Synergistic action of rapid chilling and nisin on the inactivation of Escherichia coli

The effect of rapid and slow chilling on survival and nisin sensitivity was investigated in Escherichia coli. Membrane permeabilization induced by cold shock was assessed by uptake of the fluorescent dye 1-N-phenylnapthylamine. Slow chilling (2°C min⁻¹) did not induce transient susceptibility to nisin. Combining rapid chilling (2,000°C min⁻¹) and nisin causes a dose-dependent reduction in the population of cells in both exponential and stationary growth phases. A reduction of 6 log of exponentially growing cells was achieved with rapid chilling in the presence of 100 IU ml⁻¹ nisin. Cells were more sensitive if nisin was present during stress. Nevertheless, addition of nisin to cell suspension after the rapid chilling produced up to 5 log of cell inactivation for exponentially growing cells and 1 log for stationary growing cells. This suggests that the rapid chilling strongly damaged the cell membrane by disrupting the outer membrane barrier, allowing the sensitization of E. coli to nisin post-rapid chilling. Measurements of membrane permeabilization showed a good correlation between the membrane alteration and nisin sensitivity. Application involving the simultaneous treatment with nisin and rapid cold shock could thus be of value in controlling Gram negatives, enhancing microbiological safety and stability.     

Growth temperature and OprF porin affect cell surface physicochemical properties and adhesive capacities of <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> MF37

Pseudomonads adapt to various ecological niches by forming biofilms, which first requires bacterial adhesion on surfaces. We studied the influence of growth temperature on surface physicochemical properties of Pseudomonas fluorescens MF37 and on its adhesive capacities onto inert surfaces. It presented a global hydrophilic character, measured by microbial adhesion to solvent (MATS), and showed a cell surface more hydrophilic at 8 and 28°C than at 17°C. Moreover, P. fluorescens MF37 was more adhesive at 17°C. This critical temperature thus should be carefully taken into account in food safety. Adhesion onto inert surfaces is thus influenced by the growth temperature, which modifies the bacteria cell wall properties through changes in the outer membrane components. Therefore, we studied the effect of the loss of OprF, the major outer membrane protein, known to act as an adhesin (root, and endothelial cells). The OprF-deficient mutant was able to adhere to surfaces, but showed the same physicochemical and adhesion properties on abiotic surfaces whatever the growth temperature. OprF is thus not essential in this adhesion process. However, we suggest that OprF is involved in the bacterial environmental temperature sensing by P. fluorescens.This work was supported by a grant from the Région Bretagne (Doctoral fellowship to G.H.).     

Temperature Elevation Regulates Iron Protoporphyrin IX and Hemoglobin Binding by Porphyromonas gingivalis

Porphyromonas gingivalis, an obligate anerobe with a growth requirement for iron protoporphyrin IX (FePPIX), is exposed to increased temperatures in the inflamed periodontal pocket. In this study, P. gingivalis was grown in a chemostat at 37°C (control), 39°C, and 41°C, and examined for hemagglutinating (HA) activity, hemoglobin binding and degrading activity, and iron protoporphyrin IX binding. HA activity decreased in cells as the growth temperature increased. Binding of μ-oxo bishaem (dimeric haem), and Fe(II)- and Fe(III)-monomeric forms was increased in 39°C-grown cells but decreased in 41°C-grown cells compared with controls. Cellular hemoglobin binding and degradation decreased with increased growth temperature. The decrease in cellular hemagglutination and hemoglobin degradation occurring with increased growth temperature would limit the potential overproduction of toxic monomeric haem molecules. The increased binding of μ-oxo bishaem and monomeric forms of FePPIX at 39°C may reflect a defense strategy against reactive oxidants and a mechanism of dampening down the inflammatory response to maintain an ecological balance. Received: 24 April 2000 / Accepted: 30 May 2000     

