Role of Pseudomonas aeruginosa biofilm in the initial adhesion, growth and detachment of Escherichia coli in porous media

This study systematically investigated the impact of Pseudomonas aeruginosa biofilm on the initial adhesion, growth, and detachment of indicator bacteria Escherichia coli JM109 in porous media. Two P. aeruginosa strains, the mucoid PD0300 and wide type PA01 with different extracellular polymeric substance (EPS) composition and secretion capability, were used to grow biofilm in packed beds. Results from the column breakthrough curves and retained JM109 profiles show that the amount and composition of P. aeruginosa biofilm EPS have a profound impact on the deposition and retention of E. coli in porous media. PAO1 biofilm coating improved E. coli retention in the column, whereas PDO300 biofilm coating had only a small impact on E. coli removal. Biofilm surface hydrophobicity and polymeric interactions between the biofilm and E. coli cell surfaces were found to play important roles in controlling the distribution of E. coli along the columns. After initial attachment, E. coli bacteria were able to survive and grow at similar growth rates in columns coated with either PAO1 or PDO300 biofilms with a relatively low nutrient supply. Biofilm detachment was the major mechanism that introduced E. coli bacteria to the bulk fluid long after the contamination event when E. coli cells became an integral part of the biofilm. Findings of this study suggest that biofilm plays a significant role in controlling the initial attachment, growth, and survival of bacteria in porous media, and that the interaction between bacteria and biofilm surfaces should be considered when predicting bacterial and pathogen migration in the environment.     

Persistence of Klebsiella pneumoniae on simulated biofilm in a model drinking water system

Persistence of Klebsiella pneumoniae on corroded iron surfaces in drinking water was studied using biofilm annular reactors operated under oligotrophic conditions. Reactors were inoculated with K. pneumoniae, and persistence was monitored in the bulk and biofilm phases. Initial cell concentration of 10(6) MPN/mL in the bulkwater phase resulted in significantly longer adhesion than initial concentrations 1 and 2 orders of magnitude lower. K. pneumoniae cultured in low nutrient growth medium persisted longer in dechlorinated tap water than those cultured in full strength medium. Cell surface charge was more negative under low nutrient conditions, and this influenced electrostatic attraction between the cells and the oxidized iron surface. Cells grown in full strength media persisted longer in water with both low (<0.2 mg/L) and high (>0.5 mg/L) free chlorine residuals. Growth media injected with the cells dechlorinated the water allowing adhesion without inactivation. Microelectrode measurements showed a 40-70% drop in free chlorine from the bulk to the coupon surface, which decreased disinfectant potency against adhered cells. Growth and injection conditions clearly influenced cell adhesion and persistence, but permanent colonization of the corroded iron surface by K. pneumoniae was not observed.     

Adhesion of Megasphaera cerevisiae onto solid surfaces mimicking materials used in breweries

Developments in filling technologies have led to a reduction in oxygen content in beer, thus producing an anaerobic environment suitable for the growth of anaerobic beer‐spoiling microorganisms. Anaerobic bacteria survive well in a biofilm that provides protection against environmental stress factors. The initial step in biofilm formation is adhesion of cells to a solid surface. Therefore the purpose of this research was to study theoretically and experimentally adhesion of strains of Megasphaera cerevisiae to different solid surfaces with properties covering a wide range of materials used in breweries. Experimental characterization of surface properties was used to model surface interactions, resulting in a quantitative prediction of cell adhesion. The colloidal model predictions were then compared with adhesion tests. As revealed experimentally, the most significant adhesion occurred to 3‐aminopropyltriethoxysilane‐modified glass (substitute for stainless steel) at pH 3–7. According to physicochemical interaction models, under these conditions interactions were influenced mostly by electrostatic attractions between surfaces. At pH 3, experimental data, supported by theoretical predictions, showed significant bacterial adhesion to borosilicate glass (a hydrophilic surface) and propyltriethoxysilane‐modified glass (a hydrophobic surface). Conversely, the least adhesion of M. cerevisiae was both predicted and observed at pH 10, since at an alkaline pH, electrostatic repulsion between surfaces predominates. Since adhesion can be expected mainly at an acidic pH, prevention should be based on the use of alkaline cleaning agents and/or alkaline rinse water at the end of the cleaning procedure. An elevated risk of adhesion to stainless steel was also identified, allowing appropriate measures to be taken. Copyright © 2017 The Institute of Brewing & Distilling     

