Vapor-solid-solid growth dynamics in GaAs nanowires

Semiconductor nanowires are promising material systems for coming of age nanotechnology. The usage of the vapor solid solid (VSS) route, where the catalyst used for promoting axial growth of nanowire is a solid, offers certain advantages compared to the common vapor liquid solid (VLS) route (using liquid catalyst). The VSS growth of group-IV elemental nanowires have been investigated by other groups in situ during growth in a transmission electron microscope (TEM). Though it is known that compound nanowire growth has different dynamics compared to monoatomic semiconductors, the dynamics of VSS growth of compound nanowires has not been understood. Here we investigate VSS growth of compound nanowires by in situ microscopy, using Au-seeded GaAs as a model system. The growth kinetics and dynamics at the wire-catalyst interface by ledge-flow is studied and compared for liquid and solid catalysts at similar growth conditions. Here the temperature and thermal history of the system is manipulated to control the catalyst phase. In the first experiment discussed here we reduce the growth temperature in steps to solidify the initially liquid catalyst, and compare the dynamics between VLS and VSS growth observed at slightly different temperatures. In the second experiment we exploit thermal hysteresis of the system to obtain both VLS and VSS at the same temperature. The VSS growth rate is comparable or slightly slower than VLS growth. Unlike in the VLS case, during VSS growth we see several occasions where a new layer starts before the previous layer is completely grown, i.e. multilayer growth. Understanding the VSS growth mode enables better control of nanowire properties by widening the range of usable nanowire growth parameters

Calprotectin levels in amniotic fluid in relation to intra-amniotic inflammation and infection in women with preterm labor with intact membranes: A retrospective cohort study

Objective: To evaluate the concentrations of calprotectin in amniotic fluid with respect to intra-amniotic inflammation and infection and to assess the presence or absence of bacteria in the amnio-chorionic niche with respect to presence or absence of intra-amniotic inflammation. Study design: Seventy-nine women with singleton pregnancies and preterm labor with intact membranes (PTL) were included in the study. Amniotic fluid was collected at the time of admission by amniocentesis and calprotectin levels were analyzed from frozen/thawed samples using ELISA. Interleukin (IL)-6 concentration was measured by point-of-care test. Samples from amniotic fluid and the amnio-chorionic niche (space between amniotic and chorionic membranes) were microbiologically analyzed. Microbial invasion of the amniotic cavity (MIAC) was diagnosed based on a positive PCR result for Ureaplasma species, Mycoplasma hominis, 16S rRNA or positive culture. Intra-amniotic inflammation (IAI) was defined as amniotic fluid point-of-care IL-6 concentration ≥ 745 pg/mL. The cohort of included women was divided into 4 subgroups based on the presence or absence of IAI/MIAC; i) intra-amniotic infection, ii) sterile IAI, iii) intra-amniotic colonization and iv) neither MIAC nor IAI. Results: Women with intra-amniotic infection had a significantly higher intra-amniotic calprotectin concentration (median; 101.6 \ub5g/mL) compared with women with sterile IAI (median; 9.2 \ub5g/mL), women with intra-amniotic colonization (median; 2.6 \ub5g/mL) and women with neither MIAC nor IAI (median 4.6 \ub5g/mL) (p = 0.001). Moreover, significantly higher amniotic fluid calprotectin concentration was seen in women who delivered within 7 days (p = 0.003). A significant negative correlation was found between amniotic fluid calprotectin and gestational age at delivery (rho = 0.32, p = 0.003). Relatively more bacteria in the amnio-chorionic niche were found in the sterile IAI group compared with the other groups. Conclusions: Calprotectin concentrations in amniotic fluid were significantly higher in the intra-amniotic infection group compared with the other groups. Moreover, the bacterial presence in the amnio-chorionic niche was higher in IAI group

In situ analysis of catalyst composition during gold catalyzed GaAs nanowire growth

Semiconductor nanowires offer the opportunity to incorporate novel structures and functionality into electronic and optoelectronic devices. A clear understanding of the nanowire growth mechanism is essential for well-controlled growth of structures with desired properties, but the understanding is currently limited by a lack of empirical measurements of important parameters during growth, such as catalyst particle composition. However, this is difficult to accurately determine by investigating post-growth. We report direct measurement of the catalyst composition of individual gold seeded GaAs nanowires inside an electron microscope as they grow. The Ga content in the catalyst during growth increased with both temperature and Ga precursor flux. A direct comparison of the calculated phase diagrams of the Au-Ga-As ternary system to the measured catalyst composition not only lets us estimate the As content in the catalyst but also indicates the relevance of phase diagrams to understanding nanowire growth

