Cooked meat medium( rcm media) is a types of culture media which was was originally developed by Robertson for the cultivation of aerobes and anaerobes in particular pathogenic clostridia species and for the maintenance of stock cultures.The present formulation is recommended by BIS for the detection and counting of bacteria responsible for food poisoning, in particular Clostridium welchii.This medium with the addition of a further 10 percent sodium chloride is used as a salt medium to isolate staphylococci.It is used to cultivate and maintain clostridia and to determine the proteolytic activity of anaerobes.The FDA has recommended a slight modification of this medium for counting and identifying Clostridium perfringens from foods.
What is the principle of Cooked meat medium
- Cooked Meat Medium contains beef heart, the muscle protein that supplies amino acids and other nutrients.
- It also contains glutathione, a reducing substance that enables the growth of obligate anaerobes.
- The sulfhydryl groups that give the reducing effect are more readily available in denatured protein and therefore the cooked meat is added to the medium.
- Growth in this medium is indicated by the turbidity or blistering of some organisms.
- Blackening and decay of the meat particles indicate proteolysis.
- For best results, the medium should be used on the day of preparation, otherwise it should be boiled or steamed for a few minutes without any exercise to allow to cool and then inoculated.
Composition of Cooked meat medium
|Ingredients||Grams / Litre|
|Beef heart, infusion from||500.000|
|Peptic digest of animal tissue||5.000|
|Final pH at temperature 25°C||7.8±0.2|
How to Prepare Cooked meat medium
- Suspend 11.54 grams in 100 ml distilled water.
- Mix thoroughly and allow to stand for 15 minutes until all the particles are thoroughly wetted.
- Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
Appearance of Cooked meat broth medium after preparation
Cooked meat broth medium appears amber coloured clear to slightly opalescent supernatant over insoluble granules.
How to Inoculate on Cooked meat medium
- Using a sterile inoculating loop or needle, transfer growth from a fresh subculture medium
- Heavily inoculating in the area of meat particles.
- Incubate the tubes at temperature 35 ± 2°C under anaerobic conditions for up to 7 days. It is recommended that an indicator of anaerobiosis be used.
Tube reading and Colonies morphology on Cooked meat broth medium
The following are cultural characteristics observed after an incubation at temperature 35°C for 40 – 48 hours in cooked meat broth medium.
- Robertson, 1916, J. Pathol. Bacteriol., 20:327.
- Bureau of Indian Standards IS : 5887 (Part II) 1976, Second Reprint December 1994.
- Bureau of Indian Standards IS : 5887 (Part IV) 1976.
- Lenette and others (Eds.), 1985, Manual of Clinical Microbiology, 4th ed., ASM, Washington,D.C.
- MacFaddin J.F., 1985, Media for Isolation – Cultivation – Identification – Maintenance of Medical bacteria, Vol. I, Williams & Wilkins, Baltimore.
- U.S. Food and Drug Administration, 1984, Bacteriological Analytical Manual, 6th ed., AOAC, Arlington, Va.