Inhibition on <Emphasis Type="Italic">Candida albicans</Emphasis> biofilm formation using divalent cation chelators (EDTA)

Candida albicans can readily form biofilms on both inanimate and biological surfaces. In this study we investigated a means of inhibiting biofilm formation using EDTA (Ethylenediaminetetra-acetic acid), a divalent cation chelating agent, which has been shown to affect C. albicans filamentation. Candida albicans biofilms were formed in 96-well microtitre plates. Cells were allowed to adhere for 1, 2, and 4 h at 37°C, washed in PBS, and then treated with different concentrations of EDTA (0, 2.5, 25, and 250 mM). EDTA was also added to the standardized suspension prior to adding to the microtiter plate and to a preformed 24 h biofilm. All plates were then incubated at 37°C for an additional 24 h to allow for biofilm formation. The extent and characteristics of biofilm formation were then microscopically assessed and with a semi-quantitative colorimetric technique based on the use of an XTT-reduction assay. Northern blot analysis of the hyphal wall protein (HWP1) expression was also monitored in planktonic and biofilm cells treated with EDTA. Microscopic analysis and colorimetric readings revealed that filamentation and biofilm formation were inhibited by EDTA in a concentration dependant manner. However, preformed biofilms were minimally affected by EDTA (maximum of 31% reduction at 250 mM). The HWP1 gene expression was reduced in EDTA-treated planktonic and biofilm samples. These results indicate that EDTA inhibits C. albicans biofilm formation are most likely through its inhibitory effect on filamentation and indicates the potential therapeutic effects of EDTA. This compound may serve a non-toxic means of preventing biofilm formation on infections with a C. albicans biofilm etiology.     

Alkaline iron(III) reduction by a novel alkaliphilic,halotolerant, <Emphasis Type="Italic">Bacillus</Emphasis> sp. isolated from salt flat sediments of Soap Lake

A halotolerant, alkaliphilic dissimilatory Fe(III)-reducing bacterium, strain SFB, was isolated from salt flat sediments collected from Soap Lake, WA. 16S ribosomal ribonucleic acid gene sequence analysis identified strain SFB as a novel Bacillus sp. most similar to Bacillus agaradhaerens (96.7% similarity). Strain SFB, a fermentative, facultative anaerobe, fermented various hexoses including glucose and fructose. The fructose fermentation products were lactate, acetate, and formate. Under fructose-fermenting conditions in a medium amended with Fe(III), Fe(II) accumulated concomitant with a stoichiometric decrease in lactate and an increase in acetate and CO₂. Strain SFB was also capable of respiratory Fe(III) reduction with some unidentified component(s) of Luria broth as an electron donor. In addition to Fe(III), strain SFB could also utilize nitrate, fumarate, or O₂ as alternative electron acceptors. Optimum growth was observed at 30°C and pH 9. Although the optimal salinity for growth was 0%, strain SFB could grow in a medium with up to 15% NaCl by mass. These studies describe a novel alkaliphilic, halotolerant organism capable of dissimilatory Fe(III) reduction under extreme conditions and demonstrate that Bacillus species can contribute to the microbial reduction of Fe(III) in environments at elevated pH and salinity, such as soda lakes.     

Heparin-functionalized thermoresponsive surface

Temperature-dependent regulation of affinity binding between bioactive ligands and their cell membrane receptors is an attractive approach for the dynamic control of cellular adhesion, proliferation, migration, differentiation, and signal transduction. Covalent conjugation of bioactive ligands onto thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-grafted surfaces facilitates the modulation of one-on-one affinity binding between bioactive ligands and cellular receptors by changing temperature. For the dynamic control of the multivalent affinity binding between heparin and heparin-binding proteins, thermoresponsive cell culture surface modified with heparin, which interacts with heparin-binding proteins such as basic fibroblast growth factor (bFGF), has been proposed. Heparin-functionalized thermoresponsive cell culture surface induces (1) the multivalent affinity binding of bFGF in active form and (2) accelerating cell sheet formation in the state of shrunken PIPAAm chains at 37°C. By lowering temperature to 20°C, the affinity binding between bFGF and immobilized heparin is reduced with increasing the mobility of heparin and the swollen PIPAAm chains, leading to the detachment of cultured cells. Therefore, heparin-functionalized thermoresponsive cell culture surface was able to enhance cell proliferation and detach confluent cells as a contiguous cell sheet by changing temperature. A cell cultivation system using heparin-functionalized thermoresponsive cell culture surface is versatile for immobilizing other heparin-binding proteins such as vascular endothelial growth factor, fibronectin, antithrombin III, and hepatocyte growth factor, etc. for tuning the adhesion, growth, and differentiation of various cell species.     

Reduction of Fe(II)EDTA-NO by a newly isolated <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. strain DN-2 in NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> scrubber solution

Biological reduction of nitric oxide (NO) chelated by ferrous ethylenediaminetetraacetate (Fe(II)EDTA) to N₂ is one of the core processes in a chemical absorption–biological reduction integrated technique for nitrogen oxide (NO _x ) removal from flue gases. A new isolate, identified as Pseudomonas sp. DN-2 by 16S rRNA sequence analysis, was able to reduce Fe(II)EDTA-NO. The specific reduction capacity as measured by NO was up to 4.17 mmol g DCW⁻¹ h⁻¹. Strain DN-2 can simultaneously use glucose and Fe(II)EDTA as electron donors for Fe(II)EDTA-NO reduction. Fe(III)EDTA, the oxidation of Fe(II)EDTA by oxygen, can also serve as electron acceptor by strain DN-2. The interdependency between various chemical species, e.g., Fe(II)EDTA-NO, Fe(II)EDTA, or Fe (III)EDTA, was investigated. Though each complex, e.g., Fe(II)EDTA-NO or Fe(III)EDTA, can be reduced by its own dedicated bacterial strain, strain DN-2 capable of reducing Fe(III)EDTA can enhance the regeneration of Fe(II)EDTA, hence can enlarge NO elimination capacity. Additionally, the inhibition of Fe(II)EDTA-NO on the Fe(III)EDTA reduction has been explored previously. Strain DN-2 is probably one of the major contributors for the continual removal of NO _x due to the high Fe(II)EDTA-NO reduction rate and the ability of Fe(III)EDTA reduction.     

Temperature dependence of trans plasma membrane electron transport in Zea mays L. roots

Intact Zea mays L. cv. Golden Bantam seedlings which were not cold adapted were exposed to various temperatures. Trans plasma membrane potential difference was measured in a temperature range from 0 to 40 °C using intracellular microelectrodes. The depolarization caused by electron transfer across the PM to artificial external electron acceptors was investigated. Active membrane potential increased with temperature in the range from 0 to 15 °C but was independent of temperature above 20 °C. Depolarization caused by the non-membrane-permeating electron acceptors hexacyanoferrate III (HCF III) and hexabromoiridate IV (HBIIV) took place over the whole temperature range investigated. The effect of HBI IV increased up to 10 °C whereas the HCF III effects increased up to 25 °C.     

A D-Amidase Constitutive Mutant from Arthrobacter sp. NJ-26

Foods contaminated with Salmonella enterica serovar Typhi are a mojor cause of typhoid fever, leading to public health problems and economic losses worldwide. Nisin and ρ-cymene were tested in this study for their antimicrobial activity against S. Typhi at 4 °C and 37 °C. Nisin and ρ-cymene, when used separately, did not inhibit the bacterium at either temperature. A synergistic antimicrobial effect between both compounds was observed when they were used simultaneously. This synergism was greater at 37 °C than at 4 °C. The lowest concentrations of nisin and ρ-cymene required for complete inhibition of S. Typhi at 37 °C were 0.3 ppm and 1.5 ppm, respectively, and 0.3 ppm and 2.5 ppm at 4 °C. The potential of nisin and ρ-cymene to control an S. Typhi population on ready-to-eat Thai-style pork sausage was also examined. The compounds were able to eliminate the contaminating bacterium with concentrations depending on the bacterial cell number on the food.     

