Review Question - QID 214404

A 4-year-old boy is brought to the ED with 5 days of bloody diarrhea. His father says that he was not easily able to arouse his son this morning, prompting him to come to the ED. The boy's family went on a camping trip 2 weeks ago, and he has since returned to daycare where a few children have been absent due to diarrhea. He has a history of otitis media treated with antibiotics, and his vaccinations are up to date. His temperature is 101.7°F (38.7°C), blood pressure is 110/60 mmHg, pulse is 85/min, and respirations are 20/min. On exam, his mucus membranes are dry, and his abdomen is diffusely tender to deep palpation. His stool is positive for polymorphonuclear leukocytes and blood. The causative organism is found to be a non-lactose-fermenting, oxidase-negative, gram-negative rod. When cultured on triple sugar iron agar, there is no hydrogen sulfide production. Which of the following pathogens is the most likely cause of this patient's symptoms?