Evaluation of the SpeeDx ResistancePlus® GC and SpeeDx GC 23S 2611 (beta) molecular assays for prediction of antimicrobial resistance/susceptibility to ciprofloxacin and azithromycin in Neisseria gonorrhoeae

European collaborative group: Raquel Abad Torreblanca, Lena Rós Ásmundsdóttir, Eszter Balla, Irith De Baetselier, Beatrice Bercot, Thea Bergheim, Maria José Borrego, Susanne Buder, Robert Cassar, Michelle Cole, Alje van Dam, Claudia Eder, Steen Hoffmann, Blazenka Hunjak, Samo Jeverica, Vesa Kirjavainen, Panayiota Maikanti-Charalambous, Vivi Miriagou, Beata Młynarczyk-Bonikowska, Gatis Pakarna, Peter Pavlik, Monique Perrin, Joseph Pett, Paola Stefanelli, Kate Templeton, Magnus Unemo, Jelena Viktorova, Hana ZákouckáPortugal: Maria-José Borrego (INSA)Background: Accurate molecular assays for prediction of antimicrobial resistance (AMR)/susceptibility in Neisseria gonorrhoeae (Ng) can offer individualized treatment of gonorrhoea and enhanced AMR surveillance. Objectives: We evaluated the new ResistancePlus® GC assay and the GC 23S 2611 (beta) assay (SpeeDx), for prediction of resistance/susceptibility to ciprofloxacin and azithromycin, respectively. Methods: Nine hundred and sixty-seven whole-genome-sequenced Ng isolates from 20 European countries, 143 Ng-positive (37 with paired Ng isolates) and 167 Ng-negative clinical Aptima Combo 2 (AC2) samples, and 143 non-gonococcal Neisseria isolates and closely related species were examined with both SpeeDx assays. Results: The sensitivity and specificity of the ResistancePlus® GC assay to detect Ng in AC2 samples were 98.6% and 100%, respectively. ResistancePlus® GC showed 100% sensitivity and specificity for GyrA S91 WT/S91F detection and 99.8% sensitivity and specificity in predicting phenotypic ciprofloxacin resistance. The sensitivity and specificity of the GC 23S 2611 (beta) assay for Ng detection in AC2 samples were 95.8% and 100%, respectively. GC 23S 2611 (beta) showed 100% sensitivity and 99.9% specificity for 23S rRNA C2611 WT/C2611T detection and 64.3% sensitivity and 99.9% specificity for predicting phenotypic azithromycin resistance. Cross-reactions with non-gonococcal Neisseria species were observed with both assays, but the analysis software solved most cross-reactions. Conclusions: The new SpeeDx ResistancePlus® GC assay performed well in the detection of Ng and AMR determinants, especially in urogenital samples. The GC 23S 2611 (beta) assay performed relatively well, but its sensitivity, especially for predicting phenotypic azithromycin resistance, was suboptimal and further optimizations are required, including detection of additional macrolide resistance determinant(s).This work was supported by the O¨rebro County Council Research Committee and the Foundation for Medical Research at O¨rebro University Hospital, O¨rebro, Sweden.info:eu-repo/semantics/publishedVersio

WHO laboratory validation of Xpert® CT/NG and Xpert® TV on the GeneXpert system verifies high performances.

Effective tests for diagnosis of sexually transmitted infections (STIs), used point of care to inform treatment and management decisions, are urgently needed. We evaluated the analytical sensitivity and specificity of the Xpert® CT/NG and Xpert® TV tests, examining 339 samples spiked with phenotypically and/or genetically diverse strains of Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis, and other related species that may cross-react. The APTIMA Combo 2 test and APTIMA TV test were used as reference tests. The analytical sensitivity for all three agents in the Xpert® CT/NG and Xpert® TV tests was ≤102 genome equivalents/reaction. The analytical specificity of both tests was high. False-positive results were identified in the Xpert® TV test when challenging with high concentrations of Trichomonas tenax, Trichomonas gallinae, Trichomonas stableri, and Trichomonas aotus. However, the clinical relevance of these cross-reactions can likely be neglected, because these species have not been identified in urogenital samples from humans. In conclusion, the analytical sensitivity and specificity of the user-friendly Xpert® CT/NG and Xpert® TV tests on the GeneXpert system were high. The results support the use of specimens from also extra-genital sites, for example, pharynx and rectum. However, appropriate clinical validations are additionally required