Characterization of the asialoglycoprotein receptor on isolated rat hepatocytes

Rat hepatocytes, freshly isolated by a collagenase perfusion technique, bound [3H]asialo-orosomucoid in a sugar-specific and calcium-dependent manner as expected for the hepatic asialoglycoprotein receptor. At least 90% of the total cell surface-bound [3H]asialo-orosomucoid represented specific binding and could be removed by washing with EDTA. Freshly isolated cells had about 7 x 10(4) surface receptors per cell. However, when cells were incubated at 37 degrees C, the number of surface receptors per cell rapidly increased 2- to 3-fold to about 2.2 x 10(5). This increase in receptor number occurred in the absence of serum and began within minutes, depending on the particular conditions used to keep the cells in suspension. (The maximal rate of appearance of new receptors at 37 degrees C was about 70 receptors per cell per s.) When cells were first exposed to a brief EDTA treatment at 4 degrees C, before measuring the binding of [3H]asialo-orosomucoid, the number of surface receptors per cell was found to increase by about 45%. Therefore, about 30% of the surface receptors on freshly isolated cells have already bound endogenous asialoglycoproteins or are present in the membrane in a cryptic form. At 4 degrees C the binding of [3H]asialo-orosomucoid was rapid (kon greater than or equal to 1.8 x 10(4) M-1s-1), whereas the dissociation of bound [3H]asialo-orosomucoid, measured in the presence of excess nonradioactive glycoprotein, was extremely slow (koff less than or equal to 0.9 x 10(-5) s-1). The association constant calculated from these data (Ka = 2.0 x 10(9) M-1) agreed well with that obtained from equilibrium binding experiments (Ka = 2.4 x 10(9) M-1) using untreated cells or cells which had first been treated with EDTA or incubated at 37 degrees C. In all cases, when the concentration of [3H]asialo-orosomucoid was higher than about 600 ng/ml, the Scatchard plots were curvilinear. The data are, however, consistent with the conclusion that there is a single high affinity receptor on the hepatocyte surface. The additional receptors that appear on the surface when cells are incubated at 37 degrees C or exposed to EDTA are identical with those on untreated cells,     

Production of nisin Z using <Emphasis Type="Italic">Lactococcus lactis</Emphasis> IO-1 from hydrolyzed sago starch

A membrane bioreactor for production of nisin Z was constructed using Lactococcus lactis IO-1 in continuous culture using hydrolyzed sago starch as carbon source. A strategy used to enhance the productivity of nisin Z was to maintain the cells in a continuous growth at high cell concentration. This resulted in a volumetric productivity of nisin Z, as 50,000 IU l⁻¹ h⁻¹ using a cell concentration of 15 g l⁻¹, 30^°C, pH 5.5 and a dilution rate of 1.24 h⁻¹. Adding 10 g l⁻¹ YE and 2 g l⁻¹ polypeptone, other inducers were unnecessary to maintain production of nisin. The operating conditions of the reactor removed nisin and lactate, thus minimizing their effects which allowed the maintenance of cells in continuous exponential growth phase mode with high metabolic activity.     

