Search for Gamma-Ray Spectral Lines from Dark Matter Annihilation up to 100 TeV toward the Galactic Center with MAGIC

Linelike features in TeV γ rays constitute a "smoking gun" for TeV-scale particle dark matter and new physics. Probing the Galactic Center region with ground-based Cherenkov telescopes enables the search for TeV spectral features in immediate association with a dense dark matter reservoir at a sensitivity out of reach for satellite γ-ray detectors, and direct detection and collider experiments. We report on 223 hours of observations of the Galactic Center region with the MAGIC stereoscopic telescope system reaching γ-ray energies up to 100 TeV. We improved the sensitivity to spectral lines at high energies using large-zenith-angle observations and a novel background modeling method within a maximum-likelihood analysis in the energy domain. No linelike spectral feature is found in our analysis. Therefore, we constrain the cross section for dark matter annihilation into two photons to ⟨σv⟩≲5×10^{-28}  cm^{3} s^{-1} at 1 TeV and ⟨σv⟩≲1×10^{-25}  cm^{3} s^{-1} at 100 TeV, achieving the best limits to date for a dark matter mass above 20 TeV and a cuspy dark matter profile at the Galactic Center. Finally, we use the derived limits for both cuspy and cored dark matter profiles to constrain supersymmetric wino models.

Global Tonga tsunami explained by a fast-moving atmospheric source

Volcanoes can produce tsunamis by means of earthquakes, caldera and flank collapses, pyroclastic flows or underwater explosions1-4. These mechanisms rarely displace enough water to trigger transoceanic tsunamis. Violent volcanic explosions, however, can cause global tsunamis1,5 by triggering acoustic-gravity waves6-8 that excite the atmosphere-ocean interface. The colossal eruption of the Hunga Tonga-Hunga Ha'apai volcano and ensuing tsunami is the first global volcano-triggered tsunami recorded by modern, worldwide dense instrumentation, thus providing a unique opportunity to investigate the role of air-water-coupling processes in tsunami generation and propagation. Here we use sea-level, atmospheric and satellite data from across the globe, along with numerical and analytical models, to demonstrate that this tsunami was driven by a constantly moving source in which the acoustic-gravity waves radiating from the eruption excite the ocean and transfer energy into it by means of resonance. A direct correlation between the tsunami and the acoustic-gravity waves' arrival times confirms that these phenomena are closely linked. Our models also show that the unusually fast travel times and long duration of the tsunami, as well as its global reach, are consistent with an air-water-coupled source. This coupling mechanism has clear hazard implications, as it leads to higher waves along land masses that rise abruptly from long stretches of deep ocean waters.

Global Tonga tsunami explained by a fast-moving atmospheric source

Volcanoes can produce tsunamis by means of earthquakes, caldera and flank collapses, pyroclastic flows or underwater explosions^1-4. These mechanisms rarely displace enough water to trigger transoceanic tsunamis. Violent volcanic explosions, however, can cause global tsunamis^1,5 by triggering acoustic-gravity waves^6-8 that excite the atmosphere-ocean interface. The colossal eruption of the Hunga Tonga-Hunga Ha'apai volcano and ensuing tsunami is the first global volcano-triggered tsunami recorded by modern, worldwide dense instrumentation, thus providing a unique opportunity to investigate the role of air-water-coupling processes in tsunami generation and propagation. Here we use sea-level, atmospheric and satellite data from across the globe, along with numerical and analytical models, to demonstrate that this tsunami was driven by a constantly moving source in which the acoustic-gravity waves radiating from the eruption excite the ocean and transfer energy into it by means of resonance. A direct correlation between the tsunami and the acoustic-gravity waves' arrival times confirms that these phenomena are closely linked. Our models also show that the unusually fast travel times and long duration of the tsunami, as well as its global reach, are consistent with an air-water-coupled source. This coupling mechanism has clear hazard implications, as it leads to higher waves along land masses that rise abruptly from long stretches of deep ocean waters.

A microparticle blood analogue suspension matching blood rheology

The handling of blood in vitro is demanding because of ethical, economical and safety issues. Although several Newtonian and non-Newtonian blood analogues are found in the literature, few studies have used particles to mimic red blood cells (RBCs) and built an analogue with similar rheological properties of blood. This work reports the development of a blood analogue suspension composed of polydimethylsiloxane (PDMS) microparticles with an average diameter of ∼7 μm. High throughput production of PDMS particles is possible using a multi-stage membrane emulsification process; up to ∼6 mL of microparticles are manufactured in 3 hours. PDMS particles at a concentration of around 21% (w/w) at 20 °C present steady, oscillatory and extensional rheologies very similar to those of blood under physiological conditions (37 °C and ∼41% hematocrit), making them a good candidate whole blood analogue. Also, flow studies were performed in microchannels with contraction to study the cell-free layer (CFL) formation and particle deformation, achieving good qualitative results. Using the procedure developed, it is possible to obtain blood analogue fluids with a shelf life of at least 6 months.

