A 38-year-old woman with poorly controlled diabetes mellitus (HbA1c 9.2%) presents with a 3-day history of left eye pain, tearing, and blurred vision. She reports contact lens wear (overnight use, poor hygiene). On slit-lamp examination, a 3 mm central corneal ulcer with a gray-white infiltrate, well-demarcated borders, and mucopurulent exudate is seen. Gram stain shows gram-negative rods; culture on blood agar grows mucoid colonies. What is the most likely causative organism and the immediate next step in management?

## Organism Identification **Key Point:** The clinical clues—contact lens wear (overnight), poor hygiene, gram-negative rod, **mucoid colonies** on blood agar—are diagnostic of ***Pseudomonas aeruginosa***, the most common cause of contact lens–associated bacterial keratitis. | Feature | *Pseudomonas* | *Staph. aureus* | *Neisseria* | *Moraxella* | |---------|---------------|-----------------|-------------|-------------| | **Gram stain** | Gram-negative rod | Gram-positive coccus | Gram-negative diplococcus | Gram-negative rod | | **Colony morphology** | Mucoid, green pigment | Golden, opaque | Small, translucent | Flat, grayish | | **Risk factor** | Contact lens (esp. overnight) | Trauma, lid disease | Sexual transmission | Debilitated patients | | **Corneal involvement** | Rapid, aggressive, stromal necrosis | Slower, localized | Rare in keratitis | Rare | | **Pigment production** | Pyoverdine (green), pyocyanin (blue) | None | None | None | **High-Yield:** *Pseudomonas aeruginosa* is an **obligate aerobe** and thrives under hypoxic conditions created by overnight contact lens wear. It produces **mucoid exopolysaccharide** (alginate), which appears as mucoid colonies and confers antibiotic resistance. ## Immediate Management ### Topical Therapy **Clinical Pearl:** *Pseudomonas* keratitis is a **medical emergency**. Delay in treatment risks perforation and blindness within 24–48 hours. 1. **Topical fluoroquinolone** (ciprofloxacin 0.3% or moxifloxacin 0.5%) — **first-line** for *Pseudomonas* because of excellent corneal penetration and broad gram-negative coverage. - Dosing: Every 30 minutes for first 6 hours, then hourly for 24–48 hours, then 4–6 hourly. 2. **Topical ceftazidime 5%** (fortified) — **second agent** for synergy and to reduce resistance. - Dosing: Hourly or 2-hourly. **Mnemonic:** **CEFTA-CIPRO** = **CEFTA**zidime + **CIPRO**floxacin for *Pseudomonas* keratitis. ### Why This Combination? - Fluoroquinolones penetrate cornea well and kill *Pseudomonas* rapidly. - Ceftazidime (third-generation cephalosporin) provides synergy and covers mucoid strains. - Dual therapy reduces emergence of resistance during treatment. ### Systemic Adjunct **Oral/IV fluoroquinolone** (ciprofloxacin 750 mg BD) may be added if: - Corneal perforation risk (descemetocele, >50% stromal involvement). - Immunocompromised patient. - Scleral extension. ### Supportive Care - **Immediate cessation** of contact lens wear. - Cycloplegic (atropine 1%) to relieve pain and prevent posterior synechiae. - Lubricants (preservative-free artificial tears). - Daily slit-lamp monitoring for perforation risk. **Warning:** Do NOT use topical steroids in bacterial keratitis (especially *Pseudomonas*) — they promote stromal melting and perforation.