Stainless Steel Slides Research Articles

Triboelectrification of particulate flows on surfaces: Part I — Experiments

Triboelectrification is a ubiquitous feature of dry particulate processes. It generates hazards in many industrial systems, but is exploited in several other important applications, including electrophotographic toner charging and triboelectric separation. Unfortunately, the charging of continuous particulate flows during interaction with solid surfaces is poorly understood, and design of devices to maximise or minimize triboelectrification is usually qualitative or based on trial and error. This paper presents the results of an experimental case study of the relationship between the accumulated charge and the mechanical attributes of a particulate flow, including contact time, velocity, and the mode of contact. Silica particles of ∼ 1 mm diameter and a stainless steel slide tribocharger were used for this case study.

Effect of pipe material and low level disinfectants on biofilm development in a simulated drinking water distribution system

The efficiency of chlorine and chloramines disinfection on biofilm development in a simulated drinking water distribution system was investigated by using heterotrophic bacterial spread plate technique. The experiments were carried out with four annular reactors (ARs) with stainless steel (SS) or copper (Cu) material slides. The results showed that there were fewer bacteria attached to Cu slides without a disinfectant compared with those attached to SS slides. When the water was disinfected with chloramines, the heterotrophic plate counts (HPCs) on the biofilm attached to the Cu slides were significantly lower (by 3.46 log CFU/cm2) than those attached to the SS slides. Likewise, the biofilm HPC numbers on the Cu slides were slightly lower (by 1.19 log CFU/cm2) than those on the SS slides disinfected with chlorine. In a quasi-steady state, the HPC levels on Cu slides can be reduced to 3.0 log CFU/cm2 with chlorine and to about 0.9 log CFU/cm2 with chloramines. The addition of chloramines resulted in a more efficient reduction of biofilm heterotrophic bacteria than did chlorine. We concluded that the chlorine and chloramines levels usually employed in water distribution system were not sufficient to prevent the growth and development of microbial biofilm. The combination of copper pipe slides and chloramines as the disinfectant was the most efficient combination to bring about diminished bacterial levels.

In Vitro Apatite-Forming Ability of Titania Films Depends on Their Substrates

Titania films were coated by means of sol-gel method on various substrates such as titanium, titanium alloy, silicon wafer, stainless-steel, alumina, and glass slide where they coded as C5Ti, C5Ti6Al4V, C5Si, C5SUS, C5Al2O3 and C5GS, respectively. Their in vitro apatite-forming ability was examined with the Kokubo’s simulated body fluid (SBF; pH 7.4, 36.5°C). C5Ti, C5Ti6Al4V and C5Si deposited apatite particles on their surface within 7 days, whereas, C5SUS, C5Al2O3 and C5GS did not. These results implied that the in vitro apatite-forming ability of the titania films indirectly depended on the chemical or physical properties of the substrates.

Evaluation of hydrogen peroxide vapour as a method for the decontamination of surfaces contaminated with Clostridium botulinum spores

The aim of this study was to evaluate the efficacy of hydrogen peroxide vapour (HPV) against spores of Clostridium botulinum, for use as a method for decontaminating environments where this pathogen has been handled. Spores were dried onto stainless steel slides and exposed to HPV in a sealed glovebox enclosure, transferred to a quenching agent at timed intervals during the exposure period, before survivors were cultured and enumerated. D-values were calculated from graphs of log 10 survivors plotted against time and were found to range from 1.41 to 4.38 min. HPV was found to be effective at deactivating spores of toxigenic Cl. botulinum, non-toxigenic Clostridium spp. and Geobacillus stearothermophilus dried onto stainless steel surfaces. HPV could be used to decontaminate cabinets and rooms where Cl. botulinum has been handled. The cycle parameters should be based on studies carried out with relevant spores of this organism, rather than based on inactivation data for G. stearothermophilus spores, which have been used in the past as a standard biological challenge for disinfection and sterilisation procedures. HPV could provide an attractive alternative to other decontamination methods, as it was rapid, residue-free and did not give rise to the health and safety concerns associated with other gaseous decontamination systems.

