Determination of the shear force at the balance between bacterial attachment and detachment in weak-adherence systems, using a flow displacement chamber

Effect of shear rate on early Shewanella oneidensis adhesion dynamics monitored by deep learning

Understanding pioneer bacterial adhesion is essential to appreciate bacterial colonization and consider appropriate control strategies. This bacterial entrapment at the wall is known to be controlled by many physical, chemical or biological factors, including hydrodynamic conditions. However, due to the nature of early bacterial adhesion, i.e. a short and dynamic process with low biomass involved, such investigations are challenging. In this context, our study aimed to evaluate the effect of wall shear rate on the early bacterial adhesion dynamics. Firstly, at the population scale by assessing bacterial colonization kinetics and the mechanisms responsible for wall transfer under shear rates using a time-lapse approach. Secondly, at the individual scale, by implementing an automated image processing method based on deep learning to track each individual pioneer bacterium on the wall. Bacterial adhesion experiments are performed on a model bacterium (Shewanella oneidensis MR-1) at different shear rates (0 to1250 s-1) in a microfluidic system mounted under a microscope equipped with a CCD camera. Image processing was performed using a trained neural network (YOLOv8), which allowed information extraction, i.e. bacterial wall residence time and orientation for each adhered bacterium during pioneer colonization (14 min). Collected from over 20,000 bacteria, our results showed that adhered bacteria had a very short residence time at the wall, with over 70 % remaining less than 1 min. Shear rates had a non-proportional effect on pioneer colonization with a bell-shape profile suggesting that intermediate shear rates improved both bacterial wall residence time as well as colonization rate and level. This lack of proportionality highlights the dual effect of wall shear rate on early bacterial colonization; initially increasing it improves bacterial colonization up to a threshold, beyond which it leads to higher bacterial wall detachment. The present study provides quantitative data on the individual dynamics of just adhered bacteria within a population when exposed to different rates of wall shear.

Smart self-defensive coatings with bacteria-triggered antimicrobial response for medical devices

Bacterial colonization and biofilm formation on medical devices represent one of the most urgent and critical challenges in modern healthcare. These issues not only pose serious threats to patient health by increasing the risk of infections but also exert a considerable economic burden on national healthcare systems due to prolonged hospital stays and additional treatments. To address this challenge, there is a need for smart, customized biomaterials for medical device fabrication, particularly through the development of surface modification strategies that prevent bacterial adhesion and the growth of mature biofilms. This review explores three bioinspired approaches through which antibacterial and antiadhesive coatings can be engineered to exhibit smart, stimuli-responsive features. This responsiveness is greatly valuable as it provides the coatings with a controlled, on-demand antibacterial response that is activated only in the presence of bacteria, functioning as self-defensive coatings. Such coatings can be designed to release antibacterial agents or change their surface properties/conformation in response to specific stimuli, like changes in pH, temperature, or the presence of bacterial enzymes. This targeted approach minimizes the risk of developing antibiotic resistance and reduces the need for continuous, high-dose antibacterial treatments, thereby preserving the natural microbiome and further reducing healthcare costs. The final part of the review reports a critical analysis highlighting the potential improvements and future evolutions regarding antimicrobial self-defensive coatings and their validation.

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.

Antimicrobial Polymer Surfaces Containing Quaternary Ammonium Centers (QACs): Synthesis and Mechanism of Action

Synthetic polymer surfaces provide an excellent opportunity for developing materials with inherent antimicrobial and/or biocidal activity, therefore representing an answer to the increasing demand for antimicrobial active medical devices. So far, biologists and material scientists have identified a few features of bacterial cells that can be strategically exploited to make polymers inherently antimicrobial. One of these is represented by the introduction of cationic charges that act by killing or deactivating bacteria by interaction with the negatively charged parts of their cell envelope (lipopolysaccharides, peptidoglycan, and membrane lipids). Among the possible cationic functionalities, the antimicrobial activity of polymers with quaternary ammonium centers (QACs) has been widely used for both soluble macromolecules and non-soluble materials. Unfortunately, most information is still unknown on the biological mechanism of action of QACs, a fundamental requirement for designing polymers with higher antimicrobial efficiency and possibly very low toxicity. This mini-review focuses on surfaces based on synthetic polymers with inherently antimicrobial activity due to QACs. It will discuss their synthesis, their antimicrobial activity, and studies carried out so far on their mechanism of action.

Negative role of filamentous bulking and its elimination in anammox process

In this study, the filamentous bulking (FB) with moderate and excessive levels were demonstrated to induce anammox failure by inhibiting nitrogen (N) removal and biomass retention. The low external mass transfer resulted from high liquid-surface friction and low turbulence of filamentous surface was considered the "trigger" of anammox failure, which decreased flux of nitrogen flow toward granular surface and directly limited N-removal loading, which meanwhile exposed granules with N-scarcity environment and indirectly inhibited N-removal bio-activity. Low bio-activity performed poor extracellular polymeric substances secretion further destroyed bio-aggregation with low suface hydrophobicity, which acted as "accelerator" for granule disintegration and biomass washout, ultimatly leading to anammox failure. Fortunately, incresing hydraulic shear stress could eradicate FB's negative effects without inhibiting FB itself, which promoted re-granulation and N-remval restore by enhancing external mass transfer more than hydraulic detachment. Enhancing mechanical stirring with FB level was necessary to maintain stable operation of granular anammox system.

