A 72-year-old woman with diabetes mellitus type 2 and chronic kidney disease (eGFR 28 mL/min) is admitted with a 10-day history of painful, necrotic lesion on her left foot following a puncture wound from a contaminated nail. On examination, the wound shows black eschar with surrounding erythema and edema. Tissue culture grows a gram-negative rod that is oxidase-positive and produces blue-green pigment. Histology shows extensive tissue necrosis with minimal inflammatory response. What is the primary virulence factor responsible for the tissue destruction in this infection?