Biomedical Engineering Reference
In-Depth Information
Demaret and colleagues (Demaret et al. 2008) demonstrated comprehensive
modeling and simulation of the diffusion limitations dominating antimicrobial
agent penetration into bacterial biofilms.
One promising solution to the problem of antibiotic penetration has
emerged from the manipulation of electrical fields that surround bacteria in
a biofilm. This “Bioelectric Effect”—a term coined by J. W. Costerton and
colleagues—has been postulated to electrically alter the configuration of the
EPS matrix, as well as to enhance the penetration of antimicrobial agents
across the bacterial-cell envelope (Stoodley et al. 1997). Using alternating-
current densities of less than 100
A/cm
2
, it was found that the antibiotic
concentrations required to kill biofilm cells were significantly reduced com-
pared to untreated bacterial biofilm (Stoodley et al. 1997; Caubet et al. 2004).
These concentrations, however, were still higher than those required to kill
planktonic bacteria of the same species (Costerton et al. 1994; McLeod et al.
1999). It was proposed that this phenomenon is due to the electrostatic inter-
actions between negatively charged groups in the structure of the biofilm and
the charged electrode (Stoodley et al. 1997), which will increase “fluidity”
of the matrix, allowing a better penetration of the antibiotics (Caubet et al.
2004).
µ
4.5 Concluding Remarks
Accumulating data on structural characteristics of medically important
biofilms provides a complicated and challenging description of nonhomoge-
neous, multicomponent, and continuously changing complexes of mixed pop-
ulation of microbial cells. The porosity created throughout the buildup of a
biofilm by attachment followed by cell division and secretion of EPS matrix
is inherently irregular, presenting larger channels in between condensed cell
clusters, which contain much smaller channels. Both channel categories are
partially or fully packed with viscous secreted polysaccharide. Gradients of
nutrients, oxygen, pH, and secretions are created, affecting, in turn, the
metabolic state of the film forming mixed microbial cell populations embedded
within clusters of various sizes. Moreover, biological response to the contin-
uously changing environmental conditions affects genetic, biochemical, and
structural local changes at different paces. Detailed structural information on
some of the parameters affecting the structure and porosity of biofilms is yet
very limited.
It clearly appears that medically important infectious biofilms should
not be considered as readily characterized physical three-dimensional struc-
tures, handled with tools developed for such systems: thorough understanding
and awareness of the complex nature of systems composed of viable com-
plex cell communities continuously responding to environmental conditions is
crucial—along with physical and chemical tools—for the completion of our
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