Use of a fluorescent viability stain to assess lethal and sublethal injury in food-borne bacteria exposed to high-intensity pulsed electric fields

AIMS: To apply scanning electron microscopy, image analysis and a fluorescent viability stain to assess lethal and sublethal in food-borne bacteria exposed to high-intensity pulsed electric fields (PEF). METHODS AND RESULTS: A rapid cellular staining method using the fluorescent redox probes 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4',6-diamidino-2-phylindole was used for enumerating actively respiring cells of Listeria mononcytogenes, Bacillus cereus and Escherichia coli. This respiratory staining (RS) approach provided good agreement with the conventional plate count agar method for enumerating untreated and high-intensity PEF-treated bacteria suspended in 0.1% (w/v) peptone water. However, test organisms subjected to similar levels of lethality by heating at 56 degrees C resulted in ca 3-log-unit difference in surviving cell numbers ml(-1) when enumerated by these different viability indicators. PEF-treated bacteria were markedly altered at the cellular level when examined by scanning electron microscopy. CONCLUSIONS: While PEF-treatment did not produce sublethally injured cells (P < 0.05), substantial subpopulations of test bacteria rendered incapable of forming colonies by heating may remain metabolically active. SIGNIFICANCE AND IMPACT OF THE STUDY: The fluorescent staining method offers interesting perspectives on assessing established and novel microbial inactivation methods. Use of this approach may also provide a better understanding of the mechanisms involved in microbial inactivation induced by PEF.     

Mechanism of biological effects observed in honey bees (apis mellifera,L.) hived under extra-high-voltage transmission lines: Implications derived from bee exposure to simulated intense electric fields and shocks

This work explores mechanisms for disturbance of honey bee colonies under a 765 kV, 60-Hz transmission line [electric (E) field = 7 kV/m] observed in previous studies. Proposed mechanisms fell into two categories: direct bee perception of enhanced in-hive E fields and perception of shock from induced currents. The adverse biological effects could be reproduced in simulations where only the worker bees were exposed to shock or to E field in elongated hive entranceways (=tunnels). We now report the results of full-scale experiments using the tunnel exposure scheme, which assesses the contribution of shock and intense E field to colony disturbance. Exposure of worker bees (1,400 h) to 60-Hz E fields including 100 kV/m under moisture-free conditions within a nonconductive tunnel causes no deleterious affect on colony behavior. Exposure of bees in conductive (e.g., wet) tunnels produces bee disturbance, increased mortality, abnormal propolization, and possible impairment of colony growth. We propose that this substrate dependence of bee disturbance is the result of perception of shock from coupled body currents and enhanced current densities postulated to exist in the legs and thorax of bees on conductors. Similarly, disturbance occurs when bees are exposed to step-potential-induced currents. At 275–350 nA single bees are disturbed; at 600 nA bees begin abnormal propolization behavior; and stinging occurs at 900 nA. We conclude that biological effects seen in bee colonies under a transmission line are primarily the result of electric shock from induced hive currents. This evaluation is based on the limited effects of E-field exposure in tunnels, the observed disturbance thresholds caused by shocks in tunnels, and the ability of hives exposed under a transmission line to source currents 100–1,000 times the shock thresholds.     

F2L, a peptide derived from heme-binding protein, inhibits LL-37-induced cell proliferation and tube formation in human umbilical vein endothelial cells

F2L, a peptide derived from heme-binding protein, was originally identified as an endogenous ligand for formyl peptide receptor-like (FPRL)2. Previously, we reported that F2L inhibits FPR and FPRL1-mediated signaling in neutrophils. Since endothelial cells express functional FPRL1, we examined the effect of F2L on LL-37 (an FPRL1 agonist)-induced signaling in human umbilical vein endothelial cells (HUVECs). F2L stimulated the chemotactic migration in HUVECs. However, F2L inhibited FPRL1 activity, resulting in the inhibition of cell proliferation and tube formation induced by LL-37 in HUVECs. We suggest that F2L will potentially be useful in the study of FPRL1 signaling and the development of drugs to treat diseases involving the FPRL1 in the vascular system.     

Rice field ecology and fish culture — an overview

Rice fields are an integral part of the landscape throughout most of the tropics. Rice is also grown widely in higher latitudes. Most rice cultivation is done in flooded fields where a temporary aquatic fauna is generated. Rice cultivation has sustained some of the oldest civilizations but the use of the aquatic phase for raising a crop of fish has not been practiced widely although fragmentary records indicate that rice and fish have been cultivated concurrently but rarely over 2 or 3 millennia. We have more reliable records of rice and fish culture in rice fields during the past 150 years.Rice cultivation is now very highly mechanized and uses high fertilizer and pesticide inputs and extensive irrigation facilities have been constructed to increase the area of rice cultivation and enhance yields. Rice cultivation also provides a suitable habitat for the breeding of mosquitoes, some of which are vectors for diseases. It appears that in regions outside the tropics aquatic pests of rice are also encountered. In the tropics indigenous fishes and other organisms including copepods act as biological control agents for mosquitoes and aquatic rice pests.The rice field is usually a successor of shallow marshes or a lowland area which can be supplied with adequate water. In addition deep water rice is grown in permanent marshes and rice is also grown in terraced hillsides, not to mention relatively dry localities where dry-land rice is cultivated. The marsh habitat is usually rich in plant and animal species. Some of these survive in rice fields. The water supplied to rice fields come via irrigation systems which bring a complement of plants, animals, and other organisms seasonally to colonize the rice field. The rice field is thus a new habitat, like a reservoir, with some similarities to a marsh but manipulated for cultivation of rice. This creates a unique, temporary and rapidly changing habitat which is often very productive and can be used to raise fish on an artisanal or intensive scale.Fish culture in rice fields has had a checkered history during the past 150 years when records are available. Its earlier history is obscure. Long-term records of fish culture activities are not available from any part of the world although apparently thriving enterprises seem to have existed in Japan, Italy, USSR and China. Attempts to culture fish in rice fields have been made on all continents except Australasia and Antarctica of course. At the present time the focus of rice-cultivation seems to have shifted to China, Indonesia, and Thailand. Whether this enterprise will endure even in these countries cannot be predicted with any degree of certainty.     

Representation of Visual Space in Area 7a Neurons Using the Center of Mass Equation

The firing rate of neurons in parietal area 7a of the behaving Rhesus monkey with its head fixed incorporates both visual and eye position information. This neural tuning is not in an ego-centered coordinate space. This physiological result was unexpected as behavioral deficits following parietal damage in human and monkey subjects suggested the existence of egocentric representations. A formulation to extract a world-centered system from area 7a neurons is presented that depends on the linearity of the eye position signal and the similarity of the equation describing the tuning of these neurons to the center of mass equation. This formulation permits the computation of the location of objects in world coordinates using either serial analysis of a single neuron's activity or parallel processing of a collection of neurons. Experimental predictions are made for the relationship between different parameters of angle of gaze neurons.     

A Hallucinogenic Serotonin-2A Receptor Agonist Reduces Visual Response Gain and Alters Temporal Dynamics in Mouse V1

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Cell culture dosimetry for low-frequency magnetic fields

Calculations of the current density and electric field distributions induced in cell cultures by an applied low-frequency magnetic field have assumed that the medium is uniform. This paper calculates these distributions for a more realistic, inhomogeneous, anisotropic model in which the cells are regarded as conducting squares surrounded by insulating membranes. Separate parameters are used to specify the resistivities of the cell interior, the cell membrane parallel to its surface, the cell membrane perpendicular to its surface, and the intercellular junction parallel to the membrane. The presence of gap junctions connecting the interiors of adjacent cells is also considered. For vertical applied magnetic fields, the induced currents and field distributions may deviate considerably from the homogeneous medium model if there is sufficiently tight binding of the cells to each other. The presence of gap junctions can produce relatively large transmembrane electric fields or intracellular current densities. These considerations are generally less important for horizontal applied fields. A simple microscopic model of the cell surface is also discussed. © 1996 Wiley-Liss, Inc.     

乌拉坦对青、老年猫视皮层神经元反应特性的影响(英文)

以前的电生理研究结果显示, 老年哺乳动物视皮层细胞的自发反应及对视觉刺激的诱发反应比青年动物的显著增加, 而对光栅刺激的方位和运动方向选择性却显著下降。然而, 这种视皮层细胞功能的老年性改变是否因青、老年猫细胞对不同麻醉水平的敏感性差异引起尚不清楚。为探讨该问题, 以常用的麻醉药——乌拉坦(Urethane)为实验对象, 通过改变其麻醉剂量分别记录青、老年猫初级视皮层细胞对不同方位和运动方向光栅刺激的调谐反应。研究结果显示, 在基础麻醉量的基础上, 累积增加 50 mg 和 100 mg 乌拉坦对青、老年猫视皮层细胞的自发反应和诱发反应以及对光栅刺激方位和运动方向的选择性不产生显著影响, 累积增加 150 mg 乌拉坦会导致青、老年猫视皮层细胞对视觉刺激的反应性下降, 但下降的幅度相似。以上研究结果表明, 不同剂量的乌拉坦对青、老年动物视皮层细胞的反应性具有相似的影响。     

Molecular basis underlying the biological effects elicited by extremely low-frequency magnetic field (ELF-MF) on neuroblastoma cells

Extremely low-frequency magnetic fields (ELF-MFs) may affect human health because of the possible associations with leukemia but also with cancer, cardiovascular, and neurological disorders. In the present work, human SH-SY5Y neuroblastoma cells were exposed to a 50 Hz, 1 mT sinusoidal ELF-MF at three different times, that is, 5 days (T5), 10 days (T10), and 15 days (T15) and then the effects of ELF-MF on proteome expression and biological behavior were investigated. Through comparative analysis between treated and control samples, we analyzed the proteome changes induced by ELF-MF exposure. Nine new proteins resolved in sample after a 15-day treatment were involved in a cellular defense mechanism and/or in cellular organization and proliferation such as peroxiredoxin isoenzymes (2, 3, and 6), 3-mercaptopyruvate sulfurtransferase, actin cytoplasmatic 2, t-complex protein subunit beta, ropporin-1A, and profilin-2 and spindlin-1. Our results indicated that ELF-MFs exposure altered the proliferative status and other important cell biology-related parameters, such as cell growth pattern, and cytoskeletal organization. These findings support our hypothesis that ELF radiation could trigger a shift toward a more invasive phenotype.