Multiple imaging techniques demonstrate the manipulation of surfaces to reduce bacterial contamination and corrosion

Antibacterial Effect of Stainless Steel Surfaces Treated with a Nanotechnological Coating Approved for Food Contact

Stainless steel, widely present in the food industry, is frequently exposed to bacterial colonization with possible consequences on consumers' health. 288 stainless steel disks with different roughness (0.25, 0.5 and 1 μm) were challenged with four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive bacteria (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) and underwent three different sanitizing treatments (UVC, alcohol 70% v/v and Gold lotion). Moreover, the same procedure was carried out onto the same surfaces after a nanotechnological surface coating (nanoXHAM^® D). A significant bactericidal effect was exerted by all of the sanitizing treatments against all bacterial strains regardless of roughness and surface coating. The nanoXHAM^® D coating itself induced an overall bactericidal effect as well as in synergy with all sanitizing treatments regardless of roughness. Stainless steel surface roughness is poorly correlated with bacterial adhesion and only sanitizing treatments can exert significant bactericidal effects. Most of sanitizing treatments are toxic and corrosive causing the onset of crevices that are able to facilitate bacterial nesting and growth. This nanotechnological coating can reduce surface adhesion with consequent reduction of bacterial adhesion, nesting, and growth.

Electrochemical Polishing of Austenitic Stainless Steels

Improvement of the corrosion resistance capability, surface roughness, shining of stainless-steel surface elements after electrochemical polishing (EP) is one of the most important process characteristics. In this paper, the mechanism, obtained parameters, and results were studied on electropolishing of stainless-steel samples based on the review of the literature. The effects of the EP process parameters, especially current density, temperature, time, and the baths used were presented and compared among different studies. The samples made of stainless steel presented in the articles were analysed in terms of, among other things, surface roughness, resistance to corrosion, microhardness, and chemical composition. All results showed that the EP process greatly improved the analysed properties of the stainless-steel surface elements.

Bioremediation of chromium by novel strains Enterobacter aerogenes T2 and Acinetobacter sp. PD 12 S2

PURPOSE

This study had an objective to identify the most potent chromium-resistant bacteria isolated from tannery effluent and apply them for bioremediation of chromium in tannery effluents.

METHODS

Two such strains (previously characterized and identified by us)--Enterobacter aerogenes (NCBI GenBank USA Accession no. GU265554) and Acinetobacter sp. PD 12 (NCBI GenBank USA Accession no. GU084179)--showed powerful chromium resistivity and bioremediation capabilities among many stains isolated from tannery waste. Parameters such as pH, concentration of hexavalent chromium or Cr (VI), and inoculum volume were varied to observe optimum bioconversion and bioaccumulation of Cr (VI) when the said strains were grown in M9 minimal salt media. E. aerogenes was used to remediate chromium from tannery effluents in a laboratory level experiment.

RESULTS

Observation by Scanning Electron Microscope and chromium peak in Energy Dispersive X-ray Spectroscopic microanalysis revealed that E. aerogenes helped remediate a moderate amount of Cr (VI) (8-16 mg L(-1)) over a wide range of pH values at 35-37°C (within 26.05 h). High inoculum percentage of Acinetobacter sp. PD 12 also enabled bioremediation of 8-16 mg L(-1) of Cr (VI) over a wide range of temperature (25-37°C), mainly at pH 7 (within 63.28 h). The experiment with real tannery effluent gave very encouraging results.

CONCLUSION

The strain E. aerogenes can be used in bioremediation of Cr (VI) since it could work in actual environmental conditions with extraordinarily high capacity.

