(571af) Bacterial Adhesion on Surfaces with Gradients of Bio-Inertness and Roughness

Surface chemistry and roughness play
important roles in bacterial cell adhesion and biofilm formation. We recently
reported that self-assembled monolayers (SAMs) presenting tri(ethylene) glycol (TEG)
are highly resistant to adhesion and biofilm formation of Escherichia coli,
while SAMs presenting methyl groups are non-resistant (Hou et al., Applied and Environmental
Microbiology, 2007. 73: 4300-4307). To further
study the response of cell adhesion and biofilm formation to surface conditions,
SAM surfaces with molecularly well-defined chemical and roughness gradients
were formed on gold films. The surfaces with chemical gradients were prepared with
a mixture of two SAMs to obtain the gradient in bio-inertness of TEG-SAM, with
the other one being either OH-SAM or CH₃-SAM_.Escherichia
coli RP437 was labeled with a plasmid constitutively expressing DsRed-Express
to form biofilms, which were analyzed with confocal laser scanning microscopy. The
three dimensional structure of biofilms was analyzed with the COMSTAT software to
quantify biomass, surface coverage, and thickness. Measurements of surface
coverage indicate that the amount of biofilm formed on surfaces is
linearly proportional to surface adhesiveness. In
addition to chemical gradient, a gradient with the nanometer-scale topography was introduced in
the gold films by creating a continuous increase in the angle of incidence of
gold atoms during vapor deposition. The strong correlation between cell
adhesion and surface roughness was observed. The
results obtained in this study will be useful for understanding
bacteria-surface interactions and for developing effective control methods.

Keywords: molecular gradient,
bio-inert surface, self-assembled monolayer, biofilm, cell adhesion.