Bacterial Adhesion Forces Research Articles

Bacterial adhesion force quantification by fluidic force microscopy.

Quantification of detachment forces between bacteria and substrates facilitates the understanding of the bacterial adhesion process that affects cell physiology and survival. Here, we present a method that allows for serial, single bacterial cell force spectroscopy by combining the force control of atomic force microscopy with microfluidics. Reversible bacterial cell immobilization under physiological conditions on the pyramidal tip of a microchanneled cantilever is achieved by underpressure. Using the fluidic force microscopy technology (FluidFM), we achieve immobilization forces greater than those of state-of-the-art cell-cantilever binding as demonstrated by the detachment of Escherichia coli from polydopamine with recorded forces between 4 and 8 nN for many cells. The contact time and setpoint dependence of the adhesion forces of E. coli and Streptococcus pyogenes, as well as the sequential detachment of bacteria out of a chain, are shown, revealing distinct force patterns in the detachment curves. This study demonstrates the potential of the FluidFM technology for quantitative bacterial adhesion measurements of cell-substrate and cell-cell interactions that are relevant in biofilms and infection biology.

Insights into the relation between adhesion force and chalcopyrite-bioleaching by Acidithiobacillus ferrooxidans

This paper presents a study on the relation between bacterial adhesion force and bioleaching rate of chalcopyrite, which sheds light on the influence of interfacial interaction on bioleaching behavior. In our research, Acidithiobacillus ferrooxidans (A. ferrooxidans) were adapted to grow with FeSO4·7H2O, element sulfur or chalcopyrite. Then, surface properties of Acidithiobacillus ferrooxidans and chalcopyrite were analyzed by contact angle, zeta potential and Fourier transform infrared spectroscopy (FTIR). Adhesion force between bacteria and chalcopyrite was measured by atomic force microscopy (AFM). Attachment and bioleaching behaviors were also monitored. The results showed that A. ferrooxidans adapted with chalcopyrite exhibited the strongest adhesion force to chalcopyrite and the highest bioleaching rate. Culture adapted with sulfur bacteria took second place and FeSO4·7H2O-adapted bacteria were the lowest. Bioleaching rate and bacterial attachment capacity were positively related to bacterial adhesion force, which is affected by the nature of energy source. According to this work, the attachment of bacteria to chalcopyrite surface is one of the most important aspects that influence the bioleaching process of chalcopyrite.

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

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 Δpbp4 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 Δpbp4 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 Δpbp4 mutants of 100 to 200 nm. Across naturally occurring bacterial strains, long-range forces do not vary to the extent observed here for the Δpbp4 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.

Bacterial Adhesion Forces to Ag-Impregnated Contact Lens Cases and Transmission to Contact Lenses

To measure adhesion forces of Pseudomonas aeruginosa, Staphylococcus aureus, and Serratia marcescens to a rigid contact lens (CL), standard polypropylene, and Ag-impregnated lens cases using atomic force microscopy and determine bacterial transmission from lens case to CL. Adhesion forces of bacterial strains to Ag-impregnated and polypropylene lens cases and a rigid CL were measured using atomic force microscopy. Adhesion forces were used to calculate Weibull distributions, from which transmission probabilities from lens case to CL were derived. Transmission probabilities were compared with actual transmission of viable bacteria from a lens case to the CL in 0.9% NaCl and in an antimicrobial lens care solution. Bacterial transmission probabilities from polypropylene lens cases based on force analysis coincided well for all strains with actual transmission in 0.9% NaCl. Bacterial adhesion forces on Ag-impregnated lens cases were much smaller than that on polypropylene and CLs, yielding a high probability of transmission. Comparison with actual bacterial transmission indicated bacterial killing due to Ag ions during colony-forming unit transmission from an Ag-impregnated lens case, especially for P. aeruginosa. Transmission of viable bacteria from Ag-impregnated lens cases could be further decreased by use of an antimicrobial lens care solution instead of 0.9% NaCl. Bacterial transmission probabilities are higher from Ag-impregnated lens cases than from polypropylene lens cases because of small adhesion forces, but this is compensated for by enhanced bacterial killing due to Ag impregnation, especially when in combination with an antimicrobial lens care solution. This calls for a balanced combination of antimicrobial lens care solutions and surface properties of a lens case and CL.

