Question
Robertson’s cooked meat medium
Answer
Robertson’s cooked meat (RCM) medium is a liquid, reducing culture medium widely used for the cultivation of anaerobic bacteria, particularly Clostridium species, and also for maintaining stock cultures.
Composition: contains minced, cooked (heat-treated) ox/horse-heart or other meat particles at the bottom of the tube/bottle, covered by a nutrient broth (with an unsaturated fatty acid, often a layer of paraffin/Vaseline, sealing the surface in some preparations to further limit oxygen entry).
Mechanism supporting anaerobic growth: the cooked meat particles contain reducing substances (notably glutathione and unsaturated fatty acids) that consume dissolved oxygen and lower the oxidation-reduction (redox) potential of the medium, creating a sufficiently anaerobic microenvironment near the meat particles to support the growth of obligate anaerobes even without a special anaerobic jar/chamber; the meat also provides nutrients supporting growth.
Uses:
- Primary isolation and enrichment of anaerobic organisms (e.g., Clostridium tetani, C. perfringens, C. difficile) from clinical specimens.
- Maintenance of stock/reference cultures over extended periods, since the medium supports long-term survival.
- Recognizing characteristic changes in the meat particles/broth on incubation can give presumptive clues to species (e.g., C. perfringens causes the meat to turn pink with gas production — “stormy fermentation” pattern is more classically described in litmus milk, but characteristic colour/gas changes are noted in RCM too; C. sporogenes causes blackening and putrefaction of the meat particles due to protein digestion).
Practical note: after enrichment in RCM, growth is typically subcultured onto solid anaerobic media (e.g., blood agar incubated anaerobically) for colony morphology assessment, haemolysis pattern, and further identification tests.