Biomedical Implications of the Porosity of Microbial Biofilms - Porous Media: Applications in Biological Systems and Biotechnology - page 129

FIGURE 4.3
Biofilm structure layout. (Donlan, R.M. and Costerton, J.W., Clin. Microbiol.
Rev ., 15, 2, 2002. Reproduced with permission from American Society for
Microbiology.)
acyl-HSL quorum sensing, a single enzyme is required for the synthesis of
the signal from cellular metabolites (Parsek et al. 1999). Peptide-based sig-
naling usually involves the production of small linear or cyclic peptides that
are translated as a larger pro-peptide inside the cell; these are then further
processed during secretion (Dunny and Leonard 1997). In contrast to acyl-
HSL-based signaling, peptide signals are not detected inside the cell. In some
cases, a membrane-bound sensor protein belonging to the two-component
signal transduction family interacts with the peptide. Peptide-bound sensor
then activates an associated response regulator, which modulates expression
of quorum-sensing-regulated genes.
4.2.3 Detachment
Cell detachment from biofilm surface may be affected by either the shedding
of daughter cells from dividing cells, the detachment as a result of changes in
nutrient levels, the quorum sensing, or the shearing of small segments of the
biofilm as a result of shear forces.
In case of infectious biofilms, such detached cells may affect systemic infec-
tion, depending on a number of factors, including the response of the host
immune system. Gilbert et al. (1993) showed that detached microbial cell's
surface hydrophobicity was low for newly dispersed cells but steadily increased
upon cell growth. Boyd and Chakrabarty (1994) suggested that the enzyme