Antimicrobial resistance of Neisseria gonorrhoeae isolates in south-west Germany, 2004 to 2015: increasing minimal inhibitory concentrations of tetracycline but no resistance to third-generation cephalosporins

Introduction Numbers of gonorrhoea cases have increased, and the World Health Organization has estimated 106 million new cases in adults worldwide for 2008, which was 21% higher than numbers for 2005 [1]. At the same time, rising rates of antimicrobial resistance of its causative agent, Neisseria gonorrhoeae, have been reported in many parts of the world including Europe, even against the third-generation cephalosporins, cefixime and ceftriaxone [2,3]. For this reason, cefixime alone is no longer recommended as single-drug treatment for gonorrhoea in Europe or the United States [4,5]. The European Gonococcal Antimicrobial Surveillance Programme (EURO-GASP) was established by 12 European countries in 2004 in response to the emerging antimicrobial resistance of N. gonorrhoeae, as part of the European Surveillance of Sexually Transmitted Infections Project [6]. In 2016, EURO-GASP has participation from laboratories from 21 European Union/European Economic Area countries, which regularly report gonorrhoea susceptibility testing results and epidemiological surveillance data, and submit gonococcal isolates for centralised testing or participate in decentralised testing. Since 2009, EURO-GASP has been coordinated by the European Centre for Disease Prevention and Control (ECDC). Resistance data have been published regularly and in a timely manner [7,8], but the numbers of isolates tested per country are relatively low (between 10 and 251 in 2011 [8]) and therefore most likely not representative of the epidemiological situation of the individual countries. As cases of gonorrhoea or antimicrobial resistance patterns of N. gonorrhoeae isolates are not subject to reporting in Germany, data regarding current antimicrobial susceptibility and its development over time are scarce. Only three individual studies have addressed this issue in the past 10 years. Abraham et al. analysed 50 isolates collected between 2001 and 2010 in Dresden, Saxony [9], while Horn and colleagues have reported the results of a nationwide surveillance study conducted by the Paul-Ehrlich-Society of Chemotherapy in 2010/2011 in which 213 isolates submitted by 23 laboratories were analysed [10]. Additionally, minimum inhibitory concentrations (MICs) of selected antibiotics for 65 N. gonorrhoeae isolates collected in 2004/2005 in southern Germany have been reported [11]. None of these studies has reported cephalosporin-resistant N. gonorrhoeae isolates. Data from EURO-GASP, however, have provided evidence for the presence of cephalosporin-resistant N. gonorrhoeae isolates in Germany, too [7,8]; in fact, an Austrian patient with a cefixime-resistant N. gonorrhoeae isolate acquired his infection in Munich, south Germany [12]. To gain more information on the antimicrobial susceptibility of N. gonorrhoeae in Germany and elucidate possible changes in antimicrobial resistance occurring over time, we analysed the susceptibility patterns of all N. gonorrhoeae isolates identified and tested in our laboratory between 2004 and 2015 (n = 434). Since age and sex have been identified as risk factors for harbouring antimicrobial-resistant N. gonorrhoeae isolates [13,14], we additionally analysed our data regarding these parameters. Unfortunately, the study design chosen did not provide information regarding other possible risk factors, e.g. working as professional sex worker or being a man who has sex with men (MSM)

Small Angle Shubnikov-de Haas Measurements in Silicon MOSFET's: the Effect of Strong In-Plane Magnetic Field

Measurements in magnetic fields applied at small angles relative to the electron plane in silicon MOSFETs indicate a factor of two increase of the frequency of Shubnikov-de Haas oscillations at H>H_{sat}. This signals the onset of full spin polarization above H_{sat}, the parallel field above which the resistivity saturates to a constant value. For H<H_{sat}, the phase of the second harmonic of the oscillations relative to the first is consistent with scattering events that depend on the overlap instead of the sum of the spin-up and spin-down densities of states.Comment: 4 pages; figures now inserted in text; additional referenc

Hall Coefficient of a Dilute 2D Electron System in Parallel Magnetic Field

Measurements in magnetic fields applied at a small angle with respect to the 2D plane of the electrons of a low-density silicon MOSFET indicate that the Hall coefficient is independent of parallel field from H=0 to $H>H_{sat}$, the field above which the longitudinal resistance saturates and the electrons have reached full spin-polarization. This implies that the mobilities of the spin-up and spin-down electrons remain comparable at all magnetic fields, and suggests there is strong mixing of spin-up and spin-down electron states.Comment: 4 pages, 2 figure

Projected Multi-Agent Consensus Equilibrium (PMACE) for Distributed Reconstruction with Application to Ptychography

