Characteristics and differential diagnosis of keratitis caused by Moraxella, Corynebacterium, and Haemophilus

This post explores less common but clinically relevant bacteria that can cause microbial keratitis. These include Moraxella, Corynebacterium diphtheriae, and Haemophilus influenzae. Though less frequent than Staphylococcus or Pseudomonas, they present unique challenges in diagnosis and management.

🔹 Moraxella spp.

• Risk Factors: Diabetes, alcoholism, systemic illness, autoimmune diseases
• Clinical Signs: Pain-free, round to oval ulcers, slow progression, minimal anterior chamber reaction
• Notes: Similar to other low-virulence bacteria like Klebsiella or E. coli

🔹 Corynebacterium diphtheriae

• Characteristics: Extremely rare; begins with superficial pseudomembrane opacity → can lead to necrosis
• Context: May occur in immunocompromised or chronic ocular surface disease patients

🔹 Haemophilus influenzae

• Clinical Context: Often extends from conjunctivitis
• Associated Risk Factors: Therapeutic lens use, dry eye, corneal grafts
• Hallmark Sign: Ring-shaped corneal ulcer
• Differentials: S. pneumoniae, Acanthamoeba, HSV, Listeria, Klebsiella

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📋 Summary Table: Rare Bacterial Keratitis Causes (English)

OrganismClinical FeaturesRisk FactorsDiagnostic Clues

Moraxella spp.	Painless, round/oval ulcers, slow progression	Diabetes, alcoholism, autoimmune diseases	Mild inflammation, mimics low-virulence bugs
Corynebacterium diphtheriae	Starts with pseudomembranous opacities → necrosis	Chronic conjunctivitis, immunocompromised	Severe epithelial reaction, rare agent
Haemophilus influenzae	Ring-shaped infiltrates, post-conjunctivitis extension	T-lens use, dry eye, corneal transplant	Ring ulcer pattern, common conjunctivitis agent

 

 

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