Stainless Steel Slides Research Articles

Investigations of TiC and SiC films synthesized by DC magnetron sputtering and thermal annealing

In this research article, two-dimensional thin films of titanium, hierarchical titanium-carbon, titanium carbide, hierarchical silicon-carbon, and silicon carbide films were synthesized on the plates of AISI 304 stainless steel and glass slides, individually, using DC magnetron sputtering techniques. During the sputtering process, the creation of stable plasma was affected by the vacuum level, DC potential, plasma current, and Argon gas. The results showed that the coatings of titanium, titanium-carbon, and titanium carbide modified the optical properties of stainless steel. Additionally, titanium carbide coatings displayed a shiny gold appearance with a hardness of 1500 HV. Besides this, X-ray diffraction studies revealed a hexagonal Ti in the metallic films and C60, and diamond-like structures dispersed on its surface after the carbon coating. The spherical particulates of Ti and C60/diamond-like carbon particulates anchored on its surface were observed using scanning electron microscope analysis. The structural analysis indicated C vacant sites, which are available for ionic/electronic charge diffusion, thereby rendering these structures suitable for making Li storage batteries as electrode material.

An overview on spray pyrolysis deposition of metal oxide thin films

This work provided an overview on the synthesis of metal oxide thin films on different types of substrates (soda lime glass, fluorine-doped tin oxide glass, silica glass, stainless steel, quartz, silicon and microscopic glass slide) using spray pyrolysis method. The fundamentals, advantages and limitations of this method have been described. Experimental results indicated that the properties of films were strongly depending on the specific process parameters (nozzle type, distance between nozzle and substrate, solvent type, solution flow rate, precursor concentration, compressed air pressure, spray time and substrate temperature). It was noted that deposition temperature could control the surface chemical composition based on the experimental results. The presence of amorphous or polycrystalline structure could be observed for the films prepared at different deposition times as indicated in XRD studies. The obtained films indicated excellent absorption coefficient value (104 to 105 cm-1) and high transmittance value (more than 82 %) in the visible and infrared portion.

Evaluation of the efficacy of antimicrobials against pathogens on food contact surfaces using a rapid microbial log reduction detection method

Microbial contamination of food contact surfaces in food processing industries is a significant health hazard. Evaluating the efficacy of sanitizing agents used during food processing is essential to ensure public health and safety. This study describes an optical screening method using an oCelloScope to quantify the number of surviving bacterial cells, expressed as microbial log reduction (MLR), after antimicrobial treatment. We tested the efficacy of two sanitizing agents, sodium hypochlorite and benzalkonium chloride, against desiccated cells of three pathogens, S. Enteritidis, E. coli O157: H7, and L. monocytogenes that are of concern on food processing surfaces. Stainless steel slides were used to mimic commercial food processing surfaces. Bacterial cells were desiccated at 75% relative humidity (RH) before antimicrobial treatment on stainless steel surfaces, and survivor levels were analyzed via plate counts to calculate MLR. These were compared to MLR values generated using the oCelloScope. For analysis of MLR using the oCelloScope, cells were desiccated at 75% RH on polystyrene microtiter plates, treated with antimicrobials, and surviving cell numbers were analyzed. Our results show that MLR values of treated desiccated cells calculated using the BCA algorithm of the oCelloScope were comparable to the values generated using the traditional plate count assay for the same concentration and treatment duration of the antimicrobials against all the tested pathogens. MLR could not be calculated for a non-lytic antimicrobial (curcumin and UV-A irradiation) against E. coli O157:H7, however, modified growth curves demonstrated an antimicrobial effect of curcumin and irradiation treatment. The results indicate that this method can be used for rapid screening of MLR of lytic antimicrobial compounds. Quantification of MLR using the oCelloScope is an effective tool to rapidly identify appropriate antimicrobial treatments and can be used to study novel antimicrobial compounds in the future.

Raman Microscopic Identification of Microorganisms on Metal Surfaces via Support Vector Machines.