Cell adhesion in microchannel multiple constrictions - Evidence of mass transport limitations

Biofilm growth (fouling) in microdevices is a critical concern in several industrial, engineering and health applications, particularly in novel high-performance microdevices often designed with complex geometries, narrow regions and multiple headers. Unfortunately, on these devices, the regions with local high wall shear stresses (WSS) also show high local fouling rates. Several explanations have been put forward by the scientific community, including the effect of cell transport by Brownian motion on the adhesion rate. In this work, for the first time, both WSS and convection and Brownian diffusion effects on cell adhesion were evaluated along a microchannel with intercalate constriction and expansion zones designed to mimic the hydrodynamics of the human body and biomedical devices. Convection and Brownian diffusion effects were numerically studied using a steady-state convective-diffusion model (convection, diffusion and sedimentation). According to the numerical results, the convection and Brownian diffusion effects on cell adhesion are effectively more significant in regions with high WSS. Furthermore, a good agreement was observed between experimental and predicted local Sherwood numbers, particularly at the entrance and within the multiple constrictions. However, further mechanisms should be considered to accurately predict cell adhesion in the expansion zones. The described numerical approach can be used as a way to identify possible clogging zones in microchannels, and defining solutions, even before the construction of the prototype.

Bounds on Lorentz Invariance Violation from MAGIC Observation of GRB 190114C

On January 14, 2019, the Major Atmospheric Gamma Imaging Cherenkov telescopes detected GRB 190114C above 0.2 TeV, recording the most energetic photons ever observed from a gamma-ray burst. We use this unique observation to probe an energy dependence of the speed of light in vacuo for photons as predicted by several quantum gravity models. Based on a set of assumptions on the possible intrinsic spectral and temporal evolution, we obtain competitive lower limits on the quadratic leading order of speed of light modification.

Sample treatment based on molecularly imprinted polymers for the analysis of veterinary drugs in food samples: a review

The use of veterinary drugs in medical treatments and in the livestock industry is a recurrent practice. When applied in subtherapeutic doses over prolonged times, they can also act as growth promoters. However, residues of these substances in foods present a risk to human health. Their analysis is thus important and can help guarantee consumer safety. The critical point in each analytical technique is the sample treatment and the analytical matrix complexity. The present manuscript summarizes the development, type of synthesis, characterization, and application of molecularly imprinted polymers in the separation, identification, and quantification techniques for the determination of veterinary drug residues in food samples in extraction, clean-up, isolation, and pre-concentration systems. Synthesized sorbents with specific recognition properties improve the interactions between the analytes and the polymeric sorbents, providing better analysis conditions and advantages in comparison with commercial sorbents in terms of high selectivity, analytical sensitivity, easy performance, and low cost analysis.

Occurrence of mycotoxins in talkan: a cereal-based food traditional for Turkic population

The consumption of cereal contaminated with mycotoxins poses a serious health risk for humans and animals. The present work aims to evaluate the presence of mycotoxins in talkan, a cereal-based food commonly consumed by the Turkic population. The presence of mycotoxins was investigated in a total of 50 samples obtained from Kazakhstan. After a preliminary screening using various ELISA kits, mycotoxins were confirmed and quantified by HPLC-MS/MS method. More than 28% of the samples were positive for at least one mycotoxin. The calculated probably daily intake for adults and children was 20% above the tolerable daily intake for aflatoxin B1 and deoxynivalenol, while it was above 100% for zearalenone, indicating a high risk for the Kazakh population. A total of 12 samples exhibited concentrations above the European maximum level for ochratoxin A, zearalenone and deoxynivalenol, however, these values were within the limits established by the Russia-Kazakhstan-Belarus Customs Union (TR CU 015/2011).

Assessment of food safety using a new real-time PCR assay for detection and quantification of virulence factors of enterococci in food samples

AIMS

Development of Taqman MGB real-time PCR (q-PCR) assays for the quantitative detection of virulence factor genes in pure culture and food samples with regard to food safety assessment.

METHODS AND RESULTS

New Taqman primers and probes were designed for the ace, esp and gelE genes based on the determinants of virulence profiles of enterococcal strains from GenBank. The high specificity and accuracy of the Taqman probe assay was confirmed. The limit of detection for the different virulence genes was 10²  CFU ml^-1 or CFU g^-1 for pure culture and meat samples, and 10³  CFU g^-1 for cheese samples.

CONCLUSION

This method provides the specific and rapid detection and quantification of ace, esp and gelE genes compared to conventional PCR assays, thus allowing the rapid and direct safety assessment of Enterococcus genus in food samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presents efficient methods that can be used directly on food products for the rapid quantification and tracing of virulence genes, regarding food safety assessment. Moreover, this is the first study to quantify these virulence factors using a specific Taqman q-PCR assay in food samples.

Biofilm formation, phenotypic production of cellulose and gene expression in Salmonella enterica decrease under anaerobic conditions

Salmonella enterica subsp. enterica is one of the main food-borne pathogens. This microorganism combines an aerobic life outside the host with an anaerobic life within the host. One of the main concerns related to S. enterica is biofilm formation and cellulose production. In this study, biofilm formation, morphotype, cellulose production and transcription of biofilm and quorum sensing-related genes of 11 S. enterica strains were tested under three different conditions: aerobiosis, microaerobiosis, and anaerobiosis. The results showed an influence of oxygen levels on biofilm production. Biofilm formation was significantly higher (P<0.05) in aerobiosis than in microaerobiosis and anaerobiosis. Cellulose production and RDAR (red, dry, and rough) were expressed only in aerobiosis. In microaerobiosis, the strains expressed the SAW (smooth and white) morphotype, while in anaerobiosis the colonies appeared small and red. The expression of genes involved in cellulose synthesis (csgD and adrA) and quorum sensing (sdiA and luxS) was reduced in microaerobiosis and anaerobiosis in all S. enterica strains tested. This gene expression levels were less reduced in S. Typhimurium and S. Enteritidis compared to the tested serotypes. There was a relationship between the expression of biofilm and quorum sensing-related genes. Thus, the results from this study indicate that biofilm formation and cellulose production are highly influenced by atmospheric conditions. This must be taken into account as contamination with these bacteria can occur during food processing under vacuum or modified atmospheres.

Link between deviations from Murray's Law and occurrence of low wall shear stress regions in the left coronary artery

Murray developed two laws for the geometry of bifurcations in the circulatory system. Based on the principle of energy minimization, Murray found restrictions for the relation between the diameters and also between the angles of the branches. It is known that bifurcations are prone to the development of atherosclerosis, in regions associated to low wall shear stresses (WSS) and high oscillatory shear index (OSI). These indicators (size of low WSS regions, size of high OSI regions and size of high helicity regions) were evaluated in this work. All of them were normalized by the size of the outflow branches. The relation between Murray's laws and the size of low WSS regions was analysed in detail. It was found that the main factor leading to large regions of low WSS is the so called expansion ratio, a relation between the cross section areas of the outflow branches and the cross section area of the main branch. Large regions of low WSS appear for high expansion ratios. Furthermore, the size of low WSS regions is independent of the ratio between the diameters of the outflow branches. Since the expansion ratio in bifurcations following Murray's law is kept in a small range (1 and 1.25), all of them have regions of low WSS with similar size. However, the expansion ratio is not small enough to completely prevent regions with low WSS values and, therefore, Murray's law does not lead to atherosclerosis minimization. A study on the effect of the angulation of the bifurcation suggests that the Murray's law for the angles does not minimize the size of low WSS regions.

Biofilm Formation and Morphotypes of Salmonella enterica subsp.arizonae Differs from Those of Other Salmonella enterica Subspecies in Isolates from Poultry Houses

Salmonella serovars are responsible for foodborne diseases around the world. The ability to form biofilms allows microorganisms to survive in the environment. In this study, 73 Salmonella strains, belonging to four different subspecies, were isolated from poultry houses and foodstuffs and tested. Biofilm formation was measured at four different temperatures and two nutrient concentrations. Morphotypes and cellulose production were evaluated at three different temperatures. The presence of several genes related to biofilm production was also examined. All strains and subspecies of Salmonella had the ability to form biofilms, and 46.57% of strains produced biofilms under all conditions tested. Biofilm formation was strain dependent and varied according to the conditions. This is the first study to analyze biofilm formation in a wide number of Salmonella enterica subsp. arizonae strains, and no direct relationship between the high prevalence of Salmonella enterica subsp. arizonae strains and their ability to form biofilm was established. Morphotypes and cellulose production varied as the temperature changed, with 20°C being the optimum temperature for expression of the red, dry, and rough morphotype and cellulose. Salmonella enterica subsp. arizonae, whose morphotype is poorly studied, only showed a smooth and white morphotype and lacked the csgD and gcpA genes that are implicated in biofilm production. Thus, Salmonella biofilm formation under different environmental conditions is a public health problem because it can survive and advance through the food chain to reach the consumer.

Improving acoustic streaming effects in fluidic systems by matching SU-8 and polydimethylsiloxane layers

This paper reports the use of acoustic waves for promoting and improving streaming in tridimensional polymethylmethacrylate (PMMA) cuvettes of 15mm width×14mm height×2.5mm thickness. The acoustic waves are generated by a 28μm thick poly(vinylidene fluoride) - PVDF - piezoelectric transducer in its β phase, actuated at its resonance frequency: 40MHz. The acoustic transmission properties of two materials - SU-8 and polydimethylsiloxane (PDMS) - were numerically compared. It was concluded that PDMS inhibits, while SU-8 allows, the transmission of the acoustic waves to the propagation medium. Therefore, by simulating the acoustic transmission properties of different materials, it is possible to preview the acoustic behavior in the fluidic system, which allows the optimization of the best layout design, saving costs and time. This work also presents a comparison between numerical and experimental results of acoustic streaming obtained with that β-PVDF transducer in the movement and in the formation of fluid recirculation in tridimensional closed domains. Differences between the numerical and experimental results are credited to the high sensitivity of acoustic streaming to the experimental conditions and to limitations of the numerical method. The reported study contributes for the improvement of simulation models that can be extremely useful for predicting the acoustic effects of new materials in fluidic devices, as well as for optimizing the transducers and matching layers positioning in a fluidic structure.

