Biology Reference
In-Depth Information
One disadvantage of this method is that a chemical linker is required to
attach the bacteria to the AFM cantilever or probe. Some common agents
applied are poly-L-lysine and hexadecanethiol. Control experiments must
be performed to help ensure that the linking chemical does not alter the
biological interaction forces observed.
Bacterial adhesion between model biomaterials can be easily quantiied.
For example, Boks
et al.
immobilized four different strains of
Staphylococcus
epidermidis
on AFM probes and then made measurements of interaction
forces on hydrophilic glass and a glass surface coated with a hydrophobic
chemical, dimethyldichlorosilane (DDS).
41
On the hydrophobic (DDS coated)
surface, the adhesion of all four bacterial strains was very rapid and was not
time-dependent. This was attributed to hydrophobic interactions. However,
when the bacterial strains were interacted with the hydrophilic glass, the
bond strength increased over time, and this growth was attributed to the
process of hydrogen bond formation. This inding has implications for the
development of biomaterials or coatings that resist bacterial colonization.
Since a number of types of interactions can occur within a single system,
the timescales must be considered when designing a material to inhibit a
particular type of interaction.
Hydrogen bonds have been considered an important part of the interaction
between bacteria and surfaces, and several studies have suggested that a
means to inhibit bacterial adhesion should focus on a method that disrupts
the ability of the microbe to form hydrogen bonds with the substrate.
42,43
A well-established method used for understanding bacterial interactions
with biomaterials is to study the forces between a bacterium and a surface
coated with biological molecules that form conditioning ilms on biomaterials.
For example, we studied the interaction of two strains of
with
glass and bovine serum albumin (BSA)-coated glass.
43
Biomaterials that are
implanted into the body rapidly accumulate a layer of proteins.
44
If this initial
attachment occurs, bacteria can grow into a bioilm that is very dificult
to eradicate, causing failures of biomedical devices that usually require
implant removal.
45
Although biomaterial coatings represent an active area of
research,
46,47
an antimicrobial coating will only be successful if it also resists
colonization by serum proteins. The model system we used included the
wild-type strain,
P. aeruginosa
PAO1, which contains two types of saccharides
in the LPS, the A and B bands. A band represents neutral sugars, while B
band is the serotype-speciic O-antigen. A mutant strain, AK1401, was also
examined. The mutant strain has a shorter A-band polymer, and lacks the B
band entirely. For both strains, we found that hydrogen bonds control the
association between
P. aeruginosa
P. aeruginosa
and protein-coated surfaces. The mean
adhesion force (
F
adh
) between BSA and AK1401 was 1.12 nN, compared with
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