Carrier Strains Research Articles

V doped Orth-Ga2O3: Half-metallic ferromagnetism, large magnetic anisotropy energy and high Curie temperature

Half-metallic ferromagnets have attracted intense interest worldwide and are considered to be an important component of spintronics devices. In this paper, an unpredicted Ga2O3 phase (named as Orth-Ga2O3) with good mechanical, dynamic, and thermodynamic stability is proposed by employing the adaptive genetic algorithm (AGA) crystal structure prediction approach. Surprisingly, V-doped Orth-Ga2O3 (V@Orth-Ga2O3) exhibits a strong ferromagnetic (FM) half-metallicity with a magnetic moment of 2 μB per formula. A detailed analysis of the density of states shows that the FM half-metallicity originates from the double exchange interaction between V-3d and O-2p orbitals. Besides, V@Orth-Ga2O3 has a big magnetic anisotropy energy (MAE) of 0.36 meV, mainly due to the (dxy, dx2-y2) orbitals of the V atom. According to Monte Carlo simulations, the Curie temperature TC of V@Orth-Ga2O3 is 225 K. The effect of carrier concentration and strain on the ferromagnetic stability of V@Orth-Ga2O3 system is also investigated. These unique magnetic properties make V@Orth-Ga2O3 an extremely promising material in spintronic nanodevices.

Population genomics of Streptococcus mitis in UK and Ireland bloodstream infection and infective endocarditis cases

Streptococcus mitis is a leading cause of infective endocarditis (IE). However, our understanding of the genomic epidemiology and pathogenicity of IE-associated S. mitis is hampered by low IE incidence. Here we use whole genome sequencing of 129 S. mitis bloodstream infection (BSI) isolates collected between 2001–2016 from clinically diagnosed IE cases in the UK to investigate genetic diversity, antimicrobial resistance, and pathogenicity. We show high genetic diversity of IE-associated S. mitis with virtually all isolates belonging to distinct lineages indicating no predominance of specific lineages. Additionally, we find a highly variable distribution of known pneumococcal virulence genes among the isolates, some of which are overrepresented in disease when compared to carriage strains. Our findings suggest that S. mitis in patients with clinically diagnosed IE is not primarily caused by specific hypervirulent or antimicrobial resistant lineages, highlighting the accidental pathogenic nature of S. mitis in patients with clinically diagnosed IE.

Monitoring of Haemophilus influenzae isolated from carriage, lower respiratory tract infections and blood over a six-month period in Belgium.

H. influenzae carriage may evolve into respiratory or systemic infections. However, no surveillancesystem is in place in Belgium to monitor carriage strains. This study provides a detailed description of H. influenzae strains isolated from both carriage and lower respiratory infections, collected during a six-month national surveillance. Subsequently, a comparison is conducted with invasive isolates collected during the same period at the National Reference Centre (NRC). From November 2021 to April 2022, 39 clinical laboratories collected 142 and 210 strains of H. influenzae from carriage and infection, respectively, and 56 strains of blood were submitted to the NRC. In each group, the biotype II comprised more than 40%, followed by biotypes III and I. The majority of strains were non-typeable H. influenzae, with a notable increase in the number of encapsulated strains in the invasive group (14.3% vs. 1-2%). A beta-lactamase was identified in 18.5% and 12.5% of surveillance and invasive strains, respectively. Resistance to the amoxicillin-clavulanic acid combination accounted for 7% in the surveillance strains and 10.7% in invasive strains. The overall resistance to third-generation cephalosporins at 1.2% is consistent with rates observed in other European countries. Of particular significance is the identification of mutations in the ftsI gene in both carriage and infected strains, which are associated with high-level beta-lactam resistance. NRC must engage in regular and systematic monitoring of beta-lactam susceptibility of H. influenzae to guarantee safe empiric therapy in severe cases and identify potential transitions from low-level to high-level resistance in the future.

Brief communication: Carrier rate, antimicrobial resistance and molecular typing of Staphylococcus aureus and Staphylococcus pseudintermedius in healthy dogs from Morogoro, Tanzania.

