FIG 6.

Pathology of lungs infected with Schu S4 and the waaY and waaL mutants. Lung sections are shown for mice infected for 3 and 5 days with F. tularensis Schu S4 (a and b) or for 3, 6, and 12 days with F. tularensis mutant strains (c to f). The lesions observed in samples from F. tularensis waaY and F. tularensis waaL mutant infections were indistinguishable from one another. (a) Lung section from F. tularensis Schu S4-infected mouse at 3 days postinfection. Lungs lacked overt lesions. (b) Lung section from F. tularensis Schu S4-infected mouse at 5 days postinfection. Multifocal vessels (large and small) had segmental to circumferential necrosis of the vascular wall (arrows), without overt inflammation in airways or lumens (asterisk). (c and d) Lung sections from F. tularensis mutant-infected mouse at 3 days postinfection (c) and 6 days postinfection (d). Lungs (day 3) had necrotic cellular debris and inflammation (neutrophils and lesser macrophages) that localized near distal airways/vessels, with extension into the adjacent parenchyma (c; arrows). (d) Lungs had perivascular inflammation (arrow) with progressive expansion of the lesions (necrotic debris, neutrophils, macrophages, and some edema) into adjacent parenchyma and airway lumens (asterisk). (e and f) By day 12 postinfection, pathology in the lungs of mice infected with F. tularensis mutant strains had progressed to diffuse airspace consolidation, with filling of most airways (e; asterisks) by edema, necropurulent debris (f; asterisks), and macrophages (f; arrows). The scale bar in panel a applies to panels a to e.