Compact Dry™ X-SA

Cat. no. XSA100 Compact Dry™ X-SA, 60x75mm Tray with 10x60mm Well 100 trays/box

INTENDED USE

Hardy Diagnostics Compact Dry™ X-SA is a ready-to-use test method recommended for the isolation and enumeration of Staphylococcus aureus 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

Staphylococcus aureus is a significant food borne pathogen responsible for many outbreaks of food poisoning. However, S. aureus is readily destroyed by heat treatment and nearly all sanitizing agents.(1) Detection of S. aureus in processed foods is, therefore, a clear indication of poor sanitation. Consequently, monitoring S. aureus in food processing and distribution facilities is necessary to ensure high levels of quality and sanitation. Currently, the FDA recommends a direct plate count method followed by confirmatory coagulase and biochemical tests if more than 100 S. aureus cells/gm are expected. The most probable number (MPN) method is recommended for routine surveillance of products in which small numbers of S. aureus are expected.(1)

Compact Dry™ X-SA is a ready-to-use chromogenic medium for the detection of Staphylococcus aureus . 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™ X-SA contains two chromogenic substrates that result in light blue to blue colored colonies produced by S. aureus.

Compact Dry™ X-SA performs comparably to other dry film methods and to direct plating on Baird Parker Agar.(6) Compact Dry™ X-SA is AOAC validated (AOAC no. 081001) 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™ X-SA contains dehydrated culture media, a gelling agent, and two chromogenic substrates for color development. EDTA and antibiotics are also included in the medium to inhibit the growth of other bacteria, yeast, and mold.

Final pH 7.4 +/- 0.2 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 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.

S. aureus produces light blue to blue colonies. Count the total number of light blue to blue colonies to obtain S. aureus counts. 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 S. aureus may also grow on Compact Dry™ X-SA, but will produce white or red-purple colonies. Bacillus spp. may grow and produce large, flat, matte light blue to blue colonies that are easily differentiated from S. aureus colony morphology.

LIMITATIONS

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
Staphylococcus aureus
ATCC ® 6538
J 24hr 35-37°C Aerobic Growth; light blue to blue colonies
Staphylococcus aureus
ATCC ® 29213
J 24hr 35-37°C Aerobic Growth; light blue to blue colonies
Staphylococcus aureus
ATCC ® 25923
J 24hr 35-37°C Aerobic Growth; light blue to blue colonies
Staphylococcus epidermidis
ATCC ® 12228
J 24hr 35-37°C Aerobic Growth; white colonies
Escherichia coli
ATCC ® 8739
J 24hr 35-37°C Aerobic Inhibited

USER QUALITY CONTROL

PHYSICAL APPEARANCE

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

Compact Dry X-SA

Staphylococcus aureus (ATCC® 25923) colonies growing on Compact Dry X-SA (Cat. no. XSA100). Incubated aerobically for 24 hours at 35°C.

Compact Dry X-SA #2

Staphylococcus epidermidis (ATCC® 12228) colonies growing on Compact Dry X-SA (Cat. no. XSA100). Incubated aerobically for 24 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. Teramura, H., Mizuochi, S., & Kodaka, H. 2010. Evaluation of the compact dry X-SA method for enumerating Staphylococcus aureus in artificially contaminated food samples. Biocontrol science, 15(4): 149-154.

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

AOAC approval no. 081001
MicroVal approval no. 2008-LR14 per ISO 16140:2003/DAmd. 1:2009
NordVal approval no. 042

020416hh

Manufactured for and distributed by: