Skim Milk Agar M763
Skim Milk Agar is used for cultivation and enumeration of microorganisms encountered in dairy industry.
Composition**
Ingredients Gms / Litre
Skim milk powder 28.000
Casein enzymic hydrolysate 5.000
Yeast extract 2.500
Dextrose 1.000
Agar 15.000
Final pH ( at 25°C) 7.0±0.2
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 51.5 grams of in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving
at 15 lbs pressure (121°C) for 15 minutes. Mix well and pour into sterile Petri plates.
Principle And Interpretation
Skim Milk Agar is used for the demonstration of coagulation and proteolysis of casein (1). The medium is recommended by
APHA (2) for cultivation and enumeration of microorganisms encountered in dairy industry (3). Addition of skim milk to any
nutrient-rich medium creates favourable conditions for growth of organisms, which are encountered in milk. The number of
bacteria isolated thus is more than the number of organisms isolated on a regular medium (4). Proteolytic bacteria hydrolyze
casein to form soluble nitrogenous compounds indicated as clear zone surrounding the colonies. More clear zones are seen on
milk agar if, the bacteria produce acid from fermentable carbohydrates in the medium.
Casein enzymic hydrolysate provides amino acids and other complex nitrogenous substances. Yeast extract supplies vitamin B
complex. Addition of skim milk in the medium makes the conditions optimal for microorganisms encountered in milk. Glucose
acts as the carbon source.
Quality Control
Appearance
Cream to yellow homogeneous free flowing powder
Gelling
Firm, comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Off white coloured opaque gel forms in Petri plates
Reaction
Reaction of 5.15% w/v aqueous solution at 25°C. pH : 7.0±0.2
pH
6.80-7.20
Cultural Response
M763: Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.
Organism Inoculum Growth Recovery Proteolytic
(CFU) activity
Bacillus subtilis ATCC 6633 50-100 good-luxuriant >=70% positive
reaction,
clear zone
surrounding
colonies
Please refer disclaimer Overleaf.
HiMedia Laboratories Technical Data
Enterococcus faecalis ATCC 50-100 luxuriant >=70% negative
29212 reaction, no
clear zone
surrounding
colonies
Escherichia coli ATCC 50-100 good-luxuriant >=70% negative
25922 reaction,no
clear zone
surrounding
colonies
Proteus mirabilis ATCC 50-100 luxuriant >=70% positive
25933 reaction,
clear zone
surrounding
colonies
Pseudomonas aeruginosa 50-100 luxuriant >=70% positive
ATCC 27853 reaction,
clear zone
surrounding
colonies
Serratia marcescens ATCC 50-100 luxuriant >=70% positive
8100 reaction,
clear zone
surrounding
colonies
Storage and Shelf Life
Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.
Reference
1. Frazier W. C. and Ripp P., 1928, J. Bacteriol., 16: 57.
2. Downes F. P. and Ito K., (Eds.), 2001, Compendium of Methods for the Microbiological Examination of Foods, 4th Ed.,
APHA, Washington, D.C.
3. Wehr H. M. and Frank J. H., 2004, Standard Methods for the Microbiological Examination of Dairy Products, 17th Ed.,
APHA Inc., Washington, D.C.
4. Terplan G. Rundfeldt,H.u. Zaadhof, K.J. Zur Eignung verschiedener Nährböden für die Bestimmung der Gesamtkeimzahl
der Milch. - Arch. Lebensmittelhyg., 18; 9-11 (1967).
Revision : 02 / 2015
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User must ensure suitability of the product(s) in their application prior to use. Products conform solely to the information contained in
this and other related HiMedia™ publications. The information contained in this publication is based on our research and development
work and is to the best of our knowledge true and accurate. HiMedia™ Laboratories Pvt Ltd reserves the right to make changes to
specifications and information related to the products at any time. Products are not intended for human or animal or therapeutic use but
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