Nonadhesive, silica nanoparticles-based brush-coated contact lens cases-Compromising between ease of cleaning and microbial transmission to contact lenses

Surface properties of lens cases are determinant for their cleanability and for microbial transmission from lens cases to contact lenses (CLs). PEG-polymer-brush-coatings are known to decrease microbial adhesion more than other surface-coatings. Here, we applied a robust, silica nanoparticles-based brush-coating to polypropylene cases to evaluate their ease of cleaning and probability of bacterial transmission to CLs. Adhesion forces of nine bacterial strains (Pseudomonas, Staphylococci, and Serratia) to rigid CLs, polypropylene, and silica nanoparticles-based brush-coated polypropylene were measured using atomic-force-microscopy and subjected to Weibull analyses to yield bacterial transmission probabilities. Biofilms of each strain were grown in coated and uncoated cases and rinsed with a NaCl or antimicrobial lens care solution. Residual, viable organisms were quantified. Bacterial adhesion forces of all strains were significantly, up to tenfold smaller on brush-coated than on uncoated polypropylene. This yielded, higher transmission probabilities to a CL, but mild-rinsing yielded 10-100 fold higher removal of bacteria from brush-coated than from polypropylene cases. Moreover, due to weak adhesion forces, bacteria on brush-coated cases were two-to-three fold more susceptible to an antimicrobial lens care solution than on polypropylene cases. Therewith, the design of lens case surfaces is a compromise between ease of cleaning and transmission probability to CLs.

Bacterial Adhesion Forces with Substratum Surfaces and the Susceptibility of Biofilms to Antibiotics

Biofilms causing biomaterial-associated infection resist antibiotic treatment and usually necessitate the replacement of infected implants. Here we relate bacterial adhesion forces and the antibiotic susceptibility of biofilms on uncoated and polymer brush-coated silicone rubber. Nine strains of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa adhered more weakly to brush-coated silicone rubber (-0.05 ± 0.03 to -0.51 ± 0.62 nN) than to uncoated silicone rubber (-1.05 ± 0.46 to -5.1 ± 1.3 nN). Biofilms of weakly adhering organisms on polymer brush coatings remained in a planktonic state, susceptible to gentamicin, unlike biofilms formed on uncoated silicone rubber.

Studies on Effect of Applied Potential on Bacterial Adhesion Forces on Titanium Using Atomic Force Microscopy

Studies on Effect of Applied Potential on Bacterial Adhesion Forces on Titanium Using Atomic Force Microscopy

Bacteria attachment to surfaces – AFM force spectroscopy and physicochemical analyses

Understanding bacterial adhesion to surfaces requires knowledge of the forces that govern bacterial–surface interactions. Biofilm formation on stainless steel 316 (SS316) by three bacterial species was investigated by examining surface force interaction between the cells and metal surface using atomic force microscopy (AFM). Bacterial–metal adhesion force was quantified at different surface delay time from 0 to 60 s using AFM tip coated with three different bacterial species: Gram-negative Massilia timonae and Pseudomonas aeruginosa, and Gram-positive Bacillus subtilis. The results revealed that bacterial adhesion forces on SS316 surface by Gram-negative bacteria is higher (8.53 ± 1.40 nN and 7.88 ± 0.94 nN) when compared to Gram-positive bacteria (1.44 ± 0.21 nN). Physicochemical analysis on bacterial surface properties also revealed that M. timonae and P. aeruginosa showed higher hydrophobicity and surface charges than B. subtilis along with the capability of producing extracellular polymeric substances (EPS). The higher hydrophobicity, surface charges, and greater propensity to form EPS by M. timonae and P. aeruginosa led to high adhesive force on the metal surface.

