GRAM Stain for Paraffin Tissue: Detect Bacterial Infections in FFPE Samples

At iHisto, we offer optimized GRAM staining for formalin-fixed, paraffin-embedded (FFPE) tissue, enabling precise differentiation of Gram-positive and Gram-negative bacteria directly within histological samples. This technique is vital for infection diagnosis, sepsis studies, and microbiology in biopsy-based analysis.

🧪 Overview 

Unlike classic Gram stains used in microbiology smears, the GRAM stain for paraffin tissue is modified to work on FFPE sections. It highlights bacterial cell walls while preserving the surrounding tissue architecture, making it ideal for clinical pathology and preclinical research.

iHisto’s protocol provides:

• Clear visualization of Gram-positive (purple) and Gram-negative (pink/red) organisms

• Minimal background staining

• Reliable detection even in archived or culture-negative tissues

⚙️ How GRAM Staining Works in FFPE Tissue 

The stain differentiates bacteria by cell wall structure:

• Gram-positive bacteria: Thick peptidoglycan walls retain crystal violet–iodine complex → purple

• Gram-negative bacteria: Decolorized and counterstained with safranin → pink/red

Because bacterial walls are embedded in paraffin and masked by fixation, this version includes enhanced mordanting and permeabilization to access bacterial elements.

🧬 Step-by-Step Staining Process

1. Fixation and Sectioning
   FFPE tissue is sectioned at 4–5 µm and mounted on slides.

2. Deparaffinization and Rehydration
   Slides are cleared in xylene and rehydrated through graded alcohols.

3. Crystal Violet Staining
   All bacteria are initially stained purple.

4. Iodine Mordanting
   Stabilizes dye within Gram-positive cell walls.

5. Decolorization
   Alcohol-acetone removes dye from Gram-negative organisms.

6. Safranin Counterstain
   Stains Gram-negative bacteria red/pink.

7. Dehydration and Coverslipping
   Slides are cleared and coverslipped for long-term evaluation.

🔬 Applications of GRAM Staining in Tissue 

This stain is essential when infection must be confirmed histologically, particularly in the absence of culture or PCR data.

Common use cases include:

• Lung, liver, or kidney biopsies with suspected bacterial infection

• Sepsis investigation in organ tissue

• Culture-negative infections or biopsy correlation

• Rodent infection models in preclinical trials

• Infection around implanted medical devices or prosthetics

✅ Why Choose iHisto’s GRAM Staining Services 

• ✅ Clear distinction of Gram-positive vs Gram-negative bacteria

• ✅ Optimized for FFPE human and animal tissues

• ✅ Low background with reliable bacterial retention

• ✅ Optional digital slide scanning and remote access

• ✅ Pathologist interpretation and quantification available

iHisto delivers fast, accurate GRAM stain results for infection-focused histology across research and diagnostic workflows.

❓ FAQs 

• What does the GRAM stain detect in FFPE tissue?
  It distinguishes Gram-positive (purple) and Gram-negative (pink/red) bacteria directly in tissue sections.

• How is this different from microbiology GRAM staining?
  This version is tailored for formalin-fixed, paraffin-embedded tissues, not surface smears.

• Is it validated for animal models?
  Yes — it’s compatible with mouse, rat, rabbit, and other preclinical species.

• Can the slides be scanned digitally?
  Absolutely. We offer high-resolution scanning via HistoCloud or secure offline media.

📩 Request a Quote or Consultation 

Whether you're diagnosing infection, validating treatment response, or studying bacterial disease models, iHisto provides reliable GRAM staining tailored for FFPE tissue. Fast turnaround, expert review, and digital delivery — all in one.

👉 Request a Quote or email us at info@ihisto.io