Action of a cationic surfactant on the activity and removal of bacterial biofilms formed under different flow regimes

The action of the cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated to control biofilms (aged 7d) formed by Pseudomonas fluorescens on stainless-steel slides, using flow cells reactors, under turbulent and laminar flow. The effect of CTAB was also investigated using planktonic cells in the presence and absence of BSA, by measuring the cellular respiratory activity and the ATP released. The action of CTAB on biofilms was assessed by means of cellular respiratory activity and variation of biofilm mass, immediately and 3, 7 and 12h after the application of CTAB. The physical stability of the biofilm was also assessed using a rotating device, where the effect of the surfactant on the biofilm stability was evaluated through the variation of the mass remaining on the surface. CTAB significantly reduced the activity of the planktonic cells probably due to the rupture of the cells. This effect was significantly reduced in the presence of BSA. Planktonic cells were more easily inactivated than bacteria in biofilms. Biofilms formed under laminar flow were more susceptible than those formed under turbulent flow, but in both cases total inactivation was not achieved. Biofilm recovery was observed, in terms of respiratory activity, in almost all the cases studied. CTAB application by itself did not promote the detachment of biofilms. The physical stability tests showed that the synergistic action of the surfactant and the application of high shear stress to the biofilm increase its detachment.

Evaluation of chlorines' impact on biofilms on scratched stainless steel surfaces

Biofilms of a wild type Escherichia coli were grown on 316 stainless steel slides in a nutrient starved medium. The stainless steel surfaces were either polished to a smooth finish or scribed. The scribes consisted of lines and crosses. Biofilm samples were taken after 3, 6, 12, 24 and 48 h of growth. After sampling, the slides were soaked in deionized water or 50 or 200 ppm free chlorine prior to vital staining. Images were captured and the areas of viable and total biofilm were estimated. The individual biofilm patches, circularities, total percentage coverage, and viability percentage coverage were analyzed. The biofilms tended to increase in size between 6 and 24 h. A 3–6 h old biofilm on a polished stainless steel surface detached when 200 ppm sodium hypochlorite was applied. When grown in scribes, the circularity decreased up to 24 h, but thereafter increased. As the film grew older, it detached with or without a sodium hypochlorite treatment from the part of the surface that was polished, but remained in the neighborhood of the scribe. Based on the results, we recommend sanitizing at intervals of less than 12 h for this and similar strains of bacteria and protection of stainless steel surfaces to minimize scratching.

Effect of Different Concentrations of Ortho-phthalaldehyde on Biofilms Formed by Pseudomonas fluorescens Under Different Flow Conditions

The effectiveness of different concentrations of ortho-phthalaldehyde (OPA) in controlling biofilms of Pseudomonas fluorescens formed on stainless steel slides, using flow cell reactors under laminar and turbulent flow, was investigated by determining the variation in mass and respiratory activity. The physical stability of the biofilm with and without exposure to OPA was studied in a rotating device as variation in the mass of the biofilm on the surface after exposure to different rotation velocities. The activity of OPA against bacterial suspended cultures was evaluated in the presence and absence of bovine serum albumin (BSA) in order to evaluate the interference of proteins on the activity of the biocide. The results showed that biofilms formed under different flow conditions had different properties and reacted differently after biocide application. Biofilms formed under laminar flow were more easily inactivated than those formed under turbulent conditions. However, OPA did not promote the detachment of biofilms from the surface. The exposure of biofilms to different shear stress conditions after OPA treatment enhanced removal from the surface, indicating that OPA may weaken the biofilm matrix. The biocide was more effective on suspended cells than on cells grown in biofilms. This fact may be explained by the reaction of the biocide with proteins of the polymeric matrix of the biofilm as suggested by the significant reduction of biocide action on suspended cells in the presence of BSA.

Monitoring the effects of biocide treatment of Pseudomonas fluorescens biofilms formed under different flow regimes

The effectiveness of glutaraldehyde (GTA), a very common biocide for controlling biofilms formed by Pseudomonas fluorescens on stainless steel slides, in laminar and turbulent flow, was investigated. Tests were performed using a concentration of biocide of 200 mg L(-1) and a range of exposure times. The GTA action was assessed by means of activity tests and dry weight of the biofilms. The physical stability of the biofilm without biocide application and after exposure to GTA for different periods of time was also studied and evaluated through the variation of the mass of the deposit after submission to different rotation velocities. The results showed that, in all the situations studied, biofilms were not controlled after the treatment with biocide, since they remained on the metal surface and were still active. The results also demonstrated that the physical stability of the biofilms increased with biocide application.