Experimental and theoretical examination of surface energy and adhesion of nitrifying and heterotrophic bacteria using self-assembled monolayers

Biofilm-based systems, including integrated fixed-film activated sludge and moving bed bioreactors, are becoming increasingly popular for wastewater treatment, often with the goal of improving nitrification through the enrichment of ammonia and nitrite oxidizing bacteria. We have previously demonstrated the utility of self-assembled monolayers (SAMs) as tools for studying the initial attachment of bacteria to substrata systematically varying in physicochemical properties. In this work, we expanded these studies to bacteria of importance in wastewater treatment systems and we demonstrated attachment rates were better correlated with surface energy than with wettability (water contact angle). Toward the long-term goal of improving wastewater treatment performance through the strategic design of attachment substrata, the attachment rates of two autotrophic ammonia-oxidizing bacteria (Nitrosomonas europaea and Nitrosospira multiformis) and a heterotroph (Escherichia coli) were evaluated using SAMs with a range of wettabilities, surface energies, and functional properties (methyl, hydroxyl, carboxyl, trimethylamine, and amine terminated). Cell attachment rates were somewhat correlated with the water contact angles of the SAMs with polar terminal groups (hydroxyl, carboxyl, trimethylamine, and amine). Including all SAM surfaces, a better correlation was found for all bacteria between attachment rates and surface free energy, as determined using the Lewis Acid-Base approach. The ammonia-oxidizers had higher adhesion rates on the SAMs with higher surface energies than did the heterotroph. This work demonstrated the successful application of SAMs to determine the attachment surface preferences of bacteria important to wastewater treatment, and it provides guidance for a new area of research aimed at improving treatment performance through rational attachment surface design.     

Removal of two waterborne pathogenic bacterial strains by activated carbon particles prior to and after charge modification

Waterborne diseases constitute a threat to public health despite costly treatment measures aimed at removing pathogenic microorganisms from potable water supplies. This paper compared the removal of Raoultella terrigena ATCC 33257 and Escherichia coli ATCC 25922 by negatively and positively charged types of activated carbon particles. Both strains display bimodal negative zeta-potential distributions in stabilized water. Carbon particles were suspended to an equivalent external geometric surface area of 700 cm2 in 250 mL of a bacterial suspension, with shaking. Samples were taken after different durations for plate counting. Initial removal rates were less elevated for the positively charged carbon particle than expected, yielding the conclusion that bacterial adhesion under shaking is mass-transport limited. After 360 min, however, the log-reduction of the more negatively charged R. terrigena in suspension was largest for the positively charged carbon particles as compared with the negatively charged ones, although conditioning in ultrapure or tap water of positively charged carbon particles for 21 days eliminated the favorable effect of the positive charge due to counterion adsorption from the water. Removal of the less negatively charged E. coli was less affected by aging of the (positively charged) carbon particles, confirming the role of electrostatic interactions in bacterial removal by activated carbon particles. The microporous, negatively charged coconut carbon performed less than the mesoporous, positively charged carbon particle prior to conditioning but did not suffer from loss of effect after conditioning in ultrapure or tap water.     

Attachment of Shiga toxigenic Escherichia coli to stainless steel

Shiga toxigenic Escherichia coli (STEC) are important foodborne pathogens causing gastrointestinal disease worldwide. Bacterial attachment to food surfaces, such as stainless steel may lead to cross contamination of foods and subsequent foodborne disease. A variety of STEC isolates, including E. coli O157:H7/H- strains, were grown in planktonic (broth) and sessile (agar) culture, following which initial attachment to stainless steel was determined using epifluorescence microscopy. Experiments were performed to determine whether the number of bacteria attached to stainless steel differed between STEC strains and between the two modes of growth. No relationship was found between STEC strains and the number of bacteria attached to stainless steel. Five STEC strains, including one non-toxigenic O157 isolate, attached in significantly greater (p<0.05) numbers to stainless steel following growth in planktonic culture compared to sessile culture. In contrast, two clinical strains of O157:H7 attached in significantly greater (p<0.05) numbers following growth in sessile culture compared to planktonic culture. Thirteen out of twenty E. coli strains showed no significant difference (p>0.05) in attachment when grown in planktonic or sessile culture. The change of interfacial free energy between the bacterial strains and stainless steel was calculated and the influence of free energy in attachment was determined. Although a significant variation (p<0.05) in free energy values was found between STEC strains, no correlation was found between free energy values and bacterial counts on stainless steel. In addition, no correlation was also found between bacterial hydrophobicity and surface charge values or production of surface structures (type I fimbriae or flagella) (previously determined) with the number of bacteria attached to stainless steel. The results of this study suggest that different growth conditions (planktonic and sessile) can influence the attachment of STEC to stainless steel. Factors other than bacterial physicochemical properties and these surface structures may also influence STEC attachment to stainless steel.     