Prevalence, molecular characterization and antimicrobial resistance of Salmonella serovars isolated from northwestern Spanish broiler flocks (2011-2015)

The present study investigated the prevalence, antimicrobial resistance to twenty antibiotics, and class 1 integron and virulence genes of Salmonella isolated from poultry houses of broilers in northwestern Spain between 2011 and 2015. Strains were classified to the serotype level using the Kauffman-White typing scheme and subtyping with enterobacterial repetitive intergenic consensus PCR. The prevalence of Salmonella spp. was 1.02%. Sixteen different serotypes were found, with S. typhimurium and S. arizonae 48:z4, z23:- being the most prevalent. A total of 59.70% of strains were resistant to at least one, and 19.70% were resistant to multiple drugs. All Salmonella spp. were susceptible to cefotaxime, ciprofloxacin, gentamicin, kanamycin, levofloxacin, neomycin, and trimethoprim. The highest level of resistance was to sulfamethoxazole (40.29%), doxycycline (17.91%), and nalidixic acid (17.91%). None of the isolates carried class 1 integron and only isolates of S. enterica subspecies enterica were positive for all virulence factors tested, whereas S. arizonae lacked genes related to replication and invasion in nonphagocytic cells. This study demonstrates that the prevalence and antimicrobial resistance of Salmonella spp. in poultry houses of broilers of northwestern Spain is low compared with those found in other studies and in other steps of the food chain.

Evaluation of the successive approximations method for acoustic streaming numerical simulations

This work evaluates the successive approximations method commonly used to predict acoustic streaming by comparing it with a direct method. The successive approximations method solves both the acoustic wave propagation and acoustic streaming by solving the first and second order Navier-Stokes equations, ignoring the first order convective effects. This method was applied to acoustic streaming in a 2D domain and the results were compared with results from the direct simulation of the Navier-Stokes equations. The velocity results showed qualitative agreement between both methods, which indicates that the successive approximations method can describe the formation of flows with recirculation. However, a large quantitative deviation was observed between the two methods. Further analysis showed that the successive approximation method solution is sensitive to the initial flow field. The direct method showed that the instantaneous flow field changes significantly due to reflections and wave interference. It was also found that convective effects contribute significantly to the wave propagation pattern. These effects must be taken into account when solving the acoustic streaming problems, since it affects the global flow. By adequately calculating the initial condition for first order step, the acoustic streaming prediction by the successive approximations method can be improved significantly.

A study on toxic and essential elements in rice from the Republic of Kazakhstan: comparing the level of contamination in rice from the European Community

Selected toxic elements (total As, Cd, Cr, Hg, Pb, Sr, U and V) and essential elements (Co, Cu, Fe, Mn and Zn) were analyzed using an inductively coupled plasma mass spectrometry (ICP-MS) in unpolished and milled rice collected from Kazakhstan and milled rice from Spain and Portugal to evaluate the potential health risk to the population. Arsenic species (arsenite, arsenate, arsenobetaine, dimethylarsinate and monomethilarsonate) were analyzed using HPLC-IC-MS. From 146 samples analyzed, none of them exceeded the maximum limit set by the European Legislation for Cd or Pb or values recommended by the Codex Alimentarius. Concentrations of Sr, U and V were below LOD and those of Hg, Pb, Co and Cr between <LOD and 0.54 mg/kg (highest concentration of Cr) in milled rice. Portuguese rice samples contained the highest mean concentration of As, Hg, Pb, Co, Cr, Cu, Mn and Zn. The highest mean of arsenobetaine (0.001 mg/kg), dimethylarsinate (0.27 mg/kg) and monomethilarsonate (0.02 mg/kg) was found in Spanish rice and that of arsenite (0.30 mg/kg) in Kazakh rice. Inorganic As in samples from Kazakhstan was above the ML (0.2 mg/kg) proposed by FAO/WHO, but in seven samples from Spain and in four from Portugal were above the limit. The estimated weekly intake of total or inorganic As(III, V), Cd, Hg and Pb for rice consumption by Kazakh, Spanish and Portuguese adults and children was lower than the provisional tolerable weekly intake established by Joint FAO/WHO Expert Committee on Food Additives and the European Food Safety Authority.

CFD Study of the Hydrodynamics of Slug Flow Systems: Interaction between Consecutive Taylor Bubbles

Slug flow is one of the most frequently occurring multiphase flow patterns in industrial processes. A deep knowledge of its fundamentals is necessary to accurately model not only the fluid flow but also reaction and heat and mass transfer in several operation units. A numerical study is reported on the dynamics of slug flow, under laminar regime, in vertical columns of stagnant and co-current Newtonian and non-Newtonian liquids (shear-thickening and shear-thinning). A CFD package (Ansys FLUENT) with the VOF methodology was applied to simulate the flow of individual and pairs of consecutive Taylor bubbles. The behaviour of the most relevant hydrodynamic features with the approach of the trailing bubble towards the leading one is addressed, with particular emphasis to the role of the liquid rheology and flow configuration. The main results presented are the velocity ratio curves between consecutive bubbles, the variation of the bubbles shape, and the axial velocity and viscosity fields in the surrounding liquid. This bubble-bubble interaction data can be a keystone to improve and complement continuous slug flow simulators used for very long columns.

96-well microtiter plates for biofouling simulation in biomedical settings

Microtiter plates with 96 wells are routinely used in biofilm research mainly because they enable high-throughput assays. These platforms are used in a variety of conditions ranging from static to dynamic operation using different shaking frequencies and orbital diameters. The main goals of this work were to assess the influence of nutrient concentration and flow conditions on biofilm formation by Escherichia coli in microtiter plates and to define the operational conditions to be used in order to simulate relevant biomedical scenarios. Assays were performed in static mode and in incubators with distinct orbital diameters using different concentrations of glucose, peptone and yeast extract. Computational fluid dynamics (CFD) was used to simulate the flow inside the wells for shaking frequencies ranging from 50 to 200 rpm and orbital diameters from 25 to 100 mm. Higher glucose concentrations enhanced adhesion of E. coli in the first 24 h, but variation in peptone and yeast extract concentration had no significant impact on biofilm formation. Numerical simulations indicate that 96-well microtiter plates can be used to simulate a variety of biomedical scenarios if the operating conditions are carefully set.

Macroscale versus microscale methods for physiological analysis of biofilms formed in 96-well microtiter plates

Microtiter plates with 96 wells have become one of the preferred platforms for biofilm studies mainly because they enable high-throughput assays. In this work, macroscale and microscale methods were used to study the impact of hydrodynamic conditions on the physiology and location of Escherichia coli JM109(DE3) biofilms formed in microtiter plates. Biofilms were formed in shaking and static conditions, and two macroscale parameters were assayed: the total amount of biofilm was measured by the crystal violet assay and the metabolic activity was determined by the resazurin assay. From the macroscale point of view, there were no statistically significant differences between the biofilms formed in static and shaking conditions. However, at a microscale level, the differences between both conditions were revealed using scanning electron microscopy (SEM). It was observed that biofilm morphology and spatial distribution along the wall were different in these conditions. Simulation of the hydrodynamic conditions inside the wells at a microscale was performed by computational fluid dynamics (CFD). These simulations showed that the shear strain rate was unevenly distributed on the walls during shaking conditions and that regions of higher shear strain rate were obtained closer to the air/liquid interface. Additionally, it was shown that wall regions subjected to higher shear strain rates were associated with the formation of biofilms containing cells of smaller size. Conversely, regions with lower shear strain rate were prone to have a more uniform spatial distribution of adhered cells of larger size. The results presented on this work highlight the wealth of information that may be gathered by complementing macroscale approaches with a microscale analysis of the experiments.

Improving alternate flow mixing by obstacles located along a micro-channel

An essential requirement for any practical fully integrated lab-on-a-chip device is the ability to mix two or more fluids thoroughly and efficiently, i.e., in a reasonable amount of time. This paper presents a way to improve mixing in microfluidic systems combining alternate flows with obstacles using passive mixers. Numerical simulations show that the layers of high and low solute concentration, created by the alternate flow, are split into smaller chunks of fluid, due to the obstacles inserted in the mixing channel, increasing the contact area between high and low concentration regions and decreasing the critical mixing length. This improvement can lead to shorter mixing channels and to low-cost mixers fabricated by planar lithographic technology.

Prevalence and antimicrobial resistance patterns of Salmonella from different raw foods in Mexico

The presence of Salmonella was determined in 116 samples of poultry meat, 81 samples of pork, 73 samples of beef, 33 samples of cheese, 61 samples of fish, and 78 samples of vegetables collected from retail stores and supermarkets in Hidalgo State (Mexico). Ninety-three Salmonella strains isolated from raw foods were characterized, and MICs were determined for 10 antimicrobials. Salmonella was detected in 35.3% of poultry meat, 30.3% of cheese, 21.8% of vegetable, 17.3% of pork, and 15.1% of beef samples, but no Salmonella was detected in fish samples. Significantly higher counts were obtained in chicken meat (P = 0.0001), pork (P = 0.0116), cheese (P = 0.0228), and vegetables (P = 0.0072) obtained from retail stores compared with those samples obtained from supermarkets. Salmonella isolates had high levels of resistance to ampicillin (66.7% of isolates), tetracycline (61.3%), and chloramphenicol (64.5%) and low levels of resistance to cefotaxime (0%), gentamicin (3.2%), and kanamycin (4.3%). Higher levels of quinolone resistance were found in isolates from poultry meat and vegetables compared with that in other foods tested. High levels of multiresistant strains were found in all foods tested except fish, ranging from 100% of pork samples to 47.1% of vegetable samples. The present study revealed that Salmonella prevalence was higher in foods from retail stores than in foods from supermarkets. Resistance rates observed for Salmonella were largely comparable to those reported in other countries for most antimicrobials, although resistance to chloramphenicol tended to be higher.