Effect of Bacteriocins Pediocin PD-1, Plantaricin 423, and Nisin on Biofilms ofOenococcus oenion a Stainless Steel Surface

The effect of pediocin PD-1, plantaricin 423, and nisin was tested against established biofilms formed by a commercial starter culture of <i>Oenococcus oeni</i> on stainless steel slides and planktonic (free-living) cells. The percentage viable and nonviable cells were determined by using a viability probe and an epifluorescence microscope with image analysis. Pediocin PD-1 (3000 AU/mL) removed all cells in a biofilm of <i>O. oeni</i> that formed in acidic grape medium after five hours. Plantaricin 423 (3000 AU/mL) and nisin (3000 AU/mL) killed all viable cells in the biofilm. However, approximately 42 and 49% of the original cells on the stainless steel surface remained attached, with the majority staining nonviable when treated with the latter two peptides, respectively. In a modified Chardonnay must, all cells (viable and nonviable) of <i>O. oeni</i> in the biofilm were removed after one hour when treated with pediocin PD-1 (3000 AU/mL). In similar experiments, treatment with plantaricin 423 and nisin resulted in undetectable numbers of viable cells in the biofilm. Approximately 36 and 43% of the original cells on the stainless steel surface remained attached, with the majority staining nonviable after five hours of treatment with the latter two peptides, respectively. After five hours of treatment with the respective antimicrobial peptides (3000 AU/mL), the planktonic cell numbers of <i>O. oeni</i> decreased from 1.3 x 10¹⁰ cfu/mL to undetectable numbers of viable cells in acidic grape medium. The same experiment performed in modified Chardonnay must yielded no detectable cells of <i>O. oeni.</i>

Biofilm penetration and disinfection efficacy of alkaline hypochlorite and chlorosulfamates.

The purpose of this study was to compare the efficacy, in terms of bacterial biofilm penetration and killing, of alkaline hypochlorite (pH 11) and chlorosulfamate (pH 5.5) formulations. Two species biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown by flowing a dilute medium over inclined stainless steel slides for 6 d. Microelectrode technology was used to measure concentration profiles of active chlorine species within the biofilms in response to treatment at a concentration of 1000 mg total chlorine l(-1). Chlorosulfamate formulations penetrated biofilms faster than did hypochlorite. The mean penetration time into approximately 1 mm-thick biofilms for chlorosulfamate (6 min) was only one-eighth as long as for the same concentration of hypochlorite (48 min). Chloride ion penetrated biofilms rapidly (5 min) with an effective diffusion coefficient in the biofilm that was close to the value for chloride in water. Biofilm bacteria were highly resistant to killing by both antimicrobial agents. Biofilms challenged with 1000 mg l(-1) alkaline hypochlorite or chlorosulfamate for 1 h experienced 0.85 and 1.3 log reductions in viable cell numbers, respectively. Similar treatment reduced viable numbers of planktonic bacteria to non-detectable levels (log reduction greater than 6) within 60 s. Aged planktonic and resuspended laboratory biofilm bacteria were just as susceptible to hypochlorite as fresh planktonic cells. Chlorosulfamate transport into biofilm was not retarded whereas hypochlorite transport clearly was retarded. Superior penetration by chlorosulfamate was hypothesized to be due to its lower capacity for reaction with constituents of the biofilm. Poor biofilm killing despite direct measurement of effective physical penetration of the antimicrobial agent into the biofilm demonstrates that bacteria in the biofilm are protected by some mechanism other than simple physical shielding by the biofilm matrix. This study lends support to the theory that the penetration of antimicrobial agents into microbial biofilms is controlled by the reactivity of the antimicrobial agent with biofilm components. The finding that chlorine-based biocides can penetrate, but fail to kill, bacteria in biofilms should motivate the search for other mechanisms of protection from killing by antimicrobial agents in biofilms.

Effects of the interactions between glutaraldehyde and the polymeric matrix on the efficacy of the biocide against pseudomonas fluorescens biofilms

Glutaraldehyde (GTA) is a widely used biocide due to its high effectiveness. The experimental work reported here was carried out to assess the effectiveness of GTA in controlling biofilms formed by Pseudomonas fluorescens on stainless steel slides, and to compare efficacy against both planktonic and sessile micro‐rganisms. The tests were performed using two concentrations of GTA (50 and 100mg 1‐1), biofilms of two ages (7 and 15 d), several pH values (5,7 and 9) and a range of exposure times (from 0 (control) to 1,3,7 and 24 h). The action of GTA on biofilm and planktonic populations was assessed by means of activity tests, zeta potential, and the wet weight of the biofilms. Biofilms were not completely removed after treatment with GTA in any of the conditions studied. The higher GTA concentration was more effective in reducing the bacterial activity of the biofilm. The biocide proved to be more effective for longer exposure times. GTA showed good antimicrobial activity against P. fluorescens in suspension, with higher activity at pH 9. The findings of this study suggest that when GTA is used to control biofilms, it reacts with one of the components of the matrix, the proteins, thereby reducing its antimicrobial action.

