Substratum Surface Research Articles

The effect of Dunaliella salina extracts on the adhesion of Pseudomonas aeruginosa to 3D printed polyethylene terephthalate and polylactic acid

Polyethylene terephthalate (PET) and polylactic acid (PLA) are among the polymers used in the food industry. In this study, crude extracts of Dunaliella salina were used to treat the surface of 3D printed materials studied, aiming to provide them with an anti-adhesive property against Pseudomonas aeruginosa. The hydrophobicity of treated and untreated surfaces was characterized using the contact angle method. Furthermore, the adhesive behavior of P. aeruginosa toward the substrata surfaces was also studied theoretically and experimentally. The results showed that the untreated PLA was hydrophobic, while the untreated PET was hydrophilic. It was also found that the treated materials became hydrophilic and electron-donating. The total energy of adhesion revealed that P. aeruginosa adhesion was theoretically favorable on untreated materials, while it was unfavorable on treated ones. Moreover, the experimental data proved that the adhesion to untreated substrata was obtained, while there was complete inhibition of adhesion to treated surfaces.

Can the Culture Density of the Marine Copepod Pseudodiaptomus nihonkaiensis be Improved by Installing an Artificial Substrate?

The understanding of the increasing population density of copepods in culture tanks contributes to establish their stable cultures at high productions for aquaculture industry, which are preferred live feeds for fish larvae. In the present study, the semi-benthic copepod Pseudodiaptomus nihonkaiensis were used as target species. This genus is often found from brackish water and its tolerance to a wide range of salinity and water quality has attracted attention as a potential commercial live feed for aquaculture. Population growth and egg production in the semi-benthic copepod P. nihonkaiensis are investigated. Copepods were cultured in tanks without mesh, with mesh lining tank walls, and with 2, 4 or 8 mesh partitions in each tank to identify the effect of substratum surface area on copepod population density. Linear regression revealed peaks in nauplius, copepodite, adult and total densities, and the cumulative number of eggs for all sampling events to correlate positively with substratum surface area (p<0.01). Greater substratum area within a culture tank may improve egg production by increasing habitat for ovigerous females. The simple installation of inexpensive artificial substrata in existing copepod culture tanks might improve the feasibility of using copepods as a live food in commercial-scale aquaculture.

Difference in formation of a dental multi-species biofilm according to substratum direction

ObjectivesThe aim of this study was to investigate the difference in dental biofilm formation according to substratum direction, using an artificial biofilm model. MethodsA three-species biofilm, consisting of Streptococcus mutans, Streptococcus oralis, and Actinomyces naeslundii, was formed on saliva-coated hydroxyapatite (sHA) discs oriented in three directions: downward (the discs placed in the direction of gravity), vertical (the discs placed parallel to the direction of gravity), and upward (the discs placed in opposite direction of gravity). The biofilms at 22 h and 46 h of age were analyzed using microbiological and biochemical methods, fluorescence-based assays, and scanning electron microscopy to investigate difference in bacterial adhesion, early and mature biofilm formation. ResultsThe biofilms formed in the upward direction displayed the most complex structure, with the highest number and biovolume of bacteria, as well as the lowest pH conditions at both time points. The vertical and downward directions, however, had only scattered and small bacterial colonies. In the 22-h-old biofilms, the proportion of S. oralis was similar to, or slightly higher than, that of S. mutans in all directions of substratum surfaces. However, in the 46-h-old biofilms, S. mutans became the dominant bacteria in all directions, especially in the vertical and upward directions. ConclusionsThe direction of the substratum surface could impact the proportion of bacteria and cariogenic properties of the multi-species biofilm. Biofilms in an upward direction may exhibit a higher cariogenic potential, followed by those in the vertical and downward directions, which could be related to gravity.