A New In Vitro Blood Flow Model for the Realistic Evaluation of Antimicrobial Surfaces

Device-associated bloodstream infections can cause serious medical problems and cost-intensive postinfection management, defining a need for more effective antimicrobial coatings. Newly developed coatings often show reduced bacterial colonization and high hemocompatibility in established in vitro tests, but fail in animal studies or clinical trials. The poor predictive power of these models is attributed to inadequate representation of in vivo conditions. Herein, a new single-pass blood flow model, with simultaneous incubation of the test surface with bacteria and freshly-drawn human blood, is presented. The flow model is validated by comparative analysis of a recently developed set of antiadhesive and contact-killing polymer coatings, and the corresponding uncoated polycarbonate surfaces. The results confirm the model's ability to differentiate the antimicrobial activities of the studied surfaces. Blood activation data correlate with bacterial surface coverage: low bacterial adhesion is associated with low inflammation and hemostasis. Shear stress correlates inversely with bacterial colonization, especially on antiadhesive surfaces. The introduced model is concluded to enable the evaluation of novel antimicrobial materials under in vivo-like conditions, capturing interactions between bacteria and biomaterials surfaces in the presence of key components of the ex vivo host response.

Microfluidic investigation of the impacts of flow fluctuations on the development of Pseudomonas putida biofilms

Biofilms play critical roles in wastewater treatment, bioremediation, and medical-device-related infections. Understanding the dynamics of biofilm formation and growth is essential for controlling and exploiting their properties. However, the majority of current studies have focused on the impact of steady flows on biofilm growth, while flow fluctuations are common in natural and engineered systems such as water pipes and blood vessels. Here, we reveal the effects of flow fluctuations on the development of Pseudomonas putida biofilms through systematic microfluidic experiments and the development of a theoretical model. Our experimental results showed that biofilm growth under fluctuating flow conditions followed three phases: lag, exponential, and fluctuation phases. In contrast, biofilm growth under steady-flow conditions followed four phases: lag, exponential, stationary, and decline phases. Furthermore, we demonstrated that low-frequency flow fluctuations promoted biofilm growth, while high-frequency fluctuations inhibited its development. We attributed the contradictory impacts of flow fluctuations on biofilm growth to the adjustment time (T0) needed for biofilm to grow after the shear stress changed from high to low. Furthermore, we developed a theoretical model that explains the observed biofilm growth under fluctuating flow conditions. Our insights into the mechanisms underlying biofilm development under fluctuating flows can inform the design of strategies to control biofilm formation in diverse natural and engineered systems.

Effect of Gravity on Bacterial Adhesion to Heterogeneous Surfaces

Bacterial adhesion is the first step in the formation of surface biofilms. The number of bacteria that bind to a surface from the solution depends on how many bacteria can reach the surface (bacterial transport) and the strength of interactions between bacterial adhesins and surface receptors (adhesivity). By using microfluidic channels and video microscopy as well as computational simulations, we investigated how the interplay between bacterial transport and adhesivity affects the number of the common human pathogen Escherichia coli that bind to heterogeneous surfaces with different receptor densities. We determined that gravitational sedimentation causes bacteria to concentrate at the lower surface over time as fluid moves over a non-adhesive region, so bacteria preferentially adhere to adhesive regions on the lower, inflow-proximal areas that are downstream of non-adhesive regions within the entered compartments. Also, initial bacterial attachment to an adhesive region of a heterogeneous lower surface may be inhibited by shear due to mass transport effects alone rather than shear forces per se, because higher shear washes out the sedimented bacteria. We also provide a conceptual framework and theory that predict the impact of sedimentation on adhesion between and within adhesive regions in flow, where bacteria would likely bind both in vitro and in vivo, and how to normalize the bacterial binding level under experimental set-ups based on the flow compartment configuration.

Rapid formation of bioaggregates and morphology transition to biofilm streamers induced by pore-throat flows

Bioaggregates are condensed porous materials comprising microbes, organic and inorganic matters, and water. They are commonly found in natural and engineered porous media and often cause clogging. Despite their importance, the formation mechanism of bioaggregates in porous media systems is largely unknown. Through microfluidic experiments and direct numerical simulations of fluid flow, we show that the rapid bioaggregation is driven by the interplay of the viscoelastic nature of biomass and hydrodynamic conditions at pore throats. At an early stage, unique flow structures around a pore throat promote the biomass attachment at the throat. Then, the attached biomass fluidizes when the shear stress at the partially clogged pore throat reaches a critical value. After the fluidization, the biomass is displaced and accumulated in the expansion region of throats forming bioaggregates. We further find that such criticality in shear stress triggers morphological changes in bioaggregates from rounded- to streamer-like shapes. This knowledge was used to control the clogging of throats by tuning the flow conditions: When the shear stress at the throat exceeded the critical value, clogging was prevented. The bioaggregation process did not depend on the detailed pore-throat geometry, as we reproduced the same dynamics in various pore-throat geometries. This study demonstrates that pore-throat structures, which are ubiquitous in porous media systems, induce bioaggregation and can lead to abrupt disruptions in flow.

Inhibition of Adherence and Biofilm Formation of Pseudomonas aeruginosa by Immobilized ZnO Nanoparticles on Silicone Urinary Catheter Grafted by Gamma Irradiation

Nosocomial infections caused by microbial biofilm formation on biomaterial surfaces such as urinary catheters are complicated by antibiotic resistance, representing a common problem in hospitalized patients. Therefore, we aimed to modify silicone catheters to resist microbial adherence and biofilm formation by the tested microorganisms. This study used a simple direct method to graft poly-acrylic acid onto silicone rubber films using gamma irradiation to endow the silicone surface with hydrophilic carboxylic acid functional groups. This modification allowed the silicone to immobilize ZnO nanoparticles (ZnO NPs) as an anti-biofilm. The modified silicone films were characterized by FT-IR, SEM, and TGA. The anti-adherence ability of the modified silicone films was evidenced by the inhibition of biofilm formation by otherwise strong biofilm-producing Gram-positive, Gram-negative, and yeast clinical isolates. The modified ZnO NPs grafted silicone showed good cytocompatibility with the human epithelial cell line. Moreover, studying the molecular basis of the inhibitory effect of the modified silicone surface on biofilm-associated genes in a selected Pseudomonas aeruginosa isolate showed that anti-adherence activity might be due to the significant downregulation of the expression of lasR, lasI, and lecB genes by 2, 2, and 3.3-fold, respectively. In conclusion, the modified silicone catheters were low-cost, offering broad-spectrum anti-biofilm activity with possible future applications in hospital settings.

Surface Energy and Viscoelastic Characteristics of Staphylococcus epidermidis and Cutibacterium acnes Biofilm on Commercial Skin Constructs versus agar

Biofilms are recalcitrant to both study and infectious disease treatment as it requires not only the study or management of single organism behavior, but also many dynamical interactions including but not limited to bacteria-bacteria, bacteria-host, bacteria-nutrients, and bacteria-material across multiple time scales. This study performs comparative and quantitative research of two materials used in biofilm research, TSA agar and skin epidermal, to reveal how adhesion effects viscoelastic properties of biofilms at long time scales. We show that the host surface stressors, such as wettability and surface energy, impact the biofilm's mechanical integrity and viscoelastic properties. While it is known that the bacteria-material interface influences initial biofilm formation and external stress influences mature biofilm function, this study examines the influence of the bacteria-material interface on mature biofilms. These mechanical viscoelastic properties have the potential to determine metabolite and pathogenesis pathways which means that the platform researchers use to study impacts the outcome.

Fluid Flow Induces Differential Detachment of Live and Dead Bacterial Cells from Nanostructured Surfaces

Nanotopographic surfaces are proven to be successful in killing bacterial cells upon contact. This non-chemical bactericidal property has paved an alternative way of fighting bacterial colonization and associated problems, especially the issue of bacteria evolving resistance against antibiotic and antiseptic agents. Recent advancements in nanotopographic bactericidal surfaces have made them suitable for many applications in medical and industrial sectors. The bactericidal effect of nanotopographic surfaces is classically studied under static conditions, but the actual potential applications do have fluid flow in them. In this study, we have studied how fluid flow can affect the adherence of bacterial cells on nanotopographic surfaces. Gram-positive and Gram-negative bacterial species were tested under varying fluid flow rates for their retention and viability after flow exposure. The total number of adherent cells for both species was reduced in the presence of flow, but there was no flowrate dependency. There was a significant reduction in the number of live cells remaining on nanotopographic surfaces with an increasing flowrate for both species. Conversely, we observed a flowrate-independent increase in the number of adherent dead cells. Our results indicated that the presence of flow differentially affected the adherent live and dead bacterial cells on nanotopographic surfaces. This could be because dead bacterial cells were physically pierced by the nano-features, whereas live cells adhered via physiochemical interactions with the surface. Therefore, fluid shear was insufficient to overcome adhesion forces between the surface and dead cells. Furthermore, hydrodynamic forces due to the flow can cause more planktonic and detached live cells to collide with nano-features on the surface, causing more cells to lyse. These results show that nanotopographic surfaces do not have self-cleaning ability as opposed to natural bactericidal nanotopographic surfaces, and nanotopographic surfaces tend to perform better under flow conditions. These findings are highly useful for developing and optimizing nanotopographic surfaces for medical and industrial applications.

Effects of Ethyl Lauroyl Arginate (LAE) on Biofilm Detachment: Shear Rate, Concentration, and Dosing Time

Biofilm formation is one of the main obstacles in membrane treatment. The non-oxidizing biocide ethyl lauroyl arginate (LAE) is promising for mitigating biofilm development on membrane surfaces. However, the operating conditions of LAE and their impact on biofilm detachment are not comprehensively understood. In this study, a real-time in vitro flow cell system was utilized to observe biofilm dispersal caused by the shear rate, concentration, and treatment time of LAE. This confirmed that the biofilm was significantly reduced to 68.2% at a shear rate of 3.42 s−1 due to the increased physical lifting force. LAE exhibited two different mechanisms for bacterial inactivation and biofilm dispersal. Biofilms treated with LAE at sub-growth inhibitory concentrations for a longer time could effectively detach the biofilm formed on the surface of the glass slides, which can be attributed to the increased motility of microorganisms. However, a high concentration (i.e., bactericidal concentration) of LAE should be seriously considered because of the inactivated sessile bacteria and their residual debris remaining on the surface. This study sheds light on the effect of LAE on biofilm detachment and provides insights into biofouling mitigation during the membrane process.

Cold plasma surface treatments to prevent biofilm formation in food industries and medical sectors

Environmental conditions in food and medical fields enable the bacteria to attach and grow on surfaces leading to resistant bacterial biofilm formation. Indeed, the first step in biofilm formation is the bacterial irreversible adhesion. Controlling and inhibiting this adhesion is a passive approach to fight against biofilm development. This strategy is an interesting path in the inhibition of biofilm formation since it targets the first step of biofilm development. Those pathogenic structures are responsible for several foodborne diseases and nosocomial infections. Therefore, to face this public health threat, researchers employed cold plasma technologies in coating development. In this review, the different factors influencing the bacterial adhesion to a substrate are outlined. The goal is to present the passive coating strategies aiming to prevent biofilm formation via cold plasma treatments, highlighting antiadhesive elaborated surfaces. General aspects of surface treatment, including physico-chemical modification and application of cold plasma technologies, were also presented. KEY POINTS: • Factors surrounding pathogenic bacteria influence biofilm development. • Controlling bacterial adhesion prevents biofilm formation. • Materials can be coated via cold plasma to inhibit bacterial adhesion.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

A Nanoengineered Stainless Steel Surface to Combat Bacterial Attachment and Biofilm Formation

Nanopatterning and anti-biofilm characterization of self-cleanable surfaces on stainless steel substrates were demonstrated in the current study. Electrochemical etching in diluted aqua regia solution consisting of 3.6% hydrogen chloride and 1.2% nitric acid was conducted at 10 V for 5, 10, and 15 min to fabricate nanoporous structures on the stainless steel. Variations in the etching rates and surface morphologic characteristics were caused by differences in treatment durations; the specimens treated at 10 V for 10 min showed that the nanoscale pores are needed to enhance the self-cleanability. Under static and realistic flow environments, the populations of Escherichia coli O157:H7 and Salmonella Typhimurium on the developed features were significantly reduced by 2.1–3.0 log colony-forming unit (CFU)/cm² as compared to bare stainless steel (p < 0.05). The successful fabrication of electrochemically etched stainless steel surfaces with Teflon coating could be useful in the food industry and biomedical fields to hinder biofilm formation in order to improve food safety.

Enhancing Staphylococcus aureus sterilization of stainless steel by the synergistic effect of surface structure and physical washing

Staphylococcus aureus infection is common in the clinical environment. It has been shown that the presence of micro/nano structures on material surfaces promote bacterial adhesion resistance. Herein, we assessed the S. aureus adhesion properties on laser micro/nano structured stainless-steel (316 L) surfaces after mechanical rotation and ultrasonic washing. The interaction force between S. aureus and structured surfaces was evaluated. A high concentration S. aureus solution was used to evaluate the bacterial sterilization efficiency after film formation on the stainless-steel surface. After 24 h of incubation, S. aureus films were formed on material surfaces. The comparison of static washing, surface mechanical rotation, and ultrasonic washing showed a decrease of S. aureus adhesion on the polished and laser induced periodic surface structures. However, S. aureus adhesion on the micro/nanoparticle surface after mechanical rotation washing did not display any obvious change compared to the polished one. Additionally, specimens after ultrasonic cleaning showed clear antibacterial adhesion than mechanical rotation. After the ultrasonic sterilization process, the laser induced periodic laser surface sample showed optimal bacterial adhesion inhibition. Finally, in vitro tests showed that the biocompatibility of the laser-induced structured surface did not change significantly from the polished surface one.

Bacterial nanotubes mediate bacterial growth on periodic nano-pillars

Surface topography designed to achieve spatial segregation has shown promise in delaying bacterial attachment and biofilm growth. However, the underlying mechanisms linking surface topography to the inhibition of microbial attachment and growth still remain unclear. Here, we investigated bacterial attachment, cell alignment and biofilm formation of Pseudomonas aeruginosa on periodic nano-pillar surfaces with different pillar spacing. Using fluorescence and scanning electron microscopy, bacteria were shown to align between the nanopillars. Threadlike structures ("bacterial nanotubes") protruded from the majority of bacterial cells and appeared to link cells directly with the nanopillars. Using ΔfliM and ΔpilA mutants lacking flagella or pili, respectively, we further demonstrated that cell alignment behavior within nano-pillars is independent of the flagella or pili. The presence of bacteria nanotubes was found in all cases, and is not linked to the expression of flagella or pili. We propose that bacterial nanotubes are produced to aid in cell-surface or cell-cell connections. Nano-pillars with smaller spacing appeared to enhance the extension and elongation of bacterial nanotube networks. Therefore, nano-pillars with narrow spacing can be easily overcome by nanotubes that connect isolated bacterial aggregates. Such nanotube networks may aid cell-cell communication, thereby promoting biofilm development.

Analysing the Initial Bacterial Adhesion to Evaluate the Performance of Antifouling Surfaces

The aim of this work was to study the initial events of Escherichia coli adhesion to polydimethylsiloxane, which is critical for the development of antifouling surfaces. A parallel plate flow cell was used to perform the initial adhesion experiments under controlled hydrodynamic conditions (shear rates ranging between 8 and 100/s), mimicking biomedical scenarios. Initial adhesion studies capture more accurately the cell-surface interactions as in later stages, incoming cells may interact with the surface but also with already adhered cells. Adhesion rates were calculated and results shown that after some time (between 5 and 9 min), these rates decreased (by 55% on average), from the initial values for all tested conditions. The common explanation for this decrease is the occurrence of hydrodynamic blocking, where the area behind each adhered cell is screened from incoming cells. This was investigated using a pair correlation map from which two-dimensional histograms showing the density probability function were constructed. The results highlighted a lower density probability (below 4.0 × 10⁻⁴) of the presence of cells around a given cell under different shear rates irrespectively of the radial direction. A shadowing area behind the already adhered cells was not observed, indicating that hydrodynamic blocking was not occurring and therefore it could not be the cause for the decreases in cell adhesion rates. Afterward, cell transport rates from the bulk solution to the surface were estimated using the Smoluchowski-Levich approximation and values in the range of 80–170 cells/cm².s were obtained. The drag forces that adhered cells have to withstand were also estimated and values in the range of 3–50 × 10⁻¹⁴ N were determined. Although mass transport increases with the flow rate, drag forces also increase and the relative importance of these factors may change in different conditions. This work demonstrates that adjustment of operational parameters in initial adhesion experiments may be required to avoid hydrodynamic blocking, in order to obtain reliable data about cell-surface interactions that can be used in the development of more efficient antifouling surfaces.

