A 3-day-old neonate develops pneumonia and empyema. Blood culture grows catalase-positive, CAMP test positive, beta-haemolytic Gram-positive cocci that are resistant to penicillin. The most likely organism and recommended therapy are:
- A Staphylococcus aureus — vancomycin ✓
- B Group B Streptococcus (S. agalactiae) — ampicillin plus gentamicin
- C Listeria monocytogenes — ampicillin plus gentamicin
- D Streptococcus pneumoniae — ceftriaxone
Explanation
The described organism is catalase-positive (differentiates Staphylococcus from Streptococcus/Listeria) and CAMP test positive. While CAMP test is a classic feature of Group B Streptococcus, Staphylococcus aureus also gives a positive CAMP inhibition test (different from Group B Strep's CAMP enhancement). However, catalase positivity definitively points to S. aureus. Neonatal S. aureus pneumonia with empyema and penicillin resistance (due to beta-lactamase) requires vancomycin for MRSA coverage in the neonatal ICU setting. Group B Streptococcus is catalase-negative and sensitive to ampicillin. The distinction between neonatal early-onset (<72 hours, GBS) and late-onset staphylococcal sepsis is clinically important.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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