Compact Dry™ TC

Cat. no. TPC100 Compact Dry™ TC, 60x75mm Tray with 10x60mm Well 100 trays/box


Hardy Diagnostics Compact Dry™ TC is a ready-to-use test method recommended for the determination of total aerobic bacterial counts 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.


Microbiological testing is a common practice in food and related industries to ensure product quality and a high level of environmental control. Foods, beverages, and similar finished products are usually not sterile. However, in order to ensure they are safe for human consumption, maximum cell load numbers for the finished product, as well as for raw materials used to produce them, have been established. Procedures for determining aerobic plate count (APC) of foods were developed by the Association of Official Analytical Communities (AOAC)(5) and the American Public Health Association (APHA).(2-4) Conventional plate count methods for examining frozen, chilled, precooked, or prepared foods and the automated spiral plate count method for the examination of foods and cosmetics are outlined in FDA Bacterial Analytical Manual.(1)

Compact Dry™ TC is a ready-to-use chromogenic medium for performing total viable aerobic bacterial 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. Colonies grown on Compact Dry™ TC turn red due to the redox indicator, tri-phenlytetrazolium chloride (TTC).

Compact Dry™ TC is comparable to other dry film test methods and to the spiral plate method.(6) Compact Dry™ TC is AOAC validated (AOAC no. 010404) 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.


Compact Dry™ TC contains dehydrated culture media, a gelling agent, and the redox dye, 2,3,5-triphenyl tetrazolium chloride (TTC), to facilitate differentiation of colony growth.

Final pH 7.0 +/- 0.2 at 25°C




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 dilution 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 35-37°C for 48 hours. NOTE: Use the appropriate temperature/time designation according to the legal specification of the prescribed food analysis regulation.

6. 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.

Alternate Membrane Filter Method:

1. Remove the plate cap and pipet 1.0ml of sterile water into the middle of a dry Compact Dry TC sheet. Set aside.

2. Using sterile forceps, pick up a sterile membrane filter.

3. Remove the funnel from a sterilized filtering device and set the sterilized membrane filter in place.

4. Set the funnel and pour the sample into the funnel. Filter the sample under reduced pressure.

5. After filtering, wash the inner surface of the funnel with 20-30ml of sterile water and filter. Repeat this step two or three times.

6. Detach the funnel and remove the membrane filter with sterile forceps. Place the filter--trap side up--on the pre-moistened Compact Dry TC sheet, making sure to avoid trapping air bubbles between the filter and the plate.

7. Recap and invert the plate and incubate under prescribed conditions.


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

Most colonies will be red due to reduction of TTC. Count all colonies, regardless of pigmentation, to obtain the total aerobic 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.


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.

Since some microorganisms may not reduce TTC and develop red/pink color, colonies that are not necessarily a clear red color could develop.

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, molded grid lines in the tray, 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.

Some microorganisms may not reduce TTC and may fail to develop red-colored colonies. Count all colonies present, regardless of red pigmentation.


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 Mini Light Box II (Cat. no. 378642000), incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Bacillus subtilis
ATCC ® 6633
J 48hr 35-37°C Aerobic Growth; red colonies
Escherichia coli
ATCC ® 8739
J 48hr 35-37°C Aerobic Growth; red colonies
Klebsiella pneumoniae
ATCC ® 13883
J 48hr 35-37°C Aerobic Growth; red colonies
Pseudomonas aeruginosa
ATCC ® 9027
J 48hr 35-37°C Aerobic Growth; red colonies
Staphylococcus aureus
ATCC ® 6538
J 48hr 35-37°C Aerobic Growth; red colonies



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

Compact Dry TC

Staphylococcus aureus (ATCC® 6538) and Escherichia coli (ATCC® 8739) colonies growing on Compact Dry TC (Cat. no. TC100). Incubated aerobically for 48 hours at 35°C.


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

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

6. Kodaka, Hidemasa, et al. 2005. "Comparison of the compact dry TC method with the standard pour plate method (AOAC Official Method 966.23) for determining aerobic colony counts in food samples: performance-tested method." Journal of AOAC International 88(6): 1702-1713.

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

AOAC approval no. 010404
MicroVal approval no. RQA2007LR01 per ISO 16140:2003
NordVal approval no. 033


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