An easy, inexpensive, and rapid method to identify microorganisms is in great demand in various areas such as medical diagnostics or in the food industry. In our study, we show the development of several predictive models based on Raman spectroscopy combined with support vector machines (SVM) for 21 species of microorganisms. The microorganisms, grown under standardized conditions, were placed on a silver mirror slide to record the data for model development. Additional data was obtained from microorganisms on a polished stainless-steel slide in order to validate the models in general and to assess possible negative influences of the material change on the predictions. The theoretical prediction accuracies for the most accurate models, based on a five-fold cross-validation, are 98.4%. For practical validation, new spectra (from stainless-steel surfaces) have been used, which were not included in the calibration data set. The overall prediction accuracy in practice was about 80% and the inaccurate predictions were only due to a few species. The development of a database provides the basis for further investigations such as the application and extension to single-cell analytics and for the characterization of biofilms.

Improved tissue preparation for multimodal vibrational imaging of biological tissues

The complementary nature of Infrared (IR) and Raman spectroscopies enables a thorough understanding of biological tissue – so called multimodal vibrational spectroscopic imaging. However, new approaches in terms of sample preparation and data analysis are required to release the full potential of multimodal spectroscopy. Herein, we propose an inexpensive and relatively simple sample preparation technique incorporating mirror-finished stainless-steel slides and polyethylene glycol as an embedding medium that is compatible for both infrared and Raman spectroscopy of tissue sections. K-Means Clustering and Principal Component Analysis (PCA) were used to evaluate the performance of multimodal vibrational spectroscopic imaging compared with IR and Raman spectroscopic imaging individually using a rat kidney as a model. The K-Means cluster maps generated with the multimodal dataset showed the best correlation between different tissue types identified by an adjacent section stained with Masson’s Trichrome compared to either Raman or IR spectroscopy analysed independently. PCA score maps of the multimodal dataset produced a clear separation of individual tissue types along the first three Principal Components. Additionally, PCA permitted the correlation of IR and Raman peaks arising mainly from collagen vibrational modes. Finally, polyethylene glycol embedding is shown as an attractive alternative to paraffin embedding for spectroscopic analyses, due to significantly less fluorescence in Raman measurements and retention of lipids in the tissue, without any retention of the medium within the tissue.

Rapid Detection of Clostridium difficile Toxins in Stool by Raman Spectroscopy

BackgroundClinical practice guidelines define Clostridium difficile infections (CDI) as diarrhea (≥3 unformed stools in 24 h) with either a positive C difficile stool test or detection of pseudomembranous colitis. Diagnostic modalities such as toxigenic culture and nucleic acid amplification testing can identify the presence of toxigenic C difficile in stools. But these tests are confounded by the presence of asymptomatic colonization of toxigenic C difficile and lead to overdiagnosis of CDI. The presence of two large toxins, toxin A and B (TcdA and TcdB) is necessary for pathogenicity. Detection of toxins using toxin enzyme immunoassay is difficult as it has low sensitivity and moderate specificity. Raman spectroscopy (RS) is a novel technology that is used to detect bacteria and their toxins. RS does not require any reagents for detection such as antibodies, enzymes, primers, or stains. We hypothesize that RS is a sensitive method to detect C difficile toxins in stool and will solve the problem of overdiagnosis of CDI. Materials and methodsCDI negative stool samples were spiked with concentrations (1 ng/mL, 100 pg/mL, 1 pg/mL, and 0.1 pg/mL) of TcdA and TcdB. RS was performed on air-dried smeared samples of stool supernatant on a mirror-polished stainless-steel slide. As RS of feces is difficult because of confounding background material and autofluorescence, samples were photo-bleached before spectral acquisition to reduce autofluorescence. Raman spectra were obtained, background corrected, and vector normalized. The data were split into training (70%) and test (30%) datasets. The machine learning methods used on the training data set were Support Vector Machine with Linear and Radial Kernels, Random Forest, Stochastic Gradient Boosting Machine, and Principle Component Analysis—Linear Discriminant Analysis. Results were validated using a test data set. The best model was chosen, and its accuracy, sensitivity, and specificity were determined. ResultsIn our preliminary results, at all concentrations (1 ng/mL, 100 pg/mL, 1 pg/mL, and 0.1 pg/mL), TcdA or TcdB spiked stool was distinguished from unspiked stool by all models with accuracies ranging from 64% to 77%. Gradient Boosting Machine, Principle Component Analysis—Linear Discriminant Analysis, and Support Vector Machine Linear Kernel performed best with sensitivities ranging from 69% to 90% and specificities ranging from 43% to 78%. ConclusionsUsing RS, we successfully detected TcdA and TcdB in stool samples albeit with moderate-to-high sensitivity and low-to-moderate specificity. Sensitivity and specificity could be further increased with the implementation of deep learning methods, which require large sample sizes. In terms of sensitivity, RS performs better than toxin enzyme immunoassay and has the potential to rapidly detect C difficile toxins in stool at clinically relevant concentrations and thereby help mitigate overdiagnosis of CDI.

