A 32-year-old male presents with a surgical wound infection 5 days post-appendectomy. Culture and sensitivity reveal Staphylococcus aureus. Which is the most common bacterial organism responsible for surgical site infections in India?

Explanation

## Most Common Cause of Surgical Site Infections **Key Point:** Staphylococcus aureus is the most common organism causing surgical site infections (SSIs) globally and in India, accounting for 30–40% of all SSIs. ### Epidemiology of SSIs | Organism | Frequency | Source | Clinical Significance | |----------|-----------|--------|----------------------| | Staphylococcus aureus | 30–40% | Skin flora (endogenous) | Most common; MRSA emerging | | Escherichia coli | 15–20% | GI tract flora | Common in GI surgery | | Pseudomonas aeruginosa | 10–15% | Environmental; nosocomial | Opportunistic; resistant | | Klebsiella pneumoniae | 8–12% | GI flora; nosocomial | Gram-negative; resistant | ### Pathogenesis in Wound Healing 1. **Inoculation phase:** Bacteria introduced during surgery or from skin flora 2. **Colonization:** Organisms multiply in wound; impaired local immunity 3. **Infection:** Inflammatory response overwhelmed; purulent exudate, delayed healing 4. **Tissue damage:** Collagen degradation, impaired angiogenesis, prolonged inflammatory phase **Clinical Pearl:** S. aureus is a gram-positive coccus that colonizes the skin and mucous membranes. It produces multiple virulence factors (alpha-toxin, coagulase, hyaluronidase) that breach epithelial barriers and evade immune response, making it the leading cause of SSIs even in clean-contaminated procedures. **High-Yield:** Risk factors for S. aureus SSI include obesity, diabetes, prolonged preoperative stay, and MRSA colonization. Antibiotic prophylaxis (cefazolin) targets S. aureus and reduces SSI incidence by 50–70%. **Mnemonic — SSI Risk Factors (INFECTED):** - **I**mmunity (diabetes, immunosuppression) - **N**utrition (malnutrition, obesity) - **F**oreign bodies (implants, sutures) - **E**xtended surgery (>2 hours) - **C**ontamination (clean-contaminated or contaminated) - **T**issue perfusion (hypoxia, shock) - **E**ndocrine (hyperglycemia) - **D**epth (deep/organ-space infections) [cite:Robbins 10e Ch 3]