After splenectomy, the patient is particularly susceptible to infections by which type of organisms?

• A. Encapsulated bacteria
• B. Gram-negative rods
• C. Intracellular parasites
• D. Fungi

Answer: (A)

The spleen is crucial for defense against encapsulated bacteria because it filters blood and produces rapid antibody responses to polysaccharide capsules, enabling opsonization and clearance by phagocytes. Marginal zone B cells generate IgM against these capsules, and splenic macrophages efficiently remove opsonized organisms. Without a spleen, this opsonization and clearance are impaired, making infections by encapsulated bacteria—such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b—more likely and potentially rapidly progressive. This is the classic risk after splenectomy, hence the emphasis on vaccination and, in some cases, antibiotic prophylaxis.