A 42-year-old man from rural India presents with a 3-week history of progressive pain and swelling over the left tibia. He recalls a puncture wound to the sole of his foot 6 weeks ago while walking barefoot in a paddy field. On examination, there is localized warmth, tenderness, and a draining sinus tract over the anterior tibia. Laboratory investigations show ESR 78 mm/h, CRP 12 mg/dL, and WBC 13,200/μL. X-ray of the tibia reveals a mixed lytic and sclerotic lesion with periosteal reaction. Blood culture is negative. Which organism is most likely responsible for this chronic osteomyelitis?

Explanation

## Clinical Presentation & Epidemiology This case presents with **chronic osteomyelitis** following a puncture wound to the plantar surface of the foot — a classic risk factor for **Pseudomonas aeruginosa** infection. The 6-week interval between injury and symptom onset, combined with the draining sinus tract and negative blood culture, indicates established chronic infection rather than acute hematogenous spread. ## Organism Identification **Key Point:** Pseudomonas aeruginosa is the pathognomonic organism in plantar puncture wounds to the foot, particularly in warm, moist environments (paddy fields). This organism thrives in biofilms within the puncture tract and is notoriously resistant to many antibiotics. ## Diagnostic Clues | Feature | Pseudomonas | S. aureus | TB | Nocardia | |---------|-------------|----------|----|---------| | **Puncture wound risk** | ✓ (High) | ✗ | ✗ | ✗ | | **Draining sinus** | ✓ (Common) | ✓ (Less common) | ✓ | ✓ | | **Blood culture positive** | ✗ (Rare) | ✓ (Often) | ✗ | ✗ | | **Lytic + sclerotic lesion** | ✓ | ✓ | ✓ | ✓ | | **Geographic risk** | Warm/moist | Ubiquitous | Endemic TB areas | Immunocompromised | **High-Yield:** Pseudomonas is the **single most common cause of osteomyelitis following plantar puncture wounds**, especially in tropical climates. This is a high-yield NEET PG fact. ## Why Pseudomonas Here? 1. **Puncture wound to plantar surface** — direct inoculation of environmental Pseudomonas 2. **Warm, moist environment** (paddy field) — optimal for Pseudomonas survival and biofilm formation 3. **Negative blood culture** — consistent with chronic localized infection, not hematogenous spread 4. **Draining sinus tract** — indicates established chronic infection with biofilm **Clinical Pearl:** Pseudomonas osteomyelitis from plantar puncture wounds often requires **prolonged IV antipseudomonal antibiotics** (fluoroquinolones or anti-pseudomonal beta-lactams) and frequently necessitates surgical debridement. Monotherapy often fails due to biofilm formation. [cite:Rockwood & Green's Fractures in Adults 9e Ch 12]