MANNITOL SALT AGAR (MSA)

Cat. no. J330 Tryptic Soy Agar (TSA) / Cetrimide (CET) / Mannitol Salt Agar (MSA), 15x100mm Triplate, 7ml/section 10 plates/bag

INTENDED USE

Hardy Diagnostics Mannitol Salt Agar (MSA) is recommended for use as a selective and differential medium for the isolation of pathogenic staphylococci.

SUMMARY

Koch reported the use of a medium containing 7.5% sodium chloride as a selective agent for the isolation of staphylococci in 1942.(5) The results were confirmed and improved by Chapman in 1945 by the addition of this salt concentration to Phenol Red Mannitol Agar, as Staphylococcus aureus usually ferments mannitol.(3) Non-pathogenic staphylococci usually show less luxuriant growth on this medium after the incubation period.

A sodium chloride, concentration of 7.5%, is nearly ten times the usual concentration seen in most media. It serves to inhibit most organisms except staphylococci in mixed flora specimens. The beef extract and peptones supply the essential elements carbon, nitrogen, and sulfur. Mannitol is added to show the fermentation capabilities of the organisms. Acid production as the result of fermentation of this sugar results in the formation of colonies with a yellow zone. Those staphylococci that do not ferment mannitol show a purple or red zone around the colonies.

Mannitol Salt Agar (MSA) is recommended by the American Public Health Association for the enumeration of staphylococci in food and dairy products.(9,10)

FORMULA

Ingredients per liter of deionized water:*

Sodium Chloride 75.0gm
Proteose Peptone 10.0gm
Mannitol 10.0gm
Beef Extract 1.0gm
Phenol Red 0.025gm
Agar 15.0gm

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 specimen collection.(1,2,4,7) Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport media and refrigerated until inoculation.

Method of Use: Allow the plates to warm to room temperature and the agar surface to dry before inoculating. Heavily inoculate and streak the specimen as soon as possible after collection. If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface. Streak for isolation with a sterile loop. Incubate plates aerobically at 35-37ºC for 24-48 hours. Examine colonial morphology.

INTERPRETATION OF RESULTS

Mannitol fermentors such as S. aureus appear as yellow colonies with yellow zones in the media. Non-mannitol fermentors such as S. epidermidis, if present, will have clear pink to red colonies with no yellow color change in the medium. Consult listed references for the identification of colony morphology and further biochemical tests required for identification.(1,2,4,7)

LIMITATIONS

Most organisms other than staphylococci are inhibited by the high salt concentration found in Mannitol Salt Agar except for some halophillic marine organisms.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, swabs, applicator sticks, other culture media, incinerators, 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 18hr 35°C Aerobic Growth; yellow colonies and media at 18-24 hours
Escherichia coli **
ATCC® 8739
B 72hrs 35°C Aerobic Partial to complete inhibition

USER QUALITY CONTROL

Physical Appearance

Mannitol Salt Agar (MSA) should appear clear, slightly opalescent, and pinkish-red in color.

S. aureus growing on Mannitol Salt Agar

Staphylococcus aureus (ATCC® 25923) colonies growing on Mannitol Salt Agar. Incubated aerobically for 48 hours at 35ºC.

P. mirabilis inhibited on Mannitol Salt Agar

Proteus mirabilis (ATCC® 12453) growth inhibited on Mannitol Salt Agar. Incubated aerobically for 48 hours at 35ºC.

REFERENCES

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

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

3. Chapman, G.H. 1945. J. Bacteriol.; 50:201.

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

5. Koch, F.E. 1942. Zentr. Bakt. Labt. Orig.; 149:122.

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

7. Jorgensen, J.H., et al. 2015. Manual of Clinical Microbiology, 11th ed. American Society for Microbiology, Washington, D.C.

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

9. American Public Health Association. 1993. Standard Methods for the Examination of Dairy Products, 16th ed. APHA, Washington, D.C.

10. APHA Technical Committee on Microbiological Methods for Foods. 2001. Compendium of Methods for the Microbiological Examination of Foods, 4th ed. APHA, Washington, D.C.

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

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