Biomedical Engineering Reference
In-Depth Information
FIGURE 9.3
Dental biofilms grown on hydroxyapatite chips in situ. The biofilms were stained with LIVE/DEAD
s
BacLight
t
Bacterial Viability Kit and imaged with a confocal microscope. Green cells represent live microorganisms while
red are dead. (For interpretation of the references to color in this figure legend, the reader is referred to the
web version of this topic.)
Image courtesy of The Center for Biofilm Engineering at Montana State University.
Several factors influence biofilm tolerance to antimicrobials including nanoparticles. The first
factor that sets biofilms apart is the presence of EPS. The slime layer that involves the microbial
cells may not only limit the penetration of the agents but also react with it, reducing its effective-
ness
[12]
. In addition, biofilms are very heterogeneous; so in a community there are not only highly
active cells but also dormant cells. In fact, the presence of dormant cells has been reported as the
major factor in antimicrobial tolerance
[13,14]
.
As many antimicrobial and antibiotics target macromolecule synthesis, when the cells are not
growing or dividing they are less susceptible. Other factors involved in tolerance are the phenotypic
variations, the existence of a highly developed communications system between the cells (quorum
sensing), and the bacterial multidrug efflux pumps
[13,15]
. A possible strategy to overcome biofilm
tolerance may be the use of several antimicrobials combined or even the combination of physical
and chemical treatments.
