FIG 2 .

Pneumococcal biofilms are present on mucosal epithelial cells in the septa of experimentally infected mice. Scanning electron microscopy of isolated nasal septa from naive or colonized mice. (A and B) Low (A)- and high (B)-magnification views of healthy septal epithelia. (C) 6A10-colonized nasal septa at 3 dpi. Both matrix-associated bacteria and free diplococci are present on top of ciliated epithelial cells. (D) TIGR4-colonized septa at 3 dpi. Small aggregates of bacteria are present. (E and I) 6A10-colonized septa at 7 dpi. Bacteria are encased within a matrix, and aggregates contain a number of visible host components. Large aggregates are associated with an absence of cilia. (F and J) TIGR4-colonized septa at 7 dpi. Clusters of aggregated bacteria rest on the epithelial surface and are associated with a number of host cells. (G and H) 6A10 (G)- and TIGR4 (H)-colonized respiratory epithelium at 14 dpi. Cilia are absent, and bacterial aggregates are seen on the exposed cells. Bacteria are encased within a thick, visible matrix, and individual cells are difficult to distinguish. 6A10 aggregates are large and highly structured, whereas TIGR4 aggregates were mottled and noticeably smaller. (I and J) Aggregates formed by both 6A10 (I) and TIGR4 (J) contain a number of host components, including inflammatory cells. Arrows indicate common features of biofilm architecture: exposed basement membrane, bacterial cells within matrix material, and incorporated ciliated cells and leukocytes.