Pilar Teixeira

Evaluation of Fenton and ozone-based advanced oxidation processes as mature landfill leachate pre-treatments.

Fenton treatment (Fe(2+)/H(2)O(2)) and different ozone-based Advanced Oxidation Processes (AOPs) (O(3), O(3)/OH(-) and O(3)/H(2)O(2)) were evaluated as pre-treatment of a mature landfill leachate, in order to improve the biodegradability of its recalcitrant organic matter for subsequent biological treatment. With a two-fold diluted leachate, at optimised experimental conditions (initial pH 3, H(2)O(2) to Fe(2+) molar ratio of 3, Fe(2+) dosage of 4 mmol L(-1), and reaction time of 40 min) Fenton treatment removed about 46% of chemical oxygen demand (COD) and increased the five-day biochemical oxygen demand (BOD(5)) to COD ratio (BOD(5)/COD) from 0.01 to 0.15. The highest removal efficiency and biodegradability was achieved by ozone at higher pH values, solely or combined with H(2)O(2). These results confirm the enhanced production of hydroxyl radical under such conditions. After the application for 60 min of ozone at 5.6 g O(3)h(-1), initial pH 7, and 400 mg L(-1) of hydrogen peroxide, COD removal efficiency was 72% and BOD(5)/COD increased from 0.01 to 0.24. An estimation of the operating costs of the AOPs processes investigated revealed that Fe(2+)/H(2)O(2) was the most economical system (8.2 € m(-3)g(-1) of COD removed) to treat the landfill leachate. This economic study, however, should be treated with caution since it does not consider the initial investment, prices at plant scale, maintenance and labour costs.

Adhesion to and viability of Listeria monocytogenes on food contact surfaces

Listeria monocytogenes is an important pathogen responsible for major outbreaks associated with food products. Adhesion to surfaces leads to significant modifications in cell physiology. The aim of this work was to determine the adhesion ability of 10 isolates of L. monocytogenes to eight materials commonly used in kitchens and to evaluate the viability of the adhered cells. The materials assayed were stainless steel 304, marble, granite, glass, polypropylene from a bowl and from a cutting board, and two kinds of silestone. All L. monocytogenes strains attached to all surfaces, although to different extents. L. monocytogenes adhered most tightly to granite and marble, followed by stainless steel 304, glass, silestones, and finally polypropylene surfaces. Surfaces at the threshold between hydrophobicity and hydrophilicity, with high electron acceptor capability and a regular pattern of roughness, were more prone to attachment. Polypropylene surfaces displayed the highest percentage of viable bacteria (nearly 100%), whereas marble and granite had a lower percentage of cultivable cells, 69.5 and 78.7%, respectively. The lowest percentage of culturable bacteria was found on white silestone (18.5%). These results indicate that there are differences in adhered cell viability on different materials. Cell viability assays are important to better understand the cross-contamination process because only adhered bacteria that remain viable are responsible for postprocess contamination.

Ozonation as polishing treatment of mature landfill leachate

Mature landfill leachate is typically resistant to biological processes. In order to enhance the biodegradability of a pre-treated mature landfill leachate, ozonation treatments in a lab-scale column were assayed under different ozone concentrations, contact time, initial pH, and hydrogen peroxide concentrations. Degradation of the landfill leachate by ozone was favoured at higher pH values and with the addition of H(2)O(2), both consistent with the enhanced production of the hydroxyl radical under such conditions. The highest organic reduction and biodegradability improvement was observed with the O(3)/H(2)O(2) process at 600 mg H(2)O(2) L(-1). This system was able to remove 63% of chemical oxygen demand (COD), 53% of total organic carbon (TOC), 42% of aromatic content (UV(254)) and increased the leachate 5-day biochemical oxygen demand (BOD(5)) to COD ratio from 0.01 to 0.17. Ozone combined with H(2)O(2) contributed significantly to remove and change the recalcitrant organic matter and improved leachate biodegradability, which makes this process very attractive as pre-biological treatment.