Guided Biofilm Therapy: A Novel Approach in Professional Dental Biofilm Management

There are many different kinds of microorganisms that live in the oral cavity, from good ones to those that could be harmful. It is a well-established fact that periodontal diseases are linked to dental plaque. A biofilm is a community of microcolonies of microorganisms in an aqueous solution that is surrounded by a glycocalyx matrix. This matrix also binds the bacterial cells to a solid substratum (surface), which can be hard or soft tissues or inanimate surfaces such as clear aligners, prosthetics, or orthodontic bands of the oral cavity. Although scaling and root planing (SRP) is considered the gold standard for mechanical plaque debridement, it also has some drawbacks, such as inaccessibility to deeper areas on the root surfaces and patient discomfort, including root hypersensitivity. To overcome these disadvantages, minimally invasive nonsurgical approaches have been introduced. One such novel alternative is guided biofilm therapy (GBT), which uses a disclosing agent to visualize the biofilm before removing it with a specialized air-abrasive powder and removing supra- and subgingival calculus with specialized instruments. Biofilm can be effectively removed around an implant or tooth with GBT. As a component of either supportive periodontal therapy or nonsurgical periodontal therapy, GBT was found to have a lower perception of pain and better patient compliance than SRP. GBT, as a monotherapy, can be advised as a basic treatment plan for teeth and implants. The various aspects of GBT in the management of periodontal and peri-implant diseases will be highlighted in this review.

Strategies for controlling biofilm formation in food industry

Foodborne pathogen poses a threat to the food industries as many outbreaks have been found to be associated with biofilm formation. The formation of biofilm is a self-protection growth pattern of bacteria, which increases post-processing contamination and risk to public health. It is difficult to eliminate the biofilm in the food industries, since the biofilm cells have a barrier preventing or lessening the contact with environmental stresses, antimicrobial agents and the host immune system. Bacterial biofilm formation is a complex process, including initial attachment stage, irreversible attachment stage, biofilm development stage, biofilm maturation stage, and biofilm dispersion stage. The genetic mechanism, substratum and bacterial cell surface properties involve in the biofilm formation. The biofilm inhibition methods studied are physical treatment, chemical and biochemical treatment. The potential green and safe biochemical method attracts more attention, especially, the novel strategies using the safe biochemical agents (essential oils, enzymes, biosurfactants, others) constantly emerged. The review emphasized on effective strategies for inhibiting biofilm formation in different stages (initial irreversible attachment, formation, and maturation) by use of biochemical agents, aiming to provide new insight into biofilm control in food industry thus improving food quality and safety.

A new plate-hanging method for biofilm quantification and its application to evaluate the role of surface hydrophobicity

A novel procedure for the quantitative analysis of biofilm formation by bacteria and yeasts, the Plate-hanging method, was developed. In this system, various polymer disks were hung from the lid of a 6-well plate, immersed in a cell suspension, and moderately shaken (70 rpm). In order to verify the validity of the procedure, the effects of the solid surface hydrophobicity of the test disks and the cell surface hydrophobicities of microorganisms on biofilm formation were investigated. Biofilm formation of bacteria and yeasts on the solid surface strongly depended on hydrophobic interactions between the solid surface and the cell surface. A positive correlation between the hydrophobic properties of substratum and cell surfaces was observed. On the other hand, hydrophilic yeasts preferentially adsorbed onto relatively hydrophilic surfaces. Moreover, the plate-hanging method coupled with the periodic exchange of the liquid medium enabled the quantification of long-term biofilm growth.

Incubation parameters, offspring growth, and behavioral adaptations to heat stress of Black Skimmers (Rynchops niger) in a Neotropical inland colony (Aves, Charadriiformes, Laridae)