Hydrophilic properties of surface of nanostructured tantalum films and its oxynitride compounds

The structure and hydrophilic properties of tantalum coatings on stainless steel and glass slide were investigated using atomic force microscopy (AFM) and sessile drop method. Coatings are characterized by a cellular structure. As a result of the modification, the hydrophobicity of the sample surfaces is increased.

Rapid Detection of Clostridium difficile Toxins in Serum by Raman Spectroscopy

BackgroundClostridium difficile infection (CDI) is due to the effects of toxins, toxin A and toxin B on the host. Severe CDI is associated with systemic signs of infection. Animal models of CDI demonstrate a strong correlation between systemic toxemia and the occurrence of severe disease. However, current technologies have low sensitivity to detect C difficile toxemia in human subjects. Raman spectroscopy (RS) is an upcoming technology that is used to detect bacteria and their toxins. We speculate that RS may be a sensitive method to detect clinically relevant concentrations of C difficile toxins in serum. Materials and methodsSerum samples were spiked with varying concentrations of toxin A, toxin B, and both. RS was performed on an air-dried serum drop that was placed on a mirror-polished stainless steel slide. Raman spectra were obtained, background corrected, vector normalized, and analyzed by Partial Least Square Linear Discriminant Analysis and Support Vector Machine for Classification. Model accuracy was measured by cross-validation and bootstrap methods. ResultsToxin-spiked sera of various concentrations (1 ng/mL, 1 pg/mL, and 0.1 pg/mL) were distinguished from control serum 100% with cross-validation error rate ranging from 0% to 18% and bootstrap error rate ranging from 0% to 12% for various concentrations. The sensitivity ranged from 87% to 100% and specificity ranged from 77% to 100% for various concentrations of toxin-spiked serum. ConclusionsWe conclude that RS may be a sensitive method to detect clinically relevant concentrations of C difficile toxins in serum and thus to help diagnose severe CDI in patients in real-time at the point of care.

Characterization of biofilm-forming capacity and resistance to sanitizers of a range of E. coli O26 pathotypes from clinical cases and cattle in Australia

