Which organism is commonly used as a quality-control target to verify staining compatibility after a fixative change?

• A. H pylori
• B. Staphylococcus aureus
• C. Escherichia coli
• D. Candida albicans

Answer: (A)

Stain quality control after changing fixatives relies on a target organism whose visibility is strongly affected by fixation and by the staining method used. Helicobacter pylori fits this role well because it is small and delicate, living in gastric mucosa, and its detection depends on proper fixation and specific stains (such as Giemsa, Warthin-Starry, or immunohistochemistry). Using H. pylori as a QC target helps verify that the fixative preserves morphology and that the chosen stains will still work after the fixative change. If H. pylori appears clearly, the staining system is functioning as intended; if not, there may be an issue with fixation preservation or stain compatibility.

While other organisms like Staphylococcus aureus, Escherichia coli, or Candida albicans are valuable for general stain controls (Gram staining for bacteria or fungal stains), they’re less specific for testing compatibility after a fixative change, so they’re not the best stand-alone target for this particular QA purpose.