Characterizing the adhesion of motile and nonmotile Escherichia coli to a glass surface using a parallel-plate flow chamber

Probing young drinking water biofilms with hard and soft particles

The aim of our study was to investigate, through the use of soft (Escherichia coli) and hard (polystyrene microspheres) particles, the distribution and persistence of allochthonous particles inoculated in drinking water flow chambers. Biofilms were allowed to grow for 7-10 months in tap water from Nancy's drinking water network and were composed of bacterial aggregates and filamentous fungi. Both model particles adhered almost exclusively on the biofilms (i.e. on the bacterial aggregates and on the filamentous structures) and not directly on the uncolonized walls (glass or Plexiglas). Biofilm age (i.e. bacterial density and biofilm properties) and convective-diffusion were found to govern particle accumulation: older biofilms and higher wall shear rates both increased the velocity and the amount of particle deposition on the biofilm. Persistence of the polystyrene particles was measured over a two-month period after inoculation. Accumulation amounts were found to be very different between hard and soft particles as only 0.03 per thousand of the soft particles inoculated accumulated in the biofilm against 0.3-0.8% for hard particles.

Antecedent growth conditions alter retention of environmental Escherichia coli isolates in transiently wetted porous media

The physical transport of Escherichia coli in terrestrial environments may require control to prevent its dissemination from potential high-density sources, such as confined animal feedlot operations. Biobarriers, wherein convective flows carrying pathogens pass through a porous matrix with high retentive capacity, may present one such approach. Eight environmental E. coli isolates were selected to conduct operational retention tests (ORT) with potential biobarrier materials Pyrax or dolomite, or silica glass as control. The conditions in the ORT were chosen to simulate conditioning by manure solutes, a pulse application of a bacterial load followed by rainfall infiltration, and natural drainage. Removal was limited, and likely caused by the relatively high velocities during drainage, and the conditioning of otherwise favorable adhesion sites. Flagella-mediated motility showed the strongest correlation to biobarrier retention. Significant variability was observed across the E. coli isolates, but consistently higher retention was observed for cells with external versus intestinal pregrowth histories. E. coli O157:H7 was retained the least with all examined matrices, while E. coli K-12 displayed moderate retention and may not serve as representative model strain. Pyrax is a good candidate biobarrier material given its superior removal ability across the tested E. coli strains.

Mean first-passage time for superdiffusion in a slit pore with sticky boundaries

This Brief Report examines Levy motion in a slit pore with sticky boundaries, i.e., boundaries that absorb particles for a random amount of time. A set of equations is developed that can explicitly be solved for mean travel distance to a plane for a particle released from the origin and can iteratively be used to compute mean first-passage time (MFPT). Results from the theory compare favorably with Monte Carlo simulations.

Colloidal deposition on remotely controlled charged micropatterned surfaces in a parallel-plate flow chamber

This article describes a method to influence colloid deposition by varying the zeta potential at microelectrodes with remotely applied electric potentials. Deposition experiments were conducted in a parallel-plate flow chamber for bulk substrates of glass, indium tin oxide (ITO), and ITO-coated glass microelectrodes in 10 and 60 mM potassium chloride solutions. Colloid deposition was found to be a function of solution chemistry and the small locally delivered electric surface potentials. Electric fields and physical surface heterogeneity can be ruled out as cause of the observed deposition. Results are reported using experimentally determined Sherwood numbers and compared to the predictions of a previously developed patch model. Minor deviations between predicted and experimental Sherwood numbers imply that physical and chemical interactions occur. Specifically, we propose that colloidal particles respond to local variations in surface potential through electrostatic interactions, altering particle streamlines flowing along the surface and ultimately the extent of deposition.

The role of starvation on Escherichia coli adhesion and transport in saturated porous media

The influence of bacterial starvation on cell transport has been examined using two Escherichia coli isolates: one from human (HU) and one from dairy cattle (DC). To better understand the fate of starved bacteria, experiments were conducted in a packed bed column using cells that had been incubating at room temperature without nutrients for 6, 12, and 18h, as well as cells, which had not been starved (referred to as time zero). Complimentary cell characterization techniques were conducted to evaluate the hydrophobicity, mobility, size, and surface charge density of the cells at the conditions considered. It was observed that non-starved HU cells were more adhesive than starved HU cells. This behavior is attributed to the relatively high hydrophobicity of the starved cells, which resulted from greater extracellular polymeric substance (EPS) presence. Non-starved DC cells were also the most adhesive whereas 18h starved cells were the least adhesive, although cell characterization results did not correlate to transport trends like HU cells. For both isolates, the cells after 6h of starvation showed high levels of sugar relative to protein in the EPS. Additionally, following 6h of starvation, the cells did not follow expected transport trends as anticipated from the cellular characterization. Our results suggest transport behavior of environmental E. coli isolates differs in terms of isolate host and starvation conditions. Possible mechanisms responsible for this are changes in key cell surface characteristics and synthesis of starvation-induced proteins. This study highlights the importance of consistency in bacterial preparation for experimental studies and has considerable implications for future evaluation and prediction of E. coli fate in subsurface environments.