BackgroundThe formation of biofilms and subsequent encasement of bacterial cells in a complex matrix can enhance resistance to antimicrobials and sterilizing agents making these organisms difficult to eradicate and control. The aim of this study was to evaluate and compare the capacity of 40 E. coli O26 isolates of enterohemorrhagic E. coli (EHEC, n = 27), potential EHEC (pEHEC, n = 3), atypical enteropathogenic E. coli (aEPEC, n = 8) and non-toxigenic E. coli (NTEC, n = 2) from human and cattle sources to form biofilms on different surfaces, and determine whether extracellular matrix (ECM) components (cellulose, curli), motility, prophage insertion in mlrA and cell surface hydrophobicity could influence biofilm formation. Finally, the influence of biofilm formation on the sensitivity of isolates to quaternary ammonium compounds (QACs; Profoam, Kwiksan 22) and peracetic acid-based sanitizer (Topactive Des.) for 2 min on polystyrene plate were also evaluated.ResultsBiofilm production on one surface may not indicate biofilm formation on a different surface. Biofilm was formed by different pathotypes on polystyrene (70%), stainless steel (87.5%) and glass slides (95%), however only 50% demonstrated pellicle formation. EHEC isolates were significantly more likely to form a pellicle at the air-liquid interface and biofilms on polystyrene surface at 48 h than aEPEC. Strains that don’t produce ECM (curli or cellulose), harbor a prophage insertion in mlrA, and are non-motile have lower biofilm forming capacities than those isolates possessing combinations of these attributes. Hydrophobicity had no impact on biofilm formation. After 2 min exposure, none of the disinfectants tested were able to completely inactivate all cells within a biofilm regardless of pathotypes and the amount of biofilm formed.ConclusionPathotypes of E. coli O26 showed varying capacities to form biofilms, however, most EHEC strains had the capacity to form biofilm on all surfaces and at the air-liquid interface under the conditions used in this study. Biofilms provided a protective effect to E. coli O26 strains against the three sanitizers, previously shown to successfully control the growth of their planktonic counterparts. Whether the characteristics of biofilm forming and non-biofilm forming strains observed in this study reflect their attributes within the food and meat-processing environments is unknown. Further studies that represent the food and meat-processing environments are required.

Effect of Electrolyzed Water on the Disinfection of Bacillus cereus Biofilms: The Mechanism of Enhanced Resistance of Sessile Cells in the Biofilm Matrix

This study examined the disinfection efficacy and mechanism of electrolyzed water (EW) on Bacillus cereus biofilms. B. cereus strains, ATCC 14579 and Korean Collection for Type Cultures (KCTC) 13153 biofilms, were formed on stainless steel (SS) and plastic slide (PS) coupons. Mature biofilms were treated with slightly acidic EW (SAEW), acidic EW (AEW), and basic EW (BEW). SAEW (available chlorine concentration, 25 ± 1.31 mg L-1; pH 5.71 ± 0.16; and oxidation reduction potential, 818 to 855 mV) reduced ATCC 14579 biofilms on plastic slides to below the detection limit within 30 s. However, biofilms on SS coupons showed a higher resistance to the SAEW treatment. When the disinfection activities of three types of EW on biofilms were compared, AEW showed a higher bactericidal activity, followed by SAEW and BEW. In contrast, BEW showed a significantly ( P < 0.05) higher biofilm dispersal activity than AEW and SAEW. SAEW disinfection of the B. cereus biofilms was due to the disruption of the B. cereus plasma membrane. The higher resistance of biofilms formed on the SS coupon might be due to the higher number of attached cells and extracellular polymeric substances formation that reacts with the active chlorine ions, such as hypochlorous acid and hypochlorite ion of SAEW, which decreased the disinfection efficacy of SAEW. This study showed that the EW treatment effectively disinfected B. cereus biofilms, providing insight into the potential use of EW in the food processing industry to control the biofilm formation of B. cereus.

Effect of metal surfaces on matrix-assisted laser desorption/ionization analyte peak intensities.

Different metal surfaces in the form of transmission electron microscope grids were examined as support surfaces in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with a view towards enhancement of peptide signal intensity. The observed enhancement between 5-fold and 20-fold relative to the normal stainless steel slide was investigated by applying the thermal desorption model for matrix-assisted laser desorption/ionization. A simple model evaluates the impact that the thermal properties of the metals have on the ion yield of the analyte. It was observed that there was not a direct, or strong, correlation between the thermal properties of the metals and the corresponding ion yield of the peptides. The effects of both fixed and variable laser irradiances versus ion yield were also examined for the respective metals studied. In all cases the use of transmission electron microscope grids required much lower laser irradiances in order to generate similar peak intensities as those observed with a stainless steel surface.

Assessment of Reproducibility of Laser Electrospray Mass Spectrometry using Electrospray Deposition of Analyte.

