Answer
Role of Sodium Citrate in the Concentration Procedure for Mycobacteria
Sodium citrate plays a critical supporting role during the decontamination and concentration process used for isolating Mycobacterium tuberculosis and other mycobacteria from clinical specimens such as sputum.
1. Acts as a Chelating Agent
- Sodium citrate forms soluble complexes with divalent metal ions like calcium (Ca2+) and magnesium (Mg2+), which are essential for the coagulation of proteins and mucus.
- By chelating these ions, it prevents the formation of clumps or precipitates that could trap or entrap mycobacteria.
2. Prevents Coagulation of Albumin and Mucus
- Sodium citrate helps maintain the sample in a fluid state by preventing the coagulation of proteins such as albumin.
- This action ensures a more homogenous suspension and facilitates better contact between the decontaminating agents (like NaOH) and the sample.
3. Protects Mycobacteria During Decontamination
- In the presence of sodium citrate, the mycobacteria are more likely to remain in suspension and protected from mechanical or chemical damage during processing.
- Sodium citrate has a mild buffering effect, which can mitigate overly harsh pH changes caused by NaOH.
4. Enhances Recovery Efficiency
- By preventing protein clumps and mucus aggregates, sodium citrate contributes to the effective sedimentation of mycobacteria during centrifugation.
- This improves the yield of organisms in the concentrated pellet used for smear preparation and culture.
Overall, sodium citrate ensures that the sample remains sufficiently liquefied, minimizes bacterial loss during processing, and improves the sensitivity of downstream detection methods like Ziehl-Neelsen staining and culture.