Staphylococcus pseudintermedius and S. aureus are important pathogens in dogs. This study established carrier rates, strain diversity and antimicrobial resistance of these bacteria among healthy dogs in Tanzania. Based on cultures of mouth and perineal swabs, 11.3% and 50.3% of 151 healthy dogs were carriers of S. aureus and S. pseudintermedius, respectively. Only four dogs (3%) carried meticillin-resistant S. aureus (MRSA), while none of the S. pseudintermedius strains were meticillin-resistant. 12 of 19 S. aureus strains tested were resistant to penicillin G, and resistance to enrofloxacin and tetracycline was also commonly detected. The most common resistances in 103 S. pseudintermedius strains tested were to penicillin G (28.2%) and tetracycline (22.3%). S. pseudintermedius strains showed 65 different random amplified polymorphic DNA (RAPD) fingerprints, and S. aureus strains belonged to eight different spa types, including two novel types (t18988 and t18989). MRSA strains carried SCCmec type V. Healthy dogs in Tanzania were carriers of MRSA at low frequency, and half of the dogs carried S. pseudintermedius with high strain diversity.

First-principles study of carrier mobility and strain effect in MX (M=Sn, Pb; X=P, As) monolayers

The pursuit of two-dimensional semiconductor materials that feature tunable electronic structures and high mobility is crucial for advancing nanoelectronic and optoelectronic devices. In this study, the MX monolayers (M = Sn, Pb; N = P, As) are investigated with first-principles calculations based on Boltzmann transport theory. The results show that SnP, SnAs, and PbAs all exhibit indirect band gaps, whereas PbP is the only semiconductor with a direct band gap. One important finding is that intravalley scattering has a significant impact on electron–phonon coupling. Interestingly, changes in carrier concentration do not affect the electron mobility within these MX monolayers, with SnP exhibiting the highest electron mobility among them. Subsequently, the SnP under a 6% biaxial strain is further explored and the results demonstrated a considerable increase in electron mobility to 2,511.9 cm 2V−1s−1 , which is attributable to decreased scattering. This suggests that MX monolayers, especially SnP, are promising options for 2D semiconductor materials in the future.

Global epidemiological comparison of Streptococcus pyogenes emm-types associated with pharyngitis and pharyngeal carriage

ObjectivesTo test the prevailing dogma that Streptococcus pyogenes emm-types that cause pharyngitis are the same as those associated with the carriage, using a global dataset. MethodsDrawing on our systematic review of the global distribution of S. pyogenes emm-types and emm-clusters from 1990 to 2023, we compared the distribution and diversity of strains associated with pharyngitis and pharyngeal carriage, in the context of local United Nations Development Programme Human Development Index (HDI) values. ResultsWe included 20 222 isolates from 71 studies done in 34 countries, with the vast majority of carriage strain data from studies in ‘Low HDI’ settings (550/1293; 43%). There was higher emm-type diversity for carriage than pharyngitis strains (Simpson Reciprocal Index of diversity 28.9 vs. 11.4). Compared with pharyngitis strains, carriage emm-types were disproportionately from emm-clusters E and D, usually described as ‘generalist’ or ‘skin’ strains. DiscussionA limited number of studies have compared S. pyogenes strains from cases of pharyngitis compared with carriage. Our understanding of strains associated with carriage is the poorest for high-income settings. In low and medium HDI countries, we found greater strain associated with pharyngeal carriage than pharyngitis. Improving our understanding of S. pyogenes carriage epidemiology in the pre-vaccine era will help to decipher the direct and potential indirect effects of vaccines.

Bacterial surface lipoproteins mediate epithelial microinvasion by Streptococcus pneumoniae.

