The primary function of Sodium Polyanethole Sulfonate (SPS) in blood culture media is to prevent the killing of bacteria by innate immune factors present in the blood sample.
Here's a more detailed breakdown:
-
Context: SPS is added to blood culture bottles to facilitate the growth and detection of bacteria in blood samples taken from patients suspected of bacteremia (bacteria in the bloodstream).
-
Mechanism of Action: SPS interferes with the action of several components of the body's natural defense system, preventing them from destroying the bacteria before they can be cultured and identified. These components include:
- Complement System: SPS inhibits the complement cascade, a crucial part of the immune system that can lead to bacterial lysis (destruction).
- Phagocytosis: SPS can inhibit phagocytosis, the process by which immune cells (like neutrophils and macrophages) engulf and destroy bacteria.
- Antibodies: While not directly addressed in the given reference, SPS can also, in some instances, reduce the activity of certain antibodies that might otherwise hinder bacterial growth.
- Lysozyme: SPS may also inhibit the action of lysozyme, an enzyme that damages bacterial cell walls.
-
Why is this important? Without SPS, the body's own defense mechanisms might kill or inhibit bacterial growth in the blood sample before the lab can successfully culture and identify the infectious agent. This would lead to false-negative results and delayed or inappropriate treatment.
In essence, SPS creates a more favorable environment for bacterial growth in blood cultures, allowing for accurate diagnosis of bloodstream infections.