Force Analysis of Bacterial Transmission from Contact Lens Cases to Corneas, with the Contact Lens as the Intermediary

To determine the probability of transmission of a Staphylococcus aureus strain from a contact lens case, to the contact lens (CL) surfaces, to the cornea, on the basis of bacterial adhesion forces measured by using atomic force microscopy (AFM). Adhesion forces between S. aureus strain 835 probes with rigid and soft CLs, storage cases, and porcine corneas were measured with AFM and used to calculate Weibull distributions, from which the transmission probability from one surface to another was derived. Bacterial transmission probabilities from force analyses were compared with experimentally obtained transmission data. After bond-strengthening, S. aureus adhered to the surface of a lens case with a median force of 10.8 nN. Adhesion forces were different on the soft and rigid CLs (7.7 and 13.6 nN, respectively). Adhesion forces on porcine corneas amounted to 11.8 nN. Data variations were used to calculate the Weibull distribution, from which the probability of transmission from the lens case to a CL and from the CL to the cornea can be directly read. Final transmission probabilities from lens case to the cornea were slightly higher for the rigid (24%) than for the soft (19%) CL. Bacterial transmission determined experimentally increased with increasing contact times, but were within the range of the probabilities derived from Weibull analyses. Probabilities of bacterial transmission from contaminated lens cases to corneas can be derived from Weibull analyses of measured forces of adhesion to the surfaces involved.

Surface thermodynamics and adhesion forces governing bacterial transmission in contact lens related microbial keratitis

Contact lens induced microbial keratitis results from bacterial transmission from one surface to another. We investigated the adhesion forces of Pseudomonas aeruginosa, Staphylococci and Serratia to different contact lenses, lens cases and corneal surfaces using AFM, and applied a Weibull analysis on these adhesion forces to calculate bacterial transmission probabilities from lens case to corneas with a contact lens as an intermediate. Also a new surface thermodynamic parameter was introduced, the interfacial free energy of transmission, which in essence compares the interfacial free energies of bacterial adhesion, calculated from measured contact angles with liquids on the donating and receiving surfaces in the transmission process. Bacterial adhesion forces were generally strongest among all eight strains for the lens case (−6.5 to −12.0 nN) and corneas (−3.5 to −11.5 nN), while contact lenses (−0.6 to −13.1 nN) exerted slightly smaller adhesion forces. Consequently, bacterial transmission from lens case to contact lens yielded a smaller contribution in the final transmission than from contact lens to cornea. Bacterial transmission probabilities as derived from force analyses were higher when the interfacial free energies of transmission were more negative, which is in line with surface thermodynamic principles. Therewith this parameter could provide useful in analyzing other bacterial transmission phenomena between donating and receiving surfaces as well.

Studying bacterial adhesion forces: Staphylococcus aureus on elastic poly(dimethyl)siloxane substrates

To investigate the forces acting between Staphylococcus aureus and its surrounding environment we have designed and fabricated a poly(dimethyl)siloxane substrate with microstructured pillars. The deflection of those pillars due to the adhesion of S. aureus serves as a means for force estimation and is measured in a scanning electron microscope after fixation of the incubated substrates. Our results suggest that the forces exerted by S.aureus, as a member of the class of prokaryotic cells, are higher than those typically observed for eukaryotic cells.