Influence of Surface Properties on the Adhesion of Staphylococcus epidermidis to Acrylic and Silicone

The aim of the present study was to compare the ability of eight Staphylococcus epidermidis strains to adhere to acrylic and silicone, two polymers normally used in medical devices manufacture. Furthermore, it was tried to correlate that with the surface properties of substrata and cells. Therefore, hydrophobicity and surface tension components were calculated through contact angle measurements. Surface roughness of substrata was also assessed by atomic force microscopy (AFM). No relationship was found between microbial surface hydrophobicity and adhesion capability. Nevertheless, Staphylococcus epidermidis IE214 showed very unique adhesion behaviour, with cells highly aggregated between them, which is a consequence of their specific surface features. All strains, determined as being hydrophilic, adhered at a higher extent to silicone than to acrylic, most likely due to its more hydrophobic character and higher roughness. This demonstrates the importance of biomaterial surface characteristics for bacterial adhesion.

Comparison of the adhesion ability of different Salmonella enteritidis serotypes to materials used in kitchens

Contamination of kitchen surfaces due to bacteria present in foodstuffs is one of the main causes of foodborne outbreaks. Salmonella infections are an important cause of foodborne disease, and Salmonella Enteritidis is the most common isolate in the past few years. In this study, the adhesion ability of four Salmonella Enteritidis isolates to different materials (polyethylene, polypropylene, and granite) used in kitchens was compared. The results indicated that the two plastic materials were generally less prone to colonization than was the granite. As surface properties of both bacteria and materials are a determinant in the adhesion process, surface hydrophobicity was determined through contact angle measurement, and the roughness of the materials was evaluated through the R(a) and R(z) values by a noncontact laser stylus tracing. The four Salmonella strains showed similar degrees of hydrophilicity, while the materials were hydrophobic, with granite having a very low degree of hydrophobicity (deltaG(lwl) = -4.7 mJ/m2). However, the different extents of adhesion could not be explained in terms of surface hydrophobicity and roughness of the materials tested. The main conclusion to be drawn is that Salmonella adhesion is strongly strain dependent, despite the similar degree of hydrophobicity displayed by all the strains assayed, and this can constitute a factor of virulence among the different serotypes.

Influence of surface characteristics on the adhesion of Alcaligenes denitrificans to polymeric substrates

The adhesion of Alcaligenes denitrificans to several polymeric materials was investigated. As the nature of the surfaces of the micro-organisms and the substrate materials is an important factor in the adhesion process, characteristics such as the electrokinetic potential and hydrophobicity were also determined and correlated with the capacity of bacterial cells to adhere to solid surfaces. The substrates used were high-density polyethylene (HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), and poly(methyl methacrylate) (PMMA). The electrokinetic potential of the cells and the substrates was determined by measurements of electrophoretic mobility and the hydrophobicity was determined by contact angle measurements. All the substrates studied as well as the bacterial strain have a negative zeta potential, which means that adhesion is not mediated by electrostatic interactions. As far as hydrophobicity is concerned, PP is the most hydrophobic material, PMMA is the least hydrophobic, whereas HDPE and PVC ...

An investigation of the potential application of chitosan/aloe-based membranes for regenerative medicine

A significant number of therapeutics derived from natural polymers and plants have been developed to replace or to be used in conjunction with existing dressing products. The use of the therapeutic properties of aloe vera could be very useful in the creation of active wound dressing materials. The present work was undertaken to examine issues concerning structural features, topography, enzymatic degradation behavior, antibacterial activity and cellular response of chitosan/aloe vera-based membranes. The chitosan/aloe vera-based membranes that were developed displayed satisfactory degradation, roughness, wettability and mechanical properties. A higher antibacterial potency was displayed by the blended membranes. Moreover, in vitro assays demonstrated that these blended membranes have good cell compatibility with primary human dermal fibroblasts. The chitosan/aloe vera-based membranes might be promising wound dressing materials.