Determination of the van der Waals, electron donor and electron acceptor surface tension components of static Gram-positive microbial biofilms

A large number of studies have shown the influence of the physico-chemical properties of a surface on microbial adhesion phenomenon. In this study, we considered that the presence of a bacterial biofilm may be regarded as a “conditioning film” that may modify the physico-chemical characteristics of the support, and thus the adhesion capability of planktonic micro-organisms coming into contact with this substratum. In this context, we adapted a protocol for biofilm formation that allows, under our experimental conditions, contact angle measurements, the reference method to determine the energetic surface properties of a substratum. This made it possible to determine the van der Waals, electron acceptor and electron donor properties of static biofilms grown at 25°C on stainless-steel slides with six Gram-positive bacteria isolated in dairy plants. A variance analysis indicated significant effects ( P<0.05) of the bacterial strains and of the physiological state of the micro-organisms (planktonic or sessile) on the contact angles. To link the energetic properties of the six biofilms with direct adhesion experiments, we measured the affinity of fluorescent carboxylate-modified polystyrene beads for the different biofilm surfaces. The results correlated best with the electron-acceptor components of the biofilm surface energies, stressing the importance of Lewis acid–base interactions in adhesion mechanisms.

12] Methods used to assess biofouling of material used in distribution and domestic water systems

Publisher Summary The inner surfaces of water distribution pipes and domestic plumbing pipe systems are potential sites for biofilm development. Microbial cells found as part of a biofilm contribute to the contamination of the water bulk phase, possibly due to sloughing as a result of water shear. This chapter discusses how different grades and different surface finishes of stainless steel could affect the microbiology of biofilms at different water flow rates within potable water systems. A mains water simulation system was designed to investigate the effects of flow rate on the microbiology of biofilms, using stainless steel grades 304 and 316 as the metal substratum. The chapter also discusses methods used to assess biofouling of material used in distribution and domestic water systems. All stainless steel slide surfaces used in the mains water simulation system are cleaned in 70% alcohol for a period of 1 hour prior to use. The whole simulation system is also sterilized with peracetic acid according to recommended procedures supplied by the manufacturers. Biofilms are removed from the slides, with the use of a sterile scalpel, and suspended in 10 ml double distilled water before freeze drying and being weighed.

Multi-exponentially Photoelectric Response of Bacteriorhodopsin

A thin oriented bacteriorhodopsin (bR) film is deposited on a stainlesssteel slide by the use of the electrophoretic sedimentation method. Ajunction is made with electrolyte gels having a counterelectrode toconstruct a bR-based photoelectric detector. The photoelectric responsesignal to a 10 ns laser pulse is measured. A theory on the photoelectrickinetics of bR is developed based on the concept of the charge displacementcurrent and the bR photocycle rate equations. Comparison between thetheoretical and experimental results proves that the bR photoelectricresponse to a short laser pulse is a multi-exponential process. Thedecay time constants and amplitudes of each exponential component areobtained by data fitting. PACS: 85. 60. Bt, 87. 15. Aa, 85. 65. +h

Comment: Reproducibility of spectra and threshold fluence in matrix-assisted laser desorption/ionisation (MALDI) of polymers

We represent that roughing of the stainless steel substratum by sandblasting (SB) and “fast evaporation” deposition of 2,5-dihydroxybenzoic acid (2,5-DHB) leads to more consistent and repeatable results. It was shown that sandblasting (SB) gave representative results, which had higher precision than the non-sandblasted (NSB) substrate on the stainless steel slide. The SB samples were more reproducible, as seen by theī / σ (higher value) as compared to the NSB (lowerī / σ vales). The values range from 13.46 (SB) to 1.34 (NSB). It was also shown, that the SB samples were more reproducible shot per shot. This was due to the sandblasted roughing of the slide, which gave more surface area over which the matrix could distributes itself more evenly. This treatment also gave lower thresholds. The threshold of the PEG was lower on the SB region (P100) compared to that of the NSB region (P120) for the 2,5-DHB-PEG-NaCl system.

An endoluminal brush to detect the infected central venous catheter in situ: a pilot study.

