Compact Dry™ YM

Cat. no. YM100 Compact Dry™ YM, 60x75mm Tray with 10x60mm Well 100 trays/box

INTENDED USE

Hardy Diagnostics Compact Dry™ YM is a ready-to-use test method recommended for the isolation and enumeration of yeast and mold in raw materials, finished products, or on environmental surfaces pertaining to food and related industries.

This product is not intended to be used for the diagnosis of human disease.

SUMMARY

Fungi (yeast and mold) are a large, diverse group of organisms that can live in a wide range of environments. Most fungi are obligate aerobes and can grow in broad pH and temperature ranges. This makes them capable of thriving in many types of foods, causing varying degrees of food spoilage.(1) Currently, dilution plating and direct plating methods are outlined by the FDA to detect fungi in foods.(1)

Compact Dry™ YM is a ready-to-use chromogenic medium for yeast and mold counts that contains dehydrated culture media and a cold water-soluble gelling agent in a non-woven cloth matrix. The medium is instantly hydrated when inoculated with a sample, and capillary action diffuses the sample evenly over the matrix to form a gel within seconds. Compact Dry™ YM contains the chromogenic substrate, X-Phos, that yields a blue-green color when utilized by most yeast species.

Compact Dry™ YM performs comparably to plating on Dichloran Rose Bengal Chloramphenicol (DRBC) Agar.(6) Compact Dry™ YM is AOAC validated (AOAC no. 100401) and the ready-to-use trays save space and greatly reduce the time needed to perform microbiological testing. Compared to other commenly used culture systems, Compact Dry ™ has a longer shelf life, can be stored at room temperature, does not require manual sample spreading, is rigid, stackable and easy to label, and allows for direct colony picking for further subculture.

FORMULA

Compact Dry™ YM contains dehydrated Potato Dextrose Agar, a gelling agent, and the chromogenic substrate, 5-bromo-6-chloro-3-indoxyl phosphate (X-Phos) to differentiate yeast colonies. A reduced pH and antibiotics in the medium inhibit the growth of unwanted bacteria.

Final pH 5.5 +/- 0.3 at 25°C

STORAGE AND SHELF LIFE


PRECAUTIONS


PROCEDURE


Method of Use:

1. Remove the set of four trays from the foil pouch and separate each individual tray by gently bending along the connecting edge until each tray snaps free. Alternatively, if setting up a series of the same sample, trays can be left connected to facilitate reading similar samples. Trays that are not used immediately should be resealed in the foil pouch. Refer to the "Storage and Shelf Life" section for proper storage of unused trays.

2. Remove the lid of the tray using two fingers to hold down one end of the lid and the thumb to lift the opposite end. Lids are easier to remove using a “peel back” method as opposed to a “pull off” method.

3. Inoculate by pipetting 1ml of sample directly to the center of a dry tray well, being careful not to touch the surface of the matrix with the pipet tip. Once dispensed, the sample will automatically diffuse across the surface by capillary action to form a gel; manual spreading of the inoculum is discouraged. Remember to account for the sample inoculum when calculating the dilution series.

4. Replace the lid and label the tray with appropriate information, including the sample dilution factor.

5. Invert the tray and incubate, upside down with the medium on top, at 25-30° C for 3-7 days. NOTE: Use the appropriate temperature/time designation according to the legal specification of the prescribed food analysis regulation.

6. Read plates twice; once at 3 days, and again at 5-7 days per user discretion.

7. Count colonies illuminated from the backside of the tray to calculate CFU/ml using the Mini Light Box II (Cat. no. 378642000) or comparable back lighting. If the colony count is high, use the 1cm x 1cm molded grid on the back of the tray to assist in colony counting. Use a sheet of white paper with gridded lines to diffuse the light if the molded grids in the tray are difficult to visualize with a light box.

INTERPRETATION OF RESULTS

After incubation, read trays against a white background such as the Mini Light Box II (Cat. no. 378642000) or comparable back lighting.

