A 17-year-old presents to the Emergency Department with fever, stiff neck, and vomiting.

TheGram stain showing Gram-negative diplococciin cerebrospinal fluid (CSF) is characteristic ofNeisseria meningitidis, a leading cause of bacterial meningitis in adolescents and young adults.

Step-by-Step Justification:

Gram Stain Interpretation:

Gram-negative diplococciin CSF strongly suggestNeisseria meningitidis​.

Classic Symptoms of Meningitis:

Fever,stiff neck, and vomiting are hallmark signs ofmeningococcal meningitis.

Neisseria meningitidis vs. Other Bacteria:

Haemophilus influenzae(Option A) →Gram-negative coccobacilli.

Listeria monocytogenes(Option C) →Gram-positive rods.

Streptococcus pneumoniae(Option D) →Gram-positive diplococci.

CBIC Infection Control References:

APIC Ready Reference for Microbes, "Neisseria meningitidis and Meningitis"​.