The effects of pH, ionic strength and polyvalent ions on the cell surface hydrophobicity of Escherichia coli evaluated by the BATH and HIC methods

Oil addition increases the heat resistance of Clostridium sporogenes spores in braised sauce beef: Perspectives from spore surface characteristics and microstructure

During thermal processing of braised sauce beef, the lipid content of circularly used sauce increased accordingly because of lipid migration from beef to sauce, which may impact the bacterial heat resistance in the products. This study aims to characterize the heat resistance of Clostridium sporogenes spores in braised sauce beef, and investigate the effects of oil on the spore surface characteristics and microstructure. The results indicated that the heat resistance of C. sporogenes spores in beef was significantly higher than that in sauce. Oil addition remarkably enhanced the spore heat resistance in sauce, with D95°C value three times more than that without oil added, and even higher than that in beef. The results of spore surface characteristics indicated that oil addition led to an increase of hydrophobicity and a decrease of zeta potential, which ultimately increased spore heat resistance. Microstructure analysis indicated that exosporium maintenance and cortex expansion induced by oil addition might contribute to the increase of spore heat resistance. This study has sufficiently verified the importance of oil content on the heat resistance of C. sporogenes spores, which should be taken into consideration when developing thermal processes for controlling the spores in food matrices.

Tuning surface topographies on biomaterials to control bacterial infection

Microbial contamination and subsequent formation of biofilms frequently cause failure of surgical implants and a good understanding of the bacteria-surface interactions is vital to the design and safety of biomaterials. In this review, the physical and chemical factors that are involved in the various stages of implant-associated bacterial infection are described. In particular, topographical modification strategies that have been employed to mitigate bacterial adhesion via topographical mechanisms are summarized and discussed comprehensively. Recent advances have improved our understanding about bacteria-surface interactions and have enabled biomedical engineers and researchers to develop better and more effective antibacterial surfaces. The related interdisciplinary efforts are expected to continue in the quest for next-generation medical devices to attain the ultimate goal of improved clinical outcomes and reduced number of revision surgeries.

Investigation of Bacillus licheniformis in the biodegradation of Iranian heavy crude oil: A two-stage sequential approach containing factor-screening and optimization

Oil pollution is a serious international concern due to its harmful effect on human health and the environment. This study aims to investigate the effective factors on the biodegradation of Iranian heavy crude oil by Bacillus licheniformis. For this purpose, oil removal from the artificial seawater was studied by response surface methodology (RSM). After the screening experiments, pH (4-10), NaCl concentration (0-10 g/L), and oil concentration (500-4500 ppm) were selected as influential factors. Moreover, to evaluate the bacterial capability in bioremediation of an actual polluted site, crude oil spill with a salinity of 35 g/L was experimentally simulated. The proposed model in this study clearly shows that both selected individual factors and their interactions are significantly effective on the crude oil biodegradation capacity. The results showed that Bacillus licheniformis was able to degrade crude oil at different concentrations of oil, especially at low concentrations, which are challenging in actual polluted sites. 15%-66% removal was achieved for 500-4500 ppm of crude oil after 14 days. Furthermore, according to the obtained results, this bacterium can tolerate the salinity up to 3.5%. At this salinity level, crude oil removal was 23.43 and 25.64% in neutral and alkaline conditions, respectively. Process factors were optimized, and 54.8% of crude oil was removed at optimum conditions i.e., 3500 ppm crude oil concentration, 2.5 g/L of NaCl and pH equal to 8.5. Finally, it can be concluded that the selected bacterium of this study can be more effective in harsh environments such as hypersaline and alkaline conditions.