Blue-green colonies are indicative of yeast. Molds form cottony colonies with characteristic colors. Count all colonies present to obtain the total yeast and mold count. The growth area is 20cm2. If the colony count is high, the total count can be obtained by multiplying the average number of colonies observed in one 1cm x 1cm square grid by 20.

LIMITATIONS

Some yeast do not form blue colonies.

During inoculation, do not touch the surface of medium and be careful to avoid any contamination by airborne microorganisms.

During incubation, keep cap tight on plates to avoid any possible dehydration.

A dilution may be needed when the sample has a dark color.

When the sample is viscous (thick), pipetting the sample on several points on a plate or an additional dilution may be needed for an even suspension.

When the sample contains an enzyme, it may react with the enzyme substrate in the dry sheet and affect the color.

If the nature of sample does affect the reaction of the medium, inoculate only after the factor is eliminated by means of dilution and other techniques (e.g. samples with high viscosity, colored, reactive with chromogenic substrate, and with a high or low pH).

It is recommended to use a stomacher and filter homogenized sample afterwards to eliminate carry over of tiny particles of foodstuff onto the surface of the medium.

Counting colonies may be difficult against a dark background. For best results, count colonies with the tray held against a white background such as with the Mini Light Box II (Cat. no. 378642000).

If using a light box, the molded grid lines or colonies may be difficult to view due to excessive brightness. Diffuse the light using a sheet of white, gridded (1cm x 1cm) paper underneath the tray to facilitate colony counting.

Colonies are not distinguishable on trays if concentrations are above 100 CFU/ml, as high colony counts will result in the whole surface becoming colored. The sample should be diluted to a concentration of less than 100 CFU/ml for best use.


MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, swabs such as EnviroTrans™, applicator sticks, scoops, dilution buffers such as Dilu-Lok™ II, other culture media, a light box (Cat. no. 378642000), incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Candida albicans
ATCC ® 60193
J 72hr 25-30°C Aerobic Growth; white-light blue colonies
Candida albicans
ATCC ® 10231
J 72hr 25-30°C Aerobic Growth; white-light blue colonies
Aspergillus brasiliensis
ATCC ® 16404
J 72hr 25-30°C Aerobic Growth; blue-black colonies
Bacillus subtilis
ATCC ® 6633
J 72hr 25-30°C Aerobic Inhibited
Escherichia coli
ATCC ® 8739
J 72hr 25-30°C Aerobic Inhibited

USER QUALITY CONTROL

PHYSICAL APPEARANCE

Compact Dry™ YM should appear dry, free of particles, and light yellow in color.

Compact Dry YM

Candida albicans(ATCC® 10231) colonies growing on Compact Dry YM (Cat. no. YM100). Incubated aerobically for 72 hours at 35°C.

Compact Dry YM #2

Aspergillus brasiliensis (ATCC® 16404) colonies growing on Compact Dry YM (Cat. no. YM100). Incubated aerobically for 72 hours at 35°C.

REFERENCES

1. Association of Official Analytical Communities.Official Methods of Analysis. AOAC, Washington, D.C.

2. American Public Health Association. Standard Methods for the Examination of Dairy Products. APHA, Washington, D.C.

3. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods. APHA, Washington, D.C.

4. U.S. Food and Drug Administration. Bacteriological Analytical Manual. Arlington, VA
http://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/ucm2006949.htm

5. American Public Health Association. Standard Methods for the Examination of Water and Wastewater. APHA, Washington, D.C.

6. Kodaka, Hidemasa, et al. 2006. "Comparison of the Compact Dry YM with the FDA BAM Method for Enumeration of Yeasts and Molds in Fruit-Based Products: Performance-Tested Method 100401." Journal of AOAC International, 89(1): 127-138.


ATCC is a registered trademark of the American Type Culture Collection.
Compact Dry™ is a trademark of Nissui Pharmaceutical Co., Ltd.

AOAC approval no. 100401
MicroVal approval no. RQA2008LR10 per ISO EN 16140:2003
NordVal approval no. 043

020416hh

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