A nonresonant, femtosecond (fs) laser is employed to desorb samples of Victoria blue deposited on stainless steel or indium tin oxide (ITO) slides using either electrospray deposition (ESD) or dried droplet deposition. The use of ESD resulted in uniform films of Victoria blue whereas the dried droplet method resulted in the formation of a ring pattern of the dye. Laser electrospray mass spectrometry (LEMS) measurements of the ESD-prepared films on either substrate were similar and revealed lower average relative standard deviations for measurements within-film (20.9%) and between-films (8.7%) in comparison to dried droplet (75.5% and 40.2%, respectively). The mass spectral response for ESD samples on both substrates was linear (R2 > 0.99), enabling quantitative measurements over the selected range of 7.0 × 10-11 to 2.8 × 10-9mol, as opposed to the dried droplet samples where quantitation was not possible (R2 = 0.56). The limit of detection was measured to be 210fmol. Graphical Abstract ᅟ.

Pediococcus Acidilactici Inhibit Biofilm Formation of Food-Borne Pathogens on Abiotic Surfaces

In this study, we aimed to examine the inhibitory effect of PA003, a Pediococcus acidilactici that produces lactic acid and antimicrobial peptides pediocin, on pathogenic biofilm formation on abiotic surfaces. PA003 and pathogens (Escherichia coli, Salmonella enterica serovar Typhimurium, Staphylococcus aureus and Listeria monocytogenes) were used to evaluate auto-aggregation, hydrophobicity, biofilm formation and biofilm formation inhibition on stainless steel, polyvinyl chloride and glass slides in terms of exclusion, displacement and competition. The results showed the highest auto-aggregation abilities were observed for one of the E. coli strains EAggEC (E58595) and the highest hydrophobic strain was observed with EPEC (E2348/69) (51.9%). The numbers of biofilm cells of E. coli, S. Typhimurium, S. aureus and L. monocytogenes on stainless steel, polyvinyl chloride and glass slide coupons were effectively reduced by approximately 4 log CFU/coupon. These results demonstrate that lactic acid bacteria can be used as an alternative to effectively control the formation of biofilms by food-borne pathogens.

Silver-functionalized methyl-silica hybrid materials as antibacterial coatings on surgical-grade stainless steel

Development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of commercial and medical products due to its action against fungus and bacteria. Although a large number of products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odors. On the other hand, sol-gel technology becomes the preparation of hybrid materials possible with introduction of different components, as inorganic salts or organic additives within its structure bringing up the possibility to develop functional materials for different purposes. In this work, the development of an antibacterial coating for metallic substrates is presented. The coating consists in a hybrid organic-inorganic sol-gel material doped with silver. The relation between the structure of the hybrid matrix, aggregation state of silver ions, and biocide behavior is analyzed as a function of the densifying thermal treatment. Sol-gel materials were synthesized through hydrolytic condensation, in acidic conditions, of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions. Coatings were deposited on 316L stainless steel and microscope glass slides by the dip-coating process at a constant withdrawal rate and densified at 50, 150 and 450 °C. X-ray photoelectron spectroscopy, small angle X-ray spectroscopy and electrochemical impedance spectroscopy were used as characterization techniques in order to elucidate silver aggregation and its influence on the structural evolution of the hybrid matrix, as a function of the thermal treatment. At the same time, the biocide behavior, as a function of silver state, particles size and thermal treatment, was studied by inhibitory halo identification on Escherichia-coli cultures in agar diffusion tests.

Identification of lactobacilli with inhibitory effect on biofilm formation by pathogenic bacteria on stainless steel surfaces

Two hundred and thirty individual clones of microorganisms were recovered from milk tanks and milking machine surfaces at two distinct farms (Bejaja City, Algeria). Of these clones, 130 were identified as lactic acid bacteria (LAB). In addition Escherichia coli, Salmonella, Staphylococcus aureus and Pseudomonas aeruginosa species were identified in the remaining 100 isolates—spoilage isolate. These isolates were assayed for ability to form biofilms. S. aureus, Lactobacillus brevis strains LB1F2, LB14F1 and LB15F1, and Lactobacillus pentosus strains LB2F2 and LB3F2 were identified as the best biofilm formers. Besides, these LAB isolates were able to produce proteinaceous substances with antagonism against the aforementioned spoilage isolates, when grown in MRS or TSB-YE media. During the screening, L. pentosus LB3F2 exhibited the highest antibacterial activity when grown in TSB-YE medium at 30°C. Additionally, L. pentosus LB3F2 was able to strongly hamper the adhesion of S. aureus SA3 on abiotic surfaces as polystyrene and stainless steel slides. LAB isolates did not show any hemolytic activity and all of them were sensitive to different families of antibiotic tested. It should be pointed out that LB3F2 isolate was not cytotoxic on the intestinal cells but could stimulate their metabolic activity. This report unveiled the potential of LB1F2, LB14F1, LB15F1, LB2F2, and LB3F2 isolates to be used as natural barrier or competitive exclusion organism in the food processing sector as well as a positive biofilm forming bacteria.

Distribution study of atorvastatin and its metabolites in rat tissues using combined information from UHPLC/MS and MALDI-Orbitrap-MS imaging.

The combination of ultrahigh-resolution mass spectrometry imaging (UHRMSI) and ultrahigh-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC/MS/MS) was used for the identification and the spatial localization of atorvastatin (AT) and its metabolites in rat tissues. Ultrahigh-resolution and high mass accuracy measurements on a matrix-assisted laser desorption/ionization (MALDI)-Orbitrap mass spectrometer allowed better detection of desired analytes in the background of matrix and endogenous compounds. Tandem mass spectra were also used to confirm the identification of detected metabolites in complex matrices. The optimization of sample preparation before imaging experiments included the tissue cryogenic sectioning (thickness 20 μm), the transfer to stainless steel or glass slide, and the selection of suitable matrix and its homogenous deposition on the tissue slice. Thirteen matrices typically used for small molecule analysis, e.g., 2,5-dihydroxybenzoic acid (DHB), 1,5-diaminonaphthalene (DAN), 9-aminoacridine (AA), etc., were investigated for the studied drug and its metabolite detection efficiency in both polarity modes. Particular matrices were scored based on the strength of extracted ion current (EIC), relative ratio of AT molecular adducts, and fragment ions. The matrix deposition on the tissue for the most suitable matrices was done by sublimation to obtain the small crystal size and to avoid local variations in the ionization efficiency. UHPLC/MS profiling of drug metabolites in adjacent tissue slices with the previously optimized extraction was performed in parallel to mass spectrometry imaging (MSI) measurements to obtain more detailed information on metabolites in addition to the spatial information from MSI. The quantitation of atorvastatin in rat liver, serum, and feces was also performed.

Characterization of artificially dried biofilms for air biofiltration studies

One of the main problems associated with the operation of air biofilters is the loss of performance caused by drying of the bioactive support, as the removal capacity of contaminants by the microorganisms is dependent on their water content. In this work, biofilms from a microbial consortium adapted to toluene were grown on stainless steel slides. The biofilms were dried in stoppered flasks with saturated saline solutions to obtain final water activities of 97.4 %, 83.9 %, 74.8 % and 32 %. The biofilms were characterized by a sorption isotherm Type III with toluene; the water desorption isotherm was fitted to the BET model and the biofilm hydrophobicity was also determined. Specific oxygen consumption rates decreased at lower Aw from 60 μg O2/mg protein/h to zero activity. Biofilm activity, represented by a toluene consumption rate, and others physical properties presented a critical point between Aw 0.84 and 0.97. Biological activity of dried biofilms was restored either partially or completely, depending on the extent of drying and rewetting method.