Effect of wall shear rate on biofilm deposition and grazing in drinking water flow chambers

The effect of four-wall shear rates (34.9, 74.8, 142.5, and 194.5 s(-1)) on bacterial deposition on glass slides in drinking water flow chambers was studied. Biofilm image acquisition was performed over a 50-day period. Bacterial accumulation and surface coverage curves were obtained. Microscopic observations allowed us to obtain information about the dynamics and spatial distribution of the biofilm. During the first stage of biofilm formation (210-518 h), bacterial accumulation was a function of the wall shear rate: the higher the wall shear rate, the faster the bacterial deposition (1.1 and 1.9 x 10(4) bacterial cells . cm(-2) for wall shear rates of 34.9 and 142.5 s(-1), respectively). A new similarity relationship characteristic of a non-dimensional time and function of the wall shear rate was proposed to describe initial bacterial deposition. After 50 days of exposure to drinking water, surface coverage was more or less identical under the entire wall shear rates (7.44 +/- 0.9%), suggesting that biofilm bacterial density cannot be controlled using hydrodynamics. However, the spatial distribution of the biofilm was clearly different. Under low wall shear rate, aggregates were composed of bacterial cells able to "vibrate" independently on the surface, whereas, under a high wall shear rate, aggregates were more cohesive. Therefore, susceptibility to the hydraulic discontinuities occurring in drinking water system may not be similar. In all the flow chambers, significant decreases in bacterial biomass (up to 77%) were associated with the presence of amoebae. This grazing preferentially targeted small, isolated cells.

Hydrodynamic surface interactions enable Escherichia coli to seek efficient routes to swim upstream

Escherichia coli in shear flow near a surface are shown to exhibit a steady propensity to swim towards the left (within the relative coordinate system) of that surface. This phenomenon depends solely on the local shear rate on the surface, and leads to cells eventually aligning and swimming upstream preferentially along a left sidewall or crevice in a wide range of flow conditions. The results indicate that flow-assisted translation and upstream swimming along surfaces might be relevant in various models of bacterial transport, such as in pyelonephritis and bacterial migration in wet soil and aquatic environments in general.

Intestinal versus external growth conditions change the surficial properties in a collection of environmental Escherichia coli isolates

Predicting the fate of microorganisms in the environment is increasingly warranted, especially for pathogenic strains. A major habitat of Escherichia coli, which encompasses commensal as well as pathogenic strains, is the gastrointestinal tract with conditions very different from the environment it encounters after shedding from the host or during cultivation in the laboratory. We developed two relevant growth conditions representative of intestinal (host-associated) and external (postshedding) environments to investigate the surficial properties and behaviors of a diverse subset of E. coli feedlot isolates. Surficial properties may determine an isolate's physical fate. A pronounced increase in cell hydrophobicity and concomitant biofilm mass formation was observed for isolates grown under external conditions. Isolates that exhibited the highest surface hydrophobicity also formed visible suspended aggregates under external conditions. Other than hydrophobicity, flagella-mediated motility was determinant in affecting E. coli biofilm formation under external conditions, with all four nonmotile E. coli isolates characterized as thin-biofilm formers. The majority (88%) of Ag43+ (outer membrane protein, antigen 43) isolates formed thick biofilms, whereas the majority (75%) of Ag43- isolates formed thin biofilms. The tested E. coli O157:H7 strain behaved differently from the environmental E. coli isolates: it displayed a low electrostatic charge, a small decrease in hydrophobicity upon shifts to external conditions, and very little biofilm formation. On the other hand, the commonly used laboratory strain E. coli K-12 displayed low hydrophobicity both intestinally and externally, but it formed significant biofilm mass under external conditions. Clearly, various E. coli strains manifest significant variability in surficial behavior. This variability is further modulated by growth conditions. The interacting strain-inherent and cultivation-dependent effects on surficial behavior may have broad consequences for the fate and ecology of pathogenic and commensal E. coli strains.

