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

Fluid flow drives phenotypic heterogeneity in bacterial growth and adhesion on surfaces

Bacteria often thrive in surface-attached communities, where they can form biofilms affording them multiple advantages. In this sessile form, fluid flow is a key component of their environments, renewing nutrients and transporting metabolic products and signaling molecules. It also controls colonization patterns and growth rates on surfaces, through bacteria transport, attachment and detachment. However, the current understanding of bacterial growth on surfaces neglects the possibility that bacteria may modulate their division behavior as a response to flow. Here, we employed single-cell imaging in microfluidic experiments to demonstrate that attached Escherichia coli cells can enter a growth arrest state while simultaneously enhancing their adhesion underflow. Despite utilizing clonal populations, we observed a non-uniform response characterized by bistable dynamics, with co-existing subpopulations of non-dividing and actively dividing bacteria. As the proportion of non-dividing bacteria increased with the applied flow rate, it resulted in a reduction in the average growth rate of bacterial populations on flow-exposed surfaces. Dividing bacteria exhibited asymmetric attachment, whereas non-dividing counterparts adhered to the surface via both cell poles. Hence, this phenotypic diversity allows bacterial colonies to combine enhanced attachment with sustained growth, although at a reduced rate, which may be a significant advantage in fluctuating flow conditions.

Migration of surface-associated microbial communities in spaceflight habitats

Astronauts are spending longer periods locked up in ships or stations for scientific and exploration spatial missions. The International Space Station (ISS) has been inhabited continuously for more than 20 years and the duration of space stays by crews could lengthen with the objectives of human presence on the moon and Mars. If the environment of these space habitats is designed for the comfort of astronauts, it is also conducive to other forms of life such as embarked microorganisms. The latter, most often associated with surfaces in the form of biofilm, have been implicated in significant degradation of the functionality of pieces of equipment in space habitats. The most recent research suggests that microgravity could increase the persistence, resistance and virulence of pathogenic microorganisms detected in these communities, endangering the health of astronauts and potentially jeopardizing long-duration manned missions. In this review, we describe the mechanisms and dynamics of installation and propagation of these microbial communities associated with surfaces (spatial migration), as well as long-term processes of adaptation and evolution in these extreme environments (phenotypic and genetic migration), with special reference to human health. We also discuss the means of control envisaged to allow a lasting cohabitation between these vibrant microscopic passengers and the astronauts.

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

The global outbreak of coronavirus infectious disease-2019 (COVID-19) draws attentions in the transport and spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in aerosols, wastewater, surface water and solid wastes. As pathogens eventually enter the subsurface system, e.g., soils in the vadose zone and groundwater in the aquifers, they might survive for a prolonged period of time owing to the uniqueness of subsurface environment. In addition, pathogens can transport in groundwater and contaminate surrounding drinking water sources, possessing long-term and concealed risks to human society. This work critically reviews the influential factors of pathogen migration, unravelling the impacts of pathogenic characteristics, vadose zone physiochemical properties and hydrological variables on the migration of typical pathogens in subsurface system. An assessment algorithm and two rating/weighting schemes are proposed to evaluate the migration abilities and risks of pathogens in subsurface environment. As there is still no evidence about the presence and distribution of SARS-CoV-2 in the vadose zones and aquifers, this study also discusses the migration potential and behavior of SARS-CoV-2 viruses in subsurface environment, offering prospective clues and suggestions for its potential risks in drinking water and effective prevention and control from hydrogeological points of view.

Water and biofilm in drinking water distribution systems in the Netherlands

To keep the high quality of drinking water in the future for non-chlorinated drinking water systems, knowledge about the variables that most strongly affect this quality is necessary in order to know where to focus on and possibly even change aspects of drinking water production and distribution. Therefore, the aim of this study was to investigate which variables (source of drinking water, growth potential and pipe material type) have the biggest influence on bacterial community composition and biomass concentration of drinking water and biofilm in distribution systems. Ten different distribution systems were sampled for water and biofilm, obtained from four different pipe materials, throughout the Netherlands. The distribution systems are supplied either with drinking water produced from groundwater or surface water, and differ in drinking water quality parameters such as the growth potential. We found a significant relationship for growth potential and ATP concentration in water, but for the ATP in the biofilm none of the parameters showed a significant effect. Furthermore, the source of the drinking water and the pipe material did not significantly affect the ATP concentration in water and biofilm. The bacterial composition of in both water and biofilm was significantly different between distribution systems delivering water with low and high growth potential and between drinking water produced from groundwater or surface water. In contrast, the different pipe materials did not significantly affect composition of biofilm-associated communities. We conclude from these results that the growth potential of the treated water best explains the variation in biomass and bacterial composition in water and biofilm of non-chlorinated drinking water distribution systems followed by the drinking water source, whereas pipe materials seem to be of lesser importance.

Interplay of physico-chemical and mechanical bacteria-surface interactions with transport processes controls early biofilm growth: A review

Biofilms initiate when bacteria encounter and are retained on surfaces. The surface orchestrates biofilm growth through direct physico-chemical and mechanical interactions with different structures on bacterial cells and, in turn, through its influence on cell-cell interactions. Individual cells respond directly to a surface through mechanical or chemical means, initiating "surface sensing" pathways that regulate gene expression, for instance producing extra cellular matrix or altering phenotypes. The surface can also physically direct the evolving colony morphology as cells divide and grow. In either case, the physico-chemistry of the surface influences cells and cell communities through mechanisms that involve additional factors. For instance the numbers of cells arriving on a surface from solution relative to the generation of new cells by division depends on adhesion and transport kinetics, affecting early colony density and composition. Separately, the forces experienced by adhering cells depend on hydrodynamics, gravity, and the relative stiffnesses and viscoelasticity of the cells and substrate materials, affecting mechanosensing pathways. Physical chemistry and surface functionality, along with interfacial mechanics also influence cell-surface friction and control colony morphology, in particular 2D and 3D shape. This review focuses on the current understanding of the mechanisms in which physico-chemical interactions, deriving from surface functionality, impact individual cells and cell community behavior through their coupling with other interfacial processes.

