MRS AGAR low pH ISO 15214
CAT Nº: 1433
Recommended medium for the growth of lactobacilli in general
FORMULA IN g/l
Dextrose
20.00
Triammonium Citrate
2.00
Enzymatic Digest of Casein
10.00
Tween 80
1.08
Beef Extract
10.00
Magnesium Sulfate Heptahydrate
0.20
Sodium Acetate
5.00
Manganese Sulfate Tetrahydrate
0.05
Yeast Extract
4.00
Bacteriological Agar
10.0
Dipotassium Phosphate
2.00
Final pH 5.7 ± 0.1 at 25ºC
PREPARATION
Suspend 64.00 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent
agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121ºC for 12 minutes. Cool to 45-50ºC,
mix well and dispense into plates. The prepared medium should be stored at 8-15°C. The color is amber, slightly
opalescent.
The dehydrated medium should be homogeneous, free-flowing and beige in color. If there are any physical changes,
discard the medium.
USES
MRS AGAR is a selective medium that supports the good growth of lactobacilli in general.
The medium is apt for the growth of lactic acid bacteria, including Lactobacillus, Pediococcus and Leuconostoc.
Ammonium citrate, at a low pH, inhibits most microorganisms, but allows the growth of lactobacilli. Dipotassium
phosphate and Sodium acetate are buffer agents to maintain a low pH. Tween 80 is an emulsifier. Manganese and
Magnesium sulfates are sources of ions and sulfate. Bacteriological peptone and Beef extract provide nitrogen, vitamins,
minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Dextrose
is the fermentable carbohydrate. Bacteriological agar is the solidifying agent.
The growth of some lactobacillus strains is inhibited at a pH higher than 6.0 and it is necessary to acidify the medium to
favor the growth. With a pH of 5.7 ± 0.1, this medium favors the growth of these strains.
Normative ISO 15214 recommends this medium for the enumeration of mesophilic lactic acid bacteria Colony count
technique at 30ºC. Inoculate and incubate at 30°C for 72 hours, and count the colonies on the plates that contains
between 15 and 300 colonies.
MICROBIOLOGICAL TEST
The following results were obtained in the performance of the medium from type cultures after incubation at a
temperature of 35ºC during 3 days, or at 30ºC during 5 days, under a CO2 enriched atmosphere in an anaerobic jar.
1
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Microorganisms
Growth
*Lactobacillus acidophilus ATCC 4356
Good
*Lactobacillus casei ATCC 393
Good
*Lactobacillus fermentum ATCC 9338
Moderate-Good
Escherichia coli ATCC 25922
Moderate-Good
Pseudomonas aeruginosa ATCC 27853
Inhibited
* According to ISO 15214 incubate at 30ºC during 72 hours
BIBLIOGRAPHY
ISO 15214: Microbiology of food and animal feeding stuffs -- Horizontal method for the enumeration of mesophilic lactic acid bacteria -Colony-count technique
ROGOSA, M., a. SHARPE, M.E.: An approach to the classification of the lactobacilli. – J. Appl. Bact., 22; 329-340 (1959].
ISO
STORAGE
8ºC
Once opened keep powdered medium closed to avoid hydration.
2ºC
2
LABORATORIOS CONDA, S.A.
www.condalab.com