Influence of farming methods on microbiological contamination and prevalence of resistance to antimicrobial drugs in isolates from beef

The presence of Escherichia coli, Staphylococcus aureus, Listeria monocytogenes and Salmonella spp. was determined in 75 samples of conventional beef and in 75 samples of organic beef. All samples came from cattle slaughtered and processed in the same slaughterhouse and quartering room. A total of 180 E. coli, 180 S. aureus and 98 L. monocytogenes strains were analyzed by an agar disk diffusion assay for their resistance to 11 antimicrobials, for the case of E. coli and S. aureus, or 9 antimicrobials, for the case of L. monocytogenes. Salmonella spp. were not isolated from any of the beef samples. No significant differences in prevalence were obtained for any of the bacterial species tested between organic and conventional beef. E. coli isolated from organic beef exhibited significant differences in antimicrobial resistance against 5 of the 11 antimicrobials tested as compared to isolates recovered from conventional beef. In the case of S. aureus, these differences were only found for 3 of the 11 antimicrobials tested and for L. monocytogenes, no differences were obtained between isolates obtained from organic or conventional beef. Although no significant differences were obtained in microbiological contamination, E. coli and S. aureus isolates from organically farmed beef samples showed significantly lower rates of antimicrobial resistance in E. coli and S. aureus isolates.

Comparison of antimicrobial resistance in Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes strains isolated from organic and conventional poultry meat

The presence of Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes was determined in 55 samples of organic poultry meat and in 61 samples of conventional poultry meat. A total of 220 E. coli, 192 S. aureus, and 71 L. monocytogenes strains were analyzed by an agar disk diffusion assay for their resistance to ampicillin, cephalothin, chloramphenicol, ciprofloxacin, doxycycline, fosfomycin, gentamicin, nitrofurantoin, streptomycin, and sulfisoxazole (E. coli); chloramphenicol, ciprofloxacin, clindamycin, doxycycline, erythromycin, gentamicin, nitrofurantoin, oxacillin, and sulfisoxazole (S. aureus); and chloramphenicol, doxycycline, erythromycin, gentamicin, sulfisoxazole, and vancomycin (L. monocytogenes). The results indicated a significantly higher (P < 0.0001) prevalence of E. coli but not of S. aureus and L. monocytogenes in organic poultry meat as compared with conventional poultry meat. E. coli isolated from organic poultry meat exhibited lower levels of antimicrobial resistance against 7 of the 10 antimicrobials tested as compared with isolates recovered from conventional meat. In the case of S. aureus and L. monocytogenes isolated from conventional poultry, antimicrobial resistance was significantly higher only for doxycycline as compared with strains isolated from organic poultry. In the case of E. coli, the presence of multiresistant strains was significantly higher (P < 0.0001) in conventional poultry meat as compared with organic poultry meat. Organically farmed poultry samples showed significantly lower development of antimicrobial resistance in intestinal bacteria such as E. coli.

Evolution of resistance in poultry intestinal Escherichia coli during three commonly used antimicrobial therapeutic treatments in poultry

The resistance rates of intestinal Escherichia coli populations from poultry were determined during treatment and withdrawal period with 3 antimicrobial agents commonly used as therapeutics in poultry medicine. A total of 108 chickens were considered: 18 were treated orally with enrofloxacin, 18 with doxycycline, and 18 with sulfonamides, whereas another 18 chickens were maintained as controls for each antimicrobial group. Fecal samples were taken during the treatment and after the withdrawal period, and E. coli were isolated through Fluorocult media plating. A total of 648 E. coli strains (216 per antimicrobial tested) were isolated and identified though biochemical methods. Minimal inhibitory concentrations to the antimicrobials used were also determined using a broth microdilution method. The resistance rates of intestinal E. coli to all of the antimicrobials tested significantly increased during the course of the therapeutic treatment. In addition, significant differences (P = 0.0136) in resistance rates persisted between the intestinal E. coli of the enrofloxacin-treated and control batches until the end of the withdrawal period, but this difference was not observed for the cases of doxycycline or sulfonamides treatments. Antimicrobial use in poultry medicine seems to select for antimicrobial-resistant strains of pathogenic bacterial species such as E. coli. In some cases, the higher frequencies of resistant strains may persist in the avian intestinal tract until the end of the withdrawal period, when it is legal to use these animals for human consumption.