Spatial pattern and surface-specificity of particle and microorganism deposition and attachment: Modeling, analytic solution and experimental test

HYPOTHESIS

Understanding microparticle and living cell deposition and attachment on surfaces from a flow is a long-standing surface-science problem, pivotal to developing antifouling strategies. Recent studies indicate a complex non-conservative and surface-specific nature of adhesion and mechanical contact forces that determine attachment kinetics. This requires new models and kinetic data, however, observed deposition rates (e.g., in parallel-plate flow chamber, PPFC) represent a superposition of attachment and bulk transport. Here, we propose to deduce attachment rates (as an appropriate rate constant) from spatial deposition profiles along PPFC and develop an analytical solution for the full problem, suitable for deposition data analysis and parameter fitting.

EXPERIMENTS

Analytical solution, validated by numerical simulations, reveals relation between the deposition profile along PPFC and key model parameter B, the ratio of sedimentation and attachment rates. Its use is demonstrated on experimental data obtained in a PPFC for particles and bacteria on various surfaces.

FINDINGS

Fitted B values highlight correlation with the particle/substrate nature and consistently explain the observed trends along PPFC, both decreasing and increasing. Thus derived attachment rates will serve as basis for future microscopic modelling that would relate attachment to appropriate surface and contact-mechanical characteristics of particles and substrate and flow conditions.

Antibacterial Effect of Aluminum Surfaces Untreated and Treated with a Special Anodizing Based on Titanium Oxide Approved for Food Contact

One of the main concerns of the food industry is microbial adhesion to food contact surfaces and consequent contamination. We evaluated the potential bacteriostatic/bactericidal efficacy of aluminum surfaces with different large-scale roughness (0.25, 0.5 and 1 μm) before and after the surface treatment with a special anodizing based on titanium oxide nanotechnology (DURALTI®) and after 3 different sanitizing treatments, e.g., UV, alcohol and a natural product named Gold lotion. Four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) bacteria were screened. As far as concerns aluminum surfaces without nanotechnology surface treatment, an overall bacteriostatic effect was observed for all strains with respect to the initial inoculum that was 106 CFU/mL. Conversely, an overall bactericidal effect was observed both for Gram-negative and -positive bacteria on DURALTI®-treated aluminum disks, regardless of roughness and sanitizing treatment. These results are innovative in terms of the great potential of the antibacterial activity of nanotechnologically treated food contact surfaces and their combination with some sanitizing agents that might be exploited in the food industry.

Flagellar motility mediates early-stage biofilm formation in oligotrophic aquatic environment

Flagellar motility enables resource acquisition and noxious substance evasion, underpinning imperative ecological processes in aquatic environments. Yet the underlying mechanism that links flagellar motility with surface attachment and thereby biofilm formation, especially in conditions of limited resource availability, remains elusive. Here, we present experimental and modeling evidence to unveil bacterial motility and biofilm formation under nutrient-limited stresses with Pseudomonas aeruginosa (WT) and its nonflagellated isogenic mutant (ΔfliC) as model bacteria. Results revealed that boosted flagellar motility of WT strain promoted biofilm initialization to a peak value of 0.99 × 10⁷ cells/cm² at 1/50 dilution after 20 min incubation. We hypothesized that bacteria can invoke instant motility acceleration for survival confronting nutrient-limited stress, accompanied by optimized chemotactic foraging through sensing ambient chemical gradients. Accordingly, accelerated cell motility in oligotrophic environment created increased cell-cell and cell-surface interactions and thereof facilitated biofilm initialization. It was confirmed by the consistence of modeling predictions and experimental results of cell velocity and surface attachment. With the development of biofilm, promotion effect of flagellar motility responding to nutrient deprivation-stress faded out. Instead, loss of motility profiting increased growth rates and extracellular protein excretion, associated with an enhancement of biofilm development for the mutant in oligotrophic aquatic environment. For both strains, nutrient limitation evidently reduced planktonic cell propagation as expected. Our results offer new insights into the mechanical understanding of biofilm formation shaped by environmental stresses and associating biological responses.

A practical review on the measurement tools for cellular adhesion force

Cell-cell and cell-matrix adhesions are fundamental in all multicellular organisms. They play a key role in cellular growth, differentiation, pattern formation and migration. Cell-cell adhesion is substantial in the immune response, pathogen-host interactions, and tumor development. The success of tissue engineering and stem cell implantations strongly depends on the fine control of live cell adhesion on the surface of natural or biomimetic scaffolds. Therefore, the quantitative and precise measurement of the adhesion strength of living cells is critical, not only in basic research but in modern technologies, too. Several techniques have been developed or are under development to quantify cell adhesion. All of them have their pros and cons, which has to be carefully considered before the experiments and interpretation of the recorded data. Current review provides a guide to choose the appropriate technique to answer a specific biological question or to complete a biomedical test by measuring cell adhesion.

Single-particle tracking discloses binding-mediated rocking diffusion of rod-shaped biological particles on lipid membranes

Interestingly, on the lipid membrane, E.coli displays anomalous rocking diffusion, which might facilitate the subsequent survey of stronger association sites on the two-dimensional (2D) surface.

It has been demonstrated that rod-shaped particles can achieve a high translocation efficiency for gene and drug delivery in biological samples. Previous theoretical calculations also confirmed that rod-shaped particles display higher diffusivity than their spherical counterparts in biological porous media. Understanding the diffusion dynamics of biological and non-biological rod-shaped particles in biological solutions as well as close to the lipid membrane is therefore fundamentally significant for the rational design of efficient cargos. With dark-field optical microscopy, the translational and three-dimensional (3D) orientational diffusion dynamics of individual rod-shaped particles (i.e., E. coli and upconversion microrods, UCMRs) in phosphate buffered saline (PBS) and on the lipid membrane are tracked at the single-particle level. In the buffer solution, faster rotation of E. coli in the z direction was observed even though its dynamics in the x–y plane is comparable with that of UCMRs. Interestingly, on the lipid membrane, distinct from the confined motion of UCMRs, anomalous rocking diffusion was observed, which might facilitate the subsequent survey of stronger association sites on the two-dimensional (2D) surface. These results would afford deep insight into the better understanding of the translocation mechanism by using rod-shaped particles as a delivery cargo in biological samples.

Confined Flow: Consequences and Implications for Bacteria and Biofilms

Bacteria overwhelmingly live in geometrically confined habitats that feature small pores or cavities, narrow channels, or nearby interfaces. Fluid flows through these confined habitats are ubiquitous in both natural and artificial environments colonized by bacteria. Moreover, these flows occur on time and length scales comparable to those associated with motility of bacteria and with the formation and growth of biofilms, which are surface-associated communities that house the vast majority of bacteria to protect them from host and environmental stresses. This review describes the emerging understanding of how flow near surfaces and within channels and pores alters physical processes that control how bacteria disperse, attach to surfaces, and form biofilms. This understanding will inform the development and deployment of technologies for drug delivery, water treatment, and antifouling coatings and guide the structuring of bacterial consortia for production of chemicals and pharmaceuticals.

Pyroelectric Effect Enables Simple and Rapid Evaluation of Biofilm Formation

Biofilms are detrimental to human life and industrial processes due to potential infections, contaminations, and deterioration. Therefore, the evaluation of microbial capability to form biofilms is of fundamental importance for assessing how different environmental factors may affect their vitality. Nowadays, the approaches used for biofilm evaluation are still poor in reliability and rapidity and often provide contradictory results. Here, we present what we call biofilm electrostatic test (BET) as a simple, rapid, and highly reproducible tool for evaluating in vitro the ability of bacteria to form biofilms through electrostatic interaction with a pyroelectrified carrier. The results show how the BET is able to produce viable biofilms with a density 6-fold higher than that on the control, after just 2 h incubation. The BET could pave the way to a rapid standardization of the evaluation of bacterial resistance among biofilm-producing microorganisms. In fact, due to its simplicity and cost-effectiveness, it is well suited for a rapid and easy implementation in a microbiology laboratory.

Role of antigen-43 on biofilm formation and horizontal antibiotic resistance gene transfer in non-O157 Shiga toxin producing Escherichia coli strains

BACKGROUND AND OBJECTIVES

The objectives of this study were to evaluate the antibiotic resistance profiles, biofilm formation, presence of antigen 43 (Ag43) gene, and transfer of antibiotic resistance phenotype among non-O157 Shiga toxin producing Escherichia coli (STEC).

MATERIALS AND METHODS

From October 2014 to November 2015 a total of 276 stool samples were collected from healthy calves, goats and 395 patients with the sign of nonbloody diarrhea and screened for presence of stx and serotype O157 genes by polymerase chain reaction (PCR) technique. Susceptibility to 14 antibiotics was determined as per CLSI guideline. Presence of Ag43 and intimin (eaeA) genes were detected by PCR. Biofilm formation was measured by microtiter plate method. Conjugation was carried out by membrane filter technique.

RESULTS

We isolated 74 (93.6%) non-O157 STEC strains from 41 calves, 33 goats and 5 (6.3%) patients' stools, however, no O157 serotype was detected in our study. Resistance was observed most commonly to tobramycin (66.2%), kanamycin (48.6%), and amikacin (29.7%) and less frequently to ciprofloxacin (4.1%), amoxicillin-clavulanic acid (5.4%), and ceftriaxone (9.5%) in isolates recovered from calves and goats fecal samples, whereas, all human isolates were sensitive to ceftazidime, ciprofloxacin, tobramycin and imipenem, respectively. Furthermore, Ag43 was detected in 60 STEC isolated from animals and 5 human origins (no eaeA gene was found in this study). Biofilm formation from Ag43⁺ and Ag43^- colonies showed 20 isolates with strong biofilm activities. Cefotaxime resistance phenotype was transferred to E. coli ATCC 25922.1 (Nal^r) by conjugation at a frequency of 1.6×10^-4.

CONCLUSION

From the above results we concluded that, human infections with non-O157 STEC were significantly low in Kerman. Ag43 was insignificant with biofilm quantity in most cases.

Three-Dimensional Bacterial Behavior near Dynamic Surfaces Formed by Degradable Polymers

Understanding the behavior of bacteria near biodegradable surfaces is critical for the development of biomedical and antibiofouling materials. By using digital holographic microscopy (DHM), we investigated the three-dimensional (3D) behavior of Escherichia coli and Pseudomonas sp. in lipase-containing aquatic environments near dynamic surfaces constructed by biodegradable poly(ε-caprolactone) (PCL)-based polymers in real time. As the enzymatic degradation rate increases, the percentage of near-surface subdiffusive bacteria and consequently, the irreversible adhesion decreases. Atomic force microscopy (AFM) measurements reveal that the adhesion force between bacteria and the surfaces decreases with an increasing degradation rate. In addition, the degradation products elicit a negative chemotactic response in E. coli, further driving them away from the dynamic surfaces through more frequent tumbling motion. Our study clearly demonstrates that bacterial adhesion can be reduced on dynamic surfaces formed by degradable polymers.

Transport of enterococci and F+ coliphage through the saturated zone of the beach aquifer

Coastal groundwater has been implicated as a source of microbial pollution to recreational beaches. However, there is little work investigating the transport of fecal microbes through beach aquifers where waters of variable salinity are present. In this study, the potential for fecal indicator organisms enterococci (ENT) and F+ coliphage to be transported through marine beach aquifers was investigated. Native sediment and groundwaters were collected from the fresh and saline sections of the subterranean estuary at three beaches along the California coast where coastal communities utilize septic systems for wastewater treatment. Groundwaters were seeded with sewage and removal of F+ coliphage and ENT by the sediments during saturated flow was tested in laboratory column experiments. Removal varied significantly between beach and organism. F+ coliphage was removed to a greater extent than ENT, and removal was greater in saline sediments and groundwater than fresh. At one of the three beaches, a field experiment was conducted to investigate the attenuation of F+ coliphage and ENT down gradient of a septic leach field. ENT were detected up to 24 m from the leach field. The column study and field observations together suggest ENT can be mobile within native aquifer sediments and groundwater under certain conditions.

