Overview:
Robertson's Cooked Meat Medium (RCM), also known as Cooked Meat Broth or Chopped Meat Medium, is a nutrient-rich, semi-solid enrichment and maintenance medium originally developed by Robertson in 1916 for the cultivation of anaerobic bacteria isolated from wounds. It consists of cooked meat particles (typically from fat-free minced ox heart) suspended in a peptone-based broth, providing essential amino acids, peptides, vitamins, and reducing agents to create a low oxidation-reduction potential that supports the growth of strict anaerobes, microaerophiles, and aerobes, especially Clostridium species (e.g., C. perfringens, C. tetani, C. botulinum). The meat particles detoxify oxygen and harmful byproducts via unsaturated fatty acids, glutathione, and sulfhydryl groups, while supplements like hemin and vitamin K enhance viability. It is recommended by the FDA for enumerating C. perfringens from food and by CLSI for stock culture maintenance, with growth indicated by turbidity, gas bubbles, or meat particle changes (reddening for saccharolytic, blackening for proteolytic activity) after anaerobic incubation at 35-37�C for 24-72 hours.
Applications:
?? Enrichment and isolation of Clostridium spp. and other anaerobes from clinical specimens (e.g., wounds, feces, blood) for diagnosing gas gangrene, tetanus, or foodborne illnesses
?? Maintenance and long-term storage of anaerobic stock cultures, preserving viability for months without subculturing
?? FDA-recommended enumeration and identification of C. perfringens in food samples (e.g., meat, dairy) per BAM protocols
?? Differentiation of saccharolytic (e.g., C. perfringens: red meat, rancid odor) vs. proteolytic (e.g., C. tetani: black meat, putrid odor) anaerobes in research and diagnostics
Key Features:
?? Cooked meat particles and iron filings create a natural reducing environment (Eh < -100 mV) for obligate anaerobes, supporting >90% recovery of stressed ATCC strains like C. perfringens 13124
?? Hemin and vitamin K supplementation boosts growth of fastidious anaerobes; dextrose provides fermentable energy without rapid acidification
?? Versatile for small inocula; preserves organisms long-term (up to 6-12 months at 4�C) with minimal overgrowth
?? Validated in CLSI M22-A3 and ISO 7937 standards; semi-solid consistency prevents settling and aids in gas detection
?? Clear supernatant over meat granules post-preparation; anaerobic jars or paraffin overlay recommended for strict anaerobes
Composition (per liter):
Cooked Meat Particles (fat-free minced ox heart) � 250.0 g
Peptic Digest of Animal Tissue � 17.5 g
Yeast Extract � 5.0 g
Dextrose � 5.0 g
Sodium Chloride (NaCl) � 5.0 g
Iron Filings � 10.0 g
Hemin Solution (0.05% in NaOH) � 10.0 mL
Vitamin K Solution (0.1% in 95% ethanol) � 10.0 mL
Agar (optional for semi-solid) � 2.0-3.0 g
Final pH: 6.8 � 0.3 at 25�C
Preparation:
Suspend 42.5 g of dehydrated medium (or equivalent granules) in 1 liter of purified/distilled water. Mix thoroughly and allow to soak for 5-15 minutes to wet all particles. Heat gently to boiling if needed to dissolve, but avoid overheating. Dispense into screw-capped tubes or bottles (10-15 mL per tube, ensuring meat particles are at the bottom). Autoclave at 121�C (15 psi) for 15 minutes with caps loosened. Tighten caps after cooling to room temperature. For strict anaerobes, pre-reduce by boiling (100�C for 10-15 min) or heating at 80�C for 30 min with loosened caps, then cool without agitation and overlay with 1 cm sterile paraffin oil. Inoculate deeply into meat particles using a loop or swab; incubate anaerobically at 35-37�C for 24-72 hours. Prepared medium should appear medium amber, clear to slightly opalescent supernatant over insoluble meat granules.
Storage:
Dehydrated medium: Store in a tightly closed container at 2�30�C, protected from moisture, light, and humidity; stable until expiry date (typically 3 years).
Prepared medium: Store at 2�8�C in sealed tubes; use within 6-12 months or discard if contaminated, volume changes, or meat discolors. Pre-reduce before use if stored >1 week.
?? For laboratory and research use only. Not for diagnostic procedures without proper validation. Not for human or veterinary consumption. Handle under biosafety level 2; use Universal Precautions for potentially infectious specimens�wear gloves, lab coat, and eye protection. May contain animal-derived components; treat as biohazard. Autoclave all waste before disposal. Meat turbidity may mimic growth�confirm via subculture and Gram stain. Not suitable for strict aerobes or non-spore-formers without aerobic modifications.2.8s