Streptococcus pneumoniae, a common colonizer of the upper respiratory tract, invades nasopharyngeal epithelial cells without causing disease in healthy participants of controlled human infection studies. We hypothesized that surface expression of pneumococcal lipoproteins, recognized by the innate immune receptor TLR2, mediates epithelial microinvasion. Mutation of lgt in serotype 4 (TIGR4) and serotype 6B (BHN418) pneumococcal strains abolishes the ability of the mutants to activate TLR2 signaling. Loss of lgt also led to the concomitant decrease in interferon signaling triggered by the bacterium. However, only BHN418 lgt::cm but not TIGR4 lgt::cm was significantly attenuated in epithelial adherence and microinvasion compared to their respective wild-type strains. To test the hypothesis that differential lipoprotein repertoires in TIGR4 and BHN418 lead to the intraspecies variation in epithelial microinvasion, we employed a motif-based genome analysis and identified an additional 525 a.a. lipoprotein (pneumococcal accessory lipoprotein A; palA) encoded by BHN418 that is absent in TIGR4. The gene encoding palA sits within a putative genetic island present in ~10% of global pneumococcal isolates. While palA was enriched in the carriage and otitis media pneumococcal strains, neither mutation nor overexpression of the gene encoding this lipoprotein significantly changed microinvasion patterns. In conclusion, mutation of lgt attenuates epithelial inflammatory responses during pneumococcal-epithelial interactions, with intraspecies variation in the effect on microinvasion. Differential lipoprotein repertoires encoded by the different strains do not explain these differences in microinvasion. Rather, we postulate that post-translational modifications of lipoproteins may account for the differences in microinvasion.IMPORTANCEStreptococcus pneumoniae (pneumococcus) is an important mucosal pathogen, estimated to cause over 500,000 deaths annually. Nasopharyngeal colonization is considered a necessary prerequisite for disease, yet many people are transiently and asymptomatically colonized by pneumococci without becoming unwell. It is therefore important to better understand how the colonization process is controlled at the epithelial surface. Controlled human infection studies revealed the presence of pneumococci within the epithelium of healthy volunteers (microinvasion). In this study, we focused on the regulation of epithelial microinvasion by pneumococcal lipoproteins. We found that pneumococcal lipoproteins induce epithelial inflammation but that differing lipoprotein repertoires do not significantly impact the magnitude of microinvasion. Targeting mucosal innate immunity and epithelial microinvasion alongside the induction of an adaptive immune response may be effective in preventing pneumococcal colonization and disease.

Strain-tunable electronic anisotropy of the AlSb double-layer honeycomb structure.

Two-dimensional (2D) materials show promising applications in nanoelectronic devices due to their excellent physical and chemical properties, large specific surface area, and good flexibility. 2D AlSb, a representative of a new class of two-dimensional materials with a double-layer honeycomb (DLHC) structure was recently obtained in experiments and was reported to be a direct band gap semiconductor. Strain engineering is an effective way of tuning the properties of 2D materials. Here, by first-principles calculations, the strain effects on the electronic structure of AlSb were investigated. An interesting inversion of band order near the bottom of the conduction band can be induced by applying uniaxial strain, which will introduce a large electronic anisotropy. In addition, under tensile strain along the armchair direction larger than 5%, band inversion occurs, indicating possible topological insulator properties of AlSb. Small carrier effective mass and strain tunable electronic anisotropy pave the way for the application of AlSb in future nanoelectronic devices.

Exploration of risk analysis and elimination methods for a Cr(VI)-removal recombinant strain through a biosafety assessment in mice

Though recombinant strains are increasingly recognized for their potential in heavy metal remediation, few studies have evaluated their safety. Moreover, biosafety assessments of fecal-oral pathway exposure at country as well as global level have seldom analyzed the health risks of exposure to microorganisms from a microscopic perspective. The present study aimed to predict the long-term toxic effects of recombinant strains by conducting a subacute toxicity test on the chromium-removal recombinant strain 3458 and analyzing the gut microbiome. The available disinfection methods were also evaluated. The results showed that strain 3458 induced liver damage and affected renal function and lipid metabolism at 1.0 × 1011 CFU/mL, which may be induced by its carrier strain, pET-28a. Strain 3458 poses the risk of increasing the number of pathogenic bacteria under prolonged exposure. When 500 mg L−1 chlorine-containing disinfectant or 250 mg L−1 chlorine dioxide disinfectant was added for 30 min, the sterilization rate exceeded 99.9 %. These findings suggest that existing wastewater disinfection methods can effectively sterilize strain 3458, ensuring its application value. The present study can serve a reference for the biosafety evaluation of the recombinant strain through exposure to the digestive tract and its feasibility for application in environmental pollution remediation.

Molecular characteristics of Neisseria meningitidis carriage strains in university students in Lithuania

BackgroundNeisseria meningitidis can be carried asymptomatically in the human oropharynx without causing symptoms. Meningococcal carriage is relevant to the epidemiology of invasive meningococcal disease (IMD). No carriage studies have been performed among the general population in Lithuania, whereas the incidence of IMD in Lithuania was among the highest in European countries from 2009 to 2019.ResultsWe analyzed a total of 401 oropharyngeal samples collected from university students from December 2021 to February 2023 for N. meningitidis carriage using direct swab PCR assays and culture. The overall carriage prevalence based on both or either swab PCR or culture was 4.99%. PCR-based assays were used to characterize 15 carriage isolates, including detection of genogroup, multilocus sequence typing profile, and typing of antigens PorA and FetA. The most common carriage isolates were capsule null locus (cnl), accounting for 46.7%, followed by genogroups B (26.7%) and Y (13.3%). We also performed a molecular characterization of invasive N. meningitidis isolates collected during the COVID-19 pandemic and post-pandemic period to understand better the meningococcal carriage in the context of prevailing invasive strains. Despite the substantial decrease in the incidence of IMD during the 2020–2022 period, clonal complex 32 (CC32) of serogroup B continued to be the most prevalent IMD-causing CC in Lithuania. However, CC32 was not detected among carriage isolates. The most common CCs were CC269, CC198, and CC1136. The antigen peptide variants found in most carried isolates were classified as ‘insufficient data’ according to the MenDeVAR Index to evaluate the potential coverage by the 4CMenB vaccine. Nearly half of the isolates were potentially covered by the Men-Fhbp vaccine. Resistance to ciprofloxacin was detected only for one cnl isolate. All isolates were susceptible to penicillin and ceftriaxone. Our analysis identified frequent partying (≥ 4 times/month) as a risk factor for meningococcal carriage, whereas smoking, living in a dormitory, and previous COVID-19 illness were not associated with the carriage.ConclusionsOur study revealed a low prevalence of meningococcal carriage among university students in Lithuania. The carriage isolates showed genetic diversity, although almost half of them were identified as having a null capsule locus.

Impact of Charge Carrier Transfer and Strain Relaxation on Red-Emitting InGaN/GaN Heterostructures

Impact of Charge Carrier Transfer and Strain Relaxation on Red-Emitting InGaN/GaN Heterostructures

Meningococcal carriage in children and young adults: a cross-sectional and longitudinal study, Iceland, 2019 to 2021.

BackgroundNeisseria meningitidis is a commensal bacterium which can cause invasive disease. Colonisation studies are important to guide vaccination strategies.AimThe study's aim was to determine the prevalence of meningococcal colonisation, duration of carriage and distribution of genogroups in Iceland.MethodsWe collected samples from 1 to 6-year-old children, 15-16-year-old adolescents and 18-20-year-old young adults. Carriers were sampled at regular intervals until the first negative swab. Conventional culture methods and qPCR were applied to detect meningococci and determine the genogroup. Whole genome sequencing was done on groupable meningococci.ResultsNo meningococci were detected among 460 children, while one of 197 (0.5%) adolescents and 34 of 525 young adults (6.5 %) carried meningococci. Non-groupable meningococci were most common (62/77 isolates from 26/35 carriers), followed by genogroup B (MenB) (12/77 isolates from 6/35 carriers). Genogroup Y was detected in two individuals and genogroup W in one. None carried genogroup C (MenC). The longest duration of carriage was at least 21 months. Serial samples from persistent carriers were closely related in WGS.ConclusionsCarriage of pathogenic meningococci is rare in young Icelanders. Non-groupable meningococci were the most common colonising meningococci in Iceland, followed by MenB. No MenC were found. Whole genome sequencing suggests prolonged carriage of the same strains in persistent carriers.