Kinetics and mechanism of bacterial inactivation by ultrasound waves and sonoprotective effect of milk components

Inactivation of Escherichia coli and Listeria monocytogenes were investigated in buffer and milk upon treatment with ultrasound waves (USW). In addition, sonoprotective effect of milk components and ultrasound-induced changes in bacterial cells were investigated using scanning electron microscopy (SEM). Bacterial cells were added to phosphate buffer, whole milk, skim milk, or simulated milk ultrafiltrate (SMUF). To determine the sonoprotective effect of milk components, lactose (5%), casein (3%), or β lactoglobulin (0.3%) was added to SMUF. Samples were sonicated with 24 kHz pulse USW while maintaining the system temperature between 30 to 35 °C. Aliquots were drawn at set times during sonication and bacteria were enumerated by surface plating appropriate dilutions on selective and nonselective media plates. Escherichia coli exhibited significantly higher D values in whole (2.43 min) and skim milk (2.41 min) than phosphate buffer (2.19 min). Listeria monocytogenes also showed higher D values in whole (9.31 min) and skim milk (8.61 min) compared to phosphate buffer (7.63 min). Data suggest that milk exerts a sonoprotective effect on these bacteria. Escherichia coli exhibited a log-linear inactivation kinetics followed by tailing whereas L. monocytogenes showed 1st-order kinetics throughout. Among the milk components tested, presence of lactose in SMUF resulted in significantly higher D values than SMUF for both organisms suggesting that lactose was exerting a protective effect on bacteria. SEM images showed that USW caused mechanical damage to the cell wall and cell membrane of bacteria leading to their inactivation.     

Aggregation and hydrophobicity properties of 6 dairy propionibacteria strains isolated from homemade Turkish cheeses

In the present study, 6 dairy Propionibacterium strains were assessed with regard to their hydrophobic characteristics and their autoaggregation and coaggregation abilities since these traits have been shown to be indicative of adherence in other microorganisms. Aggregation assays and bacterial adhesion to hydrocarbons demonstrated significant differences in cell surface properties among the tested propionibacteria strains. Almost all strains appeared relatively hydrophilic, which showed low affinity for p-xylene. Four of the tested strains showed the strong adhesion to ethyl acetate, a basic solvent, in comparison with microbial adhesion to chloroform, an acidic solvent, which demonstrated the particularity of propionibacteria to have an important electron donor and acidic character. Also, these strains simultaneously showed affinity to 3 hydrocarbons, suggesting a high complexity of the cell surface. All propionibacteria strains tested showed autoaggregation and coaggregation ability with the Escherichia coli ATTC 11229, but the results were strain-specific and dependent on incubation conditions. Anaerobic incubation conditions were determined as the best condition for aggregation abilities of propionibacteria strains. A relationship was obtained between aggregation abilities (auto- and coaggregation) and a correlation between adhesion to hydrocarbon (chloroform) and autoaggregation was possible. Our results indicate that the ability to autoaggregation together with cell surface hydrophobicity and coaggregation abilities with E. coli strain can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use. PRACTICAL APPLICATION: Autoaggregation, cell surface hydrophobicity, and coaggregation abilities with E. coli of the selected dairy propionibacteria strains could be used as probiotic in foods after in vivo studies.     

