A 68-year-old woman with rheumatoid arthritis on methotrexate and prednisolone presents with acute onset of left hip pain and fever (39.2°C) for 3 days. She denies recent trauma or surgery. Hip examination shows severe pain on internal rotation and flexion, with guarding. Synovial fluid obtained by ultrasound-guided aspiration shows: WBC 72,000/μL (88% neutrophils), glucose 18 mg/dL (serum 95 mg/dL), protein 5.8 g/dL, Gram stain negative, and culture pending. Inflammatory markers are elevated (CRP 12 mg/dL, ESR 68 mm/hr). What is the most likely organism?