Figure 1.

Biofilm morphology. Scanning electron micrographs of biofilm communities formed (A) on the epithelial mucosa in vivo, (B) on epithelial cells grown in vitro and (C) on a glass substratum in vitro. The major image in each panel shows the biofilm at 2000x magnification and the insert in the upper right corner shows an increased magnification of 10,000x. ECM = extracellular matrix, used here instead of the more conventional EPS (extracellular polymeric substance) as secretion of specific polymeric substances have not yet been identified or characterized in Streptococcus pneumoniae, and the matrix is not well defined. RBC = red blood cell, Spn = Streptococcus pneumoniae, Matrix = biofilm matrix composed of extracellular substances and cellular debris. In general, the in vivo biofilms display a high degree of matrix formation that originated primarily from lysed bacterial cells and consists of cellular debris and DNA. Biofilms from in vitro cultures on epithelial cells show less encapsulation in matrix and more naked bacterial cells. However, biofilms formed on glass are much less developed with less biomass and almost no matrix formation.