This study focuses on incubation parameters, egg morphometrics, and body mass development, hatching, and behavioral adaptations to heat stress within a colony of freshwater-breeding Black Skimmers (Rynchops niger) located in the private nature reserve of Serviço Social do Comércio (SESC) in the northern Pantanal, Mato Grosso, Brazil. Temperatures of nest, eggs, and surface substratum, as well as the development of embryos, were surveyed using thermal imaging, a method allowing digital recording from a distance and in a fraction of the time of traditional measuring techniques. The mean egg dimensions (n = 71) were 4.48 (± 0.13) × 3.27 (± 0.07) cm; the mean mass at hatching was 24.3 (± 1.9) g, with a significant decrease over incubation time. The mean surface temperature of eggs varied from 30.9℃ to 39.7℃, while the sand surface temperature was 20℃ at 06:00 h, rising to 47.7℃ at 11:00 h. There was a significant increase (7%) in egg surface temperature throughout incubation. Incubation-bout durations (n = 2108) were correlated with the microclimatic conditions of the substratum, becoming shorter with increasing sand-surface temperature around midday. Egg hatching lasted one day, and siblings hatched no more than 24 h apart. The mean body mass on Day 1 after hatching was 16.8 (± 1.6) g (n = 6). Three days after hatching, chicks moved to new sand depressions provided by parents near the original nest, where they remained motionless or tried to hide under riparian vegetation. The single chick that fledged had a growth rate of K = 0.117 and a t₁₀₋₉₀ value of 37.3 days. On Day 7, dorsal pintail feathers and primaries appeared, which were open on Day 15. After 14 days, the chick was able to regulate its body temperature, and no more feeding by parental birds during the daytime was observed. On Day 21, the immature plumage was fully developed. Fledging was completed on Day 27. Our study demonstrates that thermal imaging is a useful method of surveying egg and embryo development in the Black Skimmer, reducing nest disturbance and observation efforts.

Assuaging Microalgal Harvesting Woes via Attached Growth: A Critical Review to Produce Sustainable Microalgal Feedstock

Third-generation biofuels that are derived from microalgal biomass have gained momentum as a way forward in the sustainable production of biodiesel. Such efforts are propelled by the intention to reduce our dependence on fossil fuels as the primary source of energy. Accordingly, growing microalgal biomass in the form of suspended cultivation has been a conventional technique for the past few decades. To overcome the inevitable harvesting shortcomings arising from the excessive energy and time needed to separate the planktonic microalgal cells from water medium, researchers have started to explore attached microalgal cultivation systems. This cultivation mode permits the ease of harvesting mature microalgal biomass, circumventing the need to employ complex harvesting techniques to single out the cells, and is economically attractive. However, the main bottleneck associated with attached microalgal growth is low biomass production due to the difficulties the microalgal cells have in forming attachment and populating thereafter. In this regard, the current review encompasses the novel techniques adopted to promote attached microalgal growth. The physicochemical effects such as the pH of the culture medium, hydrophobicity, as well as the substratum surface properties and abiotic factors that can determine the fate of exponential growth of attached microalgal cells, are critically reviewed. This review aims to unveil the benefits of an attached microalgal cultivation system as a promising harvesting technique to produce sustainable biodiesel for lasting applications.

Diverse surface properties reveal that substratum roughness affects fungal spore binding

SummaryBinding to surfaces by fungal spores is a prerequisite to biofilm formation. The interactions of polytetrafluoroethylene (PTFE), glass, and silicon with three fungal spores, of differing shapes and sizes (Aspergillus niger 1957, Aspergillus niger 1988, and Aureobasidium pullulans), were investigated. A multifractal analysis was conducted to provide quantitative measures of density, dispersion, and clustering of spores on the surfaces. The PTFE, glass, and silicon surfaces presented a range of surface topographies and wettabilities. PTFE was the roughest and most non-wettable surface, whereas silicon was the opposite in terms of both these aspects. The A. niger species were more non-wettable than A. pullulans. Overall, A. niger 1957 attached in higher numbers to PTFE, whereas A. niger 1988 and A. pullulans bound in highest numbers to glass. The results of this work demonstrated that the overall substratum surface roughness influenced spore binding rather than the physicochemical or chemical properties of surfaces or spores.

