Compact Dry™ SL
|Cat. no. SL100||Compact Dry™ SL, 60x75mm Tray with 10x60mm Well||100 trays/box|
Hardy Diagnostics Compact Dry™ SL is a ready-to-use test method recommended for the isolation and enumeration of Salmonella 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.
Salmonella was discovered in 1895 by Theobald Smith, laboratory assistant for Dr. Daniel Elmer Salmon, after whom the genus is named. The bacterium, Salmonella enterica var. Choleraesuis, was identified as the causative agent of hog cholera, though this identification later proved false. However, continued research with this bacterium showed that Salmonella is an important agent of foodbourne disease. Today,Salmonella is estimated to cause more than 1.2 million illnesses each year in the United States alone. Of these, 23,000 cases result in hospitalization and 450 result in death. Salmonella is transmitted via a fecal-oral route, which is most often acquired through consumption of contaminated foods. Thus, it is of great importance that food manufacturers screen for and detect any food contaminated with the bacterium.
Compact Dry™ SL is a ready-to-use chromogenic medium for performing Salmonella 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™ SL contains a chromogenic substrate that causes Salmonella colonies to turn green when utilized.
Compact Dry™ SL comes in ready-to-use trays that save space and greatly reduce the time needed to perform microbiological testing. Compared to other commonly 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™ SL contains dehydrated culture media, a gelling agent, and a chromogenic substrates to assist in detecting and differentiating Salmonella bacteria.Final pH 7.0 +/- 0.2 at 25°C.
STORAGE AND SHELF LIFE
Method of Use:
1. Enrich sample in a 1:9 ratio in Buffered Peptone Water (Cat.no. D080) for 20-24 hours at 35-37 degrees C.
2. 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.
3. 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.
4. Inoculate by pipetting 0.1 ml of sample onto the dry sheet about 1 cm from the edge of the tray, being careful not to touch the surface of the matrix with the pipet tip. The dispensed sample will remain at the point of inoculation and will not spread across the whole plate.
5. After inoculation of the enriched culture, pipet 1 ml of sterilized water at the opposite side of the plate from where the specimen was dropped. Once dispensed, the sterile water will automatically diffuse across the surface by capillary action to form a gel; manual spreading of the inoculum is discouraged.
6. Replace the lid and label the tray with appropriate information, including the sample dilution factor.
7. Invert the tray and incubate, upside down with the medium on top, at 41-43°C for 20-24 hours. NOTE: Use the appropriate temperature/time designation according to the legal specification of the prescribed food analysis regulation.
8. Visualize colonies 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.
Green or blue-green colonies with or without black centers and on a yellow background are indicative of Salmonella.
Bacteria other than Salmonella may grow and produce a yellow background at the site of inoculation, such as Pseudomonas spp., but will not produce green colonies.
Shigella sonnei is known to produce a positive reaction on these plates.
During inoculation, do not touch the surface of the 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.
|Test Organisms||Inoculation Method*||Incubation||Results|
Salmonella enterica var. Typhimurium
|J||24hr||41-43°C||Aerobic||Growth; yellow agar with green colonies|
|J||24hr||41-43°C||Aerobic||Growth; yellow agar with green colonies|
USER QUALITY CONTROL
Compact Dry™ SL should appear dry, free of particles, and blue-purple in color.
Salmonella enterica subsp. enterica serovar Typhimurium (ATCC® 14028) on Compact Dry SL, grown under aerobic conditions at 42°C for 24 hours.
Salmonella enterica subsp. enterica serovar Enteritidis (ATCC® 13076) on Compact Dry SL, grown under aerobic conditions at 42°C for 24 hours.
REFERENCES1. 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. Ellis, P., G. Kirchhof, and R. Meldrum. 2003. Evaluation of the Compact Dry SL method for the detection of Salmonella in spiked food samples. Poster presentation at HPA 1st Scientific Conference, University of Warwick.
ATCC is a registered trademark of the American Type Culture Collection.
Compact Dry™ is a trademark of Nissui Pharmaceutical Co., Ltd.
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