Ionic strength controls long-term cell-surface interactions - A QCM-D study of S. cerevisiae adhesion, retention and detachment

Understanding microbial adhesion and retention is crucial for controlling many processes, including biofilm formation, antimicrobial therapy as well as cell sorting and cell detection platforms. Cell detachment is inextricably linked to cell adhesion and retention and plays an important part in the mechanisms involved in these processes. Physico-chemical and biological forces play a crucial role in microbial adhesion interactions and altering the medium ionic strength offers a potential means for modulating these interactions. Real-time studies on the effect of ionic strength on microbial adhesion are often limited to short-term bacterial adhesion. Therefore, there is a need, not only for long-term bacterial adhesion studies, but also for similar studies focusing on eukaryotic microbes, such as yeast. Hereby, we monitored, in real-time, S. cerevisiae adhesion on gold and silica as examples of surfaces with different surface charge properties to disclose long-term adhesion, retention and detachment as a function of ionic strength using quartz crystal microbalance with dissipation monitoring. Our results show that short- and long-term cell adhesion levels in terms of mass-loading increase with increasing ionic strength, while cells dispersed in a medium of higher ionic strength experience longer retention and detachment times. The positive correlation between the cell zeta potential and ionic strength suggests that zeta potential plays a role on cell retention and detachment. These trends are similar for measurements on silica and gold, with shorter retention and detachment times for silica due to strong short-range repulsions originating from a high electron-donicity. Furthermore, the results are comparable with measurements in standard yeast culture medium, implying that the overall effect of ionic strength applies for cells in nutrient-rich and nutrient-deficient media.

Vancomycin-loaded electrospun polycaprolactone/nano-hydroxyapatite membrane for the treatment of blood infections

Nowadays, because of the resistance of bacteria to antibiotics, researchers are trying to make new antibiotics or sometimes even bring them back into the treatment cycle so that they could eliminate the bacteria's resistance. On the other hand, the use of nanofibers has become widespread in many fields for their unique properties and convenient design. The present study focuses on the production of hydrophobic nanofibers to absorb the bacteria and their toxins from the bloodstream that contains the infection. Many bacterial surfaces have hydrophobic surfactant properties due to hydrophobic surface protein. According to the principle of binding two hydrophobic molecules to each other in an aqueous medium, the nanofibers are designed to physically absorb the bacteria. The use of antibiotics in the study can remove some unattached bacteria. In addition, using nanofiber manufacturing techniques can reduce the resistance of bacteria to antibiotics. The construction of the desired membrane can be used in subsequent studies as a replacement membrane for dialysis filters.

Micro- and Nanotopography Sensitive Bacterial Attachment Mechanisms: A Review

Bacterial attachment to material surfaces can lead to the development of biofilms that cause severe economic and health problems. The outcome of bacterial attachment is determined by a combination of bacterial sensing of material surfaces by the cell and the physicochemical factors in the near-surface environment. This paper offers a systematic review of the effects of surface topography on a range of antifouling mechanisms, with a focus on how topographical scale, from micro- to nanoscale, may influence bacterial sensing of and attachment to material surfaces. A good understanding of these mechanisms can facilitate the development of antifouling surfaces based on surface topography, with applications in various sectors of human life and activity including healthcare, food, and water treatment.

Impact of fouling on the decline of aeration efficiency under different operational conditions at WRRFs

Biofilm formation influences the most energy-demanding process in the waste water treatment cycle. Biofilm growth on the surface of wastewater aeration diffusers in water resource recovery facilities (WRRFs) can increase the energy requirements up to 50% in less than 2 years. The impact of biofilms in aeration diffusers was quantified and assessed for first time using molecular tools (i.e., Energy-dispersive X-ray, Ra and RMS and Pyrosequencing) and state-of-the-art techniques (i.e., EPS quantification, Hydrophobicity and DNA quantification). To provide a better understanding and quantitative connections between biological activity and aeration energy efficiency, two replicates of the most common diffusers were installed and tested in two different operational conditions (higher and lower organic loading rate processes) during 15 months. Different scenarios and conditions provided for first time comprehensive understanding of the major factors contributing to diffuser fouling. The array of analysis suggested that higher loading conditions can promote specialized microbial populations to halve aeration efficiency parameters (i.e., αF) in comparison to lower loading conditions. Biofilms adapted to certain operational conditions can trigger changes in diffuser membrane properties (i.e., biological enhanced roughness and hydrophobicity) and enhance EPS growth rates. Improved understanding of the effects of scaling, biofouling, aging and microbial population shifts on the decrease in aeration efficiency is provided.