A statistical approach for modelling the physical process of bacterial attachment to abiotic surfaces

A statistical approach using a polynomial linear model in combination with a probability distribution model was developed to mathematically represent the process of bacterial attachment and study its mechanism. The linear deterministic model was built based on data from experiments investigating bacterial and substratum surface physico-chemical factors as predictors of attachment. The prediction results were applied to a normal-approximated binomial distribution model to probabilistically predict attachment. The experimental protocol used mixtures of Streptococcus salivarius and Escherichia coli, and mixtures of porous poly(butyl methacrylate-co-ethyl dimethacrylate) and aluminum sec-butoxide coatings, at varying ratios, to allow bacterial attachment to substratum surfaces across a range of physico-chemical properties (including the surface hydrophobicity of bacterial cells and the substratum, the surface charge of the cells and the substratum, the substratum surface roughness and cell size). The model was tested using data from independent experiments. The model indicated that hydrophobic interaction was the most important predictor while reciprocal interactions existed between some of the factors. More importantly, the model established a range for each factor within which the resultant attachment is unpredictable. This model, however, considers bacterial cells as colloidal particles and accounts only for the essential physico-chemical attributes of the bacterial cells and substratum surfaces. It is therefore limited by a lack of consideration of biological and environmental factors. This makes the model applicable only to specific environments and potentially provides a direction to future modelling for different environments.

Microbial biofilms on a giant monolithic statue of Buddha: The symbiosis of microorganisms and mosses and implications for bioweathering

Monolithic statues of Buddha are important cultural heritage objects. The inevitable coverage by moss with associated microorganisms is believed to drive weathering, but the functions of moss in bioweathering are still unclear. In this study, mosses and their associated microorganisms of the Leshan Giant Buddha in China from three distinct periods (e.g., growing, senescent, and residual) were examined using High-throughput sequencing and quantitative PCR techniques. The results showed that the period of active moss growth rather than species had a regulatory role on the microenvironment, which further affected the microbial communities and metabolism. The higher frequency of nucleotide sequences related to enzymes of nutrient cycling and weathering in the growing period indicated active interaction between microorganisms and substrate. Moss growth increased energy allocation to substratum surface through photosynthesis. Higher abundance of the ammonia monooxygenase gene (amoA) of the ammonia-oxidizing archaea was detected and responsible for nitrogen transformation. In particular, moss growth promoted iron-associated processes and likely electron transport processes. Iron-reducing bacteria were the main players responsible for transforming iron oxides on the statue. It is concluded that moss growth plays an important role in driving microbial weathering. This study highlights the urgency of moss symbiosis control for protecting monolithic statues in the field.

Development of a multispecies periodontal biofilm model within a stirred bioreactor

The objective of this work was to develop a subgingival biofilm model using a stirred bioreactor. Discs of bovine teeth were adapted to a stirred bioreactor filled with a culture medium containing bacterial species associated with periodontal health or disease. After anaerobic incubation, the biofilms growing on the substratum surfaces were collected and analyzed. The mean number of Colony-forming Units (CFUs) varied, but with no difference between 3 and 7 days of biofilm formation (p > 0.05). Scanning Electron Microscopy (SEM) analysis showed a uniform biofilm layer covering the cement layer of the root surface containing bacteria with diverse morphology. In checkerboard DNA-DNA hybridization, bacterial species were identified in both biofilms. In conclusion, a subgingival biofilm model was developed using a stirred bioreactor, allowing the in vitro reproduction of complex microbial communities. This is an advanced model that may be useful to mimic complex clinical periodontal biofilms.