Swimming Motility Reduces Deposition to Silica Surfaces

The transport and fate of bacteria in porous media is influenced by physicochemical and biological properties. This study investigated the effect of swimming motility on the attachment of cells to silica surfaces through comprehensive analysis of cell deposition in model porous media. Distinct motilities were quantified for different strains using global and cluster-based statistical analyses of microscopic images taken under no-flow condition. The wild-type, flagellated strain DJ showed strong swimming as a result of the actively swimming subpopulation whose average speed was 25.6 μm/s; the impaired swimming of strain DJ77 was attributed to the lower average speed of 17.4 μm/s in its actively swimming subpopulation; and both the nonflagellated JZ52 and chemically treated DJ cells were nonmotile. The approach and deposition of these bacterial cells were analyzed in porous media setups, including single-collector radial stagnation point flow cells (RSPF) and two-dimensional multiple-collector micromodels under well-defined hydrodynamic conditions. In RSPF experiments, both swimming and nonmotile cells moved with the flow when at a distance ≥20 μm above the collector surface. Closer to the surface, DJ cells showed both horizontal and vertical movement, limiting their contact with the surface, while chemically treated DJ cells moved with the flow to reach the surface. These results explain how wild-type swimming reduces attachment. In agreement, the deposition in micromodels was also lowest for DJ compared with those for DJ77 and JZ52. Wild-type swimming specifically reduced deposition on the upstream surfaces of the micromodel collectors. Conducted under environmentally relevant hydrodynamic conditions, the results suggest that swimming motility is an important characteristic for bacterial deposition and transport in the environment.

Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface

The effects of the presence or absence of microbial flagella and the microbial motility on the colloidal behaviors of microbial cells were quantitatively evaluated. The microbial cell attachment and detachment processes on a glass surface were observed directly using a parallel-plate flow chamber. Wild-type, flagellar paralyzed, and nonflagellated Escherichia coli strains were used as model microbial cells. In the cell attachment tests, the microbial adhesion rate in a 160mM NaCl solution was approximately 10 times higher than that in a 10mM solution, for all E. coli strains. The colloidal behavior of the microbial cells agreed well with the predictions of the DLVO theory. In addition, the microbial flagella and motility did not significantly affect the cell attachment, regardless of the existence of a potential barrier between the cell and the glass substratum. In the cell detachment tests, the cumulative number of microbial cells detached from the glass substratum with increasing flow rate was fit well with the Weibull distribution function. The list of strains arranged in order of increasing median drag force required to remove them was nonflagellated strain, flagellar paralyzed strain, and wild-type strain. These results indicated that the flagella and the flagellar motility inhibited the cell detachment from the glass substratum. Furthermore, a large external force would likely be required to inhibit the microbial adhesion in the early stage of the biofilm formation.

Role of biofilm roughness and hydrodynamic conditions in Legionella pneumophila adhesion to and detachment from simulated drinking water biofilms

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.

Attachment from flow of Escherichia coli bacteria onto silanized glass substrates

We investigate the attachment of Escherichia coli on silanized glass surfaces during flow through a linear channel at flow rates of 0.1-1 mL/min using confocal microscopy. We assemble layers of organosilanes on glass and track the position and orientation of bacteria deposited on these surfaces during flow with high spatial resolution. We find that a metric based on the degree of the surface-tethered motion of bacteria driven by flagella is inversely correlated with deposition rate, whereas conventional surface characterizations, such as surface energy or water contact angle, are uncorrelated. Furthermore, the likelihood that an initially moving bacterium becomes immobilized increases with increasing deposition rate. Our results suggest that the chemistry and arrangement of silane molecules on the surface influence the transition from transient to irreversible attachment by favoring different mechanisms used by bacteria to attach to surfaces.

Measurement of microbial adhesive forces with a parallel plate flow chamber

HYPOTHESIS

It was predicted that the colloidal behaviors of archaea and bacteria with disparate surface structure were different. In this study, the effects of the physicochemical properties of microbial cell surfaces on colloidal behavior were analyzed with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, thermodynamics, and powder technology.

EXPERIMENTS

Cell attachment and detachment from model substrates were directly observed using a parallel plate flow chamber. Gram-negative Escherichia coli and archaeal Methanosarcina barkeri were used as model microbial cells, and positively and negatively charged glass slides were used as model substrates.

FINDINGS

Microbial adhesion on both substrates agreed well with predictions calculated from DLVO theory, using experimental parameters. The total number of cells detached from the substrates as a function of flow rate was fit with the Weibull distribution function. In addition, the drag force required for detachment, which was estimated from the hydrodynamic forces, had a wide distribution; however, the forces became smaller with increasing ionic strength because of reduced electrostatic interactions between the cells and the substrate. M. barkeri could not be detached from positively charged substrates because it would entail a negative change in the interfacial energy of interaction. Thus adhesion was thermodynamically favored in this case.

Escherichia coli strains expressing H12 antigens demonstrate an increased ability to attach to abiotic surfaces as compared with E. coli strains expressing H7 antigens

The role of Escherichia coli H antigens in hydrophobicity and attachment to glass, Teflon and stainless steel (SS) surfaces was investigated through construction of fliC knockout mutants in E. coli O157:H7, O1:H7 and O157:H12. Loss of FliC(H12) in E. coli O157:H12 decreased attachment to glass, Teflon and stainless steel surfaces (p<0.05). Complementing E. coli O157:H12 ΔfliC(H12) with cloned wildtype (wt) fliC(H12) restored attachment to wt levels. The loss of FliCH7 in E. coli O157:H7 and O1:H7 did not always alter attachment (p>0.05), but complementation with cloned fliC(H12), as opposed to cloned fliCH7, significantly increased attachment for both strains compared with wt counterparts (p<0.05). Hydrophobicity determined using bacterial adherence to hydrocarbons and contact angle measurements differed with fliC expression but was not correlated to the attachment to materials included in this study. Purified FliC was used to functionalise silicone nitride atomic force microscopy probes, which were used to measure adhesion forces between FliC and substrates. Although no significant difference in adhesion force was observed between FliC(H12) and FliCH7 probes, differences in force curves suggest different mechanism of attachment for FliC(H12) compared with FliCH7. These results indicate that E. coli strains expressing flagellar H12 antigens have an increased ability to attach to certain abiotic surfaces compared with E. coli strains expressing H7 antigens.

A new approach to decoupling of bacterial adhesion energies measured by AFM into specific and nonspecific components

A new method to decoupling of bacterial interactions measured by atomic force microscopy (AFM) into specific and nonspecific components is proposed. The new method is based on computing the areas under the approach and retraction curves. To test the efficacy of the new method, AFM was used to probe the repulsion and adhesion energies present between L. monocytogenes cells cultured at five pH values (5, 6, 7, 8 and 9) and silicon nitride (Si3N4). Overall adhesion energy was then decoupled into its specific and nonspecific components using the new method as well as using Poisson statistical approach. Poisson statistical method represents the most commonly used approach to decouple bacterial interactions into their components. For all pH conditions investigated, specific energies dominated the adhesion and a transition in adhesion and repulsion energies for cells cultured at pH 7 was observed. When compared, the differences in the specific and nonspecific energies obtained using Poisson analysis and the new method were on average 2.2% and 6.7%, respectively. The relatively close energies obtained using the two approaches demonstrate the efficacy of the new method as an alternative way to decouple adhesion energies into their specific and nonspecific components.

