Figure 5. Greater accumulation of exopolymeric matrix on Asc10⁺ E. faecalis biofilms, in comparison to Asc10⁻ biofilms.

Scanning electron micrographs of E. faecalis Asc10⁺ OG1SSp (pCF10) incubated 0.5 h (A) and 2 h (B) showing typical comparatively smooth appearance of the bacterial surface at early incubation times (A) compared to the fibrillar strands that became more evident over time (B). Use of a fixative containing alcian blue on the 4 h Asc10⁺ OG1SSp (pCF10)-infected valve tissue reveals the presence of an interwoven matrix covering most of the bacterial cells, which are seen as raised areas under the matrix (C). At higher magnification (D), bacterial cells can be observed clearly under the matrix, which appears more fibrillar in this view. Arrows in parts C and D indicate cells partially covered by matrix material. (E, F) Alcian blue-fixed valve sections colonized with the prgB deletion mutant (pCF10-8) revealed less matrix material as compared to the Asc10⁺ strain, in addition to a marked decrease in bacterial cells adherent to the valve tissue. In part F, the matrix material coats an Asc10⁻ E. faecalis cell, with areas of attachment to the valve tissue. Scale bars: A = 0.3 µm, B = 0.5 µm, C = 3.0 µm, D = 1.0 µm, E = 4.0 µm, F = 1.0 µm.