Diagnosis of bacterial keratitis Clinical differential diagnosis Corneal scraping staining and smear culture test

 

👁 “Microbiologic Diagnosis of Bacterial Keratitis – From Scraping to Staining”

While clinical features can suggest a probable pathogen,
the definitive diagnosis of bacterial keratitis requires microbiologic confirmation via
corneal scraping, staining, and culture to guide antibiotic choice and ensure appropriate management.

---

🔍 Diagnostic Steps for Microbial Keratitis

StepDescription

Clinical suspicion
– Pattern recognition helps estimate likely organism (e.g. serpiginous = Pneumococcus, ring = Pseudomonas)
– Accuracy ~60–70% only
Specimen collection
– Corneal scraping from base and edge of ulcer
– Avoid sampling mucus or discharge
– Hypopyon is usually sterile → avoid AC tap unless endophthalmitis suspected
Staining
– Use 3 slides: Gram stain, Acridine orange, Giemsa stain
– Inoculate culture plates first, then smear
Culture Media
– Standard: Blood agar, Chocolate agar, Thioglycollate broth
– Others: Sabouraud (fungus), LJ (NTM), anaerobic jar, E. coli-lawn for Acanthamoeba

---

🧪 Stains and Culture Guide

TestBest For

Gram stain	Differentiating Gram-positive vs Gram-negative organisms
Acridine orange	Detecting low bacterial load (fluorescent)
Giemsa stain	Best for fungi, amoebae, and cell morphology

---

✅ Clinical Tip
– Don’t delay cultures in progressive ulcers
– Always scrape multiple areas
– Choose media based on suspected pathogen