Homogenous photocatalytic decontamination of prion infected stainless steel and titanium surfaces

Prions are notorious for their extraordinary resistance to traditional methods of decontamination, rendering their transmission a public health risk. Iatrogenic Creutzfeldt–Jakob disease (iCJD) via contaminated surgical instruments and medical devices has been verified both experimentally and clinically. Standard methods for prion inactivation by sodium hydroxide or sodium hypochlorite have failed, in some cases, to fully remove prion infectivity, while they are often impractical for routine applications. Prion accumulation in peripheral tissues and indications of human-to-human bloodborne prion transmission, highlight the need for novel, efficient, yet user-friendly methods of prion inactivation. Here we show both in vitro and in vivo that homogenous photocatalytic oxidation, mediated by the photo-Fenton reagent, has the potential to inactivate the pathological prion isoform adsorbed on metal substrates. Photocatalytic oxidation with 224 μg mL⁻¹ Fe³⁺, 500 μg mL⁻¹ h⁻¹ H₂O₂, UV-A for 480 min lead to 100% survival in golden Syrian hamsters after intracranial implantation of stainless steel wires infected with the 263K prion strain. Interestingly, photocatalytic treatment of 263K infected titanium wires, under the same experimental conditions, prolonged the survival interval significantly, but failed to eliminate infectivity, a result that we correlate with the increased adsorption of PrP^Sc on titanium, in comparison to stainless steel. Our findings strongly indicate that our, user- and environmentally friendly protocol can be safely applied to the decontamination of prion infected stainless steel surfaces.     

Impact of the surface roughness of AISI 316L stainless steel on biofilm adhesion in a seawater-cooled tubular heat exchanger-condenser

The present study evaluated biofilm growth in AISI 316L stainless steel tubes for seawater-cooled exchanger-condensers that had four different arithmetic mean surface roughness values ranging from 0.14 μm to 1.2 μm. The results of fluid frictional resistance and heat transfer resistance regarding biofilm formation in the roughest surface showed increases of 28.2% and 19.1% respectively, compared with the smoothest surface. The biofilm thickness taken at the end of the experiment showed variations of up to 74% between the smoothest and roughest surfaces. The thermal efficiency of the heat transfer process in the tube with the roughest surface was 17.4% greater than that in the tube with the smoothest surface. The results suggest that the finish of the inner surfaces of the tubes in heat exchanger-condensers is critical for improving energy efficiency and avoiding biofilm adhesion. This may be utilised to reduce biofilm adhesion and growth in the design of heat exchanger-condensers.     

Physico-chemical and hygienic property modifications of stainless steel surfaces induced by conditioning with food and detergent

The effect of repeated conditioning procedures (25 runs), consisting of soiling (milk and meat products) and cleaning steps, on the hygienic status, physico-chemical properties and surface chemical composition of stainless steel (SS) surfaces, was investigated. Five SSs differing in grade and finish were used. Both soiling and surface cleaning/conditioning procedures resulted in a similar increase in the surface contamination with carbon, while the changes in the basic component of the surface free energy depended on the conditioning procedure. The passive film was also affected, the Fe/Cr ratio in particular. The hygienic status was also changed, especially with milk as shown by monitoring the number of residual adhering Bacillus cereus spores after contaminating the surface with spores followed by cleaning. The results show that in food environments, the presence and the nature of conditioning molecules play a major role in the hygienic status of SS surfaces.     

Effects of temperature and glucose concentration on glycogen synthesis in Ancylostoma caninum

The glycogen content of starved worms incubated in Krebs-Ringer bicarbonate, ox serum or dog serum, increased with increasing glucose concentrations. The pattern of increase in the presence and absence of dog serum, however, differed. A maximum of worm glycogen content was reached at a much lower glucose concentration when dog serum was present than when it was absent. Studies on temperature effects on worms incubated at 27 and 37°C, in the presence and absence of dog serum showed that for worms incubated in dog serum, a temperature coefficient of 3.31 was obtained. For worms incubated in Krebs-Ringer bicarbonate, the temperature coefficient was 0.88, thus showing that the uptake of glucose for glycogen synthesis was different when dog serum was absent from the incubating medium.     

