Robertson Cooked Meat Medium

Robertson Cooked Meat Medium is an excellent medium for the primary growth and maintenance of aerobic and anaerobic organisms. Robertson Cooked Meat Medium is also useful as an enrichment broth for cultivating organisms from a very small inoculum. Clostridium tetani normally grows in this medium. The growth of spore-forming and non-spore-forming anaerobes is supported by Robertson cooked meat medium. It is also known as cooked meat broth (CMB) as it contains pieces of fat-free minced cooked meat of ox heart and nutrient broth.

Robertson Cooked Meat Medium Composition

IngredientsGms / Litre
Beef Heart, Solids98.000
Proteose Peptone20.000
Dextrose2.000
Sodium Chloride5.000
Final pH ( at 25°C)7.2±0.2
Robertson Cooked Meat Medium Composition

Robertson Cooked Meat Medium PRINCIPLE

Cooked Meat Medium contains beef heart, the muscle protein that provides amino acids and other nutrients. It also contains glutathione a reducing substance that permits the growth of obligate anaerobes. The sulphydryl groups which impart reducing effects are more available in denatured protein and hence the cooked meat is added to the medium.

The growth in this medium is indicated by the turbidity or bubble formation by some organisms. Blackening and disintegration of the meat particles indicate proteolysis. For best results, the medium should be used on the day it is prepared, otherwise, it should be boiled or steamed for a few minutes allowed to cool without agitation, and then inoculated. Cooked Meat Medium was originally developed by Robertson for the cultivation of certain anaerobes isolated from wounds.

Robertson Cooked Meat Medium PREPARATION

Suspend 10g in 100ml of distilled water (or 1g amounts in 10ml volumes of water in tubes). Allow to stand for 15 minutes until the meat particles are thoroughly wetted. Sterilize by autoclaving at 121°C for 15 minutes. Do not cool the bottles rapidly because ebullition will expel the meat particles from the containers.

Robertson Cooked Meat Medium PROCEDURE

Anaerobic Culture: It is preferable to use a freshly reconstituted and sterile medium which is inoculated as soon as it has cooled to approximately 35°C. Tubes that are not used on the day of preparation should be placed in a boiling water bath or steamer for about 15 minutes to remove dissolved oxygen. They should be allowed to cool without agitation and then inoculated.

Inoculation should be made near the bottom of the tube in the meat particles. Clostridia may be divided into two main groups by their action on the medium. (A) Saccharolytic Organisms There is rapid production of acid and gas but no digestion of the meat. Cultures may have a slightly sour smell, with reddened protein.

(B) Proteolytic Organisms Proteolysis causes the decomposition of the meat with the formation of foul-smelling sulfur compounds and blackening. However, some saccharolytic strains also produce Hydrogen sulphide which will cause blackening but to a lesser degree. Aerobic Culture: The tube of medium is incubated with the cap loose and no seal is required. Aerobes grow at the top whilst more anaerobic species grow deeper in the medium.

Robertson Cooked Meat Medium RESULT

  • Growth in this medium is indicated by turbidity or bubble formation by some organisms.
  • Blackening and disintegration of the meat particles indicate proteolysis.
  • Aerobes grow at the top whilst more anaerobic species grow deeper in the medium.

RCM Medium Sample/Specimen Collection

  • Ensure that all samples are properly labeled.
  • Follow appropriate techniques for handling samples as per established guidelines.
  • Some samples may require special handling, such as immediate refrigeration or protection from light, following the standard procedure.
  • The samples must be stored and tested within the permissible time duration.
  • After use, contaminated materials must be sterilized by autoclaving before discarding.
  • Clinical samples – Blood; Food and dairy samples; and water samples.

Robertson Cooked Meat Medium Storage

Store the dehydrated medium below 30°C in a tightly closed container and the prepared medium at 2ºC-8°C. Avoid freezing and overheating. Use before the expiry date on the label. Once opened keep powdered medium closed to avoid hydration.

Robertson Cooked Meat Medium Quality Control

OrganismInoculum (CFU)Growth
Clostridium botulinum50-100Luxuriant
Clostridium perfringens50-100Luxuriant
Clostridium sporogenes50-100Luxuriant
Enterococcus faecalis50-100Luxuriant
Streptococcus pneumoniae50-100Luxuriant

Robertson Cooked Meat Medium Notes

Cooked Meat Medium prepared from heart tissue is a well-established medium for the cultivation of anaerobic and aerobic organisms.

It can initiate bacterial growth from very small inocula and maintain the viability of cultures over long periods. Mixed cultures of bacteria survive in Cooked Meat Medium without displacing the slower-growing organisms. The products of growth do not rapidly destroy the inoculated organisms and therefore it is an excellent medium for the storage of aerobic and anaerobic bacteria.

The addition of glucose to the formulation allows rapid, heavy growth of anaerobic bacteria in a short time and leads to a more rapid identification of important anaerobes. The improved growth also enhances the GLC identification of anaerobic bacteria.

The improved clarity of the supernatant broth permits earlier detection of growth especially when combined with the increased growth of most organisms. Slower-growing isolates will yield detectable growth within 45 hours of incubation.

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