample contains high salt concentrations, extreme pH, or antimicrobial substances, MC-Media Pad may be strongly affected by them, resulting in lower colony counts compared to agar media.

What should be description about test method/use medium for external report.

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

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.

Is boiling sterilization acceptable?

Put in a heat-resistant bag and heat for at least 30 minutes.

Direct wipe or stamp test

Points to note

If wiping with strong force, the non-woven fabric will peel off. On the other hand, if the force is not strong enough, the microorganisms cannot be wiped. For the accurate test, swab method is recommended.

The liquid overflowed from medium.

Add 1 ml of sterilized physiological saline and wait 15 minutes, use after complete absorption. Wiped-off areas may contain residual media components, cleaning with alcohol is recommended.

Is it possible to stamp directly on the food?

It is not recommended for the possibility of residual media components on the food.

should sterilized water be added 15 minutes before use?

Add it at least 15 minutes bofore to use. It can be kept refrigerated for up to 2 weeks, so it can be left out for later use.

What if there is a foreign object?

Wipe off as much foreign matter as possible. If it is difficult, swab method is recommended.

ACplus (R-AC) / For aerobic count

What is the difference of ACplus (R-AC) and "For aerobic count".

ACplus (R-AC) conteins original nutrients and redox indicator. These enable high detectvity and detection in a short time (24 hours). However, some microorganisms need 48 hours incubation.

What microorganisms are difficult to detect on the "For aerobic count".

Following microorganisms are difficult to detect.
・Lactic acid bacteria (reactivity of redox indicator is decreased by the produced acid)
・Gram-positive cocci such as some Micrococcus (high sensitivity to redox indicator)
・Some Pseudomonas

What microorganisms are difficult to detect on the ACplus (R-AC).

Following microorganisms may be needs 48 hours incubation.
・Lactic acid bacteria (Produced acid reduces the reactivity of redox indicator, or growth speed is slow)
・psychrophilic bacteria (slow growth and Low optimal temperature for growth)

No colonies are detected, even though the microorganisms should be present.

If there are so much miccroorganisms in the sample, colonies may disappere. Dilute sample appropriately.

Part of medium colored a large area.

Some molds make large and spread colonies. Count one block of the colored part as one colony.

After incubation for more than 48 hours, the number of colonies increased.

By the type and condition of microorganism, it may not grow after 48 hours incubation. However, the aerobic plate count is defined as the plate count obtained when cultured at 35°C for 48 hours under aerobic conditions. It is recommended to count after 48 hours incubation.

Can molds be detected on the ACplus and "For aerobic count"?

Some molds and yeasts also grow on the Acplus and "For aerobic count". These colonies are counted as total aerobic microbial count.

CC (For coliforms), EC (For E. coli and coliforms)

Detection mechanism of CC

The β-galactosidase activity of coliforms is used for detection by a chromogenic enzyme substrate (X-gal method). This method provides higher sensitivity than desoxycholate agar medium.

Detection mechanism of EC

E. coli has β-glucuronidase activity in addition to β-galactosidase activity. EC contains chromogenic enzyme substrates corresponding to each enzyme activity. It can distinguish E. coli and coliforms other than E. coli.

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

Enterohemorrhagic E. coli such as O157 are classified as E. coli, some of which do not have glucuronidase activity. Therefore, enterohemorrhagic E. coli that does not have glucuronidase activity are detected as coliforms in MC-Media Pad EC. Also, serotypes cannot be distinguished with MC-Media Pad.

After 2 days incubation, colonies were observed or increased.

Other than coliforms, some bacteria have β-galactosidase activity. Although the growth of these bacteria is inhibited, long incubation can not be inhibited these bacteria. Use with recommeded condition.

No colonies was detected in samples with high sugar content.

The detection performance of the chromogenic enzyme substrate may be reduced in samples with high concentrations of sugars such as glucose. Therefore, dilution is recommended for samples with high concentrations of sugars.

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?

Black colonies without blue to light blue color are not Staphylococcus aureus.

YM（For Yeast and Mold）

Is it possible to distinguish between yeast and mold?

Molds tend to form spread colonies, and yeasts form small colonies of about 1 to 2 mm.

Can all mold and yeast be detected in 48-72 hours?

High correlation was confirmed with the ISO21527-1 method for 48 hours or 72 hours. However, 72 hours incubation may be necessary for some therophilic molds and heat-resistant yeasts.

The medium surface appears pale pink before use.

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

What colors are detected for the colony other than red?

It may appear mixed with mold spores or pigment produced by yeast.

For salmonella

Is it possible to test Salmonella directly?

If the number of Salmonella in the sample is high, it can be detected. However if it is low, it may not be detected. Test with enrichment media is recommended normally. If it is expected that there will be many microorganisms other than Salmonella, test with selective enrichment media is recommended.

Can “For Salmonella” be used instead of CC?

"For Salmonella" is not intended to detect coliforms. Use the appropriate medium for your purpose.

EB（For Enterobacteriaceae）

What is red colonies without yellow zone.

It is not Enterobacteriaceae.

Why the upper limit of colonies as low as 100 colonies/plate?

Yellow zone spreads over the entire culture medium, it makes difficult to distinguish between Enterobacteriaceae and non-Enterobacteriaceae.

Are enterobacteria and enterobacteriaceae the same?

It is not the same. Enterobacteria contains many microorganisms, Enterobacteriaceae is part of the Enterobacteria.

The medium surface appears pale pink before use.

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

Hard to identify yellow zone.

Use a desk light and count in the bright environment.

Is it possible to inspect milk?

When milk is added directly, the medium may not turn purple and colonies may be difficult to count. Diluting the milk improves this problem.