Staphylococcus aureus is the most common cause of surgical site infections (SSIs) because it is a part of the normal skin flora and can easily contaminate surgical wounds during the procedure. Its ability to adhere to surgical materials and form biofilms increases its pathogenicity. Additionally, S. aureus can evade the immune response and produces toxins that contribute to tissue damage and impaired healing. Proper skin preparation and perioperative antibiotic prophylaxis target this organism to reduce SSI risk.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 9th Edition.