Relationship of cell surface charge and hydrophobicity to strength of attachment of bacteria to cantaloupe rind

The cantaloupe melon has been associated with outbreaks of Salmonella infections. It is suspected that bacterial surface charge and hydrophobicity may affect bacterial attachment and complicate bacterial detachment from cantaloupe surfaces. The surface charge and hydrophobicity of strains of Salmonella, Escherichia coli (O157:H7 and non-O157:H7), and Listeria monocytogenes were determined by electrostatic and hydrophobic interaction chromatography, respectively. Initial bacterial attachment to cantaloupe surfaces and the ability of bacteria to resist removal by washing with water were compared with surface charge and hydrophobicity. Whole cantaloupes were submerged in inocula containing individual strains or in cocktails containing Salmonella, E. coli, and L. monocytogenes, either as a mixture of strains containing all three genera or as a mixture of strains belonging to a single genus, for 10 min. Inoculated cantaloupes were dried for 1 h in a biosafety cabinet and then stored for up to 7 days at 4 degrees C. Inoculated melons were washed with water, and bacteria still attached to the melon surface, as well as those in the wash water, were enumerated. Initial bacterial attachment was highest for individual strains of E. coli and lowest for L. monocytogenes, but Salmonella exhibited the strongest attachment on days 0, 3, and 7. When mixed-genus cocktails were used, the relative degrees of attachment of the three genera ware altered. The attachment of Salmonella strains was the strongest. but the attachment of E. coli was more extensive than that of L. monocytogenes on days 0, 3, and 7. There was a linear correlation between bacterial cell surface hydrophobicity (r2 = 0.767), negative charge (r2 = 0.738), and positive charge (r2 = 0.724) and the strength of bacterial attachment to cantaloupe surfaces.     

Modulation of cell surface hydrophobicity and attachment of bacteria to abiotic surfaces and shrimp by malaysian herb extracts

The use of simple crude water extracts of common herbs to reduce bacterial attachment may be a cost-effective way to control bacterial foodborne pathogens, particularly in developing countries. The ability of water extracts of three common Malaysian herbs (Andrographis paniculata, Eurycoma longifolia, and Garcinia atroviridis) to modulate hydrophobicity and attachment to surfaces of five food-related bacterial strains (Bacillus cereus ATCC 14576, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 10145, Salmonella Enteritidis ATCC 13076, Staphylococcus aureus ATCC 25923) were determined. The bacterial attachment to hydrocarbon assay was used to determine bacterial hydrophobicity. Staining and direct microscopic counts were used to determine attachment of bacteria to glass and stainless steel. Plating on selective media was used to determine attachment of bacteria to shrimp. All extracts were capable of either significantly ( P < 0.05) increasing or decreasing bacterial surface hydrophobicity, depending on the herb extract and bacteria combination. Bacterial attachment to all surfaces was either significantly (P < 0.05) increased or decreased, depending on the herb extract and bacteria combination. Overall, hydrophobicity did not show a significant correlation (P > 0.05) to bacterial attachment. For specific combinations of bacteria, surface material, and plant extract, significant correlations (R > 0.80) between hydrophobicity and attachment were observed. The highest of these was observed for S. aureus attachment to stainless steel and glass after treatment with the E. longifolia extract (R = 0.99, P < 0.01). The crude water herb extracts in this study were shown to have the potential to modulate specific bacterial and surface interactions and may, with further work, be useful for the simple and practical control of foodborne pathogens.     

REDUCTIONS OF ESCHERICHIA COLI, COLIFORMS, AEROBIC PLATE COUNTS AND CAMPYLOBACTER JEJUNI BY A SMALL-SCALE, HIGH-PRESSURE SYSTEM DEVISED TO CLEAN A MINIATURIZED POULTRY GIBLETS TRANSPORT SYSTEM

The efficacy of using direct high-pressure hot water (60C, 140F) and a quaternary ammonium compound to clean the inside of stainless steel pipe used to transport chicken giblets was evaluated. The giblets were collected from a commercial processing plant and were inoculated with Campylobacter jejuni. The cleaning system was effective in reducing the numbers of inoculated C. jejuni and naturally occurring mesotrophic bacteria (aerobic plate counts) on the inside surface of the stainless steel pipe used to transport the giblets. However, the decreases in naturally occurring Escherichia coli and coliforms were not significant. These results suggest that additional improvements are needed to better disinfect the piping system used to transport giblets to reduce the potential for cross-contamination with C. jejuni and E. coli. The devised cleaning system could be optimized to reduce the use of chemical agents, the cleaning time and the cost of cleaning pipes in poultry processing facilities.