In-situ monitoring of the unstable bacterial adhesion process during wastewater biofilm formation: A comprehensive study

The initial bacterial adhesion phase is a pivotal and unstable step in the formation of biofilms. The initiation of biofilm formation is an unstable process caused by the reversible adhesion of bacteria, which is always time-consuming and yet to be elucidated. In this study, impedance-based real time cell analysis (RTCA) was employed to comprehensively investigate the initial bacterial adhesion process. Results showed that the time required for the unstable adhesion process was significantly (p < 0.05) reduced by increasing the initial concentration of bacteria, which is mainly attributed to the large deposition rate of bacteria at high concentrations. In addition, the unstable adhesion process is also regulated by shear stress, derived in this work from orbital shaking. Shear stress improves the reversibility of unstable bacterial attachment. Furthermore, attachment characteristics during the unstable phase vary between different species of bacteria (Sphingomonas rubra, Nakamurella multipartita and mixed bacteria). The S. rubra strain and mixed culture were more prone to adhere to the substratum surface during the unstable process, which was attributed to the smaller xDLVO energy barrier and motility of species in comparison with N. multipartita. Meanwhile, the molecular composition of extracellular polymeric substances (EPS) in the initial attachment phase presented a significant difference in expressed proteins, indicating the important role of proteins in EPS that strengthen bacterial adhesion. Overall, these findings suggest that during the biofilm reactor start-up process, seed sludge conditions, including the bacterial concentration, composition and hydraulics, need to be carefully considered.

Emergent Properties in Streptococcus mutans Biofilms Are Controlled through Adhesion Force Sensing by Initial Colonizers

Bacterial adhesion is accompanied by altered gene expression, leading to "emergent" properties of biofilm bacteria that are alien to planktonic ones. With the aim of revealing the role of environmental adhesion forces in emergent biofilm properties, genes in Streptococcus mutans UA159 and a quorum-sensing-deficient mutant were identified that become expressed after adhesion to substratum surfaces. Using atomic force microscopy, adhesion forces of initial S. mutans colonizers on four different substrata were determined and related to gene expression. Adhesion forces upon initial contact were similarly low across different substrata, ranging between 0.2 and 1.2 nN regardless of the strain considered. Bond maturation required up to 21 s, depending on the strain and substratum surface involved, but stationary adhesion forces also were similar in the parent and in the mutant strain. However, stationary adhesion forces were largest on hydrophobic silicone rubber (19 to 20 nN), while being smallest on hydrophilic glass (3 to 4 nN). brpA gene expression in thin (34 to 48 μm) 5-h S. mutans UA159 biofilms was most sensitive to adhesion forces, while expression of gbpB and comDE expressions was weakly sensitive. ftf, gtfB, vicR, and relA expression was insensitive to adhesion forces. In thicker (98 to 151 μm) 24-h biofilms, adhesion-force-induced gene expression and emergent extracellular polymeric substance (EPS) production were limited to the first 20 to 30 μm above a substratum surface. In the quorum-sensing-deficient S. mutans, adhesion-force-controlled gene expression was absent in both 5- and 24-h biofilms. Thus, initial colonizers of substratum surfaces sense adhesion forces that externally trigger emergent biofilm properties over a limited distance above a substratum surface through quorum sensing.IMPORTANCE A new concept in biofilm science is introduced: "adhesion force sensitivity of genes," defining the degree up to which expression of different genes in adhering bacteria is controlled by the environmental adhesion forces they experience. Analysis of gene expression as a function of height in a biofilm showed that the information about the substratum surface to which initially adhering bacteria adhere is passed up to a biofilm height of 20 to 30 μm above a substratum surface, highlighting the importance and limitations of cell-to-cell communication in a biofilm. Bacteria in a biofilm mode of growth, as opposed to planktonic growth, are responsible for the great majority of human infections, predicted to become the number one cause of death in 2050. The concept of adhesion force sensitivity of genes provides better understanding of bacterial adaptation in biofilms, direly needed for the design of improved therapeutic measures that evade the recalcitrance of biofilm bacteria to antimicrobials.

Artificial Channels in an Infectious Biofilm Created by Magnetic Nanoparticles Enhanced Bacterial Killing by Antibiotics.

