Biomedical Engineering Reference
In-Depth Information
9.2.2
Silver nanoparticles and biofilms
9.2.2.1
Mechanisms of action and literature data
Inorganic nanoparticles represent a new era in the nanoparticle field. They exhibit unique physical
and chemical properties and can be used in many physical, biological, biomedical, and pharmaceu-
tical applications
[16]
.
Silver nanoparticles are known for their broad-spectrum antimicrobial activity against bacteria,
fungi, and viruses
[17]
, and multifactorial mechanism of action. Nevertheless, data have shown that
biofilm-forming cells are less susceptible to nanosilver (nano-Ag) than planktonic counterparts
[18,19]
. An in vitro study found that the MIC of nano-Ag for Escherichia coli biofilms was four-
fold higher than the MIC for planktonic cells
[18]
. For Candida albicans and Candida glabrata bio-
films, the MIC was 17- to 135-fold and 16.5- to 34-fold higher, respectively, than for planktonic
cells
[19]
.
However, nano-Ag may have an important role in the prevention of biofilm formation.
Kalishwaralal et al.
[20]
verified that treating Pseudomonas aeruginosa and Staphylococcus epider-
midis with nano-Ag caused 95% inhibition in biofilm formation. A similar result was observed by
Monteiro et al.
[21]
with respect to C. albicans and C. glabrata biofilms. These authors found that
nano-Ag at 3.3
g/mL were more effective in inhibiting biofilm formation than in controlling
preformed biofilms.
Although biofilms have water channels through which nanoparticles may diffuse
[20]
, many
nanoparticles may be retained in the extracellular matrix, contributing to biofilm resistance.
Furthermore, several mechanisms have been proposed to explain why nanoparticles have a better
effect when applied to planktonic cells than on mature biofilms.
Another important aspect that may hinder the action of nano-Ag against biofilm cultures is their
predisposition to form aggregates of particles (
Figure 9.4
). This aggregation can occur due to
changes in ionic strength and interactions of nanoparticles with several substances present
ยต
in
(A)
(B)
FIGURE 9.4
Scanning electron microscopy images showing clusters of silver nanoparticles in contact with mature Candida
albicans biofilm. (B) represents an enlarged view of part of biofilm displayed in (A).