Antibacterial surface modification of titanium implants in orthopaedics

The use of biomaterials in orthopaedics for joint replacement, fracture healing and bone regeneration is a rapidly expanding field. Infection of these biomaterials is a major healthcare burden, leading to significant morbidity and mortality. Furthermore, the cost to healthcare systems is increasing dramatically. With advances in implant design and production, research has predominately focussed on osseointegration; however, modification of implant material, surface topography and chemistry can also provide antibacterial activity. With the increasing burden of infection, it is vitally important that we consider the bacterial interaction with the biomaterial and the host when designing and manufacturing future implants. During this review, we will elucidate the interaction between patient, biomaterial surface and bacteria. We aim to review current and developing surface modifications with a view towards antibacterial orthopaedic implants for clinical applications.

Adhesion forces of the sea-water bacterium Paracoccus seriniphilus on titanium: Influence of microstructures and environmental conditions

The bacterial attachment to surfaces is the first step of biofilm formation. This attachment is governed by adhesion forces which act between the bacterium and the substrate. Such forces can be measured by single cell force spectroscopy, where a single bacterium is attached to a cantilever of a scanning force microscope, and force-distance curves are measured. For the productive sea-water bacterium Paracoccus seriniphilus, pH dependent measurements reveal the highest adhesion forces at pH 4. Adhesion forces measured at salinities between 0% and 4.5% NaCl are in general higher for higher salinity. However, there is an exception for 0.9% where a higher adhesion force was measured than expected. These results are in line with zeta potential measurements of the bacterium, which also show an exceptionally low zeta potential at 0.9% NaCl. In the absence of macromolecular interactions, the adhesion forces are thus governed by (unspecific) electrostatic interactions, which can be adjusted by pH and ionic strength. It is further shown that microstructures on the titanium surface increase the adhesion force. Growth medium reduces the interaction forces dramatically, most probably through macromolecular bridging.

Lactic acid bacteria in dairy food: surface characterization and interactions with food matrix components

This review gives an overview of the importance of interactions occurring in dairy matrices between Lactic Acid Bacteria and milk components. Dairy products are important sources of biological active compounds of particular relevance to human health. These compounds include immunoglobulins, whey proteins and peptides, polar lipids, and lactic acid bacteria including probiotics. A better understanding of interactions between bioactive components and their delivery matrix may successfully improve their transport to their target site of action. Pioneering research on probiotic lactic acid bacteria has mainly focused on their host effects. However, very little is known about their interaction with dairy ingredients. Such knowledge could contribute to designing new and more efficient dairy food, and to better understand relationships between milk constituents. The purpose of this review is first to provide an overview of the current knowledge about the biomolecules produced on bacterial surface and the composition of the dairy matter. In order to understand how bacteria interact with dairy molecules, adhesion mechanisms are subsequently reviewed with a special focus on the environmental conditions affecting bacterial adhesion. Methods dedicated to investigate the bacterial surface and to decipher interactions between bacteria and abiotic dairy components are also detailed. Finally, relevant industrial implications of these interactions are presented and discussed.

Alumina surfaces with nanoscale topography reduce attachment and biofilm formation by Escherichia coli and Listeria spp

This work reports on a simple, robust and scientifically sound method to develop surfaces able to reduce microbial attachment and biofilm development, with possible applications in medicine, dentistry, food processing, or water treatment. Anodic surfaces with cylindrical nanopores 15 to 100 nm in diameter were manufactured and incubated with Escherichia coli ATCC 25922 and Listeria innocua. Surfaces with 15 and 25 nm pore diameters significantly repressed attachment and biofilm formation. Surface-bacteria interaction forces calculated using the extended Derjaguin Landau Verwey-Overbeek (XDLVO) theory indicate that reduction in attachment and biofilm formation is due to a synergy between electrostatic repulsion and surface effective free energy. An attachment study using E. coli K12 strains unable to express appendages also suggests that the small-pore surfaces may inhibit flagella-dependent attachment. These results can have immediate, far-reaching implications and commercial applications, with substantial benefits for human health and life.

An overview of the methodological approach to the in vitro study of anti-infective biomaterials

Biomaterial-associated infections have an enormous impact in terms of morbidity of the patients and costs to national health systems. Perioperative antibiotics and aseptic procedures have not proved sufficient to eradicate the occurrence of this type of infections which often lead to devastating effects. Adjunctive strategies for preventing the establishment of infections are increasingly being centered on the development of new biomaterials with anti-infective properties. The creation of new anti-infective biomaterials can be obtained by alternative approaches oriented to achieve either bacteria-repellent surfaces or bioactive surfaces expressing self-sterilizing properties when not even able to treat pre-existing infections in the surrounding tissues. Here, we offer a short overview of the currently available in vitro methods that can be used to investigate and assess the performance of anti-infective biomaterials, with special emphasis on those whose mechanism of action is based on bacteria-repellent surfaces.

Influence on Surface Characteristics of Microalgae Cell by Solution Chemistry

Considering the influence on the downstream process of microalgae recovery by cell surface characteristics, in this paper , Microelectrophoresis and Hydrocarbon adsorption have been used for researching the surface electrical property and hydrophobicity of microalgae. The influence on surface characteristics of microalgae cell have been studied by the solution chemistry condition of pH and cationic flocculant. The results show that: The surface charge of microalgae cell is negative under the natural condition. The surface electrical property decreases with the declining pH when pH is less than 7 , but the isoelectric point is not observed until pH low to 1, while it changes little with the pH increased when pH is more than 7; Within the value of experimental pH, microalgae cells have strong hydrophobicity, which increases with the decreasing pH when pH is less than 7 and rises with the pH increased when pH is more than 9. It attains to the minimum value when the pH is about 8. The hydrophobicity of microalgae increases with anhydrous ferric chloride(FeCl3) when cationic flocculant (FeCl3) is added , but the trend became weaker. So the hydrophobicity can be improved by cationic flocculant, which can promote the microalgae cohesion.

Application of waste frying oils in the biosynthesis of biodemulsifier by a demulsifying strain Alcaligenes sp. S-XJ-1

Exploration of biodemulsifiers has become a new research aspect. Using waste frying oils (WFOs) as carbon source to synthesize biodemulsifiers has a potential prospect to decrease production cost and to improve the application of biodemulsifiers in the oilfield. In this study, a demulsifying strain, Alcaligenes sp. S-XJ-1, was investigated to synthesize a biodemulsifier using waste frying oils as carbon source. It was found that the increase of initial pH of culture medium could increase the biodemulsifier yield but decrease the demulsification ratio compared to that using paraffin as carbon source. In addition, a biodemulsifier produced by waste frying oils and paraffin as mixed carbon source had a lower demulsification capability compared with that produced by paraffin or waste frying oil as sole carbon source. Fed-batch fermentation of biodemulsifier using waste frying oils as supplementary carbon source was found to be a suitable method. Mechanism of waste frying oils utilization was studied by using tripalmitin, olein and tristearin as sole carbon sources to synthesize biodemulsifier. The results showed saturated long-chain fatty acid was difficult for S-XJ-1 to utilize but could effectively enhance the demulsification ability of the produced biodemulsifier. Moreover, FT-IR result showed that the demulsification capability of biodemulsifiers was associated with the content of C=O group and nitrogen element.

