Bacterial Infections


Acute purulent exudate fills bronchioles and adjacent alveoli. B = bronchiole

Necrotizing pneumonia

Gram negative organisms often produce parenchymal destruction, which incites little fibrosis. The yellowish regions represent the necrotizing pneumonia, which produces the accompanying cavities.

Pseudomonas pneumonia

Histologically, the early lesion shows hemorrhagic necrosis (left). Later, the necrotic zone is ischemic (right). Cavitation may follow.

Pseudomonas pneumonia

In acute pseudomonas pneumonia in immunocompromised subjects, bacilli have a tropism for blood vessel walls but rarely cause thrombosis. The purple area surrounding the vessel on the left consists of myriads of organisms. A gram stain (right) shows organisms, confluent at the bottom and scattered above.