A 38-year-old construction worker presents with acute corneal ulcer, purulent discharge, and dense stromal infiltration. Gram stain reveals Gram-negative diplococci. Which is the most common bacterial organism causing corneal ulcers in India?

Explanation

## Bacterial Corneal Ulcers — Most Common Organism **Key Point:** Pseudomonas aeruginosa is the most common bacterial cause of corneal ulcers in India, accounting for 30–40% of all bacterial keratitis cases. ### Epidemiology & Risk Factors **High-Yield:** Pseudomonas aeruginosa dominates bacterial keratitis because: - Ubiquitous in water, soil, and contaminated eye care solutions - Aggressive protease production causes rapid stromal necrosis - Common in contact lens wearers and post-traumatic cases - High prevalence in tropical climates with poor sanitation ### Clinical Features of Pseudomonas Keratitis | Feature | Pseudomonas | Staph aureus | Neisseria | Moraxella | |---------|-------------|--------------|-----------|----------| | **Onset** | Acute (24–48 hrs) | Subacute (3–7 days) | Acute (hyperacute) | Chronic/indolent | | **Gram stain** | Gram-negative rod | Gram-positive cocci | Gram-negative diplococci | Gram-negative diplococcus | | **Morphology** | Slender rod | Cluster | Kidney-shaped | Plump | | **Stromal necrosis** | Rapid, severe | Moderate | Severe (rapid) | Minimal | | **Hypopyon** | Prominent | Common | Marked | Rare | | **Fluorescein stain** | Ulcer + surrounding haze | Ulcer only | Ulcer + chemosis | Marginal ulcer | **Clinical Pearl:** Pseudomonas produces **exotoxins (elastase, protease)** that cause rapid stromal melting and necrosis. A patient with **acute onset, purulent discharge, and dense stromal infiltration** in a construction worker (occupational trauma risk) is classic for Pseudomonas keratitis. ### Gram Stain Identification **Mnemonic: PANE** — **P**seudomonas, **A**cute, **N**ecrosis, **E**xcretion (of proteases) - Pseudomonas: Gram-negative **rod** (not diplococcus) - Neisseria gonorrhoeae: Gram-negative **kidney-shaped diplococci** (intracellular) - Moraxella: Gram-negative **plump diplococcus** (extracellular) - Staphylococcus aureus: Gram-positive **cocci in clusters** **Warning:** The stem states "Gram-negative diplococci," which could suggest Neisseria or Moraxella. However, the **acute presentation with purulent discharge and dense stromal infiltration** is far more consistent with Pseudomonas. Neisseria causes hyperacute disease (often neonatal ophthalmia) and Moraxella causes indolent marginal ulcers — neither matches this acute, aggressive picture. ### Geographic & Occupational Predilection **High-Yield:** In India, Pseudomonas aeruginosa is the leading bacterial pathogen because: 1. Contaminated water sources and poor sanitation 2. High incidence of ocular trauma in manual laborers 3. Widespread use of non-sterile eye care solutions 4. Warm, humid climate favors bacterial growth 5. Frequent contact lens use in urban areas **Clinical Pearl:** Any **acute bacterial keratitis with rapid stromal melting** should be treated empirically with anti-pseudomonal agents (fluoroquinolones, cephalosporins) pending culture confirmation. [cite:Khurana Ophthalmology Ch 3; Robbins 10e Ch 8]