96-well microtiter plates for biofouling simulation in biomedical settings

Microtiter plates with 96 wells are routinely used in biofilm research mainly because they enable high-throughput assays. These platforms are used in a variety of conditions ranging from static to dynamic operation using different shaking frequencies and orbital diameters. The main goals of this work were to assess the influence of nutrient concentration and flow conditions on biofilm formation by Escherichia coli in microtiter plates and to define the operational conditions to be used in order to simulate relevant biomedical scenarios. Assays were performed in static mode and in incubators with distinct orbital diameters using different concentrations of glucose, peptone and yeast extract. Computational fluid dynamics (CFD) was used to simulate the flow inside the wells for shaking frequencies ranging from 50 to 200 rpm and orbital diameters from 25 to 100 mm. Higher glucose concentrations enhanced adhesion of E. coli in the first 24 h, but variation in peptone and yeast extract concentration had no significant impact on biofilm formation. Numerical simulations indicate that 96-well microtiter plates can be used to simulate a variety of biomedical scenarios if the operating conditions are carefully set.

Role of cold climate and freeze-thaw on the survival, transport, and virulence of Yersinia enterocolitica

Surface and near-surface soils in cold climate regions experience low temperature and freeze-thaw (FT) conditions in the winter. Microorganisms that are of concern to groundwater quality may have the potential to survive low temperature and FT in the soil and aqueous environments. Although there is a body of literature on the survival of pathogenic bacteria at different environmental conditions, little is known about their transport behavior in aquatic environments at low temperatures and after FT. Herein, we studied the survival, transport, and virulence of a Gram-negative bacterial pathogen, Yersinia enterocolitica, when subjected to low temperature and several FT cycles at two solution ionic strengths (10 and 100 mM) in the absence of nutrients. Our findings demonstrate that this bacterium exhibited higher retention on sand after exposure to FT. Increasing the number of FT cycles resulted in higher bacterial cell surface hydrophobicity and impaired the swimming motility and viability of the bacterium. Moreover, the transcription of flhD and fliA, the flagellin-encoding genes, and lpxR, the lipid A 3'-O-deacylase gene, was reduced in low temperature and after FT treatment while the transcription of virulence factors such as ystA, responsible for enterotoxin production, ail, attachment invasion locus gene, and rfbC, O-antigen gene, was increased. Y. enterocolitica tends to persist in soil for long periods and may become more virulent at low temperature in higher ionic strength waters in cold regions.

Evaluating the effects of variable water chemistry on bacterial transport during infiltration

Bacterial infiltration through the subsurface has been studied experimentally under different conditions of interest and is dependent on a variety of physical, chemical and biological factors. However, most bacterial transport studies fail to adequately represent the complex processes occurring in natural systems. Bacteria are frequently detected in stormwater runoff, and may present risk of microbial contamination during stormwater recharge into groundwater. Mixing of stormwater runoff with groundwater during infiltration results in changes in local solution chemistry, which may lead to changes in both bacterial and collector surface properties and subsequent bacterial attachment rates. This study focuses on quantifying changes in bacterial transport behavior under variable solution chemistry, and on comparing the influences of chemical variability and physical variability on bacterial attachment rates. Bacterial attachment rate at the soil-water interface was predicted analytically using a combined rate equation, which varies temporally and spatially with respect to changes in solution chemistry. Two-phase Monte Carlo analysis was conducted and an overall input-output correlation coefficient was calculated to quantitatively describe the importance of physiochemical variation on the estimates of attachment rate. Among physical variables, soil particle size has the highest correlation coefficient, followed by porosity of the soil media, bacterial size and flow velocity. Among chemical variables, ionic strength has the highest correlation coefficient. A semi-reactive microbial transport model was developed within HP1 (HYDRUS1D-PHREEQC) and applied to column transport experiments with constant and variable solution chemistries. Bacterial attachment rates varied from 9.10×10(-3)min(-1) to 3.71×10(-3)min(-1) due to mixing of synthetic stormwater (SSW) with artificial groundwater (AGW), while bacterial attachment remained constant at 9.10×10(-3)min(-1) in a constant solution chemistry (AGW only). The model matched observed bacterial breakthrough curves well. Although limitations exist in the application of a semi-reactive microbial transport model, this method represents one step towards a more realistic model of bacterial transport in complex microbial-water-soil systems.

Flagella-mediated differences in deposition dynamics for Azotobacter vinelandii in porous media

A multiscale approach was designed to study the effects of flagella on deposition dynamics of Azotobacter vinelandii in porous media, independent of motility. In a radial stagnation point flow cell (RSPF), the deposition rate of a flagellated strain with limited motility, DJ77, was higher than that of a nonflagellated (Fla(-)) strain on quartz. In contrast, Fla(-) strain deposition exceeded that of DJ77 in two-dimensional silicon microfluidic models (micromodels) and in columns packed with glass beads. Both micromodel and column experiments showed decreasing deposition over time, suggesting that approaching cells were blocked from deposition by previously deposited cells. Modeling results showed that blocking became effective for DJ77 strain at lower ionic strengths (1 mM and 10 mM), while for the Fla(-) strain, blocking was similar at all ionic strengths. In late stages of micromodel experiments, ripening effects were also observed, and these appeared earlier for the Fla(-) strain. In RSPF and column experiments, deposition of the flagellated strain was influenced by ionic strength, while ionic strength dependence was not observed for the Fla(-) strain. The observations in all three setups suggested flagella affect deposition dynamics and, in particular, result in greater sensitivity to ionic strength.

Bacterial microsystems and microrobots

Microorganisms and specifically motile bacteria have been recently added to the list of micro-actuators typically considered for the implementation of microsystems and microrobots. Such trend has been motivated by the fact these microorganisms are self-powered actuators with overall sizes at the lower end of the micrometer range and which have proven to be extremely effective in low Reynolds number hydrodynamic regime of usually less than 10(-2). Furthermore, the various sensors or taxes in bacteria influencing their movements can also be exploited to perform tasks that were previously considered only for futuristic artificial microrobots. Bacterial implementations and related issues are not only reviewed, but this paper also proposes many techniques and approaches that can be considered as building blocks for the implementations of more sophisticated microsystems and microrobots.

