A 22-year-old male presents with acute right knee swelling, warmth, and intense pain. Arthrocentesis reveals cloudy synovial fluid with 85,000 WBCs/mm^3 (95% neutrophils). Gram stain reveals intracellular Gram-negative diplococci. What is the causative organism?
Answer and explanation
Correct answer: B. Neisseria gonorrhoeae
- Step 1: Identify microbiological characteristics: Gram-negative diplococci inside polymorphonuclear leukocytes.
- Step 2: In sexually active young adults presenting with acute monoarthritis or disseminated gonococcal infection, Neisseria gonorrhoeae is the leading cause.
Answer
Neisseria gonorrhoeae.
Why not the others: 'Staphylococcus aureus' is a Gram-positive coccus in clusters; 'Streptococcus pyogenes' is a Gram-positive coccus in chains; 'Borrelia burgdorferi' is a spirochete causing Lyme disease.
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