Initial colloid deposition on bare and zeolite-coated stainless steel and aluminum: influence of surface roughness

The impact of surface roughness of bare and zeolite ZSM-5 coated stainless steel and aluminum alloy on colloid deposition has been investigated using a parallel plate flow chamber system in an aqueous environment. The metals were systematically polished to alter the surface roughness from nanoscale to microscale, with the subsequent surface roughness of both the bare and coated surfaces varying from 11.2 to 706 nm. The stainless steel and aluminum alloy surfaces are extensively characterized, both as bare and as coated surfaces. Experimental results suggest that ZSM-5 coating and surface roughness have a pronounced impact on the kinetics of the colloid deposition. The ZSM-5 coating reduced colloid adhesion compared to the corresponding bare metal surface. In general, the greater surface roughness of like samples resulted in higher colloid deposition. Primarily, this is due to greater surface roughness inducing less reduction in the attractive interactions occurring between colloids and collector surfaces. This effect was sensitive to ionic strength and was found to be more pronounced at lower ionic strength conditions. For the most electrostatically unfavorable scenario (ZSM-5 coatings in 1 mM KNO(3)), the enhanced deposition may also be attributed to inherent surface charge heterogeneity of ZSM-5 coatings due to aluminum in the crystalline structure. The two exceptions are ZSM-5 coated mirror-polished stainless steel and the unpolished aluminum surfaces, which are rougher than the other two samples of the same metal type but result in the least deposition. The reasons for these observations are discussed, as well as the effect of surface charge and hydrophobicity on the adhesion. The relative importance of surface roughness versus contributions of electrostatic interactions and hydrophobicity to the colloid deposition is also discussed.

Colorimetric assay for biofilms in wet processing conditions

Controlling bacterial biofilms is necessary for food safety and industrial processing in clean room environments. Our goal was to develop a method to quantitatively measure biofilm produced by pathogens under wet poultry production and processing conditions. Stainless steel and glass coupons were incubated in aqueous media containing reduced nutrients and exposed to Listeria monocytogenes under static temperature and humidity conditions. Samples were measured separately by biofilm assay and viable cell density, and then confirmed by spectrophotometry and microscopy. The biofilm assay resulted in different t groupings from the cell density. The mean from the biofilm assay was 0.50, and the error% was 0.595. The mean of the log10 density (cfu/cm2) was 5.90, and the standard deviation ranged from 0.127 to 0.438 on 24 coupons. The typical sequence of biofilm development, followed by microscopy of biofilm grown on glass coupons, exhibited a change from dispersed single cells to an all-over pattern of clumps with few dispersed cells. L. monocytogenes formed biofilms on all of the substrata tested. Bacterial counts from planktonic cultures at 24, 48, 72, and 144 h confirmed that L. monocytogenes remained viable throughout the experiment and reached equilibrium between 6 and 24 h. The cell density log10/ml was 8.01, 8.03, 7.69, and 6.66, respectively; and the standard deviation ranged from 0.156 to 0.394. The data will be used to grow stable biofilms of Listeria spp. collected from the food processing environment for further study. This is the first use of the crystal violet assay for measurement of bacterial biofilms on stainless steel under these conditions. The methods tested are applicable to other bacteria and substrata.

Automating a 96-well microtitre plate model for Staphylococcus aureus biofilms: an approach to screening of natural antimicrobial compounds

The purpose of this study was to establish and automate an assay to be used for screening novel antimicrobial agents against biofilm-forming Staphylococcus aureus bacteria. The selected assay was based on crystal violet staining, which is a well used method for staining bacterial biofilms. The method was first optimised manually, antibiotic susceptibility was established and biofilm formation in plates was confirmed using atomic force microscopy. Automation of the assay was done using a Thermo Scientific Multidrop((R)) Combi dispenser and Biomek((R)) 3000 liquid handling workstation. A detailed comparison of the performance between the manual and the automated method was made in terms of screening window coefficient as well as other statistical parameters and repeatability measurements, such as plate-to-plate and day-to-day variability. Automated screening of an in-house library of natural products gave the same positive hits as previously reported, therefore the developed assay can be regarded as a reliable screening tool.