The Use of Ascorbate as a Probe of Opioid Receptor Structure: Evidence for two Independent Mechanisms of Receptor Destruction by Ascorbate

Abstract

Ascorbate (20 mM) pretreatment of brain membrane suspensions at 37° produced a rapid irreversible loss of specific opioid binding. There was no reduction in specific ³H-haloperidol binding. Ascorbate induced loss of opioid binding under these experimental conditions was not blocked by low concentrations of EDTA or Mn⁺⁺. In contrast, the slowly developing loss of opioid binding during exposure to 1 mM ascorbate at 23° was completely inhibited by 10^?5M EDTA or Mn⁺⁺. At 37°, D-isoasoorbate, and several other reducing agents (glutathione, dithiothreitol, oysteine) produced a loss of opioid binding similar to that seen with ascorbate. It is concluded that 1 mM ascorbate at 23°, and 20 mM ascorbate at 37°, destroy opioid binding sites by two independent mechanisms. Lipid peroxidation is implicated at low ascorbate concentrations; a reductive process appears to be responsible for the ascorbate induced loss of binding at higher concentrations.     

Synergistic antibacterial activity of the essential oil of Cuminum cyminum L. seed and nisin in a food model

Aims: To investigate effects of various concentrations of the essential oil of Cuminum cyminum L. seed alone and in combination with nisin on survival of vegetative forms of Bacillus cereus and Bacillus subtilis in a food model (commercial barley soup) and their ultrastructure. Methods and Results: Gas chromatography–mass spectrometry analysis indicated that cumin aldehyde (29·02%) and α‐terpinen‐7‐al (20·70%) constituted the highest amount of the essential oil. The lowest concentration of the essential oil significantly affected the growth of the bacteria at 8°C but not at 25°C. Synergistic effect of the essential oil in combination with the lowest concentration of nisin was observed on the bacteria at 8°C. Evaluation of the sensory properties showed that concentration of 0·15 μl ml^?1 of the essential oil was the most acceptable. Conclusions: The essential oil of C. cyminum L. seed showed the most bactericidal effects on B. cereus at 8°C. Ultrastructural studies of vegetative cells confirmed the synergistic destructive effects of the essential oil and nisin on membrane and cell wall of the bacteria. Significance and Impact of the Study: Utilization of essential oil of C. cyminum L. seed in combination with nisin can inhibit growth of food‐borne pathogens in food.     

Occurrence of variants with temperature-dependent susceptibility (TDS) to antibiotics among Stenotrophomonas maltophilia clinical strains

Susceptibility to 20 antibiotics was tested in 104Stenotrophomonas maltophilia strains at 37 and 30°C by means of a dilution micromethod to verity the phenomenon of temperature-dependent susceptibility (TDS). Trimethoprim-sulfamethoxazole, pefloxacin and ofloxacin were the most active preparations at 37°C (93, 90, and 86% of susceptible strains, respectively), whilst trimethoprim-sulfamethoxazole, cefoperazone-sulbactam and pefloxacin performed best at 30°C (94, 94, and 76% of susceptible strains, respectively). Variants 37TDS (minimum inhibitory concentration, MIC, of tested antibiotics at least 4-times lower at 37 than at 30°C) occurred in 60%. Variants 30TDS (at least 4-times lower value of MIC at 30 than at 37°C) were found in 7.7%. Both variants in susceptibility to tested antibiotics appeared in 23.1%, whilst neither of them was observed in 9.6%. The 37TDS phenomenon was recorded most of all with gentamicin (51% of strains), amikacin (47), colistin (44) and tetracycline (34). The 30TDS phenomenon was found particularly with cefoperazone-sulbactam (16.0% of strains) and colistin (10.0%). The above phenomena may be due to changes in membrane permeability, temperature-dependent ribosomal changes, and insufficient adaptation to higher temperatures of some strains of the originally environmental speciesS. maltophilia. Presented at the10th European Congress of Clinical Microbiology and Infectious Diseases, Stockholm (Sweden), 28–31 May 2000.     

