Floating and Tether-Coupled Adhesion of Bacteria to Hydrophobic and Hydrophilic Surfaces

Abstract

Models for bacterial adhesion to substratum surfaces all include uncertainty with respect to the (ir)reversibility of adhesion. In a model, based on vibrations exhibited by adhering bacteria parallel to a surface, adhesion was described as a result of reversible binding of multiple bacterial tethers that detach from and successively reattach to a surface, eventually making bacterial adhesion irreversible. Here, we use total internal reflection microscopy to determine whether adhering bacteria also exhibit variations over time in their perpendicular distance above surfaces. Streptococci with fibrillar surface tethers showed perpendicular vibrations with amplitudes of around 5 nm, regardless of surface hydrophobicity. Adhering, nonfibrillated streptococci vibrated with amplitudes around 20 nm above a hydrophobic surface. Amplitudes did not depend on ionic strength for either strain. Calculations of bacterial energies from their distances above the surfaces using the Boltzman equation showed that bacteria with fibrillar tethers vibrated as a harmonic oscillator. The energy of bacteria without fibrillar tethers varied with distance in a comparable fashion as the DLVO (Derjaguin, Landau, Verwey, and Overbeek)-interaction energy. Distance variations above the surface over time of bacteria with fibrillar tethers are suggested to be governed by the harmonic oscillations, allowed by elasticity of the tethers, piercing through the potential energy barrier. Bacteria without fibrillar tethers “float” above a surface in the secondary energy minimum, with their perpendicular displacement restricted by their thermal energy and the width of the secondary minimum. The distinction between “tether-coupled” and “floating” adhesion is new, and may have implications for bacterial detachment strategies.

Micro- and Nanotopography Sensitive Bacterial Attachment Mechanisms: A Review

“…Bacterial cells are not able to overcome the energy barrier solely by their motility or Brownian motion, yet their appendages have been hypothesized to penetrate the energy barrier due to their small radii, and then effectively bridge the cell and substratum (Hori and Matsumoto, 2010). This phenomenon has been confirmed experimentally using total internal reflection microscopy (Van Der Westen et al, 2018).…”

“…Energy barriers have been found to impede bacterial attachment of a wide variety of bacteria by “blocking” the cells from approaching the surfaces (Morisaki et al, 1999; Li and Logan, 2004; Feng et al, 2015). The secondary minimum, on the other hand, reflects a restriction of the bacterial movement by “trapping” the cells in an energy well (Van Der Westen et al, 2018). Bacterial cells are not able to overcome the energy barrier solely by their motility or Brownian motion, yet their appendages have been hypothesized to penetrate the energy barrier due to their small radii, and then effectively bridge the cell and substratum (Hori and Matsumoto, 2010).…”

Bioadhesion in the oral cavity and approaches for biofilm management by surface modifications

“…In the original theory, bacteria were treated as colloidal round spheres, ignoring surface roughness of bacteria and surface appendages attached to the bacterial membrane (e.g., pili, fimbriae, flagella). It was suggested that surface appendages have a high probability to pierce through the energy barrier and thereby tether a bacterium to the surface [ 43 , 45 ]. At this stage, a firm anchorage between the bacterium and the surface can be established involving covalent, ionic, or hydrogen bonding [ 44 ] (Fig.…”

Modeling Bacterial Adhesion to Unconditioned Abiotic Surfaces

“…Using optical microscopy, quartz crystal microbalance, or surface plasmon resonance, the number of attached cells in a certain area can be recorded over time (Filion-Côté et al, 2017;Keskin et al, 2018;Alexander et al, 2019). With the help of high-resolution optical techniques, not only the number of cells but also their motion at or above the surface can be quantified (van der Westen et al, 2018;Vissers et al, 2018). These methods can collect data of large numbers of cells simultaneously under controlled (with or without shear flow) conditions tangential to the surface.…”