Antibacterial activity of DLC films containing TiO 2 nanoparticles

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to their potential applications as surface coatings on biomedical devices. Titanium dioxide (TiO 2) in the anatase crystalline form is a strong bactericidal agent when exposed to near-UV light. In this work we investigate the bactericidal activity of DLC films containing TiO 2 nanoparticles. The films were grown on 316L stainless-steel substrates from a dispersion of TiO 2 in hexane using plasma-enhanced chemical vapor deposition. The composition, bonding structure, surface energy, stress, and surface roughness of these films were also evaluated. The antibacterial tests were performed against Escherichia coli ( E. coli) and the results were compared to the bacterial adhesion force to the studied surfaces. The presence of TiO 2 in DLC bulk was confirmed by Raman spectroscopy. As TiO 2 content increased, I D / I G ratio, hydrogen content, and roughness also increased; the films became more hydrophilic, with higher surface free energy and the interfacial energy of bacteria adhesion decreased. Experimental results show that TiO 2 increased DLC bactericidal activity. Pure DLC films were thermodynamically unfavorable to bacterial adhesion. However, the chemical interaction between the E. coli and the studied films increased for the films with higher TiO 2 concentration. As TiO 2 bactericidal activity starts its action by oxidative damage to the bacteria wall, a decrease in the interfacial energy of bacteria adhesion causes an increase in the chemical interaction between E. coli and the films, which is an additional factor for the increasing bactericidal activity. From these results, DLC with TiO 2 nanoparticles can be useful for producing coatings with antibacterial properties.

Oral bacterial adhesion forces to biomaterial surfaces constituting the bracket–adhesive–enamel junction in orthodontic treatment

Bacterial adhesion to biomaterial surfaces constituting the bracket-adhesive-enamel junction represents a growing problem in orthodontics, because bacteria can adversely affect treatment by causing demineralization of the enamel surface around the brackets. It is important to know the forces with which bacteria adhere to the surfaces of these junction materials, as the strength of these forces will determine how easy it will be to remove the bacteria. We compared the adhesion forces of five initially colonizing and four cariogenic strains of bacteria to an orthodontic adhesive, stainless steel, and enamel, with and without a salivary conditioning film. Adhesion forces were determined using atomic force microscopy and a bacterial probe. In the absence of a salivary conditioning film, the strongest bacterial adhesion forces occurred to the adhesive surface (-2.9 to -6.9 nN), while adhesion forces to the enamel surfaces were lowest (-0.8 to -2.7 nN). In the presence of a salivary conditioning film, adhesion forces were reduced strongly, to less than 1 nN, and the differences between the various materials were reduced. Generally, however, initial colonizers of dental hard surfaces presented stronger adhesion forces to the different materials (-4.7 and -0.6 nN in the absence and presence of a salivary conditioning film, respectively) than cariogenic strains (-1.8 and -0.5 nN).

Role of Cranberry on Bacterial Adhesion Forces and Implications forEscherichia coli–Uroepithelial Cell Attachment

Previous clinical research has suggested that the consumption of cranberry products prevents the adhesion of Escherichia coli to uroepithelial cells by causing changes in bacterial fimbriae. Atomic force microscopy was used to probe the adhesion forces between E. coli (nonfimbriated strain HB101 and the P-fimbriated variant HB101pDC1) and a model surface (silicon nitride), to determine the effect of growth in cranberry products on bacterial adhesion. Bacteria were grown in tryptic soy broth supplemented with either light cranberry juice cocktail (L-CJC) or cranberry proanthocyanidins (PACs). Growth of E. coli HB101pDC1 and HB101 in L-CJC or PACs resulted in a decrease in adhesion forces with increasing number of cultures. In a macroscale bacteria-uroepithelial cell adhesion assay a decrease in bacterial attachment was observed for E. coli HB101pDC1 grown in L-CJC or PACs. This effect was reversible because bacteria that were regrown in cranberry-free medium regained their ability to attach to uroepithelial cells, and their adhesion forces reverted to the values observed in the control condition. Exposure to increasing concentrations of L-CJC resulted in a decrease of bacterial attachment to uroepithelial cells for the P-fimbriated strain after L-CJC treatment (27% by weight) and after PACs treatment (345.8 microg/mL). Cranberry products affect the surface properties, such as fimbriae and lipopolysaccharides, and adhesion of fimbriated and nonfimbriated E. coli. The concentration of cranberry products and the number of cultures the bacteria were exposed to cranberry determines how much the adhesion forces and attachment are altered.

