SELENITE CYSTINE BROTH

Cat. no. K69 Selenite Cystine Broth, 16x125mm Tube, 10ml 20 tubes/box

INTENDED USE

Hardy Diagnostics Selenite Cystine Broth is recommended for the selective enrichment of Salmonella spp. in clinical and non-clinical specimens.

SUMMARY

Leifson, in 1936, described the ability of Selenite Broth to enrich the cultivation of salmonellas while inhibiting other microorganisms. Leifson found coliforms and fecal streptococci to be inhibited by selenite, thereby permitting growth of Salmonella organisms. (7)

Selenite Cystine Broth is a modification of Leifson's formulation. The Food and Drug Administration first proposed the cystine formulation for use as an enrichment medium for detecting Salmonella in food materials. It is useful in detecting Salmonella when low numbers of organisms are present in stool. (2) It is also recommended for use in detecting Salmonella in food and water. (8-9)

Amino acids and other nitrogenous substances are provided by enzymatic digests of casein and animal tissue. L-Cystine is incorporated into the medium to improve the recovery of Salmonella . Phosphate is added to maintain a stable pH, in addition to decreasing the toxicity of selenite. Lactose also serves to maintain an optimal pH. Bacteria that reduce selenite produce alkali, which increases pH. Acid produced by lactose fermentation causes a decrease in pH, thereby maintaining a neutral or slightly decreased pH. Gram-positive organisms are inhibited by the presence of sodium selenite.

FORMULA

Ingredients per liter of deionized water:*

Sodium Phosphate 10.0gm
Tryptone 5.0gm
Lactose 4.0gm
Sodium Selenite 4.0gm
L-Cystine 0.01gm

Final pH 7.0 +/- 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. Products should not be used if there are any signs of deterioration, 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 specimen collection. (1-4, 6) Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. Specimens should be delivered to the laboratory within 2-3 hours. Special attention is required for stools. They should be collected early in the course of the disease and need to be cultured within two hours after collection. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport medium and refrigerated until inoculation.

Method of use:

1. Place 1.0gm of feces or 1ml of liquid stool in tube. Swab specimens may be inserted directly into the broth.

2. Emulsify the specimen thoroughly.

3. Incubate aerobically for 18 to 24 hours at 35ºC.

4. Place one to two drops of the incubated broth onto selective plate media, such as MacConkey or Hektoen Enteric (HE) Agar and streak for isolated colonies.

5. Incubate aerobically at 35ºC.

6. Examine for pathogens in 18-48 hours.

INTERPRETATION OF RESULTS

Culture analysis is made from the media to which the enriched specimen is subcultured. Consult listed references for the interpretation of growth and other identification tests to identify growth of organism in the medium to which subculture has been made. (1-6)

LIMITATIONS

The recovery of many Salmonella is greatly jeopardized if stool specimens remain unpreserved for more than three hours before processing. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport medium and refrigerated until inoculation.

A brick red precipitate may appear if Selenite Cystine Broth is overheated during preparation or exposed to excessive moisture during storage.

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
I 24hr 35°C Aerobic Growth
Shigella sonnei
ATCC ® 9290
I 24hr 35°C Aerobic Growth**
Escherichia coli
ATCC ® 25922
I 24hr 35°C Aerobic Growth

**Note: Selenite Cystine Broth is inoculated with organism, incubated for 18-24 hours, then subcultured to a MacConkey Agar plate. The MacConkey plate should show heavy growth of Salmonella after 24 hours. E. coli will show partial to complete inhibition. Shigella should grow but recovery is variable.

User Quality Control

PHYSICAL APPEARANCE

Selenite Cystine Broth should appear clear, with a slight opalescence and very light precipitate, and light orange in color.

REFERENCES

1. Anderson, N.L., et al. 2005. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

2. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

5. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria , Vol. I. Williams & Wilkins, Baltimore, MD.

6. Quality Assurance for Commercially Prepared Microbiological Culture Media , M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

7. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

8. Speck. 1984. Compendium of Methods for the Microbiological Examination of Foods , 2nd ed. APHA, Washington, D.C.

9. Greenberg, et al. 1985. Standard Methods for the Examination of Water and Wastewater , 16th ed. APHA, Washington, D.C.


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