A 52-year-old farmer from rural Maharashtra presents with a 3-day history of left eye pain, photophobia, and purulent discharge. He reports a thorn prick injury while working in the field 5 days ago. On examination, visual acuity is 6/60, and slit-lamp biomicroscopy reveals a 4 mm central corneal ulcer with a raised, indurated border, satellite lesions, and a hypopyon of 2 mm. Gram stain of the corneal scraping shows Gram-negative rods. What is the most likely causative organism?