Question

An $82$-year-old male is admitted to the inpatient ward after developing a high fever, severe global headache, and worsening lethargy over the past $24$ hours. His medical history includes hypertension, type 2 diabetes mellitus, and benign prostatic hyperplasia. Upon arrival, his temperature is $39.1^\circ\text{C}$ ($102.4^\circ\text{F}$), blood pressure is $112/68\text{ mmHg}$, and pulse is $108\text{/min}$. Physical examination demonstrates marked nuchal rigidity and disorientation to time and place. A lumbar puncture is promptly performed, and cerebrospinal fluid (CSF) analysis reveals a leukocyte count of $1,200/\mu\text{L}$ with $85\%$ neutrophils, a glucose level of $35\text{ mg/dL}$, and a protein level of $140\text{ mg/dL}$. He is empirically started on intravenous ceftriaxone, vancomycin, ampicillin, and dexamethasone. Two days later, the CSF culture confirms the growth of *Listeria monocytogenes*. Which of the following is the most appropriate next step in the antimicrobial management of this patient?