Analyzing the effect of pH on microalgae adhesion by identifying the dominant interaction between cell and surface

Microalgae adhesion plays a critical role in developing effective photobioreactors for large-scale production of microalgae biofuel. This study focused on elucidating the influencing mechanism of liquid medium pH on microalgae adhesion by identifying the dominant interactions between cell and substratum using a criterion. Herein, the adhesion of three microalgae onto two substrata at a series of pH was observed using a flow chamber. The results indicated that the adhesion of freshwater Chlorella sp. onto PVC and glass and marine Chlorella sp. and N. oculata onto glass decreased with increasing pH, because these adhesions were dominated by the EL interaction, and the pH would influence the adhesion primarily by affecting the ζ potential of the cell and substratum. Whereas, the adhesion of marine Chlorella sp. and N. oculata onto PVC increased with increasing pH, because these adhesions were dominated by Lewis acid-base (AB) interaction, and the pH would influence the adhesion primarily by affecting the components of surface free energy of cell. The study demonstrated that the influencing mechanism of pH on adhesion can be conclusively elucidated by identifying the dominant interaction between the cell and the surface, and may have significant implications for predicting cell adhesion in various applications.

Quantitative Criterion to Predict Cell Adhesion by Identifying Dominant Interaction between Microorganisms and Abiotic Surfaces

Cell adhesion is ubiquitous and plays an important role in various scientific and engineering problems. Herein, a quantitative criterion to predict cell adhesion was proposed by identifying the dominant interaction between microorganisms and abiotic surfaces. According to the criterion, the dominant interaction in cell adhesion could be identified as a Lewis acid-base (AB) interaction or electrostatic (EL) interaction via comparison of two expressions containing the electron-donor characteristics of the microorganism (γ_mv^-) and abiotic surface (γ_sv^-) and their ζ potentials (ζ_m, ζ_s). The results revealed that when dominated by the AB interaction, adhesion would decrease with increasing [Formula: see text]. However, when the EL interaction was dominant, adhesion would decrease with increasing (ζ_m + ζ_s)². We have verified the criterion based on the adhesion of microalgae, bacteria, and fungi onto various surfaces obtained via our experiments and available in literature studies. The results demonstrated that the criterion had important implications in the prediction of cell adhesion in various applications.

Measurement and prediction of mass transfer coefficients for syngas constituents in a hollow fiber reactor

Syngas fermentation for producing biofuels and other products suffers from mass transfer limitations due to low CO and H₂ solubility in liquid medium. Therefore, it is critical to characterize mass transfer rates of these gases to guide bioreactor design and optimization. This work presents a novel technique to measure the volumetric mass transfer coefficients (k_ia) for H₂ and CO using gas chromatography in a non-porous hollow fiber reactor (HFR). The largest measured k_ia for H₂ and CO were 840 and 420 h^-1, respectively. A model was developed to predict k_ia for H₂ and CO that agreed well with experimental data. This study is the first to measure, compare, and model both H₂ and CO mass transfer coefficients in an HFR. Based on model predictions, HFRs have the potential to be a reactor of choice for syngas fermentation as a result of high mass transfer that can support high cell densities.

Control of Salmonella Enteritidis on food contact surfaces with bacteriophage PVP-SE2

Salmonella is one of the worldwide leading foodborne pathogens responsible for illnesses and hospitalizations, and its capacity to form biofilms is one of its many virulence factors. This work evaluated (bacterio)phage control of adhered and biofilm cells of Salmonella Enteritidis on three different substrata at refrigerated and room temperatures, and also a preventive approach in poultry skin. PVP-SE2 phage was efficient in reducing both 24- and 48-h old Salmonella biofilms from polystyrene and stainless steel causing 2 to 5 log CFU cm^-2 reductions with a higher killing efficiency at room temperature. PVP-SE2 phage application on poultry skins reduced levels of Salmonella. Freezing phage-pretreated poultry skin samples had no influence on the viability of phage PVP-SE2 and their in vitro contamination with S. Enteritidis provided evidence that phages prevented their further growth. Although not all conditions favor phage treatment, this study endorses their use to prevent and control foodborne pathogen colonization of surfaces.

Serine-Rich Repeat Adhesins Mediate Shear-Enhanced Streptococcal Binding to Platelets

The binding of bacteria to platelets is thought to be a central event in the pathogenesis of infective endocarditis. The serine-rich repeat (SRR) glycoproteins of viridans group streptococci have been shown to mediate platelet binding in vitro and to contribute to virulence in animal models. However, it is not known whether SRR adhesins can mediate streptococcal binding under the high fluidic shear stress conditions present on the endocardial surface. We found that three streptococcal SRR adhesins (GspB, Hsa, and SrpA) with differing structures and sialoglycan binding specificities nevertheless exhibited similar biomechanical properties. All three adhesins mediated shear-enhanced streptococcal binding to immobilized platelets through the platelet receptor GPIbα. Shear-enhanced adhesion was manifested in three ways. First, the number of circulating streptococci binding via SRR adhesins to immobilized platelet receptors peaked at 1 dyn/cm² Second, bound streptococci switched from weak rolling to strong stationary adhesion as shear stress increased to 10 dyn/cm² Third, while a few streptococci detached each time the flow was increased, the majority of streptococci bound to platelets remained firmly attached through 20 to 80 dyn/cm² (shear levels typical of arteries and the endocardium). Thus, all three adhesins mediated shear-enhanced streptococcal binding to platelets under the flow conditions found in heart valves. The ability of the SRR adhesins to mediate shear-enhanced binding strongly suggests that they form catch bonds that are activated by tensile force and provides a mechanism for the selective targeting of bacteria to platelet receptors immobilized on the endocardial surface.

