Compact Dry™ EC
|Cat. no. EC100||Compact Dry™ EC, 60x75mm Tray with 10x60mm Well||100 trays/box|
Hardy Diagnostics Compact Dry™ EC is a ready-to-use test method recommended for the isolation and enumeration of coliforms and Escherichia coli 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.
Historically, routine testing to assess the sanitary quality of foods has focused on the detection and enumeration of indicator organisms rather than pathogens. Consequently, the coliform group of organisms is recognized as the principal indicator of unsanitary conditions. Coliforms are characterized as facultative anaerobic, gram-negative, lactose-fermenting rods. (1) They are present in the intestinal tract of man and other mammals, and non-fecal coliforms are found in many areas of the environment, including in soil and on plants. Coliforms, such as Citrobacter, Klebsiella, and Enterobacter , are phenotypically similar to Escherichia coli , the principal indicator organism of fecal contamination. Currently, methods for E. coli and coliform enumeration include the Most Probable Number (MPN) method, the LST-MUG method, membrane filtration tests, or plating on Violet Red Bile Agar (VRBA). (1-5)
Compact Dry™ EC is a ready-to-use chromogenic medium for performing E. coli and coliform 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™ EC contains two chromogenic substrates, Magenta-Gal and X-Gluc, that yield a colored reaction when utilized and permit the differentiation of E. coli from other members of the coliform group.
Compact Dry™ EC performs
the FDA MPN method for enumeration of E.
coli and coliform bacteria. (6)
Compact Dry™ EC is AOAC
validated ( AOAC no. 110402)
trays save space
and greatly reduce the time needed to perform microbiological
testing. Compared to other commenly used culture systems,
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™ EC contains dehydrated culture media, a gelling agent, and the chromogenic substrates, 5-bromo- 6-chloro-3-indoxyl-beta-D-galactopyranoside (Magenta-Gal) and 5-bromo-4-chloro-3-indoxyl-beta-D-glucuronic acid, cyclohexylammonium salt (X-Gluc) to assist in differentiating E. coli from other coliforms.Final pH 7.0 +/- 0.2 at 25°C
STORAGE AND SHELF LIFE
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 24 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.
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.
Pink-purple colonies are indicative of coliforms and blue-colored colonies are indicative of Escherichia coli. Count the total number of blue colonies to obtain E. coli count. Count all pink-purple and blue-colored colonies to obtain the total coliform 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.
Bacteria other than coliforms may grow, such as Pseudomonas spp., but will produce colorless or yellow colonies and should not be included in the total coliform count.
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.
E.coli O157 will not appear as typical blue-colored colonies on Compact Dry™ EC, because E. coli O157 does not produce the enzyme β-glucuronidase required to react with X-Gluc to form the blue color. E. coli O157 develops pink-purple colonies on Compact Dry™ EC, similar to other members of the coliform group.
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.
|Test Organisms||Inoculation Method*||Incubation||Results|
ATCC ® 8739
|J||24hr||35-37°C||Aerobic||Growth; blue colonies|
| Klebsiella pneumoniae
ATCC ® 13883
|J||24hr||35-37°C||Aerobic||Growth; pink-purple colonies|
| Pseudomonas aeruginosa
ATCC ® 9027
|J||24hr||35-37°C||Aerobic||Growth; white-yellow colonies|
| Bacillus subtilis
ATCC ® 6633
| Staphylococcus aureus
ATCC ® 6538
USER QUALITY CONTROL
Compact Dry™ EC should appear dry, free of particles, and light yellow in color.
Escherichia coli (blue, ATCC® 8739) and Klebsiella pneumoniae (pink, ATCC® 13883) colonies growing on Compact Dry EC (Cat. no. EC100). Incubated aerobically for 24 hours at 35°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.
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. 2006. "Comparison of the Compact Dry EC with the Most Probable Number Method (AOAC Official Method 966.24) for Enumeration of Escherichia coli and Coliform Bacteria in Raw Meats: Performance-Tested Method 110402." Journal of AOAC International 89(1): 100-114.
ATCC is a registered trademark of the American Type Culture
Compact Dry™ is a trademark of Nissui Pharmaceutical Co., Ltd.
AOAC approval no. 110402
MicroVal approval no. 0806-004LR per ISO 16140:2003 and no. 0806-005LR per ISO 16140:2003
NordVal approval no. 036
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