Three regimes of bacterial adhesion to substratum surfaces that dictate the bacterial response to a surface.

<p>1) In the planktonic regime, adhesion forces are extremely weak as on polymer-brush coatings, and bacteria do not realize they are on a surface. Weakly adhering bacteria are mainly live (green fluorescence). This regime is called “planktonic”, because bacteria do not adapt their planktonic phenotype despite their adhering state. 2) In the “interaction” regime, bacterial responses to their adhering state increase with increasing adhesion forces, for instance by the production of EPS (blue fluorescence), encasing themselves in a protective biofilm. 3) In the “lethal regime”, strong adhesion forces, as occurring on positively charged surfaces, cause membrane deformation that causes stress de-activation of the adhering bacteria, leading to reduced growth and cell death (red fluorescence). The confocal laser scanning micrographs represent biofilms in all three regimes of adhesion forces in which bacteria were stained with <i>Bac</i>light LIVE/DEAD stain, rendering live bacteria green and membrane damaged or dead bacteria red. EPS was stained with calcofluor white, rendering blue fluorescence.</p

Summary of microbial strains for which clonal subpopulations expressing phenotypes with different cell surface properties have been found.

<p>Summary of microbial strains for which clonal subpopulations expressing phenotypes with different cell surface properties have been found.</p

Phagocytosis rate <i>versus</i> the interfacial free energy of adhesion.

<p>(A) S. epidermidis 3399, (B) S. epidermidis 7391, (C) S. epidermidis 1457, (D) <i>S. aureus</i> ATCC 12600^GFP, (E) <i>S. aureus</i> 7323, and (F) <i>S. aureus</i> LAC. Note that phagocytosis rates increase when the interfacial free energy of adhesion becomes more favorable (more negative), but phagocytosis is not ruled out by unfavorable surface thermodynamic conditions (shaded regions). Dashed lines indicate the best-fit to a linear function through the data.</p

Contact angles of water (θ_w), formamide (θ_f), methyleniodide (θ_m) and α-bromonaphthalene (θ_b) measured on lawns of the staphylococcal strains and phagocytic cell lines involved in this study(in degrees).

<p>Contact angles of water (θ_w), formamide (θ_f), methyleniodide (θ_m) and α-bromonaphthalene (θ_b) measured on lawns of the staphylococcal strains and phagocytic cell lines involved in this study(in degrees).</p

Phagocytosis rates for six staphylococcal strains by different phagocytic cell lines (cm²/min).

<p>Phagocytosis rates for six staphylococcal strains by different phagocytic cell lines (cm²/min).</p

Lifshitz-Van der Waals and acid-base components of interfacial free energy of adhesion (ΔG^LW_plb and ΔG^AB_plb, respectively) between bacteria and phagocytes, calculated from measured contact angles with liquids, as presented in Table 2 (mJ/m²).

<p>Lifshitz-Van der Waals and acid-base components of interfacial free energy of adhesion (ΔG^LW_plb and ΔG^AB_plb, respectively) between bacteria and phagocytes, calculated from measured contact angles with liquids, as presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070046#pone-0070046-t002" target="_blank">Table 2</a> (mJ/m²).</p

Direct quantification of <i>S. aureus</i> ATCC12600^GFP inside phagocytes using CLSM.

<p> (A) CLSM snapshot of <i>S. aureus</i> ATCC 12600^GFP (modified to express GFP) inside J774A.1 macrophages stained with TRITC-phalloidin and (B) reconstruction of 3D image from CLSM sections using Bitplane’s Imaris software. Note that bacteria appear green fluorescent, while the cell wall of the phagocytes is red. Bar denotes 20 µm.</p

Bacterial cell wall deformation, mechanosensing, and the measurement of cell wall deformation using surface enhanced fluorescence.

<p><b>A) Left:</b> Intact lipid membrane at equilibrium of an undeformed bacterium, with a closed mechanosensitive channel (MSC). <b>Right:</b> Bacterium adhering to a substratum surface, deformed under the influence of adhesion forces arising from the substratum, yielding hydrophobic mismatch over the thickness of the membrane (water molecules adjacent to hydrophobic lipid tails), and altered lipid bilayer tension in the lipid membrane. Hydrophobic mismatch and pressure profile changes lead to the opening of MSCs. <b>B) Left:</b> A nonactivated stress-sensitive (SS) protein on the bacterial cell surface of an undeformed bacterium and a response regulator protein (RR) suspended freely in the cytoplasm. <b>Right:</b> A SS protein senses cell wall deformation due to adhesion, changes its conformation, and phosphorylates a RR protein which regulates the expression of SS-regulated genes. <b>C) Left:</b> Lifshitz-Van der Waals forces operate between all molecular pairs in a bacterium and a substratum, decreasing with distance between the molecules. <b>Right:</b> Adhering bacterium, deformed due to attractive Lifshitz-Van der Waals forces, with more molecules in the bacterium closer to the substratum, yielding stronger adhesion and more deformation. Deformation stops once the counterforces arising from the deformation of the rigid peptidoglycan layer match those of the adhesion forces. <b>D) Left:</b> Only a small number of fluorophores inside an undeformed bacterium are sufficiently close to a metal substratum surface to experience surface-enhanced fluorescence (brighter dots). <b>Right:</b> In a deformed, adhering bacterium, the volume of the bacterium close to the surface increases and the number of fluorophores subject to surface-enhanced fluorescence becomes higher. Thus, quantitative analysis of fluorescence arising from fluorescent bacteria adhering to a metal surface provides a way to determine cell wall deformation.</p

Nanoscopic Vibrations of Bacteria with Different Cell-Wall Properties Adhering to Surfaces under Flow and Static Conditions

Bacteria adhering to surfaces demonstrate random, nanoscopic vibrations around their equilibrium positions. This paper compares vibrational amplitudes of bacteria adhering to glass. Spring constants of the bond are derived from vibrational amplitudes and related to the electrophoretic softness of the cell surfaces and dissipation shifts measured upon bacterial adhesion in a quartz-crystal-microbalance (QCM-D). Experiments were conducted with six bacterial strains with pairwise differences in cell surface characteristics. Vibrational amplitudes were highest in low ionic strength suspensions. Under fluid flow, vibrational amplitudes were lower in the direction of flow than perpendicular to it because stretching of cell surface polymers in the direction of flow causes stiffening of the polyelectrolyte network surrounding a bacterium. Under static conditions (0.57 mM), vibrational amplitudes of fibrillated <i>Streptococcus salivarius</i> HB7 (145 nm) were higher than that of a bald mutant HB-C12 (76 nm). Amplitudes of moderately extracellular polymeric substance (EPS) producing <i>Staphylococcus epidermidis</i> ATCC35983 (47 nm) were more than twice the amplitudes of strongly EPS producing <i>S. epidermidis</i> ATCC35984 (21 nm). No differences were found between <i>Staphylococcus aureus</i> strains differing in membrane cross-linking. High vibrational amplitudes corresponded with low dissipation shifts in QCM-D. In streptococci, the polyelectrolyte network surrounding a bacterium is formed by fibrillar surface appendages and spring constants derived from vibrational amplitudes decreased with increasing fibrillar density. In staphylococci, EPS constitutes the main network component, and larger amounts of EPS yielded higher spring constants. Spring constants increased with increasing ionic strength and strains with smaller electrophoretically derived bacterial cell surface softnesses possessed the highest spring constants

Maximal adhesion forces as a function of surface delay.

<p>Maximal adhesion forces, obtained using the LMM on the measured data, as a function of the surface delay time for the three strains of identical staphylococcal pairs involved in this study, with their 95% confidence intervals indicated by the dotted lines.</p