Cultivation of Anaerobes—Cooked Meat Broth, Anaerobes—Cooked Meat Broth, A Photographic Atlas for the Microbiology Laboratory 4th edition 2011
Purpose
The purpose of Cooked Meat Broth is to grow anaerobes, especially pathogenic clostridia such as Clostridium perfringens, C. tetani, C. botulinum, and C. difficile. Certain clostridia are proteolytic, whereas others are saccharolytic. Because it is the medium that becomes anaerobic, these tubes can be incubated in an aerobic incubator, thus eliminating the need for expensive equipment.
Principle
Cooked Meat Broth (Figure 3-44) is a nutrient-rich medium, with beef heart, peptone, and dextrose acting as carbon and nitrogen sources. The beef heart is in the form of meat particles, whereas the other ingredients are dissolved in the broth. Anaerobic conditions occur as a result of several factors. One, cardiac muscle contains glutathione, a tripeptide that can reduce free molecular oxygen in the medium. Two, the meat is cooked prior to use. This denatures proteins and exposes their sulfhydryl groups, which perform the same function—oxygen reduction. Lastly, the medium with caps loosened is either incubated in an anaerobic jar for 24 hours to remove O2 or boiled to drive off the O2. Caps are immediately tightened to prevent the reentry of O2. Blackening and disintegration of the meat particles indicate proteolytic growth. Acid (not indicated directly) and gas production indicate saccharolytic growth.
3-44 COOKED MEAT BROTH
The meat particles are visible in each broth.
From left to right: Clostridium butyricum, uninoculated, C. sporogenes.
Blackening of the meat particles by C. sporogenes is indicative
of proteolytic activity. C. butyricum grew, but is not proteolytic.
Suggested Reading
- Michael J. Leboffe & Burton E. Pierce. A Photographic Atlas for the Microbiology Laboratory 4th edition 2011
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