Photocatalytic Activity of Nanosized TiO2 Thin Film Prepared by Magnetron Sputtering Method

Nanosized TiO2 thin film on the substrate such as stainless steel plate and slide glass film were prepared by magnetron sputtering method, and these TiO2 thin films were characterized by field emission-scanning electron microscopy (FE-SEM). Photocatalytic activity for Methyl-ethyl-ketone (MEK) and acetaldehyde were measured using a closed circulating reaction system through the various ultra violet (UV) sources. From the results of SEM images, nanosized TiO2 thin film was uniformly coated on slide glass, ranging from 360 nm to 370 nm. Photocatalytic activity of MEK over TiO2 thin film on stainless steel plate did not occur by UV-A irradiation, but was efficiently decomposed by UV-B and UV-C. Also, acetaldehyde could be decomposed than MEK. The effect of sputtering conditions on their structure and photocatalytic activities were investigated in detail.

Bactericidal efficacy of some commercial disinfectants on biofilm on stainless steel surfaces of food equipment

This study aimed to determine the most effective concentration of the most effective disinfectant for use in the disinfection of food processing equipment to remove Gram positive and/or Gram negative bacterial biofilms. Eight disinfectants [10% NaOH (sodium hydroxide), 70% C2H5OH (ethanol), 30% H2O2 (hydrogen peroxide), 4–6% NaOCl (sodium hypochlorite), C3H7OH (isopropyl alcohol), mixtures of H2O2 and NaOCl, H2O2 and C2H5OH, H2O2 and C3H7OH] were used against bacteria that commonly contaminate food-processing equipment and cause food poisoning, namely: Bacillus subtilis and Staphylococcus aureus (Gram positive bacteria), and Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi (Gram negative bacteria). The bacteria were grown on stainless steel slides to allow biofilm formation. The most effective disinfectant on all tested bacteria was found to be H2O2. Spread plate enumeration (CFU/ml) showed that the difference in the number of cells between untreated and treated samples decreased from 7 log units to 3, and from 7 log units to 0 at minimal inhibitory concentration (MIC) for P. aeruginosa and S. aureus, respectively. The results were confirmed by scanning electron microscopy (SEM) of untreated and treated biofilms of the two organisms at MIC and minimal bactericidal concentration (MBC) of H2O2. The MICs were equal to MBCs for all tested bacteria (Gram positive and negative) except for Pseudomonas (Gram negative), with values of 0.23 and 0.47% for MIC and MBC, respectively—the lowest concentration value of all tested bacteria. This study revealed that the MBC of H2O2 was completely effective and could remove all viable bacterial cells in the bacterial biofilm.

Using enzymes to remove biofilms of bacterial isolates sampled in the food-industry

The aim of this study was to analyze the cleaning efficiency of polysaccharidases and proteolytic enzymes against biofilms of bacterial species found in food industry processing lines and to study enzyme effects on the composition of extracellular polymeric substances (EPS) and biofilm removal in a Clean-in-Place (CIP) procedure. The screening of 7 proteases and polysaccharidases for removal of biofilms of 16 bacterial species was first evaluated using a microtiter plate assay. The alkaline pH buffer removed more biofilm biomass as well as affecting a larger range of bacterial species. The two serine proteases and α-amylase were the most efficient enzymes. Proteolytic enzymes promoted biofilm removal of a larger range of bacterial species than polysaccharidases. Using three isolates derived from two bacterial species widely found in food processing lines (Pseudomonas fluorescens and the Bacillus cereus group), biofilms were developed on stainless steel slides and enzymatic solutions were used to remove the biofilms using CIP procedure. Serine proteases were more efficient in removing cells of Bacillus biofilms than polysaccharidases. However, polysaccharidases were more efficient in removing P. fluorescens biofilms than serine proteases. Solubilization of enzymes with a buffer containing surfactants, and dispersing and chelating agents enhanced the efficiency of polysaccharidases and proteases respectively in removing biofilms of Bacillus and P. fluorescens. A combination of enzymes targeting several components of EPS, surfactants, dispersing and chelating agents would be an efficient alternative to chemical cleaning agents.