New method to study bacterial adhesion to meat.

A new method was developed for the study of bacterial adhesion to meat surfaces. Thin slices of meat (40 microns thick) were inserted into a specially designed observation chamber. The meat slices were then exposed to a bacterial suspension (ca. 10(6) CFU.ml-1) to initiate adhesion (20 min of contact time) and subsequently rinsed to eliminate nonadherent bacteria. Because of the special chamber design, the disruptive force exerted on the bacteria during rinsing (shear stress) was uniform over the whole surface of the meat slices, was constant, and could be varied from 0 to 0.08 N.m-2. After being rinsed, the meat slices were stained with basic fuschin and observed under light microscopy to determine the number and distribution of adherent bacteria. This new method was used to study the adhesion of Acinetobacter strain LD2, a Lactobacillus sp., and Pseudomonas fluorescens to slices of beef fat and tendon. At 25 degrees C, most (greater than or equal to 99.9%) of the cells of the Lactobacillus sp. deposited on the meat were washed off the surface during rinsing (0.05 N.m-2), whereas a large number (ca. 10(5) CFU.cm-2) of Acinetobacter strain LD2 and P. fluorescens cells remained adherent. The extent of adhesion was similar on fat and tendon, and adherent bacteria were distributed evenly over the whole surface of the slices. This preliminary study indicates that the combined use of thin slices of meat and of the observation chamber provides us with the means to more accurately study bacterial adhesion to meat surfaces.     

Interaction between Streptococcus lactis and Aspergillus flavus on production of aflatoxin

The inoculation of Aspergillus flavus spores into a culture of Streptococcus lactis in Lablemco tryptone broth medium resulted in little or no aflatoxin accumulation even though the growth of the fungus was not hindered. The drop in pH and reduced nutrient levels in the medium as a result of the S. lactis growth were not the cause of the observed inhibition. The inhibition was not eliminated by the addition of carbohydrate equal to the amount used by the bacterium before the inoculation with the fungus. Aflatoxin levels were also markedly reduced when S. lactis was inoculated into a growing A. flavus culture. In addition to inhibiting the synthesis of aflatoxin, S. lactis also degraded preformed toxin. A. flavus, on the other hand, not only reduced the growth of S. lactis but also affected the morphology of the bacterial cell; the cells became elongated and formed long chains. S. lactis produced and excreted the inhibitor into the medium late in its growth phase. The inhibitor was a heat-stable low-molecular-weight compound. Chloroform extracts of A. flavus grown in the presence of S. lactis were toxic to Bacillus megaterium but did not exhibit mutagenic or carcinogenic activity in the Salmonella/mammalian microsome mutagenicity test.     

A model study of factors involved in adhesion of Pseudomonas fluorescens to meat.

A study was undertaken to investigate the factors involved in the adhesion of Pseudomonas fluorescens to model meat surfaces (tendon slices). Adhesion was fast (less than 2.5 min) and was not suppressed by killing the cells with UV, gamma rays, or heat, indicating that physiological activity was not required. In various salt solutions (NaCl, KCl, CaCl2, MgCl2), adhesion increased with increasing ionic strength up to 10 to 100 mM, suggesting that, at low ionic strengths, electrostatic interactions were involved in the adhesion process. At higher ionic strengths (greater than 10 to 100 mM) or in the presence of Al3+ ions, adhesion was sharply reduced. Selectively blocking of carboxyl or amino groups at the cell surface by chemical means did not affect adhesion. These groups are therefore not directly involved in an adhesive bond with tendon. Given a sufficient cell concentration (10(10) CFU.ml-1) in the adhesion medium, the surface of tendon was almost entirely covered with adherent bacteria. This suggests that if the adhesion is specific, the attachment sites on the tendon surface must be located within collagen or proteoglycan molecules.     

Role of flagella in adhesion of Pseudomonas fluorescens to tendon slices.

Tendon slices were used as model surfaces to investigate the role of flagella in the adhesion of Pseudomonas fluorescens to meat. The slices were introduced into a specially designed flow chamber, which was then filled with a suspension of the organism, and the tendon surface was observed at a x640 magnification. The same events that occur during the colonization of glass surfaces (apical adhesion of cells with rotation around the contact point, longitudinal adhesion, detachment of apically and longitudinally adherent cells) were also observed on tendon. Mechanical removal of the flagella resulted in no change in the contact angles with 0.1 M saline or alpha-bromonaphthalene, in the electrophoretic mobility, or in the adhesion of the organism to hydrophobic and ion-exchange resins. In addition, cells from which flagella had been mechanically removed still adhered extensively to tendon. Nevertheless, under comparable conditions (bacterial concentration, contact time), flagellated cells adhered to tendon in larger numbers than did deflagellated cells. This was entirely due to the ability of the motile flagellated cells to reach tendon in greater numbers than deflagellated cells.     

