10 research outputs found
Chlorhexidine-induced elastic and adhesive changes of Escherichia coli cells within a biofilm
Chlorhexidine is a widely used, commercially available cationic antiseptic. Although its mechanism of action on planktonic bacteria has been well explored, far fewer studies have examined its interaction with an established biofilm. The physical effects of chlorhexidine on a biofilm are particularly unknown. Here, the authors report the first observations of chlorhexidine-induced elastic and adhesive changes to single cells within a biofilm. The elastic changes are consistent with the proposed mechanism of action of chlorhexidine. Atomic force microscopy and force spectroscopy techniques were used to determine spring constants and adhesion energy of the individual bacteria within an Escherichia coli biofilm. Medically relevant concentrations of chlorhexidine were tested, and cells exposed to 1% (w/v) and 0.1% more than doubled in stiffness, while those exposed to 0.01% showed no change in elasticity. Adhesion to the biofilm also increased with exposure to 1% chlorhexidine, but not for the lower concentrations tested. Given the prevalence of chlorhexidine in clinical and commercial applications, these results have important ramifications on biofilm removal technique
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Epitaxy of Crystal Monolayers
Epitaxial growth, or the oriented growth of a crystalline monolayer on an ordered substrate, appears in a wide range of systems and applications, from novel device fabrication to freshwater remediation. Despite this, methodical studies of the phenomenon are rare, and the mechanisms governing epitaxial growth are poorly understood. This investigation employs AFM techniques to monitor the epitaxial growth of ion crystal systems at the initial stages of growth. By using systems with well-known physical properties, we are able to relate growth modes to two key parameters, crystal lattice mismatch, Îr/râ, and affinity between the overgrowth and the substrate ions, Ο. We found wetting growth occurs for systems in which Îr/râ is expansive (overgrowth lattice must expand to accommodate substrate) or mildly compressive (overgrowth compresses to accommodate substrate). Additionally, a strong affinity between the substrate and overgrowth ions, in combination with an expansive system, allows for epitaxial growth from undersaturated solutions. We also have observed several instances where the lateral force contrast on the growing film exhibits a strong dependence on the time of exposure to the growth solution and on the driving force for growth (solute concentration). We present results for three epitaxial growth systems in aqueous solutions: CaSOâ on CaCOâ, PbSOâ on BaSOâ, and BaSOâ on BaSOâ. Chemically and topographically identical regions grown at higher concentrations exhibit higher friction than regions grown at lower concentrations. These observations suggest that epitaxial growth occurs by a fast condensation step incorporating a high defect density
The Effects of Contact Time on the Adhesive Properties of an Established Bacterial Biofilm
Characterizing Pilus-Mediated Adhesion of Biofilm-Forming E. coli to Chemically Diverse Surfaces Using Atomic Force Microscopy
Biofilms are complex communities of microorganisms living together at an interface. Because biofilms are often associated with contamination and infection, it is critical to understand how bacterial cells adhere to surfaces in the early stages of biofilm formation. Even harmless commensal Escherichia coli naturally forms biofilms in the human digestive tract by adhering to epithelial cells, a trait that presents major concerns in the case of pathogenic E. coli strains. The laboratory strain E. coli ZK1056 provides an intriguing model system for pathogenic E. coli strains because it forms biofilms robustly on a wide range of surfaces.E. coli ZK1056 cells spontaneously form living biofilms on polylysine-coated AFM cantilevers, allowing us to measure quantitatively by AFM the adhesion between native biofilm cells and substrates of our choice. We use these biofilm-covered cantilevers to probe E. coli ZK1056 adhesion to five substrates with distinct and well-characterized surface chemistries, including fluorinated, amineterminated, and PEG-like monolayers, as well as unmodified silicon wafer and mica. Notably, after only 0â10 s of contact time, the biofilms adhere strongly to fluorinated and amine-terminated monolayers as well as to mica and weakly to âantifoulingâ PEG monolayers, despite the wide variation in hydrophobicity and charge of these substrates. In each case the AFM retraction curves display distinct adhesion profiles in terms of both force and distance, highlighting the cellsâ ability to adapt their adhesive properties to disparate surfaces. Specific inhibition of the pilus protein FimH by a nonhydrolyzable mannose analogue leads to diminished adhesion in all cases, demonstrating the critical role of type I pili in adhesion by this strain to surfaces bearing widely different functional groups. The strong and adaptable binding of FimH to diverse surfaces has unexpected implications for the design of antifouling surfaces and antiadhesion therapies
Probing the Interactive Forces Between Bacterial Biofilm Cells and Surfaces with Atomic Force Microscopy
Characterizing Pilus-Mediated Adhesion of Biofilm-Forming <i>E. coli</i> to Chemically Diverse Surfaces Using Atomic Force Microscopy
Biofilms are complex communities
of microorganisms living together
at an interface. Because biofilms are often associated with contamination
and infection, it is critical to understand how bacterial cells adhere
to surfaces in the early stages of biofilm formation. Even harmless
commensal <i>Escherichia coli</i> naturally forms biofilms
in the human digestive tract by adhering to epithelial cells, a trait
that presents major concerns in the case of pathogenic <i>E.
coli</i> strains. The laboratory strain <i>E. coli</i> ZK1056 provides an intriguing model system for pathogenic <i>E. coli</i> strains because it forms biofilms robustly on a
wide range of surfaces.<i>E. coli</i> ZK1056 cells spontaneously
form living biofilms on polylysine-coated AFM cantilevers, allowing
us to measure quantitatively by AFM the adhesion between native biofilm
cells and substrates of our choice. We use these biofilm-covered cantilevers
to probe <i>E. coli</i> ZK1056 adhesion to five substrates
with distinct and well-characterized surface chemistries, including
fluorinated, amine-terminated, and PEG-like monolayers, as well as
unmodified silicon wafer and mica. Notably, after only 0â10
s of contact time, the biofilms adhere strongly to fluorinated and
amine-terminated monolayers as well as to mica and weakly to âantifoulingâ
PEG monolayers, despite the wide variation in hydrophobicity and charge
of these substrates. In each case the AFM retraction curves display
distinct adhesion profiles in terms of both force and distance, highlighting
the cellsâ ability to adapt their adhesive properties to disparate
surfaces. Specific inhibition of the pilus protein FimH by a nonhydrolyzable
mannose analogue leads to diminished adhesion in all cases, demonstrating
the critical role of type I pili in adhesion by this strain to surfaces
bearing widely different functional groups. The strong and adaptable
binding of FimH to diverse surfaces has unexpected implications for
the design of antifouling surfaces and antiadhesion therapies