Influence of Type I Fimbriae and Fluid Shear Stress on Bacterial Behavior and Multicellular Architecture of Early Escherichia coli Biofilms at Single-Cell Resolution

Biofilm formation on abiotic surfaces in the food and medical industry can cause severe contamination and infection, yet how biological and physical factors determine the cellular architecture of early biofilms and the bacterial behavior of the constituent cells remains largely unknown. In this study, we examined the specific role of type I fimbriae in nascent stages of biofilm formation and the response of microcolonies to environmental flow shear at the single-cell resolution. The results show that type I fimbriae are not required for reversible adhesion from plankton, but they are critical for the irreversible adhesion of Escherichia coli strain MG1655 cells that form biofilms on polyethylene terephthalate (PET) surfaces. Besides establishing firm cell surface contact, the irreversible adhesion seems necessary to initiate the proliferation of E. coli on the surface. After the application of shear stress, bacterial retention is dominated by the three-dimensional architecture of colonies, independent of the population size, and the multilayered structure could protect the embedded cells from being insulted by fluid shear, while the cell membrane permeability mainly depends on the biofilm population size and the duration of the shear stress.IMPORTANCE Bacterial biofilms could lead to severe contamination problems in medical devices and food processing equipment. However, biofilms are usually studied at a rough macroscopic level; thus, little is known about how individual bacterium behavior within biofilms and the multicellular architecture are influenced by bacterial appendages (e.g., pili/fimbriae) and environmental factors during early biofilm formation. We applied confocal laser scanning microscopy (CLSM) to visualize Escherichia coli microcolonies at a single-cell resolution. Our findings suggest that type I fimbriae are vital to the initiation of bacterial proliferation on surfaces. We also found that the fluid shear stress affects the biofilm architecture and cell membrane permeability of the constituent bacteria in a different way: the onset of the biofilm is linked with the three-dimensional morphology, while membranes are regulated by the overall population of microcolonies.

Combination of aquifer thermal energy storage and enhanced bioremediation: Biological and chemical clogging

Interest in the combination concept of aquifer thermal energy storage (ATES) and enhanced bioremediation has recently risen due to the demand for both renewable energy technology and sustainable groundwater management in urban areas. However, the impact of enhanced bioremediation on ATES is not yet clear. Of main concern is the potential for biological clogging which might be enhanced and hamper the proper functioning of ATES. On the other hand, more reduced conditions in the subsurface by enhanced bioremediation might lower the chance of chemical clogging, which is normally caused by Fe(III) precipitate. To investigate the possible effects of enhanced bioremediation on clogging with ATES, we conducted two recirculating column experiments with differing flow rates (10 and 50mL/min), where enhanced biological activity and chemically promoted Fe(III) precipitation were studied by addition of lactate and nitrate respectively. The pressure drop between the influent and effluent side of the column was used as a measure of the (change in) hydraulic conductivity, as indication of clogging in these model ATES systems. The results showed no increase in upstream pressure during the period of enhanced biological activity (after lactate addition) under both flow rates, while the addition of nitrate lead to significant buildup of the pressure drop. However, at the flow rate of 10mL/min, high pressure buildup caused by nitrate addition could be alleviated by lactate addition. This indicates that the risk of biological clogging is relatively small in the investigated areas of the mimicked ATES system that combines enhanced bioremediation with lactate as substrate, and furthermore that lactate may counter chemical clogging.

Measuring a critical stress for continuous prevention of marine biofouling accumulation with aeration

When cleaning the hull of a ship, significant shear stresses are needed to remove established biofouling organisms. Given that there exists a link between the amount of time that fouling accumulates and the stress required to remove it, it is not surprising that more frequent grooming requires less shear stress. Yet, it is unclear if there is a minimum stress needed to prevent the growth of macrofouling in the limit of continuous grooming. This manuscript shows that single bubble stream aeration provides continuous grooming and prevents biofouling accumulation in regions where the average wall stress exceeds ~0.01 Pa. This value was found by comparing observations of biofouling growth from field studies with complementary laboratory measurements that probe the associated flow fields. These results suggest that aeration and other continuous grooming systems must exceed a wall stress of 0.01 Pa to prevent macrofouling accumulation.

Nanoengineered Superhydrophobic Surfaces of Aluminum with Extremely Low Bacterial Adhesivity

Bacterial adhesion and biofilm formation on surfaces are troublesome in many industrial processes. Here, nanoporous and nanopillared aluminum surfaces were engineered by anodizing and postetching processes and made hydrophilic (using the inherent oxide layer) or hydrophobic (applying a Teflon coating) with the aim of discouraging bacterial adhesion. Adhesion of Staphylococcus aureus ATCC 12600 (Gram-positive, spherically shaped) and Escherichia coli K-12 (Gram-negative, rod-shaped) was evaluated to the nanoengineered surfaces under both static and flow conditions (fluid shear rate of 37 s^-1). Compared to a nonstructured electropolished flat surface, the nanostructured surfaces significantly reduced the number of adhering colony forming units (CFUs) for both species, as measured using agar plating. For the hydrophilic surfaces, this was attributed to a decreased contact area, reducing bacterial adhesion forces on nanoporous and nanopillared surfaces to 4 and 2 nN, respectively, from 8 nN on flat surfaces. Reductions in the numbers of adhering CFUs were more marked on hydrophobic surfaces under flow, amounting to more than 99.9% and 99.4% for S. aureus and E. coli on nanopillared surfaces, respectively. Scanning electron microscopy revealed a few bacteria found on the hydrophobic nanopillared surfaces adhered predominantly to defective or damaged areas, whereas the intact area preserving the original nanopillared morphology was virtually devoid of adhering bacteria. The greater decrease in bacterial adhesion to hydrophobic nanopillared surfaces than to hydrophilic or nanoporous ones is attributed to effective air entrapment in the three-dimensional pillar morphology, rendering them superhydrophobic and slippery, in addition to providing a minimized contact area for bacteria to adhere to.

