Anaerobic culture characteristics: In Robertson’s cooked meat medium, reddening of the meat is classically produced by which Clostridium species due to its proteolytic activity and pigment change?

Introduction / Context:
Robertson’s cooked meat (RCM) medium is used to cultivate anaerobes and observe characteristic changes in the meat particles. Different clostridia display distinct proteolytic, saccharolytic, and pigmentary effects that aid presumptive identification.

Given Data / Assumptions:

• “Reddening” refers to a pink to red discoloration of meat pieces in RCM.
• C. sporogenes is strongly proteolytic and is known to cause a pink-red color change with digestion of meat.
• C. perfringens is more saccharolytic (e.g., stormy fermentation in milk) and typically causes gas and turbidity rather than marked reddening of meat.

Concept / Approach:

In RCM, proteolysis and reduction of meat pigments can yield characteristic colors. Matching typical lab observations to species behavior (proteolysis vs saccharolysis) guides the choice. C. sporogenes is a reference proteolytic anaerobe used as a control organism in many labs and produces the described reddening.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory bench guides often cite C. sporogenes for proteolysis and meat digestion with reddish discoloration; C. histolyticum is proteolytic but is more associated with extensive liquefaction rather than the classic “reddening” descriptor.

Why Other Options Are Wrong:

C. perfringens: saccharolytic, gas production prominent; reddening is not a hallmark.

C. tetani: minimal proteolysis; does not produce this characteristic change.

C. histolyticum: proteolytic but typically noted for rapid meat digestion, not the specific reddening feature emphasized in teaching texts.

Common Pitfalls:

Assuming all proteolytic clostridia cause identical changes; subtle differences (color vs liquefaction) matter in presumptive identification.

Final Answer:

C sporogenes