The Salty Medium: Milk Salt Agar

 

Milk Salt Agar Base is used for the selective isolation and cultivation of Staphylococcus species. Koch reported that only Staphylococci could grow on agar media containing 7.5% sodium chloride. Chapman used this property in his modification of Koch's medium to make the medium selective due to the high salt content.

Staphylococcus is a Gram-positive bacterial genus. They are spherical (cocci) in shape and form grape-like clusters. They are facultative anaerobic organisms, which means they can grow in both aerobic and anaerobic environments. It can cause a wide range of diseases in humans and animals by producing toxins or penetrating the skin. Toxins produced by Staphylococcus aureus are a common cause of food poisoning.

Composition of Milk Salt Agar

Ingredients	Gms / Ltr
Peptic digest of animal tissue	5.00
Beef extract	3.00
Sodium chloride	65.00
Agar	15.00
pH (at 25°C)	7.4±0.2

Principle

This is a simple but nutritious medium. Beef extract, peptic digest of animal tissue, and skim milk all contain significant amounts of nutrients, primarily nitrogenous and carbonaceous compounds, as well as trace ingredients for Staphylococci. Sodium chloride at a concentration of 6.5% makes the medium highly selective as the majority of the contaminating organisms are inhibited by the high salt concentration, but Staphylococci are able to tolerate the high sodium chloride concentration.

Instruction To Use TM Media Milk Salt Agar

• In 900 ml of distilled water, dissolve 88 grams of TM Media Dehydrated Milk Salt Agar Base.
• Heat the medium to boiling to dissolve it completely.
• Dispense and sterilize by autoclaving at 15 psi (121°C) for 15 minutes.
• Cool to 60 °C. Aseptically add 10 ml of sterile skim milk (10% w/v skim milk powder solution) to every 90 ml of basal medium.
• Mix well and pour into sterile Petri plates.
• After 10% v/v sterile milk is added, a yellow-colored, opaque gel forms in Petri plates.

Cultural characteristics

Microorganism	ATCC	Inoculum (CFU/ml)	Growth	Incubation Temperature	Incubation Period
Escherichia coli	25922	>=10³	Inhibited	35-37°C	18-48 hours
Staphylococcus aureus	25923	50-100	Good-luxuriant	35-37°C	18-48 Hours

Storage Conditions

Store the dehydrated powder in a dry place in tightly sealed containers. Store the hygroscopic powder between 25-30 °C and protect it from direct sunlight. After removing the desired amount of medium, replace the cap tightly to prevent hydration.

At TM Media, we also offer a wide range of culture media for bacterial or fungal isolation. Over 2,000 Dehydrated Culture Media are available in our portfolio. Culture Media is also available as a Ready-To-Use product. The Read-To-Use Culture Media collection is available in plates, tubes, bottles, and bags. Along with Culture Media, we also provide Laboratory Consumables, Biological Media Bases, Media Supplements, Antibiotic Sensitivity Discs, and many more.

For more, visit https://www.tmmedia.in/.