Growth phase-dependent surface properties of Legionella pneumophila and their role in adhesion to stainless steel coated QCM-D sensors

Legionella pneumophila cell surface hydrophobicity and charge are important determinants of their mobility and persistence in engineered water systems (EWS). These surface properties may differ depending on the growth phase of L. pneumophila resulting in variable adhesion and persistence within EWS. We describe the growth-dependent variations in L. pneumophila cell surface hydrophobicity and surface charge using the microbial adhesion to hydrocarbon assay and microelectrophoresis, respectively, and their role in cell adhesion to stainless steel using a quartz crystal microbalance with dissipation (QCM-D) monitoring instrument. We observed a steady increase in L. pneumophila hydrophobicity during their lifecycle in culture media. Cell surfaces of stationary phase L. pneumophila were significantly more hydrophobic than their lag and midexponential counterparts. No significant changes in L. pneumophila cell surface charge were noted. Morphology of L. pneumophila remained relatively constant throughout their lifecycle. In the QCM-D study, lag and exponential phase L. pneumophila weakly adhered to stainless steel surfaces resulting in viscoelastic layers. In contrast, stationary phase bacteria were tightly and irreversibly bound to the surfaces, forming rigid layers. Our results suggest that the stationary phase of L. pneumophila would highly favour their adhesion to plumbing surfaces and persistence in EWS.     

In situ detection of bacteria involved in cathodic depolarization and stainless steel surface corrosion using microautoradiography

Aims: To examine the activity of bacteria involved in cathodic depolarization and surface corrosion on stainless steel in an in situ model system. Methods and Results: The microautoradiographic technique (MAR) was used to evaluate the activity of bacterial populations on stainless steel surfaces with a single cell resolution. Anaerobic uptake and fixation of ¹⁴C‐labelled bicarbonate occurred within corrosion sites in the absence of atmospheric hydrogen or other external electron donors, whereas it was taken up and fixed by bacteria at all other stainless steel surfaces in the presence of atmospheric hydrogen. This indicates that the bacteria utilized electrons originating from the corrosion sites due to the ongoing corrosion (cathodic depolarization). Conclusion: Under in situ conditions, bacteria were fixating ¹⁴C‐labelled bicarbonate at corrosion sites in the absence of atmospheric hydrogen. This indicates that electrons transferred to the bacteria provided energy for bicarbonate fixation due to cathodic depolarization. Significance and Impact of the Study: Application of the MAR method showed ongoing biocorrosion in the applied in situ model system and allowed in situ examination of bacterial activity on a single cell level directly on a metal surface providing information about potential corrosion mechanisms. Furthermore, application of fluorescence in situ hybridization in combination with MAR allows for identification of the active bacteria.     

Biomolecule-based antibacterial coating on a stainless steel surface: multilayer film build-up optimization and stability study

The goal of this paper was to establish the durability profile of antibacterial multilayer thin films under storage and usage conditions. Thin films were built on stainless steel (SS) by means of a layer-by-layer process alternating a negatively charged polyelectrolyte, polyacrylic acid, with a cationic antibacterial peptide, nisin. SS coupons coated with the antibacterial film were challenged under environmental and usage conditions likely to be encountered in real-world applications. The change in antibacterial activity elicited by the challenge was used as an indicator of multilayer film resistance. Antibacterial SS samples could be stored for several weeks at 4°C in ambient air and antibacterial films were resistant to dipping and mild wiping in water and neutral detergent. The multilayer coating showed some weaknesses, however, that need to be addressed.     

