MRSA MSA MODIFIED AGAR

Technical Data #1778a / 2005.08.18

MRSA MSA Modified Agar is a solid medium used for the detection of oxacillin-resistant Staphylococcus aureus. High concentration of salt increases production of Staphylococcus aureus and release of beta-lactamase.


FORMULA
in grams per liter purified filtered water

Casein Peptone

5,0

Meat Peptone

5,0

Beef Extract

1,0

D-Mannitol

10,0

Sodium Chloride

75,0

Phenol Red

0,025

Agar

15,0

Antibiotic

 

Cefoxitin

0,008

 

pH 7,4 +/- 0,2 25 C

This approximate formula may be adjusted and/or enriched to obtain best results.


PRECAUTIONS
This medium is for laboratory use only.


STORAGE
Store prepared media at 2-8 C protected from direct light and dehydrated powder, in a dry place, in tightly-sealed containers at 2-25 C.


SIGN OF DETERIORATION
Media should not be used if the expiry date has passed. Prepared media should not be used if there are signs of contamination or deterioration (shrinking, cracking, evaporation or discoloration). Do not use dehydrated media if it is caked.


DIRECTIONS
Suspend 111 g of dehydrated media in 1000 ml of purified filtered water. Heat with frequent agitation and boil for one minute. Sterilize at 121 C for 15 minutes. Cool to 45-50 C and aseptically add a 8 mg of sterile cefoxitin solution. Mix gently and dispense into sterile Petri dishes.


PROCEDURE
Prior to inoculate, the prepared media should be brought to room temperature.

  1. Into a Mueller Hinton Broth with 4-5 similar colonies from an overnight growth, prepare a solution and adjust to 0,5 Mc Farland Standard.
  2. Inoculate plates by a straight line on the surface.
  3. Incubate at 35 C for 24 hours.


QUALITY CONTROL

Results after 24 hrs at 35C

Organisms

ATCC

Growth

Staphylococcus aureus

25923

-

Staphylococcus aureus

25913

-

Staphylococcus aureus

43300

+


LIMITATIONS OF METHOD
This medium is only a part of the identification.
Other tests may be required.


REFERENCES

  1. Lally, R.T., M.N. Ederer, B.F. Woolfrey 1985 Evaluation of Mannitol Salt Agar with Oxacillin as a Screening Medium for Methicillin-Resistant Staphylococcus aureus. J. Clin. Microbiol. 22:501-504.
  2. La Zonby, J.G., M.J. Starzyk 1986 Screening Method for Recovery of Methicillin-Resistant Staphylococcus aureus from Primary Plates J. Clin. Microbiol. 24:186-188
  3. Mc Dougal, L.K., C. Thornsberry. 1984 New recommendations for disk diffusion antimicrobial susceptibility tests for Methicillin-Resistant (heteroresistant) Staphylococci. J. Clin. Microbiol. 19:482-488.
  4. Smyth, R.W., G Kahlmeter Mannitol Salt Agar Cefoxitin Combination as a Screening Medium for MRSA Central Hospital, Dept. of Clinical Microbiology, S-351-85, Vaxjo, Sweden


CATALOGUE NUMBERS

Dehydrated media

 

 

Mannitol Salt Agar

500 g

QB-39-2906

 

 

 

Prepared media

 

 

Plates, 100x15 mm

10/pkg

1778

Mono-plates, 100x15 mm

10/pkg

1778M

Mueller Hinton Broth, Tubes, 16x125 mm, 5ml

10/pkg

2663


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