Effect of surface roughness and stainless steel finish on Listeria monocytogenes attachment and biofilm formation

The purpose of this study was to evaluate the effect of surface roughness (Ra) and finish of mechanically polished stainless steel (Ra = 0.26 +/- 0.05, 0.49 +/- 0.10, and 0.69 +/- 0.05 microm) and electropolished stainless steel (Ra = 0.16 +/- 0.06, 0.40 +/- 0.003, and 0.67 +/- 0.02 microm) on Listeria adhesion and biofilm formation. A four-strain cocktail of Listeria monocytogenes was used. Each strain (0.1%) was added to 200 ml of tryptic soy broth (TSB), and coupons were inserted to the mixture for 5 min. For biofilm formation, coupons with adhesive cells were incubated in 1:20 diluted TSB at 32 degrees C for 48 h. The experiment was performed by a randomized block design. Our results show that the level of Listeria present after 48 h of incubation (mean = 7 log CFU/cm2) was significantly higher than after 5 min (mean = 6.0 log CFU/cm2) (P < 0.01). No differences in initial adhesion were seen in mechanically finished (mean = 6.7 log CFU/cm2) when compared with electropolished stainless steel (mean = 6.7 log CFU/cm2) (P > 0.05). Listeria initial adhesion (values ranged from 5.9 to 6.1 log CFU/cm2) or biofilm formation (values ranged from 6.9 to 7.2 log CFU/cm2) was not significantly correlated with Ra values (P > 0.05). Image analysis with an atomic force microscope showed that bacteria did not colonize the complete surface after 48 h but were individual cells or grouped in microcolonies that ranged from 5 to 10 microm in diameter and one to three cell layers in thickness. Exopolymeric substances were observed to be associated with the colonies. According to our results, electropolishing stainless steel does not pose a significant advantage for food sanitation over mechanically finished stainless steel.

Effects of inoculation level, material hydration, and stainless steel surface roughness on the transfer of listeria monocytogenes from inoculated bologna to stainless steel and high-density polyethylene

The influence of inoculation level, material hydration, and stainless steel surface roughness on the transfer of Listeria monocytogenes from inoculated bologna to processing surfaces (stainless steel and polyethylene) was assessed. Slices of bologna (14 g) were inoculated with Listeria at different levels, from 10(5) to 10(9) CFU/cm2. Transfer experiments were done at a constant contact time (30 s) and pressure (45 kPa) with a universal testing machine. After transfer, cells that had been transferred to sterile stainless steel and polyethylene were removed and counted, and the efficiency of transfer (EOT) was calculated. As the inoculation level increased from 10(5) to 10(9) CFU/cm(2), the absolute level of transfer increased in a similar fashion. By calculating EOTs, the data were normalized, and the initial inoculation level had no effect on the transfer (P > 0.05). The influence of hydration level on stainless steel, high-density polyethylene, and material type was investigated, and the EOTs ranged from 0.1 to 1 under all the conditions tested. Our results show that transfers to wetted processing surfaces (mean EOT = 0.43) were no different from dried processing surfaces (mean EOT = 0.35) (P > 0.05). Material type was shown to be a significant factor, with greater numbers of Listeria transferring from bologna to stainless steel (mean EOT = 0.49) than from bologna to polyethylene (mean EOT = 0.28) (P < 0.01). Stainless steel with three different surface roughness (Ra) values of <0.8 microm (target Ra = 0.25, 0.50, and 0.75 Vmicrom) and two different finishes (mechanically polished versus mechanically polished and further electropolished) was used to evaluate its effect on the transfer. The surface roughness and finish on the stainless steel did not have any effect on the transfer of Listeria (P > 0.05). Our results showed that when evaluating the transfer of Listeria, the use of EOTs rather than the absolute transfer values is essential to allow comparisons of transfer conditions or comparisons between research groups.

Material properties of and tissue reaction to the Slocum TPLO plate

OBJECTIVE

To determine the material properties of Slocum TPLO plates and assess the soft tissue reaction adjacent to these plates in dogs that had undergone tibial plateau leveling osteotomy (TPLO).