Antimicrobial resistance in Enterococcus spp. strains isolated from organic chicken, conventional chicken, and turkey meat: a comparative survey

The mean counts of Enterococcus spp. were determined for 30 samples each of organic chicken meat, conventional chicken meat, and turkey meat, and differences for Enterococcus contamination in meat were determined. Two enterococci strains from each sample were isolated to obtain a total of 180 strains, and resistance to ampicillin, chloramphenicol, doxycycline, ciprofloxacin, erythromycin, gentamicin, nitrofurantoin, and vancomycin was determined by a disk diffusion method. Average counts obtained showed that Enterococcus mean counts from organic chicken meat (3.18 log CFU/g) were significantly higher than those obtained from conventional chicken meat (2.06 log CFU/g) or conventional turkey meat (1.23 log CFU/g). However, the resistance data obtained showed that isolates from organic chicken meat were less resistant than enterococci isolates from conventional chicken meat to ampicillin (P = 0.0067), chloramphenicol (P = 0.0154), doxycycline (P = 0.0277), ciprofloxacin (P = 0.0024), erythromycin (P = 0.0028), and vancomycin (P = 0.0241). In addition, isolates from organic chicken were less resistant than conventional turkey meat isolates to ciprofloxacin (P = 0.001) and erythromycin (P = 0.0137). Multidrug-resistant isolates were found in every group tested, but rates of multidrug-resistant strains were significantly higher in conventional chicken and turkey than those obtained from organic chicken meat. Enterococcus faecalis was the most common species isolated from organic chicken (36.67%), whereas Enterococcus durans was the most common species isolated from conventional chicken (58.33%) and turkey (56.67%). The rates obtained for antimicrobial resistance suggest that although organic chicken meat may have higher numbers of Enterococcus, these bacteria present a lower level of antimicrobial resistance.

Differential analysis of donor characteristics for pancreas and islet transplantation

Suitable selection of donors is key to the success of human islet isolation and transplantation. Although several important donor-related factors have been identified previously, they needed to be confirmed in our setting. The aims of this study were: (1) to compare the characteristics of islet donors with those of pancreas donors (national transplant registry). (2) to compare the characteristics of islet donors resulting in a successful isolation in our facility with the characteristics of pancreas donors, and (3) to compare the characteristics of islet donors at this facility, whether or not isolation was successful, with donors elsewhere whose islets were transplanted and included in the Collaborative Islet Transplant Registry. The 35 islet isolations completed at our facility were analyzed for various characteristics. Significant differences were seen in donor age body mass index (BMI), and body weight between our islet donors and our pancreas donors (P < .001). These differences were maintained in the subgroup analysis corresponding to donors of successful isolations compared to pancreas donors (P < .01). Most successful isolations in our islet isolation facility were associated with donors of BMI >25. The percentage of successful isolation (>300,000 IEq) was higher among donors with a body weight >90 kg. We concluded that there was little overlap between the donor profiles for pancreas transplantation and for islet transplantation. More specific selection criteria relative to both BMI and body weight for islet donors may result in greater success of pancreas islet isolation and transplantation.

Dielectric characterization of bacterial cells using dielectrophoresis

Measurements of dielectrophoretic collection spectra of Escherichia coli and Staphylococcus aureus suspensions are used for obtaining dielectric characteristics of both types of bacteria. The experiments are interpreted using a numerical method that models the cells as compartmented spherical or rod-like particles. We show the usefulness of this simple method to extract significant information about the electrical properties of Gram-negative and -positive bacteria.

Tolerogenic response: Allorecognition pathways

The induction of immune tolerance in transplant recipients has been sought for many years but only a fundamental understanding of the immunological mechanisms underlying graft rejection will allow manipulation of the anti-graft immune response. In general, acute rejection is better understood and treated than chronic rejection, as they occur through partially different mechanisms. It is now generally accepted that recognition of same-species, non-self antigens (allorecognition) occurs through at least two different mechanisms, the direct and indirect pathways. In the direct pathway, donor MHC molecules on the surface of donor antigen-presenting cells (APCs) are recognised directly by the recipient's T cells. This mechanism is so immediate that it seems to be primarily involved in acute graft rejection. Since APCs of donor origin are depleted with time a second mechanism, the indirect pathway, takes over to cause chronic rejection, in which foreign MHC molecules are internalised, partially digested and presented as peptides to recipient T cells. Nonetheless, a number of studies are only fully understood when a third proposed allorecognition mechanism is taken into account. This is the semi-indirect pathway, as discussed in this short report.