Inactivation of Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa and Staphylococcus aureus on stainless steel and glass surfaces by neutral electrolysed water

AIM: To ascertain the efficacy of neutral electrolysed water (NEW) in reducing Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes on glass and stainless steel surfaces. Its effectiveness for that purpose is compared with that of a sodium hypochlorite (NaClO) solution with similar pH, oxidation-reduction potential (ORP) and active chlorine content. METHODS AND RESULTS: First, the bactericidal activity of NEW was evaluated over pure cultures (8.5 log CFU ml-1) of the abovementioned strains: all of them were reduced by more than 7 log CFU ml-1 within 5 min of exposure either to NEW (63 mg l-1 active chlorine) or to NaClO solution (62 mg l-1 active chlorine). Then, stainless steel and glass surfaces were inoculated with the same strains and rinsed for 1 min in either NEW, NaClO solution or deionized water (control). In the first two cases, the populations of all the strains decreased by more than 6 log CFU 50 cm-2. No significant difference (P相似文献   

Interaction of Desulfovibrio desulfuricans biofilms with stainless steel surface and its impact on bacterial metabolism

AIMS: To study the influence of some metallic elements of stainless steel 304 (SS 304) on the development and activity of a sulfate-reducing bacterial biofilm, using as comparison a reference nonmetallic material polymethylmethacrylate (PMMA). METHODS AND RESULTS: Desulfovibrio desulfuricans biofilms were developed on SS 304 and on a reference nonmetallic material, PMMA, in a flow cell system. Steady-state biofilms were metabolically more active on SS 304 than on PMMA. Activity tests with bacteria from both biofilms at steady state also showed that the doubling time was lower for bacteria from SS 304 biofilms. The influence of chromium and nickel, elements of SS 304 composition, was also tested on a cellular suspension of Des. desulfuricans. Nickel decreased the bacterial doubling time, while chromium had no significant effect. CONCLUSIONS: The following mechanism is hypothesized: a Des. desulfuricans biofilm grown on a SS 304 surface in anaerobic conditions leads to the weakening of the metal passive layer and to the dissolution in the bulk phase of nickel ions that have a positive influence on the sulfate-reducing bacteria metabolism. This phenomenon may enhance the biocorrosion process. SIGNIFICANCE AND IMPACT OF THE STUDY: A better understanding of the interactions between metallic surfaces such as stainless steel and bacteria commonly implied in the corrosion phenomena which is primordial to fight biocorrosion.     

Characterisation of conditioning layers formed by exopolymeric substances of Pseudomonas NCIMB 2021 on surfaces of AISI 316 stainless steel

This investigation aimed to characterise conditioning layers formed on AISI 316 stainless steel by different types of extracellular polymeric substances (EPS), i.e. biofilm, planktonic and capsular exopolymers, isolated from continuous cultures of marine Pseudomonas received from the National Collection of Industrial and Marine Bacteria (strain NCIMB 2021). Colorimetric assays and gas chromatography‐mass spectrometry analysis confirmed previously obtained results based on a FTIR and SDS‐PAGE study of Pseudomonas NCIMB 2021 EPS demonstrating the presence of protein, neutral and amino sugars and uronic acids. The content and the ratio of these macromolecules differed depending on the type of EPS. X‐ray photoelectron spectroscopy revealed that conditioning layers formed upon exposure of steel to EPS solutions were chemically dissimilar. It is proposed that the observed difference in the chemistry of conditioning layers is the likely reason for reported differences in attachment of Pseudomonas cells to EPS‐conditioned steel surfaces.     

Electrochemical concepts and techniques in the study of stainless steel ennoblement

Electrochemical theory and technique used to investigate microbially influenced corrosion is discussed with a focus on methods used to demonstrate the manganic-oxide mechanism of stainless steel Ennoblement. The concept of mixed potential and its relationship to the current-voltage behavior of stainless steel is developed. This concept is used to interpret microbially induced changes in corrosion potential, polarization behavior, surface-oxide abundance, and the redox environment at submerged metal surfaces. Microelectrode, capacitance, and coulometric methods are described that can be used to discriminate electrochemical effects caused by changes in solution properties from those caused by mineral deposition at the metal surface. The variety of electrochemical, wet-chemical, microbiological, and surface analytical techniques used to demonstrate the effect of biomineralized manganese dioxide on the electrochemical behavior of stainless steel are summarized.     