Catheter related sepsis is a potentially life threatening infection caused by an indwelling intravenous catheter, with the same organism cultured from peripheral blood and from the removed catheter. If such sepsis is suspected the catheter is usually removed, although subsequent bacterial culture shows most catheters to be sterile.1 2 We evaluated a new brush (Endoluminal, FAS Medical, London) for detecting infection in the lumen of a central venous catheter. The brush has nylon bristles wound tightly around the distal end of a stainless steel wire and slides along the lumen of the catheter to its distal (inner) end. It is then removed for culture. The technique is based on the principle that bacteria collect on the fibrin sleeve on the catheter's inner surface; fibrin thus becomes enmeshed in the brush's bristles. We studied …

Effects of ultrasonic treatment on the efficacy of gentamicin against established Pseudomonas aeruginosa biofilms

The effect of simultaneous ultrasonic treatment on the efficacy of gentamicin against planktonic and established biofilm cells of Pseudomonas aeruginosa was investigated. Planktonic cells were treated with 6 or 12 μg ml −1 of gentamicin for 4 h with ultrasonic treatment at three levels of power density (0.2, 2 and 15 mW cm −2). Biofilm cells grown on stainless steel slides in a continuous flow reactor were treated with 30 μg ml −1 of gentamicin and ultrasound. Ultrasound itself at these power levels did not cause cell killing or lysis in planktonic and biofilm cultures. Concentrations of 6 and 12 mg ml −1 gentamicin led to 2.65- and 2.75-log reductions of the surviving fraction in planktonic cultures in the absence of ultrasound. The addition of ultrasound did not show further reduction compared with those without ultrasonication. Gentamicin (30 μg ml −1) caused variable killing in biofilms which ranged from 0.83- to 2.86-log reductions of the surviving fraction without ultrasonication. Gentamicin efficacy measured by the surviving fraction was improved by 0.28-, 1.12- and 0.58-log when coupled with 0.2, 2 and 15 mW cm −2 ultrasonic treatments, respectively. Experimental results indicated that ultrasound modestly improved the efficacy of gentamicin against established P. aeruginosa biofilms.

Biofilm parameters influencing biocide efficacy

The influence of biofilm areal cell density, species composition, and the presence of abiotic particles on the disinfection and removal of bacterial biofilms by monochloramine was investigated. Mono- and binary population biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown on stainless-steel slides in a continuous flow annular reactor. Biofilms were treated in the reactor with a pulse/step dose of 4 mg/L monochloramine for 2 h. Biofilm samples were disaggregated and assayed for colony formation on R2A agar and for total cell numbers by acridine orange direct counts. These data were used to determine apparent first order rate coefficients for the processes of disinfection and detachment. Disinfection rate coefficients exceeded detachment rate coefficients by as much as an order of magnitude and the two coefficients were poorly correlated (r = 0.272). The overall decay rate coefficient (disinfection plus detachment) depended strongly on the initial biofilm areal cell density. It displayed a parabolic dependence on cell density with a maximum near 10(8) cfu/cm(2). This result points to multiple factors influencing biofilm susceptibility to antimicrobial challenge. Decay rates of K. pneumoniae measured in binary population biofilms were comparable with those measured in monopopulation biofilms (p = 0.61). P. aeruginosa decayed more slowly in biofilm dominated by K. pneumoniae (p = 0.028), indicating some interaction between species. The presence of kaolin and calcium carbonate particles in the biofilm reduced disinfection efficacy.

The ‘Allan Johnson’ voice prosthesis. A modification of the Bivona voice prosthesis for immediate post-fitting aphonia after secondary tracheo—oesophageal puncture

The combination of a narrow oesophageal lumen and a hypertonic pharyngo-oesophageal (P-E) segment following laryngectomy and secondary tracheo-oesophageal puncture (TEP) can cause obstruction of a voice prosthesis and consequently prevent phonation. The 'Allan Johnson' modification of the Bivona voice prosthesis incorporates a stainless steel slide and has been successfully used to remedy such a circumstance.

Effects of various metal substrata on accumulation ofPseudomonas aeruginosabiofilms and the efficacy of monochloramine as a biocide

Monochloramine at 4 mg·l−1 was used to treat biofilms of Pseudomonas aeruginosa grown in annular reactors on various metal substrata, including stainless steel, mild steel and copper. Disinfection of in situ biofilms was most efficient on the stainless steel slides. The treatment reduced viable cells in the biofilm on the stainless steel slides by more than 4 orders of magnitude after 60 min, while the same treatment reduced viable cells in the biofilms on the other slides (mild steel and copper) by only 2 orders of magnitude. Mild steel corrosion products retarded the disinfection of homogenized biofilm cells. The composition of steady state biofilms on the various substrata (before biocide treatment) differed. Biofilm on stainless steel slides had more viable cells but less extracellular polymeric substance (EPS). Biofilms on mild steel and copper slides had fewer viable cells but more EPS. Almost 95% of total cells in the biofilm on the copper slides were dead cells. The lower efficacy of disinfection ...