XLT-4 AGAR

Cat. no. G165 XLT-4 Agar, 15x100mm Plate, 18ml 10 plates/bag
Cat. no. G277 XLT-4 Agar, 15x60mm Plate, 7ml 10 plates/bag
Cat. no. J37 HardyCHROMô Salmonella / XLT-4 Agar, 15x100mm Biplate, 10ml/10ml 10 plates/bag
Cat. no. J127BX XLT-4 Agar/Brilliant Green Agar with Novobiocin, 15x100mm Biplate, 10ml/10ml 100 plates/box
Cat. no. J131 XLT-4 Agar / Brilliant Green Agar with Sulfadiazine, 15x100mm Biplate, 10ml/10ml 10 plates/bag

INTENDED USE

Hardy Diagnostics XLT-4 Agar is a highly selective plating medium for the detection and isolation of non-typhi Salmonella species.

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

SUMMARY

Numerous media have been developed for the isolation and differentiation of enteric bacteria, most designed to recover a broad spectrum of enteric pathogens. As a result of this, overgrowth of inconsequential bacteria can be a problem, when recovery of a specific species is desired. This is true of Salmonella isolation media where Proteus, Providencia, and Pseudomonas can interfere with the desired results.

Xylose-Lysine-Deoxycholate (XLD) media was developed as a selective and differential media for the isolation of gram-negative enteric pathogens. The sodium deoxycholate found in the XLD media is replaced by Tergitol 4 in Xylose-Lysine-Tergitol 4 (XLT-4) Agar. This addition makes XLT-4 more highly selective for Salmonella than its predecessor.(1-5)

Proteose Peptone No.3 in XLT-4 Agar provides a source of complex nitrogen compounds. Yeast extract is added to supply vitamins and co-factors. Differentiation on this medium is based on xylose, lactose, sucrose, lysine decarboxylation, and hydrogen sulfide production. The pH shifts in the medium due to the fermentation and decarboxylation reactions are visualized by the addition of phenol red. The Tergitol 4 in the XLT-4 Agar inhibits all gram-positive bacteria and molds, and inhibits the growth of numerous gram-negative bacteria including Proteus, Providencia and Pseudomonas species.(1-5) This attribute makes XLT-4 Agar excellent for the isolation and detection of non-typhi Salmonella.

FORMULA

Ingredients per liter of deionized water:*

Lactose 7.5gm
Sucrose 7.5gm
Sodium Thiosulfate 6.8gm
Sodium Chloride 5.0gm
L-Lysine 5.0gm
Xylose 3.75gm
Yeast Extract 3.0gm
Proteose Peptone No. 3 1.6gm
Ferric Ammonium Citrate 0.8gm
Phenol Red 80.0mg
Tergitol 4 4.6ml
Agar 18.0gm

Final pH 7.4 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Storage: Upon receipt store at 2-8ºC away from direct light. Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.

PRECAUTIONS

PROCEDURE

Specimen Collection: Consult listed references for information on sample collection.(5)

Samples should be submitted directly to the laboratory without delay and protected from excessive heat and cold.

1. Process the specimen as appropriate.

2. Inoculate a Salmonella enrichment broth (Tetrathionate Broth, Cat. no. K65, or Lactose Broth, Cat. no. K137) and incubate for 18-24 hours at 35°C.

3. Allow the plates to warm to room temperature, and the agar surface to dry before inoculating.

4. Streak for isolation with a sterile loop or swab.

5. Incubate plates aerobically at 35°C for 18-24 hours.

6. Examine colonial morphology, characteristics, and color reactions.

INTERPRETATION OF RESULTS

After 18-24 hours incubation, Salmonella colonies appear as black or black-centered with a yellow periphery. If the plates are incubated further, the colonies will become entirely black, or pink to red with black centers.(1-2) Salmonella strains that do not produce H2S appear pink-yellow on XLT-4 Agar. Citrobacter colonies will appear yellow without evidence of blackening. Escherichia coli and Enterobacter aerogenes colonies that are not inhibited will be yellow with no blackening. Growth of Proteus, Providencia, Pseudomonas, Alteromonas putrefaciens, Yersinia enterocolitica, and Acinetobacter calcoaceticus are partially to completely inhibited on XLT-4 Agar.

LIMITATIONS

Rare strains of Salmonella do not produce H2S and will not appear black on XLT-4 Agar. However, these colonies will be pink to pinkish yellow, which differentiates them from the bright yellow colonies of non-Salmonella species.

XLT-4 Agar is used to aid in the isolation and differentiation of Salmonella species. Additional biochemical and serological tests are required for complete identification. See listed references for more information.(1-5)

Some strains of Salmonella may fail to grow, or grow poorly on this medium due to nutritional variances.

Non-Salmonella strains that are not completely inhibited on XLT-4 Agar may be encountered, and must be differentiated from Salmonella. Consult listed references for more information.(1-5)

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, 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
Salmonella enterica
ATCC® 14028
A 18-24hr 35°C Aerobic Growth; yellow to red colonies with black centers
Escherichia coli
ATCC® 25922
B 18-24hr 35°C Aerobic Partial to complete inhibition; yellow colonies
Proteus mirabilis
ATCC® 12453
B 18-24hr 35°C Aerobic Inhibited
Staphylococcus aureus
ATCC® 25923
B 18-24hr 35°C Aerobic Inhibited

User Quality Control

PHYSICAL APPEARANCE

XLT-4 Agar should appear slightly opalescent, and red in color.

S. typhimurium growing on XLT-4 Agar

Salmonella enterica (ATCC® 14028) colonies growing on XLT-4 Agar (Cat. no. G165). Incubated aerobically for 24 hours at 35°C.

E. coli inhibited on XLT-4 Agar

Escherichia coli (ATCC® 25922) growth inhibited on XLT-4 Agar (Cat. no. G165). Incubated aerobically for 24 hours at 35°C.

REFERENCES

1. Miller, R.G., et al. 1992. Xylose-Lysine-Tergitol 4: An improved selective agar medium for the isolation of Salmonella. Poultry Science; 71:398.

2. Miller, R.G., et al. 1991. Xylose-Lysine-Tergitol 4: An improved selective agar medium for the isolation of Salmonella. Poultry Science; 70:2429-2432.

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

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

5. USDA/FSIS. Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized Egg, and Catfish Products and Carcass and Environmental Sponges. Microbiology Laboratory Guidebook. CH 4.08.


ATCC is a registered trademark of the American Type Culture Collection.

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