Adhesion force of staphylococcus aureus on various biomaterial surfaces

Staphylococcus comprises of more than half of all pathogens in orthopedic implant infections and they can cause major bone infection which can result in destruction of joint and bone. In the current study, adhesion force of bacteria on the surface of various biomaterial surfaces is measured using atomic force microscope (AFM). Staphylococcus aureus was immobilized on an AFM tipless cantilever as a force probe to measure the adhesion force between bacteria and biomaterials (viz. ultra-high molecular weight poly ethylene (UHMWPE), stainless steel (SS), Ti-6Al-4V alloy, hydroxyapatite (HA)). At the contact time of 10s, UHMWPE shows weak adhesion force (~4nN) whereas SS showed strong adhesion force (~15nN) due to their surface energy and surface roughness. Bacterial retention and viability experiment (3M™ petrifilm test, agar plate) dictates that hydroxyapatite shows the lowest vaibility of bacteria, whereas lowest bacterial retention is observed on UHMWPE surface. Similar results were obtained from live/dead staining test, where HA shows 65% viability, whereas on UHMWPE, SS and Ti-6Al-4V, the bacterial viability is 78%, 94% and 97%, respectively. Lower adhesion forces, constrained pull-off distance (of bacterial) and high antibacterial resistance of bioactive-HA makes it a potential biomaterial for bone-replacement arthroplasty.

Oligomerized backbone pilin helps piliated Lactococcus lactis to withstand shear flow

The present work focuses on the role of pili present at the cell surface of Lactococcus lactis in bacterial adhesion to abiotic (hydrophobic polystyrene) and biotic (mucin-coated polystyrene) surfaces. Native pili-displaying strains and isogenic derivatives in which pilins or sortase C structural genes had been modified were used. Surface physico-chemistry, morphology and shear-flow-induced detachment of lactococcal cells were evaluated. The involvement of pili in L. lactis adhesion was clearly demonstrated, irrespective of the surface characteristics (hydrophobic/hydrophilic, presence or not of specific binding sites). The accessory pilin, PilC, and the backbone pilin, PilB, were revealed to play a major role in adhesion, provided that the PilB was present in its polymerized form. Within the population fraction that remained attached to the surface under increasing shear flow, different association behaviors were observed, showing that pili could serve as anchoring sites thus hampering the effect of shear flow on cell orientation and detachment.

Photocatalytic antibacterial effects on TiO2-anatase upon UV-A and UV-A/VIS threshold irradiation

Photocatalysis mediated by the anatase modification of titanium dioxide (TiO2) has shown antibacterial effects in medical applications. The aim of this study was to investigate the possibility of expanding the excitation wavelengths for photocatalytic antibacterial effects from ultraviolet (UV) into the visible light range. After deposition of salivary pellicle and adhesion of Streptococcus gordonii on anatase, different irradiation protocols were applied to induce photocatalysis: ultraviolet A (UV-A) > 320 nm; ultraviolet/visible (UV-A/VIS) light > 380 nm and > 390 nm; and VIS light 400-410 nm. A quartz crystal microbalance with dissipation (QCM-D) tests and microscopic examination were used to observe the photoinduced antibacterial effects. Salivary pellicle could be photocatalytically decomposed under all irradiation protocols. In contrast, effective photocatalytic attack of bacteria could be observed by UV-A as well as by UV-A/VIS at 380 nm < λ < 390 nm only. Wavelengths above 380 nm show promise for in situ therapeutic antifouling applications.

Effects of polishing methods on Candida albicans adhesion on cast pure titanium surfaces

OBJECTIVE

To explore the effects of different polishing methods on Candida albicans adhesion to cast pure titanium surfaces.

METHODS

Pure titanium test specimens randomly divided into 4 groups: not specially treated (CT), manual polishing (MPT), electrolytic polishing (EPT), and centrifugal barrel polishing (CPT). Surface roughness was measured with surface profilometer. Contact angles of water, diiodomethane, and ethylene glycol on specimen surface were measured, and the free energy was calculated. Each group were immersed in a C. albicans suspension for 48 hours, and cell count of C. albicans adhesion were taken. Morphology of C. albicans adhesion was observed by SEM.

RESULTS

Surface roughness (Ra) were in the following order: CT > EPT > MPT > CPT. The amount of C. albicans adhesion to the surface of CPT was significantly less than CT, MPT, and EPT by cells count (P < 0.05). In SEM, less C. albicans aggregation formed on the surface of CPT than other 3 groups.

CONCLUSIONS

Specimens treated by the CPT method showed superior effect to the specimens treated with MPT and EPT methods in reducing the adhesion of C. albicans.

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.

Antibacterial Efficacy of Iron-Oxide Nanoparticles against Biofilms on Different Biomaterial Surfaces

Biofilm growth on the implant surface is the number one cause of the failure of the implants. Biofilms on implant surfaces are hard to eliminate by antibiotics due to the protection offered by the exopolymeric substances that embed the organisms in a matrix, impenetrable for most antibiotics and immune cells. Application of metals in nanoscale is considered to resolve biofilm formation. Here we studied the effect of iron-oxide nanoparticles over biofilm formation on different biomaterial surfaces and pluronic coated surfaces. Bacterial adhesion for 30 min showed significant reduction in bacterial adhesion on pluronic coated surfaces compared to other surfaces. Subsequently, bacteria were allowed to grow for 24 h in the presence of different concentrations of iron-oxide nanoparticles. A significant reduction in biofilm growth was observed in the presence of the highest concentration of iron-oxide nanoparticles on pluronic coated surfaces compared to other surfaces. Therefore, combination of polymer brush coating and iron-oxide nanoparticles could show a significant reduction in biofilm formation.