PRACTICAL APPLICATIONS

These experiments suggest that the traditional use of hot water and quaternary ammonium compounds to clean the inside of the piping system used to transport chicken giblets may not be sufficient to reduce the contamination with Campylobacter jejuni and mesotrophic bacteria (aerobic plate count). Poultry processors should be aware of the limitations of cleaning closed piping systems and develop and test high-pressure systems to thoroughly clean the pipes used to transport giblets after processing to avoid potential sources of cross-contamination with C. jejuni and mesotrophic bacteria.     

Effects of nonionic surfactants on the cell surface hydrophobicity and apparent hamaker constant of a Sphingomonas sp

Nonionic surfactants of the form CxEy were studied for their ability to alter the cell surface hydrophobicity and apparent Hamaker constants of a Sphingomonas sp. Through contact angle measurements on hydrated and dried bacterial lawns, it was found that the cell surface hydrophobicity changed systematically with both the alkyl (x) and polyoxyethylene (y) chain lengths. While differences in contact angles were observed between hydrated and dried lawns, they could not be attributed to the mere presence or absence of water, suggesting that reorientation of cell surface components may occur during drying. All surfactants examined reduced the hydrophilicity of the bacterial cell surface, with one surfactant (C18E10) making the cells hydrophobic. Effective bacterial Hamaker constants for bacteria interacting across a vacuum (Abb) and water (Abwb) and bacteria interacting in water with quartz sand (Abws) were calculated from the contact angles. It was found that the surfactants have the potential to reduce the Hamaker constants, but that the overall effects differed between dried and hydrated lawns, indicating that lawn preparation method can have a significant impact in interpretation of cell surface properties. The results also indicate that the Abws value of 10-20 J, which is often assumed in bacterial attachment and transport studies, may be an order of magnitude higher than the actual value. Finally, the results suggest that alteration of bacterial adhesion due to the presence of surfactants cannot be attributed to a single cell surface property but is rather due to multiple interactions.     

Indigenous dadih lactic acid bacteria: cell-surface properties and interactions with pathogens

ABSTRACT:  Cell surface properties of dadih lactic acid bacteria strains were studied for adhesion to hydrocarbons (BATH) and aggregation abilities. Autoaggregation correlates with adhesion, which is a prerequisite for colonization and infection of the gastrointestinal tract by many pathogens, whereas coaggregation has been related to the ability to interact closely with pathogens. The results demonstrated significant differences in cell surface properties among the tested natural lactic acid bacteria food strains. Hydrophobicity increased when the cells were heat inactivated. All strains showed aggregation abilities with the pathogen strains tested, but the coaggregation properties were strain-specific. Our results indicate that the ability to autoaggregate, together with cell surface hydrophobicity and coaggregation abilities with pathogen strains, can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use. This study suggest the importance to identify and characterize bacterial cell-wall properties to understand their role in adhesion to hydrocarbons, autoaggregation and relation to coaggregation mechanisms, and also the relevance to future probiotic food development from natural strains.     

Role of lipopolysaccharides in the adhesion,retention, and transport of Escherichia coli JM109

The role of lipopolysaccharides (LPS) in bacterial adhesion was investigated via atomic force microscopy (AFM). Adhesion between a silicon nitride tip and Escherichia coli JM109 was measured in water and 0.01 M phosphate-buffered saline (PBS) on untreated cells and on a sample of E. coli treated with 100 mM ethylenediaminetetraacetic acid (EDTA), which removes approximately 80% of the LPS molecules. LPS removal decreased the adhesion affinity between the bacterial cells and the AFM tip from -2.1 +/- 1.8 to -0.40 +/- 0.36 nN in water and from -0.74 +/- 0.44 to -0.46 +/- 0.23 nN in 0.01 M PBS (statistically different, Mann-Whitney rank sum test, P < 0.01). The distributions of adhesion affinities between E. coli LPS macromolecules and the AFM tip could be described by gamma distribution functions. Direct measurements of the adhesive force between E. coil and a surface were compared with adhesion in batch and column experiments, and agreement was observed between the influences of LPS on adhesion in each system. Bacterial batch retention to glass or in packed beds to quartz sand decreased after LPS removal. When interaction forces were measured during the approach of the AFM tip to a bacterium, steric repulsive forces were seen for both treated and untreated cells, but the repulsion was greater when the LPS was intact A model for steric repulsion predicted a reduction of the equilibrium length of the surface polymers from 242 to 64 nm in water and from 175 to 81 nm in buffer, after removal of a portion of the LPS. DLVO calculations based on conventional and soft-particle DLVO theories predicted higher energy barriers to adhesion for all surfaces after LPS removal, consistent with experimental findings. Adhesion forces between the AFM tip and bacterial polymers were correlated with bacterial attachment and retention, while measurements of interaction forces during the approach of the AFM tip to the bacterium did not correlate with subsequent adhesion behavior to glass or quartz sand.     