The poor penetrability of many biofilms contributes to the recalcitrance of infectious biofilms to antimicrobial treatment. Here, a new application for the use of magnetic nanoparticles in nanomedicine to create artificial channels in infectious biofilms to enhance antimicrobial penetration and bacterial killing is proposed. Staphylococcus aureus biofilms are exposed to magnetic-iron-oxide nanoparticles (MIONPs), while magnetically forcing MIONP movement through the biofilm. Confocal laser scanning microscopy demonstrates artificial channel digging perpendicular to the substratum surface. Artificial channel digging significantly (4-6-fold) enhances biofilm penetration and bacterial killing efficacy by gentamicin in two S. aureus strains with and without the ability to produce extracellular polymeric substances. Herewith, this work provides a simple, new, and easy way to enhance the eradication of infectious biofilms using MIONPs combined with clinically applied antibiotic therapies.

Enhancing Scenedesmus obliquus biofilm growth and CO2 fixation in a gas-permeable membrane photobioreactor integrated with additional rough surface

Microalgae biofilm photobioreactors (PBRs) have been gaining more and more attention worldwide attributed to their advantages of lower water requirement and simpler harvesting process. In this work, aiming at enhancing microalgae biofilm growth and gas-liquid mass transfer based on previous biofilm PBRs, a gas-permeable membrane PBR integrated with additional rough surface (GMPBR-RS) was designed. By attaching an additional piece of stainless steel mesh onto the upper surface of the newly prepared gas-permeable membrane, the roughness of the substratum surface for Scenedesmus obliquus biofilm adhesion was enhanced and therefore resulted in a 28.27% improvement in areal biomass density of S. obliquus relative to the control PBR. Moreover, responses of S. obliquus biofilm adsorption growth and CO2 fixation in the GMPBR-RS to various liquid flow rates and gas flow rates were investigated. Notably, the maximum areal biomass density of S. obliquus biofilm and CO2 removal efficiency of the GMPBR-RS reached 31.44 g m−2 and 65.05%, respectively.

Influence of Amorphous, Carbon‐Derived Wrinkled Surface Topologies on the Colonization of Pseudomonas aeruginosa Bacteria

AbstractSurface wrinkling is a natural phenomenon that has inspired an emerging technology in surface patterning. Here, it is demonstrated that thermal treatment planar thin films of amorphous graphite‐like carbon (G‐aC) coatings deposited on shape memory polystyrene could be used to prepare substratum surfaces with topologies ranging from smooth undulations to those with rough distortion features. A comparative analysis of the attachment propensity of Pseudomonas aeruginosa ATCC 9721 and alginate‐overproducing P. aeruginosa PW2390 bacterial cells, together with the associated production of extracellular polymeric substances (EPS), reveal that at least a 13‐fold increase in the cell attachment density could be achieved, reaching up to 1.3 × 105 and 1.8 × 105 cells mm−2 being attached to the surface for both bacterial strains on G‐aC wrinkled surfaces. The P. aeruginosa PW2390 cells attached to a greater extent than the P. aeruginosa ATCC 9721 cells (≈45%) and without any increased production of EPS material. It is suggested that the increased level of cell attachment is related to the associated substantial increase in available substratum surface area. The results of this study afford a useful insight toward the production of substrata using a straightforward, tunable, and low cost microfabrication approach.