Analysis of the electric field induced forces in erythrocyte membrane pores using a realistic cell model

We calculate the induced electric stress forces on transient hydrophobic pores in the membrane of an erythrocyte exposed to an electric field. For this purpose, we use a finite element numerical technique and a realistic shape for the biconcave erythrocyte represented by a set of parametric equations in terms of Jacobi elliptic functions. The results clearly show that the electrical forces on the base and sidewalls of the pore favour the opening of the pore. A comparison of the force densities obtained for an unstretched flat membrane and for the realistic erythrocyte model shows that the thinning and curvature of the membrane cannot be neglected. We also show that the pore deformation depends strongly on the orientation of the pore with respect to the external field, and in particular is very small when the field is tangent to the membrane surface.

Effect of cooking on enrofloxacin residues in chicken tissue

The aim of this study was to determine the effect of different cooking processes (microwaving, roasting, boiling, grilling and frying) on naturally incurred enrofloxacin residues in chicken muscle. Enrofloxacin and its metabolite, ciprofloxacin, were analysed using a validated LC-MS method with limits of detection (LOD) and quantification (LOQ), respectively, of 2 and 5 ng g-1 quinolones in muscle samples. The method was shown to be linear over the range 5-500 ng g-1. Mean intra-day relative standard deviation (RSD) at a concentration of 50 ng g-1 (n = 6) was 6%; inter-day RSD was 12%. A recovery study demonstrated that 65-101%, of the drug and metabolite could be recovered from the tissue. The RSD with naturally incurred roasted chicken breast was 9.18% at a concentration of 11 +/- 1.01 ng g-1 (n = 6). In water, enrofloxacin remained stable for 3 h when heated at 100 degrees C. It was concluded that residue data from raw tissue are valid for estimation of consumer exposure to this drug, as well as the ADI calculations because cooking procedures did not affect enrofloxacin residues, which remained stable during heating. However, there was an apparent decrease in quinolone concentration in tissue because some was lost by exudation into the liquid used for cooking. Conversely, for a cooking procedure with water loss, there was an apparent increase in residue concentration.

Variable Very-High-Energy Gamma-Ray Emission from the Microquasar LS I +61 303

Microquasars are binary star systems with relativistic radio-emitting jets. They are potential sources of cosmic rays and can be used to elucidate the physics of relativistic jets. We report the detection of variable gamma-ray emission above 100 gigaelectron volts from the microquasar LS I 61 + 303. Six orbital cycles were recorded. Several detections occur at a similar orbital phase, which suggests that the emission is periodic. The strongest gamma-ray emission is not observed when the two stars are closest to one another, implying a strong orbital modulation of the emission or absorption processes.

Internal assessment of a novel islet isolation facility in Spain

Islet transplantation is a promising therapy in the treatment of diabetes mellitus. Herein we present the result from the first series of islet isolations carried out in our new islet isolation facility. The aims of study were to analyze the influence of various donor characteristics on the success of islet isolation and compare these outcomes with other European and American groups. Data from 22 completed islet isolation were used to compare donor and isolation variables among successful (>300,000 IEQs) versus unsuccessful isolations. The successful isolation rate from our laboratory was 31.8%. We did not see any significant differences between successful and unsuccessful groups according to donor characteristics, although age was close to significance (38.57 +/- 10.29 versus 48.33 +/- 12.39; P = .08). Donor age (1.12 [1.23; 0.99]) and body mass index (0.065 [1.32; 3.08]) were associated with isolation success in a logistic regression model. We did not find differences among intraprocedure variables with the exception of IEQ prepurification (409,073 +/- 115,041 versus 263,776 +/- 128,988; P < .05). IEQpre and IEQpost were positively correlated (P < .05). In comparison with other groups, we observed differences in some cases related to islet yield prepurification (P < .05) but not postpurification. Purity from our islet preparations was the highest from all considered groups (P < .05). Recovery was similar in all groups.

CONCLUSIONS

In our experience, donor characteristics have no influence on the success rate. The digestion step is a critical factor for success. Our results with respect to IE yield were close to that of experienced groups.

Evaluation of ChromocultR enterococci agar for the isolation and selective enumeration of Enterococcus spp. in broilers

AIMS

To investigate the productivity and specificity of a new chromogenic enterococci selective medium (Chromocult enterococci agar) recently developed by Merck.

METHODS AND RESULTS

The study was carried out comparing Chromocult enterococci agar with MRS agar (Merck), a basal lactic acid bacteria medium in current use. A total of 216 faecal samples from poultry were collected and enterococci populations were counted. Likewise, 100 randomly selected strains were identified for each medium. The differences found between the two media were analysed and discussed.

CONCLUSIONS

A good sensitivity of 98% was obtained for Chromocult agar and all false-positive isolates obtained were identified as Leuconostoc spp. However significant differences (P<0.01) were obtained between the enterococci species isolation rates identified from these two media, suggesting the poor growth of some species in Chromocult enterococci agar. Viable counts of Enterococcus spp. obtained with MRS agar were significantly higher than those obtained with Chromocult enterococci agar.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of chromogenic media for microbiological analysis is increasing. Independent studies are important to evaluate newly developed chromogenic media.