Pulsed electric fields inactivation of attached and free-living Escherichia coli and Listeria innocua under several conditions

The use of pulsed electric fields (PEF) is considered as a mild process in the inactivation of microorganisms present in liquid food products. PEF treatments of Escherichia coli and Listeria innocua suspended in milk and phosphate buffer, with same pH and same conductivities, yielded to similar inactivation. Reduction rates obtained in distilled water indicated that conductivity of the food product is a main parameter in bacterial inactivation. Bacteria attached to polystyrene beads were inactivated by PEF at a greater (E. coli) or equal rate (L. innocua) than free-living bacteria. Base on the use of selective and non-selective enumeration media, no clear indications were obtained for sublethal damage of microorganisms surviving the PEF treatment. E. coli cells subjected to 60 pulses at 41 kV/cm were examined by transmission and scanning electron microscopy. Changes in the cytoplasm were observed and the cell surface appeared rough. The cells outer membranes were partially destroyed allowing leaking of cell cytoplasm.     

多孔钛片表面ZnO薄膜的表征及其对腐败希瓦氏菌生物被膜的抑制性能

为研究ZnO薄膜微观形貌对其抑制腐败希瓦氏菌生物被膜性能的影响,采用水热合成法制备了ZnO薄膜,并对其进行X射线衍射(XRD)、扫描电子显微镜(SEM)和水接触角表征分析。结果表明,ZnO为六方纤锌矿晶体结构,水热反应时间影响ZnO薄膜的微观形貌。延长水热反应时间,薄膜表面ZnO均匀堆积,其附着量不断增加。多孔钛片呈疏水性,水热合成ZnO薄膜呈亲水性。ZnO薄膜表面的生物被膜附着量随菌体培养时间延长而增加。0~2 h,ZnO薄膜表面生物被膜粘附率和被膜菌总数上升很快,菌体在生物被膜内迅速繁殖;2~12 h,生物被膜粘附率和被膜菌总数持续增长,生物被膜进入生长期;12~36 h,被膜粘附率及被膜菌菌落总数变化较小,生物被膜进入成熟期;36 h后,生物被膜粘附率和被膜菌总数下降,生物被膜进入衰退期。由于ZnO具有杀菌性能,ZnO薄膜对生物被膜的抑制性能增强,且制备ZnO薄膜的水热反应时间越长,样品对生物被膜的抑制性能越优。ZnO杀菌性能对材料表面抗生物被膜粘附性能的贡献远优于材料表面的疏水性能。     

The effects of the surface charge and hydrophobicity of Escherichia coli on its adhesion to beef muscle

The surface characteristics of Escherichia coli strains were studied to evaluate the effect upon bacterial adhesion to beef muscle. The influence of suspension conditions upon the surface charge of a pathogenic strain, E. coli O157:H7 (EC01), and a saprophytic laboratory strain, E. coli JM109 (EC22) were investigated and compared. The cellular surface charge of most E. coli O157:H7 strains were much less affected by changes in the pH, ionic strength or concentration of surfactants in the suspending medium than was the surface charge of E. coli JM109 cells. Strong adhesion to beef muscle was found in suspending conditions of pH 4 or 10, and with a lowered ionic strength. All E. coli strains tested were negatively charged in 150 mM PBS buffer (pH 7.4) as measured by zeta potentials, ranging from -4.9 to -33.9 mV. Based on the results of adhesion to hexadecane, nine out of 22 strains tested were moderately hydrophobic with about 50% of the cells bound to the solvent. Cellular adhesion of 16 E. coli strains to beef muscle was examined in 150 mM PBS buffer. Generally, O157:H7 strains had lower adhesive properties (Sr value less than 0.10) to beef muscle than other serotypes (up to 0.39). No correlation was found between E. coli cell surface charge, hydrophobicity and adhesion to beef muscle.     