Effects of short-term heat stress on oxidative damage and responses of antioxidant system in Lilium longiflorum

This paper aims to determine the changes in reactive oxygen species (ROS) and the responses of the lily (Lilium longiflorum L.) antioxidant system to short-term high temperatures. Plants were exposed to three levels of heat stress (37°C, 42°C, 47°C) for 10 h when hydrogen peroxide (H₂O₂) and superoxide (O₂⁻) production rate along with membrane injury indexes, and changes in antioxidants were measured. Compared with the control (20°C), electrolyte leakage and MDA concentration varied slightly after 10 h at 37°C and 42°C, while increased significantly at 47°C. During 10 h at 37°C and 42°C, antioxidant enzyme activities, such as SOD, POD, CAT, APX and GR, were stimulated and antioxidants (AsA and GSH concentrations) maintained high levels, which resulted in low levels of O₂⁻ and H₂O₂ concentration. However, after 10 h at 47°C, SOD, APX, GR activities and GSH concentration were similar to the controls, while POD, CAT activities and AsA concentration decreased significantly as compared with the control, concomitant with significant increase in O₂⁻ and H₂O₂ concentrations. In addition, such heat-induced effects on antioxidant enzymes were also confirmed by SOD and POD isoform, as Cu/ZnSOD maintained high stability under heat stress and the intensity of POD isoforms reduced with the duration of heat stress, especially at 47°C. It is concluded that in lily plants, the oxidative damage induced by heat stress was related to the changes in antioxidant enzyme activities and antioxidants.     

Influence of washing on elemental analysis of leaves of fieldgrown crop plants

Summary Information is limited on soil contamination of leaves from field-grown row crops, especially with respect to aluminum (Al) analyses. The objective of this study was to determine the influence of washing leaf samples with either deionized water or detergent solution on elemental analyses for several agronomic crop plants. The crop plants sampled were corn (Zea mays L.), soybean (Glycine max L. Merr.), grain sorghum (Sorghum bicolor L. Moench), and wheat (Triticum aestivum L.). The crops were grown on a range of soil types, soil pH values, and tillage practices. Samples of upper leaves and lower leaves were collected separately. The samples were either not washed, washed with deionized water, or washed with detergent solution. After drying, grinding, and digesting, the samples were analyzed for Al, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). For all crop plants and conditions studied, there was no effect on measured N, P, K, Ca, Mg, Mn, Zn, or Cu concentrations, but measured Al and Fe concentrations were influenced by washing. In general, washing had a greater effect on Al analyses than on Fe analyses. Soybean samples were most affected by washing, while wheat samples seemed to be least affected. The results reflected greater contamination of lower leaves than upper leaves. Decontamination procedures appear necessary prior to Al and Fe analyses of field-grown crop plants.     

Intermediate steps in cellular iron uptake from transferrin. II. A cytoplasmic pool of iron is released from cultured cells via temperature-dependent mechanical wounding

Summary A previous study described a cytoplasmic, transferrin (Tf)-free, iron (Fe) pool that was detected only when cells were mechanically detached from the culture substratum at 4°C, after initial incubation with⁵⁹Fe-¹²⁵I-Tf at 37°C (Richardson and Baker, 1992a). The release of this internalized⁵⁹Fe could be markedly reduced if the cells were treated with proteases or incubated at 37°C prior to detachment. The present study was designed to characterize this Fe pool and understand the mechanism of its release. The results show that cellular⁵⁹Fe release increased linearly as a function of preincubation time with⁵⁹Fe-Tf subsequent to mechanical detachment at 4°C using a spatula. These data suggest that the⁵⁹Fe released was largely composed of end product(s) and was not an “intermediate Fe pool.” When the Fe(II) chelator, dipyridyl (DP), was incubated with⁵⁹Fe-Tf and the cells, it prevented the accumulation of⁵⁹Fe that was released following mechanical detachment at 4°C. Other chelators had much less effect on the proportion of⁵⁹Fe released. Examination of the⁵⁹Fe released showed that after a 4-h preincubation with⁵⁹Fe-Tf, approximately 50% of the⁵⁹Fe was present in ferritin. These data indicate that mechanical detachment of cells at 4°C resulted in membrane disruptions that allow the release of high M, molecules. Moreover, electron microscopy studies showed that detachment of cells from the substratum at 4°C resulted in pronounced membrane damage. In contrast, when cells were detached at 37°C, or at 4°C after treatment with pronase, membrane damage was minimal or not apparent. These results may imply that temperature-dependent processes prevent the release of intracellular contents on membrane wounding, or alternatively, prevent wounding at 37°C. The evidence also indicates that caution is required when interpreting data from expriments where cells have been mechanically detached at 4°C.     