SAMPLE POPULATION

3 new TPLO plates, 8 retrieved TPLO plates, and 1 new Synthes dynamic compression plate.

PROCEDURES

Metallurgic analyses were performed. Tissue samples were obtained from areas adjacent to retrieved plates and submitted for histologic examination.

RESULTS

All of the TPLO plates had a 2-phase microstructure consisting of austenite and ferrite in various amounts. Residua, inclusions, and cavities were seen during microscopic examination of the plate surface. The major differences between new and retrieved TPLO plates were the presence of small gaps separating many inclusions from the surrounding matrix and the presence of various-sized pits on the surface of the retrieved plates. The dynamic compression plate had a nearly pure austenitic structure and was largely free from residua, inclusions, and cavities. Histologic examination of tissue samples obtained from areas adjacent to retrieved TPLO plates revealed intra- and extracellular particulate debris. Two types of particles (one consisting of chromium, nickel, molybdenum, and iron and the other consisting of aluminum and silicon) were seen.

CONCLUSIONS AND CLINICAL RELEVANCE

Results determined that new and retrieved TPLO plates were manufactured from 316L stainless steel and produced by a casting process, but not all plates met specifications for chemical composition of cast surgical implants (American Society for Testing Materials standard F745); tissues surrounding retrieved plates had evidence of adverse reactions, probably as a result of plate corrosion.

Effect of cast molded rifampicin/silicone onstaphylococcus epidermidis biofilm formation

Infection is one of the most common catheter-related complications, especially in shunt systems used to treat hydrocephalus. Staphylococcus epidermidis is directly related to biomaterial infections owing to its ability to form a biofilm on implanted materials. In this study, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the effect of the antibiotic rifampicin on the colonization and growth of S. epidermidis 35984 on the surface of silicone. A cast molding method was used to load rifampicin into the silicone precursor before it was cured. Bacteria with a diameter of 800-1000 nm and height of 200-500 nm were found to be embedded in the biofilm. Compact multilayer biofilm structures were found on silicone surfaces upon incubation for 4 and 24 h. On the other hand, sparser biofilm structures were observed on rifampicin-loaded surfaces after incubation for the same duration. Deformation of bacteria was observed by AFM. Moreover, different bacterial colony structures on the surfaces of silicone and rifampicin-loaded silicone were observed by AFM and SEM.

The Pseudomonas aeruginosa type IV pilin receptor binding domain functions as an adhesin for both biotic and abiotic surfaces

Pseudomonas aeruginosa readily binds to stainless steel and other abiotic surfaces, causing major problems in both the medical and food industries. In this study, we show that P. aeruginosa binds to abiotic surfaces in a concentration-dependent, saturable manner during the initial stages of biofilm formation. P. aeruginosa type IV pili mediate binding to stainless steel as a pilus-deficient strain does not bind to steel, purified type IV pili bound in a concentration-dependent, saturable manner, and purified pili competitively inhibited whole cell binding. PAK pili can also bind polystyrene and polyvinylchloride in a concentration-dependant and saturable manner. As an antibody specific for the C-terminal pilin receptor binding domain inhibited adherence to abiotic surfaces, the role of the C-terminal receptor binding domain in mediating binding to steel surfaces was examined. A synthetic peptide of the PAK pilin epithelial cell receptor binding domain [PAK(128-144)ox] bound directly to steel with high affinity. The interaction of pili with steel was specifically inhibited by this peptide with an apparent Ki of approximately 0.2 nM and effectively inhibited the binding of viable homologous and heterologous P. aeruginosa strains to steel with an apparent Ki of approximately 4 nM. A single point mutation (K130I) in the PAO receptor binding domain was observed to abolish binding to stainless steel while binding to human buccal epithelial cells was enhanced. Therefore, the C-terminal receptor binding domain appears to have evolved for binding a variety of surfaces.