We investigate the attachment of Escherichia coli
on silanized glass surfaces during flow through a linear channel
at flow rates of 0.11 mL/min using confocal microscopy. We
assemble layers of organosilanes on glass and track the position
and orientation of bacteria deposited on these surfaces during
flow with high spatial resolution. We find that a metric based on
the degree of the surface-tethered motion of bacteria driven by
flagella is inversely correlated with deposition rate, whereas
conventional surface characterizations, such as surface energy or
water contact angle, are uncorrelated. Furthermore, the
likelihood that an initially moving bacterium becomes immobilized increases with increasing deposition rate. Our results
suggest that the chemistry and arrangement of silane molecules on the surface influence the transition from transient to
irreversible attachment by favoring different mechanisms used by bacteria to attach to surfaces.
We investigated the transition from transient to irreversible
attachment of E. coli bacteria deposited onto surfaces coated
with self-assembled silanes. By analyzing the trajectories of
hundreds of bacteria on each surface, we found that the rate at
which bacteria were deposited varied nonmonotonically with
surface wettability and energy. Instead, we found that
deposition rate was inversely correlated with the degree of
surface-attached flagella-driven motion. For a given flow rate,
bacteria less readily detached and more readily became
immobilized on the surfaces onto which they most rapidly
deposited. We posit that flagella enable bacteria to transiently
attach to surfaces; the fate of transiently attached bacteria,
however, is ultimately determined by physicochemical interactions
(electrostatic or van der Waals) between bacteria and
surfaces. Because the transition from transient to immobilized
attachment was also correlated with short-time deposition rate,
our results suggest that initial transient surface motility may
serve as a metric to rapidly determine the efficacy of surfaces to
reduce fouling by bacteria and thereby speed the design of
improved antifouling materials for medical, technological, and
environmental settings.
These initial results suggest multiple pathways for future
studies. First, we examined only the initial rate of deposition of
bacteria over relatively short times; as bacteria continue to
attach over long time scales, we expect that that interactions
between bacteria may influence the deposition rate and the
transition to irreversible attachment (as suggested by Figure 9).
Experiments to correlate initial motion to long-time deposition
are required to establish the predictive power of the
correlations that we identify here. Second, we showed that
our motility metric inversely correlates with deposition rate
across multiple flow rates. Variations in detachment rates,
however, suggest that bacteria may use different shear-ratedependent
attachment mechanisms on surfaces of different
properties; this idea is consistent with earlier experiments on E.
coli that suggest that the role of flagella in initial attachment
changes as the flow rate is increased.60 Future experiments
using motility- and appendage- or adhesin-deficient mutants
will provide further insight into the roles of motility on initial
attachment. Finally, we examined only one strain of E. coli.
Bacteria that readily form biofilms, such as the opportunistic
Gram-negative pathogen Pseudomonas aeruginosa, release
extracellular polymeric substances (EPS) that modify the
surface properties and facilitate initial adhesion and attachment61
and microcolony formation.22 Experiments in biofilmforming
strains may therefore provide insight into the role of
EPS in the transition from transient to irreversible attachment.
We expect that applying our high-throughput methods to
analyze bacterial trajectories in these different scenarios will
provide additional insight into the role of bacterial, surface, and
fluid conditions on the transition to irreversible adhesion.