Graphene on SiO2/Si and Al2O3 under thermal annealing and electric current: Competition of dopant desorption and conformation to substrate

In this work, we study phonon and electronic properties of graphene on SiO2/Si and Al2O3 by simultaneous Raman and electrical measurements in the temperature range from room temperature to 550 °C, or at voltages from 20 to −20 V. The dependencies of G and 2D peak parameters and electrical resistance on temperature and voltage made it possible to observe in situ a competition between the p-type adsorbate removal from graphene surface and substrate-induced doping due to graphene-substrate conformality increase, both stimulated by either ambient or Joule heating. The analyzed parameters were dominated by the conformality increase, with the hole density increasing significantly and unidirectionally, while resistance and I-V curves fluctuated due to the competition. Having calculated Raman peak shift temperature coefficients, resistance temperature coefficients, total variations of carrier density, resistance and strain, we show that Al2O3 substrate can be used to reduce the desorption barrier, the overall doping, the impact on graphene resistance and on phonon anharmonicity – however, it should be used with regard to the possibility of introducing strain or stronger doping after longer treatments. The conformality effects should be taken into account when performing annealing, as well as graphene applications for sensors or strong electric currents.

The Impact of Nasal Staphylococcus aureus Carriage on Surgical-Site Infections after Immediate Breast Reconstruction: Risk Factors and Biofilm Formation Potential.

BACKGROUND Despite the benefits of implant-based breast reconstruction in patients with breast cancer, the procedure can be complicated by surgical site infections (SSI). This study aimed to evaluate the association between nasal carriage of Staphylococcus aureus strains and the incidence of SSI among patients who underwent reconstructive procedures. We also assessed the ability of colonizing S. aureus strains to form biofilm. MATERIAL AND METHODS Medical data from 124 patients with 132 post-mastectomy breast reconstructions performed at the Oncology Center in Bydgoszcz, Poland, between June 2020 and August 2021 were analyzed. A 90-day incidence of SSI was found in 7/132 reconstructions (5.3%). The study group included 132 reconstructions, and was divided into those with infection (n=7) and without infection (n=125). Between-group differences were assessed using the t test for continuous variables and chi-square test for categorical variables. Biofilm formation among 32 S. aureus strains was determined by using quantitative and qualitative assays. RESULTS There were no significant differences in relation to the patients' S. aureus colonization status. Infections occurred both in patients colonized and not colonized with S. aureus. S. aureus nasal carriage did not affect the rate of SSI at 90 days after surgery. About 97.0% of the strains had a strong capacity for biofilm formation. CONCLUSIONS There was no association between nasal carriage of strains of S. aureus and the incidence of SSI. However, further investigations on a larger group of patients and longer observation time are needed to investigate this potential risk factor in detail.

The Diversity and Zoonotic Potential of Staphylococcus pseudintermedius in Humans and Pet Dogs in Trinidad and Tobago.

Staphylococcus pseudintermedius is an opportunistic pathogen that is frequently isolated from canines. It is of escalating interest because of its increasing antimicrobial resistance and zoonotic potential. Although many published articles are available that describe isolates obtained from diseased dogs and humans, this study focused on isolates obtained from healthy dogs and their owners who presented at clinics for routine veterinary care and utilized whole genome sequencing-based analyses for strain comparisons. A total of 25 humans and 27 canines were sampled at multiple sites, yielding 47 and 45 isolates, respectively. Whole genome sequence analysis was performed. We detected mostly new sequence types (STs) and a high diversity. Strains carried few antimicrobial resistance genes and plasmids, albeit three MRSP strains were found that belonged to two internationally distributed STs. The virulence content did not provide insights toward a tendency to colonization of humans but supported that there may be differences in the surface proteins between carrier strains and those causing pyoderma. We identified 13 cases in which humans were infected with strains from the dog they owned.