Bacterial flagella explore microscale hummocks and hollows to increase adhesion

Biofilms, surface-bound communities of microbes, are economically and medically important due to their pathogenic and obstructive properties. Among the numerous strategies to prevent bacterial adhesion and subsequent biofilm formation, surface topography was recently proposed as a highly nonspecific method that does not rely on small-molecule antibacterial compounds, which promote resistance. Here, we provide a detailed investigation of how the introduction of submicrometer crevices to a surface affects attachment of Escherichia coli. These crevices reduce substrate surface area available to the cell body but increase overall surface area. We have found that, during the first 2 h, adhesion to topographic surfaces is significantly reduced compared with flat controls, but this behavior abruptly reverses to significantly increased adhesion at longer exposures. We show that this reversal coincides with bacterially induced wetting transitions and that flagellar filaments aid in adhesion to these wetted topographic surfaces. We demonstrate that flagella are able to reach into crevices, access additional surface area, and produce a dense, fibrous network. Mutants lacking flagella show comparatively reduced adhesion. By varying substrate crevice sizes, we determine the conditions under which having flagella is most advantageous for adhesion. These findings strongly indicate that, in addition to their role in swimming motility, flagella are involved in attachment and can furthermore act as structural elements, enabling bacteria to overcome unfavorable surface topographies. This work contributes insights for the future design of antifouling surfaces and for improved understanding of bacterial behavior in native, structured environments.

Dynamics of detachment of Escherichia coli from plasma-mediated coatings under shear flow

A series of plasma-mediated coatings, containing silver nanoparticles embedded in an organosilicon or silica-like matrix, were deposited onto stainless steel and chemically characterized. Their anti-adhesive properties were evaluated in vitro towards Escherichia coli by performing shear-flow induced detachment experiments. Increasing the wall shear stress facilitated E. coli cell detachment, irrespective of the coating characteristics. When nanosilver was incorporated, cell detachment was lower, probably due to the affinity of the embedded silver for biological components of the cell wall. The presence of methyl groups in the matrix network could also promote enhanced hydrophobic interactions. Within the population fraction remaining attached to the coating under increasing shear flow, different association phenotypes were observed, viz. progressively lying flat, moving laterally, remaining tethered, or rotating by a single anchoring point, until alignment with the flow direction. This re-orientation phenotype and its relation with detachment were dependent of the coating. The effects of such heterogeneities should be more deeply explored.

Deposition mechanisms of TiO2 nanoparticles in a parallel plate system

In this study, a microscope-based technique was utilized to understand the fundamental mechanisms involved in deposition of TiO(2) nanoparticles (TNPs). Transport and deposition studies were conducted in a parallel plate (PP) flow chamber with TNP labeled with fluorescein isothiocyanate (FITC) for visualization. Attachment of FITC-labeled TNPs on surfaces is a function of a combination of parameters, including ionic strength (IS), pH and flowrate. Significantly higher deposition rates were observed at pH 5 versus pH 7. This is attributed to the conditions being chemically favorable for deposition at pH 5 as compared to pH 7, as predicted by DLVO theory. Additionally, deposition rates at pH 5 were reduced with IS below 10 mM due to the decrease in range of electrostatic attractive forces. Above 10 mM, aggregate size increased, resulting in higher deposition rates. At pH 7, no deposition was observed below 10 mM and above this concentration, deposition increased with IS. The impact of flowrate was also observed, with decreasing flowrate leading to greater deposition due to the reduction in drag force acting on the aggregate (regardless of pH). Comparisons between experimental and theoretical approximations indicate that non-DLVO type forces also play a significant role. This combination of observations suggest that the deposition of these model nanoparticles on glass surfaces was controlled by a combination of DLVO and non-DLVO-type forces, shear rate, aggregation state, and gravitational force acting on TNPs.

Interactions of Bacteria and Fungi at the Surface

The increased life span of humans and the dynamic development of Biomaterials' industry have led to widespread use of implants in modern medicine. Microorganisms, mostly opportunistic flora,are able to adapt perfectly to the changing environment of their host. Bacteria, once regarded as non-pathogenic, successfully bind to artificial surfaces resulting in diseases that are difficult to treat. The Chapter discusses the process of microbial adhesion to the surfaces. It provides the brief description of the most important infections of humans, which result from the microbial colonization of implanted biomaterials. This adhesion is characterized in the context of physicochemical and biological interactions between microorganism and the surface. We describe the effects of environmental factors and the contribution of bacterial/fungal cell structures on microbial adhesion. Finally, the Chapter presents the most important aspects of interactions between bacteria and charged surfaces.

Motility of Pseudomonas aeruginosa in saturated granular media as affected by chemoattractant

To examine and quantify the effects of glass beads and chemoattractant on bacterial motility in granular media, we examined the motile behavior of P. aeruginosa in a saturated granular medium and quantified the effects of glass beads and the presence of a chemoattractant. By recording individual cell trajectories in microfluidic channels under a high-speed confocal microscope, we directly measured the cell's run direction and corresponding run-length, speed and turn angle. Bacterial run speed increased in the presence of chemoattractant in both aqueous and granular media. But it decreased in glass-beads compared to in aqueous media due to the restricted pore geometry and interactions between bacteria and grain surfaces. Notably, the relatively higher frequency distribution at turn angles of 170° decreased dramatically, while the smaller peak at 70° increased and became dominant on a bimodal distribution, showing more bacteria changed directions at smaller turn angles rather than reverse their swimming directions. Additionally, the presence of glass beads also decreased the chemotactic velocity and random motility by similar proportions due to the restrictive geometry and the interactions between bacteria and glass beads surface. Our study indicates that the swimming parameters measured from aqueous media cannot be directly adopted in models for predicting bacteria travel in granular media.

