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

Abstract

Adhesion of bacteria occurs on virtually all natural and synthetic surfaces and is crucial for their survival. Once they are adhering, bacteria start growing and form a biofilm, in which they are protected against environmental attacks. Bacterial adhesion to surfaces is mediated by a combination of different short-and long-range forces. Here we present a new atomic force microscopy (AFM)-based method to derive long-range bacterial adhesion forces from the dependence of bacterial adhesion forces on the loading force, as applied during the use of AFM. The long-range adhesion forces of wild-type Staphylococcus aureus parent strains (0.5 and 0.8 nN) amounted to only one-third of these forces measured for their more deformable isogenic ⌬pbp4 mutants that were deficient in peptidoglycan cross-linking. The measured long-range Lifshitz-Van der Waals adhesion forces matched those calculated from published Hamaker constants, provided that a 40% ellipsoidal deformation of the bacterial cell wall was assumed for the ⌬pbp4 mutants. Direct imaging of adhering staphylococci using the AFM peak force-quantitative nanomechanical property mapping imaging mode confirmed a height reduction due to deformation in the ⌬pbp4 mutants of 100 to 200 nm. Across naturally occurring bacterial strains, long-range forces do not vary to the extent observed here for the ⌬pbp4 mutants. Importantly, however, extrapolating from the results of this study, it can be concluded that long-range bacterial adhesion forces are determined not only by the composition and structure of the bacterial cell surface but also by a hitherto neglected, small deformation of the bacterial cell wall, facilitating an increase in contact area and, therewith, in adhesion force. Bacteria adhere to virtually all natural and synthetic surfaces (1, 2), as adhesion is crucial for their survival. Bacterial adhesion to surfaces is followed by their growth and constitutes the first step in the formation of a biofilm, in which organisms are protected against antimicrobial treatment and environmental attacks. Accordingly, the biofilm mode of growth is highly persistent and biofilms are notoriously hard to remove, causing major problems in many industrial and biomedical applications, with high associated costs. On the other hand, biofilms can be beneficial, too, as in the bioremediation of soil, for instance. Surface thermodynamics and (extended) DLVO (Derjaguin and Landau, Verwey, and Overbeek) approaches have been amply applied in current microbiology to outline that bacterial adhesion to surfaces is mediated by an interplay of different fundamental physicochemical interactions, including Lifshitz-Van der Waals, electric double-layer, and acid-base forces (3-5). Assorted according to their different effective ranges, these different fundamental interactions can be alternatively categorized into two groups, short-range and long-range forces (6), that act over distances of a few nm up to 10s of nm, respectively.Long-range adhesion forces are generally associated with Lifshitz-Van der ...

Influence of Adhesion Force on icaA and cidA Gene Expression and Production of Matrix Components in Staphylococcus aureus Biofilms

“…Importantly, due to the extreme sensitivity of surface-enhanced fluorescence measurements, other wild-type strains have also been shown to deform upon adhesion to a surface (19). As an important aspect of surface-enhanced fluorescence, the number of bacteria involved in a single analysis is much larger than the number that can be determined by any other microscopic method presently used, like AFM, while surface-enhanced fluorescence also measures deformation under the naturally occurring adhesion forces that are not present under an applied force, as in AFM (21). Therefore, it can be anticipated that differences in adhesion forces between S. aureus and various substratum surfaces may actually induce different degrees of cell wall deformation, which supports our hypothesis that adhesion forces cause nanoscale cell wall deformations and membrane stresses that act as mechanisms signaling an organism to enter its adhering state.…”

“…Adhesion forces arising from substratum surfaces have recently been demonstrated to induce nanoscopic cell wall deformation, yielding membrane stresses (21). Deformation of lipid bilayers has been shown to result in the opening of mecha- nosensitive channels involved in adhesion force sensing, as they transduce a mechanical force into chemical signals (30).…”

“…In order to measure adhesion forces between the S. aureus strains and different biomaterials, staphylococci were immobilized on a cantilever for atomic force microscopy (AFM), as described before (21). Bacteria were cultured as described above, with the difference that they were washed and suspended in demineralized water.…”

van der Waals forces influencing adhesion of cells

“…Since these early results concerning van der Waals force influencing cell adhesion, many more recent papers have appeared discussing such effects [15][16][17].…”

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

“…15 This phase can be explained by the Derjaguin, Landau, Vervey, and Overbeek colloidal theory. 16 In the subsequent locking phase, bacterial receptors attach to the surface in an irreversible manner and secure the bacterium into place. 17 Bacterial appendages such as pili and capsule are also thought to be involved in this irreversible locking phase stage, where surface de-adhesion can only be obtained by mechanical or chemical removal.…”