Shear stress, temperature, and inoculation concentration influence the adhesion of water-stressed Helicobacter pylori to stainless steel 304 and polypropylene

Although molecular techniques have identified Helicobacter pylori in drinking water-associated biofilms, there is a lack of studies reporting what factors affect the attachment of the bacterium to plumbing materials. Therefore, the adhesion of H. pylori suspended in distilled water to stainless steel 304 (SS304) coupons placed on tissue culture plates subjected to different environmental conditions was monitored. The extent of adhesion was evaluated for different water exposure times, using epifluorescence microscopy to count total cell numbers. High shear stresses-estimated through computational fluid dynamics-negatively influenced the adhesion of H. pylori to the substrata (P < 0.001), a result that was confirmed in similar experiments with polypropylene (P < 0.05). However, the temperature and inoculation concentration appeared to have no effect on adhesion (P > 0.05). After 2 hours, H. pylori cells appeared to be isolated on the surface of SS304 and were able to form small aggregates with longer exposure times. However, the formation of a three-dimensional structure was only very rarely observed. This study suggests that the detection of the pathogen in well water described by other authors can be related to the increased ability of H. pylori to integrate into biofilms under conditions of low shear stress. It will also allow a more rational selection of locations to perform molecular or plate culture analysis for the detection of H. pylori in drinking water-associated biofilms.

Residence time, loading force, pH, and ionic strength affect adhesion forces between colloids and biopolymer-coated surfaces

Exopolymers are thought to influence bacterial adhesion to surfaces, but the time-dependent nature of molecular-scale interactions of biopolymers with a surface are poorly understood. In this study, the adhesion forces between two proteins and a polysaccharide [Bovine serum albumin (BSA), lysozyme, or dextran] and colloids (uncoated or BSA-coated carboxylated latex microspheres) were analyzed using colloid probe atomic force microscopy (AFM). Increasing the residence time of an uncoated or BSA-coated microsphere on a surface consistently increased the adhesion force measured during retraction of the colloid from the surface, demonstrating the important contribution of polymer rearrangement to increased adhesion force. Increasing the force applied on the colloid (loading force) also increased the adhesion force. For example, at a lower loading force of approximately 0.6 nN there was little adhesion (less than -0.47 nN) measured between a microsphere and the BSA surface for an exposure time up to 10 s. Increasing the loading force to 5.4 nN increased the adhesion force to -4.1 nN for an uncoated microsphere to a BSA surface and to as much as -7.5 nN for a BSA-coated microsphere to a BSA-coated glass surface for a residence time of 10 s. Adhesion forces between colloids and biopolymer surfaces decreased inversely with pH over a pH range of 4.5-10.6, suggesting that hydrogen bonding and a reduction of electrostatic repulsion were dominant mechanisms of adhesion in lower pH solutions. Larger adhesion forces were observed at low (1 mM) versus high ionic strength (100 mM), consistent with previous AFM findings. These results show the importance of polymers for colloid adhesion to surfaces by demonstrating that adhesion forces increase with applied force and detention time, and that changes in the adhesion forces reflect changes in solution chemistry.

Relations between macroscopic and microscopic adhesion of Streptococcus mitis strains to surfaces

Application of physico-chemical models to describe bacterial adhesion to surfaces has hitherto only been partly successful due to the structural and chemical heterogeneities of bacterial surfaces, which remain largely unaccounted for in macroscopic physico-chemical characterizations of the cell surfaces. In this study, the authors attempted to correlate microscopic adhesion of a collection of nine Streptococcus mitis strains to the negatively charged, hydrophilic silicon nitride tip of an atomic force microscope (AFM) with macroscopic adhesion of the strains to a negatively charged, hydrophilic glass in a parallel-plate flow chamber. The repulsive force probed by AFM upon approach of the tip to a bacterial cell surface ranged from 1.7 to 7.7 nN depending on the strain considered and was found to correspond to an activation barrier, governing initial, macroscopic adhesion of the organisms to the glass surface. Moreover, maximum distances at which attractive forces were probed by the AFM upon retraction of the tip (120 to 1186 nm) were related to the area blocked by an adhering bacterium, i.e. the distance kept between adhering bacteria. Bacterial desorption could not be related to adhesive forces as probed by the AFM, possibly due to the distinct nature of the desorption process occurring in the parallel-plate flow chamber and the forced detachment in AFM.

Effect of cell physicochemical characteristics and motility on bacterial transport in groundwater

The influence of physicochemical characteristics and motility on bacterial transport in groundwater were examined in flow-through columns. Four strains of bacteria isolated from a crystalline rock groundwater system were investigated, with carboxylate-modified and amidine-modified latex microspheres and bromide as reference tracers. The bacterial isolates included a gram-positive rod (ML1), a gram-negative motile rod (ML2), a nonmotile mutant of ML2 (ML2m), and a gram-positive coccoid (ML3). Experiments were repeated at two flow velocities, in a glass column packed with glass beads, and in another packed with iron-oxyhydroxide coated glass beads. Bacteria breakthrough curves were interpreted using a transport equation that incorporates a sorption model from microscopic observation of bacterial deposition in flow-cell experiments. The model predicts that bacterial desorption rate will decrease exponentially with the amount of time the cell is attached to the solid surface. Desorption kinetics appeared to influence transport at the lower flow rate, but were not discernable at the higher flow rate. Iron-oxyhydroxide coatings had a lower-than-expected effect on bacterial breakthrough and no effect on the microsphere recovery in the column experiments. Cell wall type and shape also had minor effects on breakthrough. Motility tended to increase the adsorption rate, and decrease the desorption rate. The transport model predicts that at field scale, desorption rate kinetics may be important to the prediction of bacteria transport rates.

