Biofims are heterogenous: variations in biofim structure exist
within individual biofims and between diffrent types of biofims.
However, a number of structural features that are common to many
biofims have been noted. For example, biofims frequently contain
microcolonies of bacterial cells. Water channels are commonly
found in biofims, and these can form a primitive circulatory
system, removing waste products and bringing fresh nutrients to
the deeper layers of the fim. Surface structures, such as fronds, can
dissipate the energy of flid flwing over the biofim. In mixedspecies biofims, there is often heterogeneity in the distribution of
diffrent species. Steep chemical gradients exist, such as oxygen or
pH, and these produce distinct microenvironments within the
biofim.
Microbial populations on the surfaces of teeth (dental plaque)
are excellent examples of biofim communities (Figure 23-7). Th
architecture of a dental plaque biofim has many features in
common with other biofims. It is heterogeneous in structure, with
clear evidence of open flid-filed channels running through the
plaque mass.64,65,428 (see Figure 23-5). Nutrients make contact with
the sessile (attached) microcolonies by diffsion from the water
channels to the microcolony, rather than from the matrix. Th
bacteria exist and proliferate within the intercellular matrix through
which the channels run. Th matrix confers a specialized environment, which distinguishes bacteria that exist within the biofim
from those that are free-flating, the so-called planktonic state in
solutions such as saliva or crevicular flid. Th biofim matrix functions as a barrier. Substances produced by bacteria within the
biofim are retained and concentrated, which fosters metabolic
interactions among the diffrent bacteria.
Th intercellular matrix consists of organic and inorganic materials derived from saliva, gingival crevicular flid (GCF), and bacterial products.
Organic constituents of the matrix include polysaccharides, proteins, glycoproteins, lipid material, and (perhaps) DNA. Albumin,
probably originating from crevicular flid, has been identifid as a
component of the plaque matrix. Th lipid material consists of
debris from the membranes of disrupted bacterial and host cells,
đang được dịch, vui lòng đợi..