Micro-Raman analysis of HVPE grown etched GaN epilayer with porous formation

The GaN epilayer grown by hydride vapor phase epitaxy was wet etched by phosphoric acid as the etchant. X-ray diffraction confirms that the GaN has a wurtzite structure. Scanning electron microscopy shows various sizes of hexagonal pits for different times of etchant reactions. Atomic force microscopy shows increase in surface roughness with different etchant rate. The photoluminescence gives a 3.4 eV luminescence for the pristine GaN epilayer. In the etched films, the deep-level defect belonging to yellow and green luminescence was found. The deconvoluted Ga 3d peaks of etched samples show Ga-rich epilayers. Micro-Raman spectroscopy is a non-destructive method for measuring carrier concentration, phonon lifetime and strain using A 1 (LO) spectra of Raman vibration mode was utilized via the Lorentz fitting method. The carrier concentration increases while the phonon lifetime decreases with etching rate. Overall, in the 9 min reaction, the epilayer was etched heavily with a perfect hexagonal etch pit structure.

Multi-resistant Bacteria to Antibiotics in Hospitals: The Case of Neonatology Services of the University Hospitals Centers of Abidjan, Côte d'Ivoire

Background: Multidrug-resistant bacteria (MDR) represent a global health scourge. Their emergence in hospital services complicates the clinical management of infections caused in particular in immunocompromised persons. The objective of our work was to evaluate the prevalence of MDR in the neonatal services of the University Hospitals Centers of Abidjan.
 Materials and Methods: The present study took place from September to November 2020 and from January to June 2021. The samples collected consisted of venous blood samples for blood cultures, rectal swabs from newborns, nasal and hand swabs from health care workers, and swabs from inert surfaces and neonatal care equipment. Bacterial identification methods, antibiotic susceptibility testing, and Chi-square testing were performed.
 Results: A total of 513 samples were obtained from which 215 organisms were isolated and identified. These bacteria consisted of 52.1% Gram-negative bacilli, of which 77.7% were Enterobacteriaceae and 47.9% Gram-positive cocci. Klebsiella pneumoniae (K. pneumoniae) (25.6%), coagulase-Negative Staphylococcus (CoNS) (24.6%), and Staphylococcus aureus (S. aureus) (23.2%) were the most isolated bacteria. The overall prevalence of MDR was 73.9%. The main antibiotic resistance phenotypes described were the production of Broad Spectrum β-lactamases (ESBL) in 71.9% of Enterobacteriaceae and methicillin resistance (Meti-R) in 75.6% of Staphylococcus. ESBL-producing Enterobacteriaceae (E-ESBL) were mainly observed in rectal carriage and Meti-R strains in blood cultures in newborns in the respective proportions of 45.6% and 56.4%.
 Conclusion: In our work, the results obtained showed a high prevalence of MDR in neonatal services and newborns are the most affected subjects. Improving hygiene rules and control and rationalizing the use of antibiotics are highly recommended control strategies to reduce the hospital dissemination of MDR.

Intrinsic ferromagnetic half-metal: Non-equivalent alloying compounds CrMnI6 monolayer

Spintronics, the golden era of modern magnetism.Nowadays, intrinsic two-dimensional (2D) half-metal materials with pure spin sources possess a broad prospect in the practical application of modern spintronics. Therefore, based on first-principles calculations, we systematically predict the electronic structures and magnetic properties of non-equivalent alloying compounds CrMnI6 monolayer and fortunately find that the monolayer is a dynamically and thermally stable half-metal with a large in-plane magnetic anisotropy energy (MAE) of 36.75 meV/cell. Its Curie temperature is 145 K, significantly higher than that of CrI3 monolayer. In addition, the half-metallicity of monolayer CrMnI6 can be remained in almost the entire range of carrier doping and strain. Moreover, the in-plane MAE can be further improved to 68.41 and 60.58 meV/cell under 0.1 hole doping and 6% tensile strain, respectively. Simultaneously, according to the second-order perturbation theory, the larger in-plane MAE of CrMnI6 monolayer mainly originates from the couplings of 〈pxLxpz〉 in the different spin channel of I atom and the couplings of 〈dx2-y2Lzdxy〉 in the same spin channel of Mn and Cr atoms. Our prediction of such a novel 2D FM half-metal CrMnI6 monolayer may serve as a good candidate for the next-generation high-performance spintronic nanodevices and high- density magnetic recording and sensors.