Characterization of bone-marrow-derived rat mesenchymal stem cells depending on donor age

It is generally accepted that autologous transfers, as non-immunogenic, constitute the safest approach in cellular transplantations. However, this attitude is often associated with the need for isolation and extracorporeal propagation of cells derived from aged patients. Thus the knowledge about relationship between aging and the properties of MSCs (mesenchymal stem cells) is crucial in developing new clinical strategies. The aim of this study was to perform complex comparison of MSC derived from young and aged individuals, which included phenotype, proliferating rate, osteogenic and adipogenic potential and secretory activity. Evaluated populations were isolated from bone marrow of 3-month-old and 24-month-old rats. There was no significant difference in membrane antigen expression and PDT (population doubling time). Additionally, the adipogenic and osteogenic potential did not vary between studied populations. The reaction of MSCs to either mitogen [bFGF (basic fibroblas t growth factor)] or oxidative stress (H2O2) in vitro displayed a very similar pattern in both analysed populations. There was no difference in TGFβ1 (transforming growth factor β1) and VEGF (vascular endothelial growth factor) secretion measured by ELISA test and gene expression evaluated by real-time PCR. However, the expression of the gene for IL-1α (interleukin-1α) was 8-fold lower in oMSC (MSC isolated from old rats). These results indicate that aging individuals can be considered as candidates for autologous transplantation of bone-marrow-derived MSCs.     

The dynamic recruitment of TRBP to neuronal membranes mediates dendritogenesis during development

MicroRNAs are important regulators of local protein synthesis during neuronal development. We investigated the dynamic regulation of microRNA production and found that the majority of the microRNA‐generating complex, consisting of Dicer, TRBP, and PACT, specifically associates with intracellular membranes in developing neurons. Stimulation with brain‐derived neurotrophic factor (BDNF), which promotes dendritogenesis, caused the redistribution of TRBP from the endoplasmic reticulum into the cytoplasm, and its dissociation from Dicer, in a Ca²⁺‐dependent manner. As a result, the processing of a subset of neuronal precursor microRNAs, among them the dendritically localized pre‐miR16, was impaired. Decreased production of miR‐16‐5p, which targeted the BDNF mRNA itself, was rescued by expression of a membrane‐targeted TRBP. Moreover, miR‐16‐5p or membrane‐targeted TRBP expression blocked BDNF‐induced dendritogenesis, demonstrating the importance of neuronal TRBP dynamics for activity‐dependent neuronal development. We propose that neurons employ specialized mechanisms to modulate local gene expression in dendrites, via the dynamic regulation of microRNA biogenesis factors at intracellular membranes of the endoplasmic reticulum, which in turn is crucial for neuronal dendrite complexity and therefore neuronal circuit formation and function.     

Controlled Release of Food Lipids Using Monoglyceride Gel Phases Regulates Lipid and Insulin Metabolism in Humans

We describe a solid vegetable oil–water gel structure which is stabilized through the use of low concentrations of monoglycerides, containing no added trans fats or saturated fats. The resulting structure consists of oil droplets encapsulated in self-assembled crystalline monoglyceride multilayers, surrounded by a continuous water phase. Acute ingestion human feeding trials indicated that the serum triglyceride loading was significantly lower after ingestion of the structured gel rather than a simple oil–water mixture, resulting in an attenuated increase in serum insulin. This indicates the effectiveness of encapsulation in modulating blood lipid and insulin response in humans, and suggests a strategy that can be employed for the controlled release of food macronutrients. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interaction between Streptococcus lactis and Aspergillus flavus on production of aflatoxin.

The inoculation of Aspergillus flavus spores into a culture of Streptococcus lactis in Lablemco tryptone broth medium resulted in little or no aflatoxin accumulation even though the growth of the fungus was not hindered. The drop in pH and reduced nutrient levels in the medium as a result of the S. lactis growth were not the cause of the observed inhibition. The inhibition was not eliminated by the addition of carbohydrate equal to the amount used by the bacterium before the inoculation with the fungus. Aflatoxin levels were also markedly reduced when S. lactis was inoculated into a growing A. flavus culture. In addition to inhibiting the synthesis of aflatoxin, S. lactis also degraded preformed toxin. A. flavus, on the other hand, not only reduced the growth of S. lactis but also affected the morphology of the bacterial cell; the cells became elongated and formed long chains. S. lactis produced and excreted the inhibitor into the medium late in its growth phase. The inhibitor was a heat-stable low-molecular-weight compound. Chloroform extracts of A. flavus grown in the presence of S. lactis were toxic to Bacillus megaterium but did not exhibit mutagenic or carcinogenic activity in the Salmonella/mammalian microsome mutagenicity test.     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

A model study of factors involved in adhesion of Pseudomonas fluorescens to meat.

A study was undertaken to investigate the factors involved in the adhesion of Pseudomonas fluorescens to model meat surfaces (tendon slices). Adhesion was fast (less than 2.5 min) and was not suppressed by killing the cells with UV, gamma rays, or heat, indicating that physiological activity was not required. In various salt solutions (NaCl, KCl, CaCl2, MgCl2), adhesion increased with increasing ionic strength up to 10 to 100 mM, suggesting that, at low ionic strengths, electrostatic interactions were involved in the adhesion process. At higher ionic strengths (greater than 10 to 100 mM) or in the presence of Al3+ ions, adhesion was sharply reduced. Selectively blocking of carboxyl or amino groups at the cell surface by chemical means did not affect adhesion. These groups are therefore not directly involved in an adhesive bond with tendon. Given a sufficient cell concentration (10(10) CFU.ml-1) in the adhesion medium, the surface of tendon was almost entirely covered with adherent bacteria. This suggests that if the adhesion is specific, the attachment sites on the tendon surface must be located within collagen or proteoglycan molecules.