抗菌和防细菌黏附整理剂在棉织物改性中的应用

为制备同时具有抗菌和防细菌黏附功能的棉织物,采用光控葡萄糖氧化酶体系引发自由基聚合反应,分别以[2-(甲基丙烯酰基氧基)乙基]二甲基-(3-磺酸丙基)氢氧化铵(SBMA)或甲基丙烯酸二甲氨基乙酯(DMAEMA)与3-(异丁烯酰氧)丙基三甲氧基硅烷(TMSPMA)聚合,得到防细菌黏附聚合物P(TMSPMA-co-SBMA)和抗菌聚合物P(TMSPMA-co-DMAEMA)。然后,通过浸渍-焙烘法将2种聚合物单独或共同整理到棉织物上。测试了整理织物的化学结构、表面元素含量、抗菌性能、防死/活细菌黏附性能等。结果表明：2种聚合物成功整理到棉织物上;抗菌整理棉织物抑菌率达到99.9%,表面较多死细菌;防细菌黏附整理棉织物具有85%以上抑菌率,表面黏附的死/活细菌均较少;抗菌防细菌黏附棉织物抑菌率与防活细菌黏附率达到98%和81%以上,且织物表面可防止死细菌黏附。     

The effects of a biocide and a surfactant on the detachment of Pseudomonas fluorescens from glass surfaces

Application of antimicrobial chemicals is a general procedure in the cleaning and disinfection of food-contacting surfaces. Adhesion to glass surfaces and chemically induced detachment of Pseudomonas fluorescens ATCC 13525(T) were studied in situ, under flow conditions, in a well-controlled parallel plate flow chamber (PPFC). Ortho-phthalaldehyde (OPA) and cetyltrimethyl ammonium bromide (CTAB) were applied separately, at several concentrations, to attached bacteria and their subsequent detachment was monitored. Following treatments the remaining adhered bacteria were characterized in terms of viability and cell size. Simultaneously, the planktonic cell surface was characterized in order to correlate PPFC results with thermodynamic approaches for adhesion evaluation, and surface free energy of chemically treated cells with adhesion strength. About 2.8x10(6) cells/cm(2) adhered to the glass surface after 30 min of bacterial flow, although thermodynamic analyses evidenced unfavourable adhesion. The independent application of OPA and CTAB promoted bacterial detachment to a small extent (16% of total cells). The remaining adhering bacteria were totally non-viable for OPA> or =0.75 mM and CTAB> or =0.25 mM, showing a lack of correlation between bacterial viability and detachment. The cellular size decreased as attachment proceeded and with chemical treatment. Both chemicals altered the cell surface properties, increasing the cell-glass adhesion strength, and promoting the emergence of polar characteristics. The overall results emphasize that OPA and CTAB were markedly ineffective in removing glass-attached P. fluorescens, demonstrating that bacteria can be non-viable but remain strongly attached to the adhesion surface.     

QUALITY OF RESTRUCTURED PORK ROASTS AS INFLUENCED BY SALT, PHOSPHATE AND ROASTING ENVIRONMENT

A split plot design was used to evaluate the effect of 3 salt (0.0, 0.5, 1.0%), 3 phosphate (0.0, 0.25, 0.5%) levels and 2 roasting environments (moist, dry) on the quality of restructured pork roasts. Emulsion stability, yield (cooked or sliced), Instron adhesion (bind), pH, water holding capacity, proximate composition and color measurements were obtained. Increasing salt or phosphate level increased emulsion stability and cooked yield. Increasing salt level and the addition of phosphate decreased expressible moisture and increased slice count and moisture content. Increased levels of salt decreased protein content, while increasing phosphate, increased pH and redness in the cooked slices. Salt and phosphate reacted synergistically to increase slice yield and adhesion bind. Roasts cooked in a moist environment were lower in pH, were darker in color and required less time to cook. Restructured pork roast quality was enhanced when salt and phosphate were included in the formulation.