Adhesion of Salmonella Enteritidis to stainless steel surfaces

Adhesion of microorganisms to food processing surfaces and the problems it causes are a matter of strong concern to the food industry. Contaminated food processing surfaces may act as potential sources of transmission of pathogens in food industry, catering and in the domestic environments. Several studies have shown that adhesion of bacteria to surfaces partly depends upon the nature of the inert surfaces and partly upon the bacterial surface properties. The aim of this study was to compare the adhesion of four different strains of Salmonella Enteritidis to stainless steel 304 (SS 304). The effect of surface hydrophobicity and surface elemental composition on the adhesion process was also analysed. Hydrophobicity was evaluated through contact angle measurements using the sessile drop method. All the strains studied showed positive values of the degree of hydrophobicity (DGlwl) and so can be considered hydrophilic while stainless steel revealed a hydrophobic character. Bacterial cell surface composition was measured using X-ray photoelectron spectroscopy (XPS). The XPS results corroborated the similarity of the values of the degree of hydrophobicity obtained by contact angles. The different Salmonella strains showed similar elemental composition and cell surface physico-chemical properties. Nevertheless, S. Enteritidis MUSC presented higher adhesion ability to SS 304 (p<0.05). It can be concluded that the physico-chemical properties of the strain does not explain the ability of adhesion to stainless steel. Other factors like the production of polysaccharides must be considered.

Denitrification in a closed rotating biological contactor: effect of disk submergence

Several studies have employed rotating biological contactors (RBCs) for nitrogen removal. However, partially submersed disks are used for nitrification, while completely submersed disks are used for denitrification. The objective of this study was to investigate the effect of disk submergence in the performance of rotating biological contactors, in terms of the denitrification process. Two RBCs, one with completely submersed disks (100% submergence) and the other with partially submersed disks (64.5%), were operated under the same conditions. Their performance was evaluated in terms of denitrification efficiency as well as biofilm characteristics, composition and activity. As far as the denitrification process is concerned, the RBC with a completely submersed biofilm was more efficient than the other but had a longer delay in start-up. The biofilm of both reactors was very thick (0.6 mm), but with different structures. Biofilm activity seems to be directly dependent on the biofilm structure, namely on the degree of hydration.

In vitro Activity of Daptomycin, Linezolid and Rifampicin on Staphylococcus epidermidis Biofilms

Owing to their massive use, Staphylococcus epidermidis has recently developed significant resistance to several antibiotics, and became one of the leading causes of hospital-acquired infections. Current antibiotics are typically ineffective in the eradication of bacteria in biofilm-associated persistent infections. Accordingly, the paucity of effective treatment against cells in this mode of growth is a key factor that potentiates the need for new agents active in the prevention or eradication of biofilms. Daptomycin and linezolid belong to the novel antibiotic therapies that are active against gram-positive cocci. On the other hand, rifampicin has been shown to be one of the most potent, prevalent antibiotics against S. epidermidis biofilms. Therefore, the main aim of this study was to study the susceptibility of S. epidermidis biofilm cells to the two newer antimicrobial agents previously mentioned, and compare the results obtained with the antimicrobial effect of rifampicin, widely used in the prevention/treatment of indwelling medical device infections. To this end the in vitro activities of daptomycin, linezolid, and rifampicin on S. epidermidis biofilms were accessed, using these antibiotics at MIC and peak serum concentrations. The results demonstrated that at MIC concentration, rifampicin was the most effective antibiotic tested. At peak serum concentration, both strains demonstrated similar susceptibility to rifampicin and daptomycin, with colony-forming units (CFUs) reductions of approximately 3–4 log10, with a slightly lower response to linezolid, which was also more strain dependent. However, considering all the parameters studied, daptomycin was considered the most effective antibiotic tested, demonstrating an excellent in vitro activity against S. epidermidis biofilm cells. In conclusion, this antibiotic can be strongly considered as an acceptable therapeutic option for S. epidermidis biofilm-associated infections and can represent a potential alternative to rifampicin in serious infections where rifampicin resistance becomes prevalent.