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.

Unraveling the role of surface mucus-binding protein and pili in muco-adhesion of Lactococcus lactis

Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (100−200 nm) and long distances (up to 600−800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants.

A comparison of mass transfer coefficients between trickle-bed, hollow fiber membrane and stirred tank reactors

Trickle-bed reactor (TBR), hollow fiber membrane reactor (HFR) and stirred tank reactor (STR) can be used in fermentation of sparingly soluble gasses such as CO and H2 to produce biofuels and bio-based chemicals. Gas fermenting reactors must provide high mass transfer capabilities that match the kinetic requirements of the microorganisms used. The present study compared the volumetric mass transfer coefficient (K(tot)A/V(L)) of three reactor types; the TBR with 3 mm and 6 mm beads, five different modules of HFRs, and the STR. The analysis was performed using O2 as the gaseous mass transfer agent. The non-porous polydimethylsiloxane (PDMS) HFR provided the highest K(tot)A/V(L) (1062 h(-1)), followed by the TBR with 6mm beads (421 h(-1)), and then the STR (114 h(-1)). The mass transfer characteristics in each reactor were affected by agitation speed, and gas and liquid flow rates. Furthermore, issues regarding the comparison of mass transfer coefficients are discussed.

Comparison of anti-fouling surface coatings for applications in bacteremia diagnostics

To accurately diagnose microbial infections in blood, it is essential to recover as many microorganisms from a sample as possible. Unfortunately, recovering such microorganisms depends significantly on their adhesion to the surfaces of diagnostic devices. Consequently, we sought to minimize the adhesion of methicillin-sensitive Staphylococcus aureus (MSSA) to the surface of polypropylene- and acrylic-based bacteria concentration devices. These devices were treated with 11 different coatings having various charges and hydrophobicities. Some coatings promoted bacterial adhesion under centrifugation, whereas others were more likely to prevent it. Experiments were run using a simple buffer system and lysed blood, both inoculated with MSSA. Under both conditions, Hydromer's 7-TS-13 and Aqua65JL were most effective at reducing bacterial adhesion.

Shear stress-dependent cell detachment from temperature-responsive cell culture surfaces in a microfluidic device

A new approach to quantitatively estimate the interaction between cells and material has been proposed by using a microfluidic system, which was made of poly(dimethylsiloxane) (PDMS) chip bonding on a temperature-responsive cell culture surface consisted of poly(N-isopropylacrylamide) (PIPAAm) grafted tissue culture polystyrene (TCPS) (PIPAAm-TCPS) having five parallel test channels for cell culture. This construction allows concurrently generating five different shear forces to apply to cells in individual microchannels having various resistance of each channel and simultaneously gives an identical cell incubation condition to all test channels. NIH/3T3 mouse fibroblast cells (MFCs) and bovine aortic endothelial cells (BAECs) were well adhered and spread on all channels of PIPAAm-TCPS at 37 °C. In our previous study, reducing culture temperature below the lower critical solution temperature (LCST) of PIPAAm (32 °C), cells detach themselves from hydrated PIPAAm grafted surfaces spontaneously. In this study, cell detachment process from hydrated PIPAAm-TCPS was promoted by shear forces applied to cells in microchannels. Shear stress-dependent cell detachment process from PIPAAm-TCPS was evaluated at various shear stresses. Either MFCs or BAECs in the microchannel with the strongest shear stress were found to be detached from the substrate more quickly than those in other microchannels. A cell transformation rate constant C(t) and an intrinsic cell detachment rate constant k(0) were obtained through studying the effect of shear stress on cell detachment with a peeling model. The proposed device and quantitative analysis could be used to assess the possible interaction between cells and PIPAAm layer with a potential application to design a cell sheet culture surface for tissue engineering.

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.

Microfluidics-based assay on the effects of microenvironmental geometry and aqueous flow on bacterial adhesion behaviors

A new microfluidic system with four different microchambers (a circle and three equilateral concave polygons) was designed and fabricated using poly(dimethylsiloxane) (PDMS) and the soft lithography method. Using this microfluidic device at six flow rates (5, 10, 20, 30, 40, and 50 μL/h), the effects of microenvironmental geometry and aqueous flow on bacterial adhesion behaviors were investigated. Escherichia coli HB101 pGLO, which could produce a green fluorescent protein induced by l-arabinose, was utilized as the model bacteria. The results demonstrated that bacterial adhesion was significantly related to culture time, microenvironment geometry, and aqueous flow rates. Adhered bacterial density increased with the culture time. Initially, the adhesion occurred at the microchamber sides, and then the entire chamber was gradually covered with increased culture time. Adhesion densities in the side zones were larger than those in the center zones because of the lower shearing force in the side zone. Also, the adhesion densities in the complex chambers were larger than those in the simple chambers. At low flow rates, the orientation of adhered bacteria was random and disorderly. At high flow rates, bacterial orientation became close to the streamline and oriented toward the flow direction. All these results implied that bacterial adhesion tended to occur in complicated aqueous flow areas. The present study provided an on-chip flow system for physiological behavior of biological cells, as well as provided a strategic cue for the prevention of bacterial infection and biofilm formation.