Significant lung pathology in Klebsiella pneumonia infected animals. Histopathology of mouse lungs two (upper row) and five days (bottom row) after mock (left column) and K. pneumoniae (right column) infection: No changes were present in mock infected mice. In contrast, extensive interstitial infiltration by predominantly neutrophils and macrophages was present at two days after infection of mice with K. pneumoniae. After five days, additional, predominantly perivascular, lymphocytic infiltrates were seen. Hematoxylin & Eosin stained lung sections at 200 × magnification.