Idling time of motile bacteria contributes to retardation and dispersion in sand porous medium

The motility of microorganisms affects their transport in natural systems by altering their interactions with the solid phase of the soil matrix. To assess the effect of these interactions on transport parameters, a series of breakthrough curves (BTCs) for motile and nonmotile bacteria, including E. coli and P. putida species, were measured from a homogeneously packed sand column under three different interstitial velocities of 1 m/d, 5 m/d, and 10 m/d. BTCs for the nonmotile bacteria were nearly identical for all three flow rates, except that the recovery percentage at 1 m/d was reduced by 5% compared to the higher flow rates. In contrast, for the motile bacteria, the recovery percentages were not affected by flow rate, but their BTCs exhibited a higher degree of retardation and dispersion as the flow velocity decreased, which was consistent with increased idling times of the motile strains. The smooth-swimming mutant E. coli HCB437, which is unable to change its swimming direction after encountering the solid surfaces and thus has the largest idling time, also exhibited the greatest degree of retardation and dispersion. All of the experimental observations were compared to results from an advection-dispersion transport model with three fitting parameters: retardation factor (R), longitudinal dispersivity (α(L)), and attachment rate coefficient (k(att)). In addition, the single-collector efficiency (η₀) and collision efficiency (α) were calculated according to the colloid filtration theory (CFT), and confirmed that motile bacteria had lower collision efficiencies than nonmotile bacteria. This is consistent with previously reported observations that motile bacteria can avoid attachment to a solid surface by their active swimming capabilities. By quantifying the effect of bacterial motility on various transport parameters, more robust fate and transport models can be developed for decision-making related to environmental remediation strategies and risk assessment.

Shear stress increases the residence time of adhesion of Pseudomonas aeruginosa

Although ubiquitous, the processes by which bacteria colonize surfaces remain poorly understood. Here we report results for the influence of the wall shear stress on the early-stage adhesion of Pseudomonas aeruginosa PA14 on glass and polydimethylsiloxane surfaces. We use image analysis to measure the residence time of each adhering bacterium under flow. Our main finding is that, on either surface, the characteristic residence time of bacteria increases approximately linearly as the shear stress increases (∼0-3.5 Pa). To investigate this phenomenon, we used mutant strains defective in surface organelles (type I pili, type IV pili, or the flagellum) or extracellular matrix production. Our results show that, although these bacterial surface features influence the frequency of adhesion events and the early-stage detachment probability, none of them is responsible for the trend in the shear-enhanced adhesion time. These observations bring what we believe are new insights into the mechanism of bacterial attachment in shear flows, and suggest a role for other intrinsic features of the cell surface, or a dynamic cell response to shear stress.

Control of microbial attachment by inhibition of ATP and ATP-mediated autoinducer-2

In this study, 2,4-dinitrophenol (DNP), a typical chemical uncoupler, was employed to investigate the possible roles of ATP and autoinducer-2 (AI-2) of suspended microorganisms in attachment onto nylon membrane and glass slide surfaces. Results showed that DNP could disrupt ATP synthesis, subsequently led to a reduced production of AI-2 which is a common signaling molecule for cellular communication. Attachment of suspended microorganisms exposed to DNP was significantly suppressed as compared to microorganisms without contact with DNP. These suggest that an energized state of suspended microorganisms would favor microbial attachment to both nylon membrane and glass slide surfaces. The extent of microbial attachment was found to be positively related to the AI-2 content of microorganisms. This study offers insights into the control of biofouling by preventing initial microbial attachment through inhibition of energy metabolism.

Adhesion of Pathogenic Bacteria to Food Contact Surfaces: Influence of pH of Culture

The adhesion of Aeromonas hydrophila, Escherichia coli O157:H7, Salmonella Enteritidis, and Staphylococcus aureus to hydrophobic and hydrophilic surfaces in cultures with different pHs (6, 7, and 8) was studied. The results indicated that the type of material had no effect on the attachment capacity of microorganisms, while environmental pH influenced the adhesion of A. hydrophila, E. coli, and S. aureus to both solid substrates. The attachment of S. Enteritidis (P > .05) was not affected by the type of substrate or the culture pH, whereas E. coli displayed the weakest affinity for both polystyrene and glass surfaces. No correlation was established between the physicochemical properties of the materials, or the bacterial and the rate of bacterial adhesion, except for S. aureus. Photomicrographs have shown that surfaces were contaminated by small clusters of S. Enteritidis while S. aureus invaded the food contact surfaces in the form of small chains or cell aggregates.

Initial colloid deposition on bare and zeolite-coated stainless steel and aluminum: influence of surface roughness

The impact of surface roughness of bare and zeolite ZSM-5 coated stainless steel and aluminum alloy on colloid deposition has been investigated using a parallel plate flow chamber system in an aqueous environment. The metals were systematically polished to alter the surface roughness from nanoscale to microscale, with the subsequent surface roughness of both the bare and coated surfaces varying from 11.2 to 706 nm. The stainless steel and aluminum alloy surfaces are extensively characterized, both as bare and as coated surfaces. Experimental results suggest that ZSM-5 coating and surface roughness have a pronounced impact on the kinetics of the colloid deposition. The ZSM-5 coating reduced colloid adhesion compared to the corresponding bare metal surface. In general, the greater surface roughness of like samples resulted in higher colloid deposition. Primarily, this is due to greater surface roughness inducing less reduction in the attractive interactions occurring between colloids and collector surfaces. This effect was sensitive to ionic strength and was found to be more pronounced at lower ionic strength conditions. For the most electrostatically unfavorable scenario (ZSM-5 coatings in 1 mM KNO(3)), the enhanced deposition may also be attributed to inherent surface charge heterogeneity of ZSM-5 coatings due to aluminum in the crystalline structure. The two exceptions are ZSM-5 coated mirror-polished stainless steel and the unpolished aluminum surfaces, which are rougher than the other two samples of the same metal type but result in the least deposition. The reasons for these observations are discussed, as well as the effect of surface charge and hydrophobicity on the adhesion. The relative importance of surface roughness versus contributions of electrostatic interactions and hydrophobicity to the colloid deposition is also discussed.

Identifying the role of flagella in the transport of motile and nonmotile Salmonella enterica serovars

The influence of bacterial flagella on cell transport has been examined using three Salmonella enterica serovars with different motility phenotypes. Both a packed bed (PB) column and radial stagnation point flow system (RSPF) were employed to investigate bacterial deposition kinetics onto quartz over a range of conditions. The aim of this study was to better understand the role of motility on the deposition behavior of Salmonella, an important food- and waterborne pathogen. In both the PB column and RSPF systems, flagellated strains showed higher deposition, indicating the nonmotile cells can be transported further than the motile. At late-exponential growth phase, the deposition of the functional flagellated motile strain was enhanced, much more so than the dysfunctionally flagellated nonmotile and nonflagellated strains, highlighting the role of flagellar motion in cellular deposition and retention through available pore spaces and irregularities on quartz surfaces.