High diversity among environmental Escherichia coli isolates from a bovine feedlot

Approximately 280 Escherichia coli isolates were isolated from a bovine feedlot at the University of Connecticut campus via enrichment in lauryl tryptose broth and random selection from MacConkey plates. The E. coli subspecies diversity was estimated by employing whole-cell BOX-PCR genomic fingerprints. A total of 89 distinct operational taxonomic units (OTUs) were identified by employing a criterion of 85% fingerprint similarity as a surrogate for an OTU, while the Chao1 index estimated the E. coli population richness at 128 OTUs. One genotype (at a similarity level of 60%) dominated the population at 66% regardless of sampling depth or location, while no significant vertical distribution pattern was observed in terms of genotype, mobility, antibiotic resistance profile, or biofilm-forming ability. Motility, measured by a soft agar assay, had a very broad range among the E. coli population and was positively correlated with biofilm-forming ability in minimal medium (Spearman's rank correlation coefficient r = 0.619, P < 10(-4)) but not in Luria broth. Only an estimated 48% of the population possessed gene agn43, which encodes Ag43, a phase-variable outer membrane protein that has been implicated in biofilm formation in minimal medium. We observed significantly more biofilm formation in both minimal medium and Luria broth for agn43(+) strains, with a larger effect in minimal medium. This study represents an exhaustive inventory of extant E. coli population diversity at a bovine feedlot and reveals significant subspecies heterogeneity in interfacial behavior.

Oriented adhesion of Escherichia coli to polystyrene particles

The adhesion of nonflagellated Escherichia coli strain K-12 to polystyrene (PS) latex spheres or glass capillaries has been observed by using several techniques. Attention was focused on the orientation of the rod-shaped bacteria as they adhered to the surfaces in 100 mM phosphate-buffered saline. Data show that PS particles adhered to the ends of the bacteria more than 90% of the time. Moreover, the PS particles adhered to one end only, never to both. Similarly, for experiments with bacteria adhering to glass, the bacteria adhered on their ends. In order to determine whether the end of a bacterium had a different charge density from that of the middle, rotational electrophoresis experiments were used. These experiments indicated no measurable charge nonuniformity. In order to examine how strongly adhered the bacteria were to the PS particles, differential electrophoresis was used. Almost always, bacteria were found to be irreversibly adhered to the PS spheres. The cause of the oriented adhesion is not likely due to surface lipopolysaccharides (LPS), since the three strains of K-12 that were used, each having a different length of LPS, showed similar behavior. The results are discussed in terms of bacterial cell polarity. The data indicate that nanodomains on the bacterial ends are important for adhesion and that the time scale for irreversible adhesion is short.

Reversal of flagellar rotation is important in initial attachment of Escherichia coli to glass in a dynamic system with high- and low-ionic-strength buffers

The attachment rates of wild-type, smooth-swimming, tumbly, and paralyzed Escherichia coli to glass was measured at fluid velocities of 0.0044 and 0.044 cms(-1) (corresponding to shear rates of 0.34 and 3.4 s(-1), respectively), in 0.02 and 0.2 M buffer solutions. At the highest ionic strength, we did not observe a significant difference in the attachment rate of wild-type and paralyzed cells at either fluid velocity. However, when the ionic strength was reduced, paralyzed bacteria attached at rates 4 and 10 times lower than that of the wild type under fluid velocities of 0.0044 and 0.044 cms(-1), respectively. This suggested that the rotation of the flagella assisted in attachment. We then compared the attachment rates of smooth-swimming (counterclockwise rotation only) and tumbly (clockwise rotation only) cells to the wild type to determine whether the direction of rotation was important to cell attachment. At 0.0044 cms(-1), the smooth-swimming cells attached at rates similar to that of the wild type in both buffer solutions but significantly less at the higher fluid velocity. Tumbly cells attached at much lower rates under all conditions. Thus, the combination of clockwise and counterclockwise flagellar rotation and their coupling appeared to be important in cell attachment. We considered a number of hypotheses to interpret these observations, including a residence time analysis and a comparison of traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to soft-particle theory.