Section: USMLE

13) A letter carrier is severely bitten by a pit bull guarding a junkyard. The wound is cleansed, and the letter carrier receives a booster injection of tetanus toxoid and an injection of penicillin G. Several days later, the wound is inflamed and purulent. The exudate is cultured on blood agar and yields gram-negative rods. Antibiotic sensitivity tests are pending. The most likely agent to be isolated is