Ion‐Exchange and Adsorption of Fe(III) by Sepia Melanin

Sepia eumelanin is associated with many metal ions, yet little is known about its metal binding capacity and the chemical nature of the binding site(s). Herein, the natural concentrations of metal ions are presented and the ability to remove metals by exposure of the melanin granules to EDTA is quantified. The results reveal that the binding constants of melanin at pH 5.8 for Mg(II), Ca(II), Sr(II) and Cu(II) are, respectively, 5, 4, 14 and 34 times greater than the corresponding binding constants of these ions with EDTA. By exposing Sepia eumelanin to aqueous solutions of FeCl₃, the content of bound Fe(III) can be increased from a natural concentration of ～180 ppm to a saturation limit of ～80 000 ppm or 1.43 mmol/g of melanin. Similar saturation limits are found for Mg(II) and Ca(II). Exposure of Sepia melanin granules to aqueous solutions containing Ca(II) results in the stoichiometric replacement of the initially bound Mg(II), arguing that these two ions occupy the same binding site(s) in the pigment. The pH‐dependent binding of Mg(II) and Ca(II) suggests coordination of these ions to carboxylic acid groups in the pigment. Mg(II) and Ca(II) can be added to a Fe(III)‐saturated melanin sample without affecting the amount of Fe(III) pre‐adsorbed, clearly establishing Fe(III) and Mg(II)/Ca(II) occupy different binding sites. Taking recent Raman spectroscopic data into account, the binding of Fe(III) is concluded to involve coordination to o‐dihydroxyl groups. The effects of metal ion content on the surface morphology were analyzed. No significant changes were found over the full range of Fe(III) concentration studied, which is supported by the Brunauer–Emmett–Teller surface area analysis. These observations imply the existence of channels within the melanin granules that can serve to transport metal ions.     

Improved antimicrobial activity of nisin-incorporated polymer films by formulation change and addition of food grade chelator

AIMS: The following polymers were developed: polyethylene (PE), a PE and polyethylene oxide (70% PE and 30% PEO; PE + PEO) blend, PE and nisin (PE + nisin), PE, nisin, and EDTA (PE + nisin + EDTA), and PE + PEO with nisin (PE + PEO + nisin). METHODS AND RESULTS: Of the polymers tested, PE and PE + PEO did not exhibit any antimicrobial activity against Brochothrix thermosphacta (BT); however, PE + nisin, PE + nisin + EDTA, and PE + PEO + nisin did. Beef surfaces were experimentally inoculated with 3.50 log10 cfu/cm2 of BT, vacuum packaged with each of the five polymers, and held at 4 degrees C for 21 d. After 3 d at 4 degrees C, BT was reduced > 1.70 log(10) by PE + nisin and > 3.50 log(10) with PE + nisin + EDTA or PE + PEO + nisin. By 21 d at 4 degrees C, BT was reduced to 0.30 log(10) cfu/cm(2) when treated with PE + PEO + nisin. CONCLUSION: It appears that PE + PEO + nisin or PE + nisin + EDTA were more effective for reducing BT, as compared to polymers composed of PE + nisin. SIGNIFICANCE AND IMPACT OF THE STUDY: Nisin-incorporated polymers may control the growth of undesirable bacteria, thereby extending the shelf life and possibly enhancing the microbial safety of meats.     

The influence of chelating agents upon the dissimilatory reduction of Fe(III) by Shewanella putrefaciens

The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O₂, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction.