A study of pH effects on the bacterial surface physicochemical properties of Acinetobacter baumannii

Dynamic Adhesive Behavior and Biofilm Formation of Staphylococcus aureus on Polylactic Acid Surfaces in Diabetic Environments

Interest in biodegradable implants has focused attention on the resorbable polymer polylactic acid. However, the risk of these materials promoting infection, especially in patients with existing pathologies, needs to be monitored. The enrichment of a bacterial adhesion medium with compounds that are associated with human pathologies can help in understanding how these components affect the development of infectious processes. Specifically, this work evaluates the influence of glucose and ketone bodies (in a diabetic context) on the adhesion dynamics of S. aureus to the biomaterial polylactic acid, employing different approaches and discussing the results based on the physical properties of the bacterial surface and its metabolic activity. The combination of ketoacidosis and hyperglycemia (GK2) appears to be the worst scenario: this system promotes a state of continuous bacterial colonization over time, suppressing the stationary phase of adhesion and strengthening the attachment of bacteria to the surface. In addition, these supplements cause a significant increase in the metabolic activity of the bacteria. Compared to non-enriched media, biofilm formation doubles under ketoacidosis conditions, while in the planktonic state, it is glucose that triggers metabolic activity, which is practically suppressed when only ketone components are present. Both information must be complementary to understand what can happen in a real system, where planktonic bacteria are the ones that initially colonize a surface, and, subsequently, these attached bacteria end up forming a biofilm. This information highlights the need for good monitoring of diabetic patients, especially if they use an implanted device made of PLA.

Pickering emulsion-enhanced Vibrio fischeri assay for ecotoxicity assessment of highly hydrophobic polycyclic aromatic hydrocarbons

Accurate ecotoxicity assessment of contaminated soil is critical to public health, and the luminescent bacteria (Vibrio fischeri) method is the most commonly used. Hydrophobic compounds such as polycyclic aromatic hydrocarbons (PAHs) in soil cannot be in contact with luminescent bacteria due to their low water solubility so that the luminescence inhibitory effect cannot be observed. The underestimated biological toxicity makes the test unreliable and en-dangers public health and safety. The commonly adopted improved method of adding cosolvents has limited effect, it was only effective for low-hydrophobicity chemicals and could not be used for ecotoxicity evaluation of high-hydrophobicity chemicals. Therefore, we constructed Pickering emulsions using luminescent bacteria modified with n-dodecanol in which PAHs were dissolved in the oil phase, n-tetradecane. Then the luminescent bacteria could tightly adhere to the oil-water interface and contact PAHs. As a result, their bioluminescence was suppressed to varying degrees depending on the chemical species and concentrations. With no solubility limitation, highly hydrophobic PAHs could even completely inhibit bacterial bioluminescence, hence the toxicity information was accurately displayed and the median effect concentration (EC₅₀) values could be calculated. This Pickering emulsion-based method was successfully applied for the accurate ecotoxicity evaluation of highly hydrophobic PAHs and soil samples contaminated with them, which all previous methods could not achieve. This method overcomes the problem of ecotoxicity evaluation of hydrophobic compounds, and has great potential for practical application, whether it is pure chemicals or various real samples from the ecological environment.

A new approach to overcoming antibiotic-resistant bacteria: Traditional Chinese medicine therapy based on the gut microbiota

With the irrational use of antibiotics and the increasing abuse of oral antibiotics, the drug resistance of gastrointestinal pathogens has become a prominent problem in clinical practice. Gut microbiota plays an important role in maintaining human health, and the change of microbiota also affects the activity of pathogenic bacteria. Interfering with antibiotic resistant bacteria by affecting gut microbiota has also become an important regulatory signal. In clinical application, due to the unique advantages of traditional Chinese medicine in sterilization and drug resistance, it is possible for traditional Chinese medicine to improve the gut microbial microenvironment. This review discusses the strategies of traditional Chinese medicine for the treatment of drug-resistant bacterial infections by changing the gut microenvironment, unlocking the interaction between microbiota and drug resistance of pathogenic bacteria.

The Effect of Different Vegetable Oils on Cedar Wood Surface Energy: Theoretical and Experimental Fungal Adhesion

Despite having been used for ages to preserve wood against several effects (biological attack and moisture effects) that cause its degradation, the effect of vegetable oils on the cedar wood physicochemical properties is poorly known. Thus, in this study, the hydrophobicity, electron-acceptor (γ⁺), and electron-donor (γ⁻) properties of cedar wood before and after treatment with vegetable oils have been determined using contact angle measurement. The cedar wood has kept its hydrophobic character after treatment with the different vegetable oils. It has become more hydrophobic quantitatively with values of surface energy ranged from −25.84 to −43.45 mJ/m² and more electron donors compared to the untreated sample. Moreover, the adhesion of four fungal strains (Penicillium commune (PDLd”), Thielavia hyalocarpa, Penicillium commune (PDLd10), and Aspergillus niger) on untreated and treated cedar wood was examined theoretically and experimentally. For untreated wood, the experimental adhesion showed a positive relationship with the results obtained by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach which found that all fungal strains could adhere strongly to the cedar wood material. In contrast, this relationship was not always positive after treatment. The Environmental Scanning Electron Microscopy (ESEM) has shown that P. commune (PDLd10) and A. niger were found unable to adhere to the wood surface after treatment with sunflower and rapeseed oils. In addition, the results showed that the four fungal strains' adhesion was decreased with olive and linseed oils treatment except that of P. commune (PDLd10) treated with linseed oil.

Modification of physico-chemical surface properties and growth of Staphylococcus aureus under hyperglycemia and ketoacidosis conditions

Diabetes is a widely spread disease affecting the quality of life of millions of people around the world and is associated to a higher risk of developing infections in different parts of the body. The reasons why diabetes enhances infection episodes are not entirely clear; in this study our aim was to explore the changes that one of the most frequently pathogenic bacteria undergoes when exposed to hyperglycemia and ketoacidosis conditions. Physical surface properties such as hydrophobicity and surface electrical charge are related to bacterial growth behavior and the ability of Staphylococcus aureus to form biofilms. The addition of glucose made bacteria more negatively charged and with moderate-intermediate hydrophobicity. Ketone bodies increased hydrophobicity to approximately 75% and pathological concentrations hindered some of the bacterial surface charge by decreasing the negative zeta potential of cells. When both components were present, the bacterial physical surface changes were more similar to those observed in ketone bodies, suggesting a preferential adsorption of ketone bodies over glucose because of the more favorable solubility of glucose in water. Glucose diabetic concentrations gave the highest number of bacteria in the stationary phase of growth and provoked an increase in the biofilm slime index of around 400% in relation to the control state. Also, this situation is related with an increase of bacterial coverage. The combination of a high concentration of glucose and ketone bodies, which corresponds to a poorly controlled diabetic situation, appears associated with an early infection phase; increased hydrophobic attractive force and reduced electrostatic repulsion between cells results in better packing of cells within the biofilm and more efficient retention to the host surface. Knowledge of bacterial response in high amount of glucose and ketoacidosis environments can serve as a basis for designing strategies to prevent bacterial adhesion, biofilm formation and, consequently, the development of infections.

Efficient chemical hydrophobization of lactic acid bacteria - One-step formation of double emulsion

A novel concept of stabilizing multiple-phase food structure such as emulsion using solely the constitutional bacteria enables an all-natural food grade formulation and thus a clean label declaration. In this paper, we propose an efficient approach to hydrophobically modifying the surface of lactic acid bacteria Lactobacillus rhamnosus (LGG) using lauroyl ahloride (LC) in non-aqueous media. Compared to the unmodified bacteria, cell hydrophobicity was dramatically altered upon modification, according to the higher percentages of microbial adhesion to hexadecane (MATH) and water contact angles (WCA) of LC-modified bacteria. No evident changes were found in bacterial surface charge before and after LC modification. By using one-step homogenization, all the modified bacteria were able to generate stabile water-in-oil-in-water (W/O/W) double emulsions where bacteria were observed on oil-water interfaces of the primary and secondary droplets. Modification using high LC concentrations (10 and 20 w/w%) led to rapid autoaggregation of bacteria in aqueous solution. A long-term lethal effect of modification primarily came from lyophilization and no apparent impact was detected on the instantaneous culturability of modified bacteria.

Gut microbes modulate bioaccessibility of lead in soil

Metabolic uptake of lead (Pb) is controlled by its bioaccessibility. Most studies have examined bioaccessibility of Pb in the absence of gut microbes, which play an important role in the metabolic uptake of nutrients and metal(loid)s in intestine. In this study, we examined the effect of three gut microbes, from various locations in the gut, on the bioaccessibility of soil ingested Pb. The gut microbes include Lactobacillus acidophilus, Lactobacillus rhamnosus and Escherichia coli. Lead toxicity to these three microbes was also examined at various pH values. Bioaccessibility of Pb was measured using gastric and intestinal extractions. Both Pb spiked and Pb-contaminated shooting range field soils were used to measure Pb bioaccessibility in the presence and absence of gut microbes. The results indicated that Pb toxicity to gut microbes, as measured by LD₅₀ value, decreased with increasing pH, and was higher for Lactobacillus species. Gut microbes decreased the bioaccessible Pb; the effect was more pronounced at low pH, mimicking gastric conditions than in conditions closer to the intestine. Lead adsorption by these microbes increased at the higher pH tested, and E. coli adsorbed higher amounts of Pb than did the Lactobacillus species. The effect of gut microbes on reducing Pb bioaccessibility may be attributed to microbially-induced immobilization of Pb through adsorption, precipitation, and complexation reactions. The study demonstrates that bioaccessibility and subsequently bioavailability of metal(loid)s can be modulated by gut microbes, and it is important to undertake bioaccessibility measurements in the presence of gut microbes.

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.