Europe-wide expansion and eradication of multidrug-resistant Neisseria gonorrhoeae lineages: a genomic surveillance study

Background: Genomic surveillance using quality-assured whole-genome sequencing (WGS) together with epidemiological and antimicrobial resistance (AMR) data is essential to characterise the circulating Neisseria gonorrhoeae lineages and their association to patient groups (defined by demographic and epidemiological factors). In 2013, the European gonococcal population was characterised genomically for the first time. We describe the European gonococcal population in 2018 and identify emerging or vanishing lineages associated with AMR and epidemiological characteristics of patients, to elucidate recent changes in AMR and gonorrhoea epidemiology in Europe. Methods: We did WGS on 2375 gonococcal isolates from 2018 (mainly Sept 1-Nov 30) in 26 EU and EEA countries. Molecular typing and AMR determinants were extracted from quality-checked genomic data. Association analyses identified links between genomic lineages, AMR, and epidemiological data. Findings: Azithromycin-resistant N gonorrhoeae (8·0% [191/2375] in 2018) is rising in Europe due to the introduction or emergence and subsequent expansion of a novel N gonorrhoeae multi-antigen sequence typing (NG-MAST) genogroup, G12302 (132 [5·6%] of 2375; N gonorrhoeae sequence typing for antimicrobial resistance [NG-STAR] clonal complex [CC]168/63), carrying a mosaic mtrR promoter and mtrD sequence and found in 24 countries in 2018. CC63 was associated with pharyngeal infections in men who have sex with men. Susceptibility to ceftriaxone and cefixime is increasing, as the resistance-associated lineage, NG-MAST G1407 (51 [2·1%] of 2375), is progressively vanishing since 2009-10. Interpretation: Enhanced gonococcal AMR surveillance is imperative worldwide. WGS, linked to epidemiological and AMR data, is essential to elucidate the dynamics in gonorrhoea epidemiology and gonococcal populations as well as to predict AMR. When feasible, WGS should supplement the national and international AMR surveillance programmes to elucidate AMR changes over time. In the EU and EEA, increasing low-level azithromycin resistance could threaten the recommended ceftriaxone-azithromycin dual therapy, and an evidence-based clinical azithromycin resistance breakpoint is needed. Nevertheless, increasing ceftriaxone susceptibility, declining cefixime resistance, and absence of known resistance mutations for new treatments (zoliflodacin, gepotidacin) are promising.This study was supported by the European Centre for Disease Prevention and Control, the Centre for Genomic Pathogen Surveillance, the Li Ka Shing Foundation (Big Data Institute, University of Oxford), the Wellcome Genome Campus, the Foundation for Medical Research at Örebro University Hospital, and grants from Wellcome (098051 and 099202). LSB was funded by Conselleria de Sanitat Universal i Salut Pública, Generalitat Valenciana (Plan GenT CDEI-06/20-B), Valencia, Spain, and Ministry of Science, Innovation and Universities (PID2020–120113RA-I00), Spain, at the time of analysing and writing this manuscript.S

Variation of the factor H-binding protein of Neisseria meningitidis

There is currently no comprehensive meningococcal vaccine, due to difficulties in immunizing against organisms expressing serogroup B capsules. To address this problem, subcapsular antigens, particularly the outer-membrane proteins (OMPs), are being investigated as candidate vaccine components. If immunogenic, however, such antigens are often antigenically variable, and knowledge of the extent and structuring of this diversity is an essential part of vaccine formulation. Factor H-binding protein (fHbp) is one such protein and is included in two vaccines under development. A survey of the diversity of the fHbp gene and the encoded protein in a representative sample of meningococcal isolates confirmed that variability in this protein is structured into two or three major groups, each with a substantial number of alleles that have some association with meningococcal clonal complexes and serogroups. A unified nomenclature scheme was devised to catalogue this diversity. Analysis of recombination and selection on the allele sequences demonstrated that parts of the gene are subject to positive selection, consistent with immune selection on the protein generating antigenic variation, particularly in the C-terminal region of the peptide sequence. The highest levels of selection were observed in regions corresponding to epitopes recognized by previously described bactericidal monoclonal antibodies