Statistical Analysis of Long- and Short-Range Forces Involved in Bacterial Adhesion to Substratum Surfaces as Measured Using Atomic Force Microscopy

Abstract

Surface thermodynamic analyses of microbial adhesion using measured contact angles on solid substrata and microbial cell surfaces are widely employed to determine the nature of the adhesion forces, i.e., the interplay between Lifshitz-van der Waals and acid-base forces. While surface thermodynamic analyses are often viewed critically, atomic force microscopy (AFM) can also provide information on the nature of the adhesion forces by means of Poisson analysis of the measured forces. This review first presents a description of Poisson analysis and its underlying assumptions. The data available from the literature for different combinations of bacterial strains and substrata are then summarized, leading to the conclusion that bacterial adhesion to surfaces is generally dominated by short-range, attractive acid-base interactions, in combination with long-range, weaker Lifshitz-van der Waals forces. This is in line with the findings of surface thermodynamic analyses of bacterial adhesion. Comparison with single-molecule ligand-receptor forces from the literature suggests that the short-range-force contribution from Poisson analysis involves a discrete adhesive bacterial cell surface site rather than a single molecular force. The adhesion force arising from these cell surface sites and the number of sites available may differ from strain to strain. Force spectroscopy, however, involves the tedious task of identifying the minor peaks in the AFM retraction force-distance curve. This step can be avoided by carrying out Poisson analysis on the work of adhesion, which can also be derived from retraction force-distance curves. This newly proposed way of performing Poisson analysis confirms that multiple molecular bonds, rather than a single molecular bond, contribute to a discrete adhesive bacterial cell surface site.Bacteria can adhere to various natural (33) and synthetic (11) surfaces, a phenomenon with widely different fields of application ranging from marine fouling, soil remediation, and food and drinking water processing to medicine and dentistry. In order to avoid the problems sometimes associated with bacterial adhesion, or to take advantage of it, better understanding of the mechanisms by which bacteria adhere to surfaces is required.Bacterial adhesion to surfaces can be approached by biochemical methods, by which the molecular structures mediating adhesion are unraveled (5, 18, 22, 31), or by physicochemical methods. Surface thermodynamic analyses of bacterial cell and substratum surfaces using measured contact angles with liquids have not only indicated when thermodynamic conditions are favorable or unfavorable for adhesion (1, 37) but can also be employed in combination with measured zeta potentials of the interacting surfaces to determine the nature of the adhesion forces that mediate initial adhesion, i.e., the interplay among long-range (Lifshitz-van der Waals [LW] and electrical double-layer [EDL]) and short-range (Lewis acid-base [AB]) interaction forces (35). Surface thermodynamic analyses of bacterial ad...

Nanoscale Cell Wall Deformation Impacts Long-Range Bacterial Adhesion Forces on Surfaces

“…Moreover, in a long-range approach, surface appendages may be less important, as the concept of distance between bacteria and substratum surfaces is lost upon close approach. Long-range Lifshitz-Van der Waals adhesion forces can be derived from contact angles with liquids on the interacting surfaces and surface thermodynamic modeling (25,26) or decoupling of AFM adhesion force measurements using Poisson analysis (27)(28)(29)(30). However, among different strains, long-range adhesion forces vary considerably less than short-range forces (27)(28)(29)(30).…”

“…Long-range Lifshitz-Van der Waals adhesion forces can be derived from contact angles with liquids on the interacting surfaces and surface thermodynamic modeling (25,26) or decoupling of AFM adhesion force measurements using Poisson analysis (27)(28)(29)(30). However, among different strains, long-range adhesion forces vary considerably less than short-range forces (27)(28)(29)(30). Similarity in long-range adhesion forces is to be expected, because these forces arise from the entire bacterial cell, i.e., its DNA content, cytoplasm, cell membrane, peptidoglycan layer, and outermost cell wall structures (Fig.…”

Probing the nanoadhesion of Streptococcus sanguinis to titanium implant surfaces by atomic force microscopy

“…Minor unbinding events observed at 60 seconds surface delays were fitted to predict contour lengths according to the previously described worm-like chain (WLC) model. 28 Further decoupling of bacterial adhesion forces was performed with Poisson analysis according to a previously reported approach, 29 obtaining values for both short-range (F SR ) and long-range force (F LR ) components.…”

“…To decouple the adhesion between S. sanguinis and Ti, a previously reported statistical method known as Poisson analysis was employed 29 ( Figure 3B and C). By plotting a linear regression between mean adhesion force (nN) and variance (nN 2 ) of the minor unbinding peaks observed between four independent bacterial probes and substrate, it was possible to determine values for F SR and F LR .…”

Characterisation of spin coated engineered Escherichia coli biofilms using atomic force microscopy

“…More recently, the adhesion forces between Gram negative with Gram positive bacterial biofilms have been compared [18], with the interesting result that Gram positive bacteria are densely packed with EPS, possessing high adhesion forces and short distance snap-off events, compared to the smaller adhesion forces and less dense packing found in Gram negative bacterial biofilms. Statistical analyses of Staphylococcus epidermis adhesion forces as measured by AFM, employing single bacterial cells immobilised at the cantilever apex, have offered insight into the mechanisms of bacterial adhesion, encompassing both long-range and short-range forces [19].…”