Sodium polyanetholesulfonate (SPS) acts as an anticoagulant in blood, primarily by inhibiting the antimicrobial systems of blood, which is why it's commonly used in blood culture media.
Here's a more detailed breakdown:
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Anticoagulation: SPS prevents blood from clotting. This is crucial in blood cultures to ensure that any bacteria present can grow freely without being trapped in a clot.
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Inhibition of Antimicrobial Systems: Blood has natural defense mechanisms to fight off infections. SPS interferes with these mechanisms. Specifically, it can:
- Inhibit complement activation: The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. SPS prevents this activation.
- Inhibit phagocytosis: Phagocytosis is the process by which certain cells (phagocytes) engulf and destroy microorganisms, cellular debris, and foreign particles. SPS can inhibit this process, allowing bacteria to survive and multiply in the blood sample.
- Neutralize the bactericidal effect of serum: Serum contains substances that can kill bacteria. SPS neutralizes these substances, creating a more favorable environment for bacterial growth.
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Use in Blood Culture Media: Because SPS prevents clotting and inhibits the antimicrobial activity of blood, it's an ideal additive for blood culture bottles. This allows any bacteria present in the blood sample to grow and be identified, aiding in the diagnosis of bloodstream infections (bacteremia or septicemia).
In summary, SPS is essential in blood cultures because it ensures that any bacteria present can be accurately detected by preventing blood clots and suppressing the blood's natural defenses against infection.