Flagellated but not hyperfimbriated Salmonella enterica serovar Typhimurium attaches to and forms biofilms on cholesterol-coated surfaces

The asymptomatic, chronic carrier state of Salmonella enterica serovar Typhi occurs in the bile-rich gallbladder and is frequently associated with the presence of cholesterol gallstones. We have previously demonstrated that salmonellae form biofilms on human gallstones and cholesterol-coated surfaces in vitro and that bile-induced biofilm formation on cholesterol gallstones promotes gallbladder colonization and maintenance of the carrier state. Random transposon mutants of S. enterica serovar Typhimurium were screened for impaired adherence to and biofilm formation on cholesterol-coated Eppendorf tubes but not on glass and plastic surfaces. We identified 49 mutants with this phenotype. The results indicate that genes involved in flagellum biosynthesis and structure primarily mediated attachment to cholesterol. Subsequent analysis suggested that the presence of the flagellar filament enhanced binding and biofilm formation in the presence of bile, while flagellar motility and expression of type 1 fimbriae were unimportant. Purified Salmonella flagellar proteins used in a modified enzyme-linked immunosorbent assay (ELISA) showed that FliC was the critical subunit mediating binding to cholesterol. These studies provide a better understanding of early events during biofilm development, specifically how salmonellae bind to cholesterol, and suggest a target for therapies that may alleviate biofilm formation on cholesterol gallstones and the chronic carrier state.

Quantitative analysis of transverse bacterial migration induced by chemotaxis in a packed column with structured physical heterogeneity

A two-dimensional mathematical model was developed to simulate transport phenomena of chemotactic bacteria in a sand-packed column designed with structured physical heterogeneity in the presence of a localized chemical source. In contrast to mathematical models in previous research work, in which bacteria were typically treated as immobile colloids, this model incorporated a convective-like chemotaxis term to represent chemotactic migration. Consistency between experimental observation and model prediction supported the assertions that (1) dispersion-induced microbial transfer between adjacent conductive zones occurred at the interface and had little influence on bacterial transport in the bulk flow of the permeable layers and (2) the enhanced transverse bacterial migration in chemotactic experiments relative to nonchemotactic controls was mainly due to directed migration toward the chemical source zone. On the basis of parameter sensitivity analysis, chemotactic parameters determined in bulk aqueous fluid were adequate to predict the microbial transport in our intermediate-scale porous media system. Additionally, the analysis of adsorption coefficient values supported the observation of a previous study that microbial deposition to the surface of porous media might be decreased under the effect of chemoattractant gradients. By quantitatively describing bacterial transport and distribution in a heterogeneous system, this mathematical model serves to advance our understanding of chemotaxis and motility effects in granular media systems and provides insights for modeling microbial transport in in situ microbial processes.

Colloidal and bacterial deposition: role of gravity

The role of gravitational force on the deposition of 0.5, 1.1, and 1.8 mum carboxylate-modified polystyrene latex (CML) microspheres and bacterium Burkholderia cepacia G4g has been evaluated using a parallel plate flow chamber system. This experimental system utilized an inverted and an upright optical microscope attached with image-capturing devices to directly observe and determine the deposition kinetics onto glass surfaces located at the top and bottom of the flow chamber. Deposition kinetics was quantified at 10 mM KCl under electrostatically unfavorable and favorable attachment conditions and at two flow rates (0.06 and 3 mL/min), simulating the range of flow velocities from groundwater to rapid granular filtration. Comparing the particle deposition kinetics on the top and bottom surfaces under identical flowing exposure time, fluid chemistries, and hydrodynamic conditions, results showed that significant differences were observed between the two surfaces, suggesting that gravity was a significant driving force for the initial stages of deposition of particles that were larger than 1 mum size. Simulation results utilizing a particle trajectory model confirmed these experimental observations. This was further supported by additional deposition experiments with 1.1 mum microspheres suspended in a deuterium oxide (D(2)O)/water mixture (heavy water) where the density of colloid and the suspending heavy water were effectively the same. Under this condition, deposition rates were observed to be identical between the top and bottom surfaces. Results from normal and heavy water solutions indicated that the greater deposition of colloidal particles larger than 1 mum on the bottom in normal water solutions is due to gravity. Finally, the experimental results were compared with deposition studies using smaller 0.5 mum colloids as well as some theoretical calculations of expected rates of particle deposition.

Signals, regulatory networks, and materials that build and break bacterial biofilms

Biofilms are communities of microorganisms that live attached to surfaces. Biofilm formation has received much attention in the last decade, as it has become clear that virtually all types of bacteria can form biofilms and that this may be the preferred mode of bacterial existence in nature. Our current understanding of biofilm formation is based on numerous studies of myriad bacterial species. Here, we review a portion of this large body of work including the environmental signals and signaling pathways that regulate biofilm formation, the components of the biofilm matrix, and the mechanisms and regulation of biofilm dispersal.

Initial bacterial deposition on bare and zeolite-coated aluminum alloy and stainless steel

In this study, the impact of zeolite thin film coatings on bacterial deposition and "biofouling" of surfaces has been investigated in an aqueous environment. The synthesis of two types of zeolite coatings, ZSM-5 coated on aluminum alloy and zeolite A coated on stainless steel, and the characterization of the coated and bare metal surfaces are described. The extent of cell deposition onto the bare and zeolite-coated aluminum alloy and stainless steel surfaces is investigated in a parallel plate flow chamber system under a laminar flow conditions. The initial rates of bacterial transfer to the various surfaces are compared by utilizing a marine bacterium, Halomonas pacifica g, under a range of ionic strength conditions. H. pacifica g deposited onto bare metal surfaces to a greater extent as compared with cells deposited onto the zeolite coatings. The surface properties found to have the most notable effect on attachment are the electrokinetic and hydrophobicity properties of the metal and zeolite-coated surfaces. These results suggest that a combination of two chemical mechanisms-hydrophobic and electrostatic interactions-contribute to the antifouling nature of the zeolite surface. Additional observations on the relative role of the hydrodynamic and physical phenomena are also discussed.