Salmonella Sofia differs from other poultry-associated Salmonella serovars with respect to cell surface hydrophobicity

Salmonella enterica is one of the most important foodborne pathogens. Salmonella enterica subsp. II 4,12:b:- (Salmonella Sofia) is commonly found in Australian poultry. It has been suggested that physicochemical properties such as surface charge and hydrophobicity may affect bacterial attachment to surfaces and their ability to persist in food systems. A possible link between hydrophobicity cell surface charge and persistence of Salmonella from the poultry system was examined. Hydrophobicity of Salmonella Sofia (n = 14), Salmonella Typhimurium (n = 6), Salmonella Infantis (n = 3), and Salmonella Virchow (n = 2) was assayed using hydrophobic interaction chromatography, bacterial adherence to hydrocarbons (BATH), using xylene or hexadecane, and the contact angle method (CAM). Cellular surface charge (CSC) of the isolates was determined using zeta potential measurements. The majority (12 of 14) of Salmonella Sofia isolates were found to be hydrophobic when assayed using BATH with xylene, except isolates S1635 and S1636, and the other serovars were found to be hydrophilic. Salmonella Sofia isolates were not significantly different (P > 0.05) from isolates of other serovars as measured by hydrophobic interaction, BATH with hexadecane, or the CAM. No significant differences (P > 0.05) in zeta potential measurements were observed between isolates. Principal component analysis using results from all four measures of hydrophobicity allowed clear differentiation between isolates of the serovar Salmonella Sofia (except S1635 and S1636) and those of other Salmonella serovars. Differences in physicochemical properties may be a contributing factor to the Salmonella Sofia serovar's ability to attach to surfaces and persist in a food system.

Physicochemical properties of Shiga toxigenic Escherichia coli

AIMS

To investigate the physicochemical surface properties, such as cellular surface charge, hydrophobicity and electron donor/acceptor potential of a selection of Shiga toxigenic Escherichia coli (STEC) isolates grown in broth and agar culture.

METHODS AND RESULTS

Cellular surface charge was determined using zeta potential measurements. Hydrophobicity of the isolates was determined using bacterial adhesion to hydrocarbons assay, hydrophobic interaction chromatography and contact angle measurements. Microbial adhesion to solvents was used to determine the electron donor/acceptor characteristics. No differences of surface charge measurements were found between broth and agar grown cultures. Isolates belonging to serogroup O157 and serotypes O26:H11 and O111:H- were significantly (P < 0.05) less negatively charged than other STEC serotypes tested. All strains were hydrophilic with most methods and demonstrated a lower hydrophobicity in agar culture compared with broth culture. All strains demonstrated a strong microbial adhesion to chloroform indicating that STEC possess an electron donor and basic character. A relationship between serogroup O157 and other STEC serotypes was apparent using principal-component analysis (PCA).

CONCLUSIONS

Combining the results for physicochemical properties using PCA differentiated between strains belonging to the O157 serogroup and other STEC/non-STEC strains. PCA found similar results for broth and agar grown cultures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Particular serotypes of STEC possess similar physicochemical properties which may play a role in their pathogenicity or potential attachment to various surfaces.

Reversible and irreversible adhesion of motile Escherichia coli cells analyzed by total internal reflection aqueous fluorescence microscopy

The initial events in bacterial adhesion are often explained as resulting from electrostatic and van der Waals forces between the cell and the surface, as described by DLVO theory (developed by Derjaguin, Landau, Verwey, and Overbeek). Such a theory predicts that negatively charged bacteria will experience greater attraction toward a negatively charged surface as the ionic strength of the medium is increased. In the present study we observed both smooth-swimming and nonmotile Escherichia coli bacteria close to plain, positively, and hydrophobically coated quartz surfaces in high- and low-ionic-strength media by using total internal reflection aqueous fluorescence microscopy. We found that reversibly adhering cells (cells which continue to swim along the surface for extended periods) are too distant from the surface for this behavior to be explained by DLVO-type forces. However, cells which had become immobilized on the surface did seem to be affected by electrostatic interactions. We propose that the "force" holding swimming cells near the surface is actually the result of a hydrodynamic effect, causing the cells to swim at an angle along the glass, and that DLVO-type forces are responsible only for the observed immobilization of irreversibly adhering cells. We explain our observations within the context of a conceptual model in which bacteria that are interacting with the surface may be thought of as occupying one of three compartments: bulk fluid, near-surface bulk, and near-surface constrained. A cell in these compartments feels either no effect of the surface, only the hydrodynamic effect of the surface, or both the hydrodynamic and the physicochemical effects of the surface, respectively.