Effect of laser and environmental parameters on reducing microbial contamination of stainless steel surfaces with Nd:YAG laser irradiation

AIMS: The effect of laser (pulse repetition frequency, pulse energy and exposure time) and environmental parameters (pH, NaCl concentration and wet or dry samples) of Nd:YAG laser decontamination of stainless steel inoculated with Escherichia coli, Staphylococcus aureus and Listeria monocytogenes was investigated. METHODS AND RESULTS: Stainless steel discs were inoculated with the bacterial samples and exposed to laser energy densities to about 900 J cm(-2). These inactivation curves allowed selection of laser parameters for two-level multifactorial designed experiments, the results of which allowed comparisons to be made between effects of individual and combined parameters on the laser inactivation efficiency. Escherichia coli was inactivated most effectively as a wet film with L. monocytogenes and S. aureus showing similar response. For the multifactorial experiments all laser parameters were significant and were smallest for S. aureus as a wet film. CONCLUSIONS: pH and NaCl concentration had little effect on the efficacy of laser inactivation but dry or wet states and all laser parameters were significant. SIGNIFICANCE AND IMPACT OF THE STUDY: Such systems may prove to be applicable in industrial processes where stainless steel may be contaminated with acidic solutions or salt, e.g. in the food industry with laser inactivation seeming to be independent of these parameters. Parameters have been identified that allow optimization of the treatment process.     

Comparison of fluorinated polymers against stainless steel, glass and polypropylene in microbial biofilm adherence and removal

Biofilm formation is a long-standing problem in ultrapure water and bioprocess fluid transport lines. The standard materials used in these applications (316L stainless steel, polypropylene and glass) have long been known to be good surfaces for the attachment of bacteria and other biological materials. To compare the relative tenacity of biofilms grown on materials used in manufacturing processes, a model system for biofilm attachment was constructed that approximates the conditions in industrial process systems. New fluorinated polymers were compared to the above materials by evaluating the surface area coverage of bacterial populations on materials before and after mild chemical treatment. In addition, contact angle studies compared the relative hydrophobicity of surfaces to suspensions of bacteria in growth media, and scanning electron microscopy and atomic force microscopy studies were used to characterize surface smoothness and surface defects. Biofilm adherence to polymer-based substrata was determined to be a function of both surface finish and surface chemistry. Specifically, materials that are less chemically reactive, as indicated by higher contact angle, can have rougher surface finishes and still be amenable to biofilm removal. Received 20 March 1997/ Accepted in revised form 15 July 1997     

城市扩张过程中不透水面空间格局演变及其对地表温度的影响——以乌鲁木齐市为例

伴随着城市热岛问题的日益显现,关于不透水面与地表温度的关系研究成为热点。在遥感技术的支持下,以乌鲁木齐市主城区为研究对象,从不透水面出发,分别对不透水面类型、变化强度进行研究,探讨不透水面的时空变化特征。引入景观生态学理论,分析不透水面景观类型的空间格局及规律。以反演的地表温度为基础,分析了不透水面相关变量与地表温度的关系。结论如下:(1)研究区不透水面指数主要集中在0.3—0.7之间,占总面积的90%以上;(2) 2000年以来,15.89%的区域不透水面指数连年下降,分布在主城区,20.07%的区域不透水面指数连年上升,分布在城市的郊区,增长区域的幅度主要集中在10%以下;(3)不透水面的景观类型多样性减弱,以中、高覆盖区为主,其中高覆盖区的聚集指数最高,高达87.71,不透水面类型斑块形状由复杂向规则化推移;(4)研究区地表温度,增温明显,2000年地表温度均值25.94℃,2016年地表温度的平均值高达35.51℃;(5)不透水面对地表温度影响,存在阶段性、正负相关的交替性特征,整体表现为"M"形状;(6)不透水面类型面积百分比、不透水面类型景观指数对地表温度的影响相对复杂、差异明显,不能从单一的不透水面覆盖分析对地表温度的影响。