Poisson Analysis of Streptococcal Bond Strengthening on Stainless Steel with and without a Salivary Conditioning Film

Poisson analysis of retract force-distance curves in atomic force microscopy (AFM) has yielded a new dimension to the decoupling of individual bond forces into a hydrogen bonding and nonspecific force component. Accordingly, bacterial adhesion forces have been decoupled into a hydrogen bonding and nonspecific Lifshitz-Van der Waals contribution. Due to the forced nature of AFM contact, the nonspecific force contribution has hitherto turned out to be repulsive in the analysis of bacterial adhesion forces on nonconducting surfaces. In this study, we present the results of a Poisson analysis of adhesion forces for streptococci adhering to a conducting surface. Adhesion forces measured between stainless steel, both in the absence and presence of an adsorbed salivary conditioning film, increased with increasing contact time between the streptococcal AFM probe and the surface. Concurrent with the increase in adhesion force, there was an increase in the number of minor force peaks in the retract force-distance curves. Poisson analyses of the adhesion forces indicated repulsive nonspecific Lifshitz-Van der Waals forces for streptococci adhering to saliva-coated stainless steel, but interestingly and for the first time, attractive nonspecific forces were revealed on stainless steel in the absence of a salivary conditioning film. We tentatively attribute this to attraction between the negatively charged streptococci and their positive image charges in the conducting material, which cannot develop in a nonconducting material or in the presence of a nonconductive protein layer on the stainless steel surface.

Bond-Strengthening in Staphylococcal Adhesion to Hydrophilic and Hydrophobic Surfaces Using Atomic Force Microscopy

Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface hydrophobicity on initial adhesion forces for the four different S. epidermidis strains was observed. Over time, strengthening of the adhesion forces was virtually absent on hydrophobic dimethyldichlorosilane (DDS)-coated glass, although in a few cases multiple adhesion peaks developed in the retract curves. Bond-strengthening on hydrophilic glass occurred within 5-35 s to maximum adhesion forces of -1.9 +/- 0.7 nN and was concurrent with the development of multiple adhesion peaks upon retract. Poisson analysis of the multiple adhesion peaks allowed separation of contributions of hydrogen bonding from other nonspecific interaction forces and revealed a force contribution of -0.8 nN for hydrogen bonding and +0.3 nN for other nonspecific interaction forces. Time-dependent bacterial adhesion forces were comparable for all four staphylococcal strains. It is concluded that, on DDS-coated glass, the hydrophobic effect causes instantaneous adhesion, while strengthening of the bonds on hydrophilic glass is dominated by noninstantaneous hydrogen bond formation.

Bond Strengthening in Oral Bacterial Adhesion to Salivary Conditioning Films

Transition from reversible to irreversible bacterial adhesion is a highly relevant but poorly understood step in initial biofilm formation. We hypothesize that in oral biofilm formation, irreversible adhesion is caused by bond strengthening due to specific bacterial interactions with salivary conditioning films. Here, we compared the initial adhesion of six oral bacterial strains to salivary conditioning films with their adhesion to a bovine serum albumin (BSA) coating and related their adhesion to the strengthening of the binding forces measured with bacteria-coated atomic force microscopy cantilevers. All strains adhered in higher numbers to salivary conditioning films than to BSA coatings, and specific bacterial interactions with salivary conditioning films were accompanied by stronger initial adhesion forces. Bond strengthening occurred on a time scale of several tens of seconds and was slower for actinomyces than for streptococci. Nonspecific interactions between bacteria and BSA coatings strengthened twofold faster than their specific interactions with salivary conditioning films, likely because specific interactions require a closer approach of interacting surfaces with the removal of interfacial water and a more extensive rearrangement of surface structures. After bond strengthening, bacterial adhesion forces with a salivary conditioning film remained stronger than those with BSA coatings.