A Novel CovS Variant Harbored by a Colonization Strain Reduces Streptococcus pyogenes Virulence.

Streptococcus pyogenes, also known as group A Streptococcus, causes a wide variety of diseases ranging from mild noninvasive to severe invasive infections. To identify possible causes of colonization-to-invasive switches, we determined the genomic sequences of 10 isolates from five pairs each composed of an invasive strain and a carriage strain originating from five infectious clusters. Among them, one pair displayed a single-nucleotide difference in covS, encoding the sensor histidine kinase of the two-component CovRS system that controls the expression of 15% of the genome. In contrast to previously described cases where the invasive strains harbor nonfunctional CovS proteins, the carriage strain possessed the mutation covST115C, leading to the replacement of the tyrosine at position 39 by a histidine. The CovSY39H mutation affected the expression of the genes from the CovR regulon in a unique fashion. Genes usually overexpressed in covS mutant strains were underexpressed and vice versa. Furthermore, the covS mutant strain barely responded to the addition of the CovS-signaling compounds Mg2+ and LL-37. The variations in the accumulation of two virulence factors paralleled the transcription modifications. In addition, the covST115C mutant strain showed less survival than its wild-type counterpart in murine macrophages. Finally, in two murine models of infection, the covS mutant strain was less virulent than the wild-type strain. Our study suggests that the CovSY39H protein compromises CovS phosphatase activity and that this yields a noninvasive strain. IMPORTANCE Streptococcus pyogenes, also known as group A Streptococcus, causes a wide variety of diseases, leading to 517,000 deaths yearly. The two-component CovRS system, which responds to MgCl2 and the antimicrobial peptide LL-37, controls the expression of 15% of the genome. Invasive strains may harbor nonfunctional CovS sensor proteins that lead to the derepression of most virulence genes. We isolated a colonization strain that harbors a novel covS mutation. This mutant strain harbored a transcriptome profile opposite that of other covS mutant strains, barely responded to environmental signals, and was less virulent than the wild-type strain. This supports the importance of the derepression of the expression of most virulence genes, via mutations that impact the phosphorylation of the regulator CovR, for favoring S. pyogenes invasive infections.

Charge carrier density dependent Raman spectra of graphene encapsulated in hexagonal boron nitride

We present low-temperature Raman measurements on gate tunable graphene encapsulated in hexagonal boron nitride, which allows to study in detail the Raman G and 2D mode frequencies and line widths as function of the charge carrier density. We observe a clear softening of the Raman G mode (of up to 2.5 cm$^{-1}$) at low carrier density due to the phonon anomaly and a residual G~mode line width of $\approx$ 3.5 cm$^{-1}$ at high doping. From analyzing the G mode dependence on doping and laser power we extract an electron-phonon-coupling constant of $\approx$ 4.4 $\times$ 10$^{-3}$ (for the G mode phonon). The ultra-flat nature of encapsulated graphene results in a minimum Raman 2D peak line width of 14.5 cm$^{-1}$ and allows to observe the intrinsic electron-electron scattering induced broadening of the 2D peak of up to 18 cm$^{-1}$ for an electron density of 5$\times$10$^{12}$ cm$^{-2}$ (laser excitation energy of 2.33 eV). Our findings not only provide insights into electron-phonon coupling and the role of electron-electron scattering for the broadening of the 2D peak, but also crucially shows the limitations when it comes to the use of Raman spectroscopy (i.e. the use of the frequencies and the line widths of the G and 2D modes) to benchmark graphene in terms of charge carrier density, strain and strain inhomogenities. This is particularly relevant when utilizing spatially-resolved 2D Raman line width maps to assess substrate-induced nanometer-scale strain variations.