A 28-year-old woman with no significant past medical history presents to the emergency department with a 12-hour history of fever, severe headache, and neck stiffness. Temperature is 39.2°C, heart rate 102/min, blood pressure 118/76 mmHg, respiratory rate 18/min, and oxygen saturation 98% on room air. Physical examination confirms neck stiffness and a positive Kernig sign. Lumbar puncture reveals cerebrospinal fluid with protein 180 mg/dL, glucose 32 mg/dL (serum glucose 98 mg/dL), and pleocytosis with 850 cells/μL (92% neutrophils). Gram stain is pending. The patient denies recent travel, drug use, or immunocompromising conditions. Empiric antimicrobial therapy with ceftriaxone and vancomycin is initiated immediately. Which of the following best explains why vancomycin is added to the regimen despite cephalosporin coverage?

1. A)Vancomycin covers Listeria monocytogenes, which is intrinsically resistant to third-generation cephalosporins and causes meningitis in nonelderly immunocompetent hostsGABARITO
2. B)Vancomycin achieves superior cerebrospinal fluid penetration compared to ceftriaxone, reducing bacterial burden more effectively
3. C)Vancomycin provides coverage for penicillin-resistant Streptococcus pneumoniae strains that may not respond to cephalosporin monotherapy
4. D)Vancomycin is bactericidal whereas ceftriaxone is bacteriostatic, requiring dual therapy for synergistic killing in the central nervous system
5. E)Vancomycin reduces the risk of complications such as subdural empyema by preventing antibiotic resistance emergence during treatment