FilmplateTM mold & yeast count plate

1. Principle & application scope

Molds and yeasts exist widely in air, water and soil. Most of them are harmless, but some are harmful for human health, such as aspergillus flavus. It could secrete aflatoxin which is a strong carcinogen. Mold can stimulate human stomach and intestine, even cause food poisoning and injure liver. Filmplate^TM mold & yeast count plate which consists of nutrient medium, bibulous gel, and chromogenic reagent could greatly save the time of medium preparation, disinfection, and dish cleaning. This kind of plate which is easy to use and very convenient could be widely used in institutes of food hygiene inspection and food factories.

Executive standard: National food safety standard

Food microbiological examination: Enumeration of molds and yeasts (GB 4789.15)

2. Using method

2.1 Sample preparation: Prepare 1:10 dilution by placing 25mL (g) of sample into 225mL of sterile distilled water, then prepare 1:100 dilution by sucking 1mL of dilution (1:10) into 9mL of sterile distilled water. By analogy, prepare tenfold increasing serial dilution of sample.

2.2 Inoculation: Select 2~3 appropriate dilutions to do the test for ordinary food, while for some liquid sample which has little coliform, directly suck original sample to do the test. Place the count plate onto sterile experiment table; uncover the film on the surface. Suck 1mL of solution with sterile pipette, and then drip it slowly and evenly onto the count plate, cover the film gently and stand it for 10s to let the medium solidify. Inoculate two count plates for each dilution, and in the meantime do a blank control.

2.3 Culture: Superimpose these count plates and place them back into original ziplock bag. Seal it well and put it in the incubator at 28℃±1℃ for 48-72hs with the transparent side up. The quantity of superimposed count plates should not be more than 12.

3. Results

Mold and yeast would show blue spots after cultivation, colony of mold is radial and relatively large, while colony of yeast is relatively small, round and smooth. 

4. Counting method and report

4.1 Counting 

4.1.1 Select the count plates of which the colony quantity is between 10CFU and 150CFU to do the counting. Multiply the average number of colonies by the corresponding dilution multiple.

4.1.2 If the average numbers of colonies on count plates from all dilutions are more than 150CFU, select the count plates of maximum dilution to do the counting, then multiply the average number by corresponding dilution multiple as report data, other count plates can be recorded as TNTC (too numerous to count). (see Example 1 in the following table)

4.1.3 If the average numbers of colonies on count plates from all dilutions are less than 10CFU, count the average number of colonies on count plates of the minimum dilution, then multiply it by the minimum dilution multiple. (see Example 2 in the following table)

4.1.4 If no colonies was found on the count plates from all dilutions (incl. original liquid sample), report it in terms of less than one multiplied the minimum dilution multiple. (see Example 3 in the following table)

4.2 Report

4.2.1 If the quantity of colonies is less than 100CFU, round it as per rounding-off rule and use two effective digits to report it in terms of scientific notation.

4.2.2 If the quantity of colonies is not less than 100, round the third digit as per rounding-off rule, and use the first two digits to report it in terms of scientific notation.

4.2.3 Use CFU/g as report unit for solid sample, and use CFU/mL as report unit for liquid sample.

5. Additional explanatory note

Mold and yeast widely spread in air in the form of spore. It is demanded that mold and yeast cannot be detected in most samples; therefore, it is essential to operate carefully when using Filmplate^TM mold and yeast count plate. All the sampling tools, diluted water, sucker and other utensils should be thoroughly disinfected. In order to avoid airflow during the inoculation, inoculate as quickly as possible. It’s better to make two blank controls with sterilized saline to avoid the false positive results.

6. Preservation condition

This kind of count plate should be placed in the fridge at 4℃-10℃, and the expiration time is one year. Once the package is opened, those unused count plates should be placed back to the package and then seal it well. Store them in the fridge and exhaust them within one month. Condensation may occur in high humid environment, it is better to warm it to room temperature before unfolding the package.