Multi-Agent Consensus Equilibrium (MACE) formulates an inverse imaging problem as a balance among multiple update agents such as data-fitting terms and denoisers. However, each such agent operates on a separate copy of the full image, leading to redundant memory use and slow convergence when each agent affects only a small subset of the full image. In this paper, we extend MACE to Projected Multi-Agent Consensus Equilibrium (PMACE), in which each agent updates only a projected component of the full image, thus greatly reducing memory use for some applications.We describe PMACE in terms of an equilibrium problem and an equivalent fixed point problem and show that in most cases the PMACE equilibrium is not the solution of an optimization problem. To demonstrate the value of PMACE, we apply it to the problem of ptychography, in which a sample is reconstructed from the diffraction patterns resulting from coherent X-ray illumination at multiple overlapping spots. In our PMACE formulation, each spot corresponds to a separate data-fitting agent, with the final solution found as an equilibrium among all the agents. Our results demonstrate that the PMACE reconstruction algorithm generates more accurate reconstructions at a lower computational cost than existing ptychography algorithms when the spots are sparsely sampled

Parallel magnetic field induced giant magnetoresistance in low density {\it quasi}-two dimensional layers

We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density {\it quasi}-two dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the {\it orbital} motion arising from the {\it finite} layer thickness and the large Fermi wavelength of the {\it quasi}-two dimensional system at low carrier densities.Comment: 4 pages with 4 figures. Accepted for Publication in Physical Review Letter

Temperature-Dependence of the Resistivity of a Dilute 2D Electron System in High Parallel Magnetic Field

We report measurements of the resistance of silicon MOSFETs as a function of temperature in high parallel magnetic fields where the 2D system of electrons has been shown to be fully spin-polarized. A magnetic field suppresses the metallic behavior observed in the absence of a magnetic field. In a field of 10.8 T, insulating behavior is found for densities up to n_s approximately 1.35 x 10^{11} cm^{-2} or 1.5 n_c; above this density the resistance is a very weak function of temperature, varying less than 10% between 0.25 K and 1.90 K. At low densities the resistance goes to infinity more rapidly as the temperature is reduced than in zero field and the magnetoresistance diverges as T goes to 0.Comment: 4 pages, including 4 figures. References adde

Metal-insulator transition in a 2D electron gas: Equivalence of two approaches for determining the critical point

The critical electron density for the metal-insulator transition in a two-dimensional electron gas can be determined by two distinct methods: (i) a sign change of the temperature derivative of the resistance, and (ii) vanishing activation energy and vanishing nonlinearity of current-voltage characteristics as extrapolated from the insulating side. We find that in zero magnetic field (but not in the presence of a parallel magnetic field), both methods give equivalent results, adding support to the existence of a true zero-field metal-insulator transition.Comment: As publishe

In-plane magnetic field-induced spin polarization and transition to insulating behavior in two-dimensional hole systems

Using a novel technique, we make quantitative measurements of the spin polarization of dilute (3.4 to 6.8*10^{10} cm^{-2}) GaAs (311)A two-dimensional holes as a function of an in-plane magnetic field. As the field is increased the system gradually becomes spin polarized, with the degree of spin polarization depending on the orientation of the field relative to the crystal axes. Moreover, the behavior of the system turns from metallic to insulating \textit{before} it is fully spin polarized. The minority-spin population at the transition is ~8*10^{9} cm^{-2}, close to the density below which the system makes a transition to an insulating state in the absence of a magnetic field.Comment: 4 pages with figure

Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons

Two-dimensional (2D) electrons in an in-plane magnetic field become fully spin polarized above a field B_P, which we can determine from the in-plane magnetoresistance. We perform such measurements in modulation-doped AlAs electron systems, and find that the field B_P increases approximately linearly with 2D electron density. These results imply that the product |g*|m*, where g* is the effective g-factor and m* the effective mass, is a constant essentially independent of density. While the deduced |g*|m* is enhanced relative to its band value by a factor of ~ 4, we see no indication of its divergence as 2D density approaches zero. These observations are at odds with results obtained in Si-MOSFETs, but qualitatively confirm spin polarization studies of 2D GaAs carriers.Comment: 4 pages, 5 figure

Parallel Magnetic Field Induced Transition in Transport in the Dilute Two-Dimensional Hole System in GaAs

A magnetic field applied parallel to the two-dimensional hole system in the GaAs/AlGaAs heterostructure, which is metallic in the absence of an external magnetic field, can drive the system into insulating at a finite field through a well defined transition. The value of resistivity at the transition is found to depend strongly on density