Bacteria–surface interaction in the presence of proteins and surface attached poly(ethylene glycol) methacrylate chains

This study analyzes the adhesion behavior of the gram positive bacteria, Staphylococcus aureus (S. aureus), and the gram negative bacteria, Escherichia coli (E. coli), on polypyrrole (PPY) surfaces in the presence of poly(ethylene glycol) methacrylate (PEGMA) chains and plasma proteins (bovine serum albumin and bovine plasma fibrinogen) either preadsorbed on the film surface or in the bacterial suspension. Bacterial adhesion experiments performed in a suspension of bacterial cells and protein may give important insights on the behavior of bacterial adhesion in an in vivo environment. Protein adsorption and bacterial adhesion on PEGMA-grafted PPY films were reduced by about a factor of 2-4 compared with those on the pristine PPY films. In addition, the number of bacterial cells adhering on the substrate is dependent not only on the type of protein present, but also the sequence of exposure to the protein relative to the bacteria. Furthermore, bacteria-surface adhesion force was measured using the atomic force microscopy with increasing lateral force to detach the individual cell. The adhesion force of S. aureus is influenced by PEGMA and plasma protein modification and is significantly higher than that of E. coli for all substrates tested. The number of adherent cells on the substrate is shown to be directly correlated to the bacterial adhesion force.

Force measurements of bacterial adhesion on metals using a cell probe atomic force microscope

The adhesion of microbial cells to metal surfaces in aqueous media is an important phenomenon in both the natural environment and engineering systems. The adhesion of two anaerobic sulfate-reducing bacteria ( Desulfovibrio desulfuricans and a local marine isolate) and an aerobe ( Pseudomonas sp.) to four polished metal surfaces (i.e., stainless steel 316, mild steel, aluminum, and copper) was examined using a force spectroscopy technique with an atomic force microscope (AFM). Using a modified bacterial tip, the attraction and repulsion forces (in the nano-Newton range) between the bacterial cell and the metal surface in aqueous media were quantified. Results show that the bacterial adhesion force to aluminum is the highest among the metals investigated, whereas the one to copper is the lowest. The bacterial adhesion forces to metals are influenced by both the electrostatic force and metal surface hydrophobicity. It is also found that the physiological properties of the bacterium, namely the bacterial surface charges and hydrophobicity, also have influence on the bacteria–metal interaction. The adhesion to the metals by Pseudomonas sp. and D. desulfuricans was greater than by the marine SRB isolate. The cell–cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Cell probe atomic force microscopy has provided some useful insight into the interactions of bacterial cells with the metal surfaces.

Role of cranberry juice on molecular‐scale surface characteristics and adhesion behavior of Escherichia coli

Cranberry juice has long been believed to benefit the prevention and treatment of urinary tract infections (UTIs). As the first step in the development of infection, bacterial adhesion is of great research interest, yet few studies have addressed molecular level adhesion in this context. P-fimbriated Escherichia coli play a major role in the development of a serious type of UTI, acute pyelonephritis. Experiments were conducted to investigate the molecular-scale effects of cranberry juice on two E. coli strains: HB101, which has no fimbriae, and the mutant HB101pDC1 which expresses P-fimbriae. Atomic force microscopy (AFM) was used to investigate both bacterial surface characteristics and adhesion forces between a probe surface (silicon nitride) and the bacteria, providing a direct evaluation of bacterial adhesion and interaction forces. Cranberry juice affected bacterial surface polymer and adhesion behavior after a short exposure period (<3 h). Cranberry juice affected the P-fimbriated bacteria by decreasing the adhesion forces between the bacterium and tip and by altering the conformation of the surface macromolecules on E. coli HB101pDC1. The equilibrium length of polymer (P-fimbriae) on this bacterium decreased from approximately 148 to approximately 48 nm upon being exposed to cranberry juice. Highly acidic conditions were not necessary for the prevention of bacterial adhesion, since neutralization of cranberry juice solutions to pH = 7.0 allowed us to observe differences in adhesion between the E. coli strains. Our results demonstrate molecular-level changes in the surfaces of P-fimbriated E. coli upon exposure to neutralized cranberry juice.