Applicability of two-dimensional surface model in bacterial biosorption system: an advanced approach in bioremediation of metal ions

The surface of Bacillus VMSDCM (accession no. HQ108109) has been characterized at various pH values of the experimental solution. The boundary values of conditional parameter were used to develop a mathematical six lumped stochastic model for studying the surface chemistry of the bacterium cells. The results of the model were statistically analyzed to understand the strength of the proposed model. The simulation of the model was performed in Turbo C++ interface. The convergence values of the model were recorded and all the asymptotic points were neglected. The optimum values of model were reiterated to identify the intermittent values of maximum number of active sites, concentration of hydrides and hydroxides of calcium and magnesium and difference between the theoretical and experimental count of active sites. The values of zeta potential indicated towards the ionization of negatively charged surface functional groups at higher values of pH. The results of the present investigation revealed the fact that changes in the values of conditional parameter (pH) may create a drift in design parameters of a batch or continuous column reactor, fabricated for biosorption-cum-bioaccumulation of metal ions (Ca²⁺ and Mg²⁺) across liquid phase.

Biofilm formation and antibiotic susceptibility in dispersed cells versus planktonic cells from clinical, industry and environmental origins

We examined the cell-surface physicochemical properties, the biofilm formation capability and the antibiotic susceptibility in dispersed cells (from an artificial biofilm of alginate beads) and compared with their planktonic (free-swimming) counterparts. The strains used were from different origins, such as clinical (Acinetobacter baumannii AB4), cosmetic industry (Klebsiella oxytoca EU213, Pseudomonas aeruginosa EU190), and environmental (Halomonas venusta MAT28). In general, dispersed cells adhered better to surfaces (measured as the "biofilm index") and had a greater hydrophobicity [measured as the microbial affinity to solvents (MATS)] than planktonic cells. The susceptibility to two antibiotics (ciprofloxacin and tetracycline) of dispersed cells was higher compared with that of their planktonic counterparts (tested by the "bactericidal index"). Dispersed and planktonic cells exhibited differences in cell permeability, especially in efflux pump activity, which could be related to the differences observed in susceptibility to antibiotics. At 1 h of biofilm formation in microtiter plates, dispersed cells treated with therapeutic concentration of ciprofloxacin yielded a lower biofilm index than the control dispersed cells without ciprofloxacin. With respect to the planktonic cells, the biofilm index was similar with and without the ciprofloxacin treatment. In both cases there were a reduction of the number of bacteria measured as viable count of the supernatant. The lower biofilm formation in dispersed cells with ciprofloxacin treatment may be due to a significant increase of biofilm disruption with respect to the biofilm from planktonic cells. From a clinical point of view, biofilms formed on medical devices such as catheters, cells that can be related to an infection were the dispersed cells. Our results showed that early treatment with ciprofloxacin of dispersed cells could diminishe bacterial dispersion and facilitate the partial elimination of the new biofilm formed.

Development of a transparent, non-cytotoxic, silver ion-exchanged glass with antimicrobial activity and low ion elution

We investigated the antimicrobial, cytotoxicity, skin irritation, and ion elution behaviors of glass doped with silver ions with respect to its application to electronic equipment such as phones and tablet screens. The microbes tested were Escherichia coli, Staphylococcus aureus, and Penicillium funiculosum. AgNO3 powder was spread on both sides of aluminosilicate glass, and it was heated to 250-280°C for 10min. Under optimized heating conditions (260°C, 10min), the antimicrobial activity of ion-exchanged glass against bacteria and fungi was over 99.9% after 24 weeks. The glass failed to irritate the skin of experimental animals and was considered non-cytotoxic. The maximum amount of Ag ions that were eluted from the ion-exchanged glass into drinking water was measured at 0.037±0.003μgL(-1), an amount which is several orders of magnitude below the standard limit of 0.1mgL(-1) in drinking water. Ag ion-exchanged glass had characteristics suitable for use as a display screen, such as a light transmittance of 90% and a surface roughness of 0.704nm. Our findings suggest that glass doped with silver ions is more hygienic than non-doped glass is, and should be applied to display screens and glassware.

Laboratory Maintenance of Acinetobacter baumannii

Acinetobacter baumannii has recently drawn great interest in the microbiology research community due to the increase in clinical antibiotic resistance of this organism, and persistence of this bacterial species in the hospital environment. This unit outlines protocols for the growth and maintenance of A. baumannii in the laboratory.

Rapid spectrophotometric method for determining surface free energy of microalgal cells

Microalgae are one of the most promising renewable energy sources with environmental sustainability. The surface free energy of microalgal cells determines their biofouling and bioflocculation behavior and hence plays an important role in microalgae cultivation and harvesting. To date, the surface energetic properties of microalgal cells are still rarely studied. We developed a novel spectrophotometric method for directly determining the surface free energy of microalgal cells. The principles of this method are based on analyzing colloidal stability of microalgae suspensions. We have shown that this method can effectively differentiate the surface free energy of four microalgal strains, i.e., marine Chlorella sp., marine Nannochloris oculata, freshwater autotrophic Chlorella sp., and freshwater heterotrophic Chlorella sp. With advantages of high-throughput and simplicity, this new spectrophotometric method has the potential to evolve into a standard method for measuring the surface free energy of cells and abiotic particles.