Floriferous herbaceous and substrates for use on extensive green roofs

In general, extensive green roofs are defined as all cover covered with herbaceous vegetation and surface substratum, however, in Brazil there are few information regarding the materials for installation and maintenance of these systems, being essential the search for better species and substrates adapted to the tropical conditions. Thus, the objective was to evaluate the performance of floriferous herbaceous and substrates for use in extensive green roofs. The experiment was carried out in the field and in full sunlight, in black plastic containers (8.46 L and 15.5 cm high), elevated 90 cm from the ground, in a 3x2 factorial scheme. Being 3 herbaceous floriferous species (Torenia var. Kauai, Periwinkle var. Pacifica XP and Petunia var. Bacopa) and 2 substrates [S1-Charcoal + pine bark + peat + expanded vermiculite (1v:1v:1v:1v) and S2- Coconut fiber + carbonized rice husk + peat + expanded vermiculite (1v:1v:1v:1v)], with 3 replicates per treatment. It was evaluated in the substrates: pH, electrical conductivity, macro and microporosity, total porosity, density and water retention capacity. For the development of the species, 60 days after the experiment installation, were evaluated, chlorophyll content of leaves, number of flowers and vegetation surface temperature. It was observed that the substrate S2 presented the best results in the physico-chemical analyzes, and this possibly came to reflect on the performance of the species, and that Torenia when cultivated in this substrate had the highest chlorophyll content (42.67 SPAD). The number of flowers was statistically the same for Torenia and Periwinkle in both substrates, while the three floriferous herbaceous plants showed a decrease in surface temperature. Thus, it is recommended for use on extensive green roofs the substrate composed of coconut fiber + carbonized rice husk + peat + expanded vermiculite (1v:1v:1v:1v), and the floriferous herbaceous Torenia var. Kauai.

Physicochemical characterization of Pseudomonas aeruginosa isolated from catering substratum surface and investigation of their theoretical adhesion

The physicochemical properties of six Pseudomonas aeruginosa isolated from catering environment surface at a health establishment and of different types of substratum surfaces were investigated. These physicochemical properties were determined by contact angles measurements via sessile drop technique. The strains of Pseudomonas aeruginosa (P3, P14, and P18) were hydrophobic, the others were hydrophilic. The results show also that all strains were predominantly electron donors (γ−) and weakly electron acceptors (γ+). Three types of marble (yellow, white and black), four types of granite (Bleu-Pearl, Rosa-Porrino, Galaxy and Green-Pinhel), corian, stainless steel 304 and polypropylene were studied. Except yellow marble and granite (Green-Pinhel) that classified as hydrophilic surfaces, the others were hydrophobic. The finding shows that yellow marble and Green-Pinhel granite were predominantly electron donating (γ−) and other substratum surfaces were weakly electron donating. Except yellow marble which has a high electron acceptor, the others have a weak electron acceptor character. The free energy of adhesion between the bacteria and substratum surface was calculated and used in this study to predict the adhesion of Pseudomonas aeruginosa on the studied substratum surface. For all studied the substratum, except P18, the adhesion of all Pseudomonas aeruginosa is thermodynamically favorable only to polyethylene. Moreover P11 has the ability to adhere to all substratum surfaces.

Floating and Tether-Coupled Adhesion of Bacteria to Hydrophobic and Hydrophilic Surfaces.

Models for bacterial adhesion to substratum surfaces all include uncertainty with respect to the (ir)reversibility of adhesion. In a model, based on vibrations exhibited by adhering bacteria parallel to a surface, adhesion was described as a result of reversible binding of multiple bacterial tethers that detach from and successively reattach to a surface, eventually making bacterial adhesion irreversible. Here, we use total internal reflection microscopy to determine whether adhering bacteria also exhibit variations over time in their perpendicular distance above surfaces. Streptococci with fibrillar surface tethers showed perpendicular vibrations with amplitudes of around 5 nm, regardless of surface hydrophobicity. Adhering, nonfibrillated streptococci vibrated with amplitudes around 20 nm above a hydrophobic surface. Amplitudes did not depend on ionic strength for either strain. Calculations of bacterial energies from their distances above the surfaces using the Boltzman equation showed that bacteria with fibrillar tethers vibrated as a harmonic oscillator. The energy of bacteria without fibrillar tethers varied with distance in a comparable fashion as the DLVO (Derjaguin, Landau, Verwey, and Overbeek)-interaction energy. Distance variations above the surface over time of bacteria with fibrillar tethers are suggested to be governed by the harmonic oscillations, allowed by elasticity of the tethers, piercing through the potential energy barrier. Bacteria without fibrillar tethers “float” above a surface in the secondary energy minimum, with their perpendicular displacement restricted by their thermal energy and the width of the secondary minimum. The distinction between “tether-coupled” and “floating” adhesion is new, and may have implications for bacterial detachment strategies.