Layered Ferromagnetic Structure Caused by the Proximity Effect and Interlayer Charge Transfer for LaNiO3/LaMnO3 Superlattices.

Magnetic proximity-induced magnetism in paramagnetic LaNiO3 (LNO) has spurred intensive investigations in the past decade. However, no consensus has been reached so far regarding the magnetic order in LNO layers in relevant heterostructures. This paper reports a layered ferromagnetic structure for the (111)-oriented LNO/LaMnO3 (LMO) superlattices. It is found that each period of the superlattice consisted of an insulating LNO-interfacial phase (five unit cells in thickness, ∼1.1 nm), a metallic LNO-inner phase, a poorly conductive LMO-interfacial phase (three unit cells in thickness, ∼0.7 nm), and an insulating LMO-inner phase. All four of these phases are ferromagnetic, showing different magnetizations. The Mn-to-Ni interlayer charge transfer is responsible for the emergence of a layered magnetic structure, which may cause magnetic interaction across the LNO/LMO interface and double exchange within the LMO-interfacial layer. This work indicates that the proximity effect is an effective means of manipulating the magnetic state and associated properties of complex oxides.

Direct Observation of Magnetic Skyrmions and Their Current-Induced Dynamics in Epitaxial Single-Crystal Oxide Films.

Magnetic skyrmions are scarcely investigated for single-crystal quality films, for which skyrmions may have a remarkable performance. Even in the limited studies in this aspect, the skyrmions are usually probed by the topological Hall effect, missing important information on dynamic properties. Here, we present a comprehensive investigation on the generation/manipulation of magnetic skyrmions in La0.67Ba0.33MnO3 single-crystal films. Using the technique of magnetic force microscopy, the current-driven skyrmion dynamics are directly observed. Unlike isolated skyrmions produced by magnetic field alone, closely packed skyrmions can be generated by electric pulses in a magnetic background, with a high density (∼60/µm2) and a small size (dozens of nanometers). The threshold current moving skyrmions is ∼2.3 × 104 A/cm2, 2-3 orders of magnitude lower than that required by metallic multilayers or van der Waals ferromagnetic heterostructures. Our work demonstrates the great potential of single-crystal oxide films in developing skyrmion-based devices.

Liquid Phase Edge Epitaxy of Transition-Metal Dichalcogenide Monolayers.

Precise monolayer epitaxy is important for two-dimensional (2D) semiconductors toward future electronics. Here, we report a new self-limited epitaxy approach, liquid phase edge epitaxy (LPEE), for precise-monolayer epitaxy of transition-metal dichalcogenides. In this method, the liquid solution contacts 2D grains only at the edges, which confines the epitaxy only at the grain edges and then precise monolayer epitaxy can be achieved. High-temperature in situ imaging of the epitaxy progress directly supports this edge-contact epitaxy mechanism. Typical transition-metal dichalcogenide monolayers (MX2, M = Mo, W, and Re; X = S or Se) have been obtained by LPEE with a proper choice of molten alkali halide solvents (AL, A = Li, Na, K, and Cs; L = Cl, Br, or I). Furthermore, alloying and magnetic-element doping have also been realized by taking advantage of the liquid phase epitaxy approach. This LPEE method provides a precise and highly versatile approach for 2D monolayer epitaxy and can revolutionize the growth of 2D materials toward electronic applications.

Enhancing Interfacial Ferromagnetism and Magnetic Anisotropy of CaRuO3 /SrTiO3 Superlattices via Substrate Orientation.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. One of the most interesting phenomena is the interfacial magnetism formed between two non-magnetic compounds. Here, a robust ferromagnetic phase emerged at the (111)-oriented heterointerface between paramagnetic CaRuO3 and diamagnetic SrTiO3 is reported. The Curie temperature is as high as ≈155 K and the saturation magnetization is as large as ≈1.3 µB per formula unit for the (111)-CaRuO3 /SrTiO3 superlattices, which are obviously superior to those of the (001)-oriented counterparts and are comparable to the typical itinerant ferromagnet SrRuO3 . A strong in-plane magnetic anisotropy with six-fold symmetry is further revealed by the anisotropic magnetoresistance measurements, presenting a large in-plane anisotropic field of 3.0-3.6 T. More importantly, the magnetic easy axis of the (111)-oriented superlattices can be effectively tuned from 〈 11 2 ¯ $11\overline{2}$ 1〉 to 〈 1 1 ¯ 0 $1 \bar{1}0$ 〉 directions by increasing the layer thickness of SrTiO3 . The findings demonstrate a feasible approach to enhance the interface coupling effect by varying the stacking orientation of oxide heterostructures. The tunable magnetic anisotropy also shows potential applications in low-power-consumption or exchange spring devices.

Thermal Spin Injection and Inverse Edelstein Effect of the Two-Dimensional Electron Gas at EuO-KTaO3 Interfaces.

With the help of the two-dimensional electron gas (2DEG) at the LaAlO3-SrTiO3 interface, spin and charge currents can be interconverted. However, the conversion efficiency has been strongly depressed by LaAlO3, which blocks spin transmission. It is therefore highly desired to explore 2DEGs sandwiched between ferromagnetic insulators that are transparent for magnons. By constructing epitaxial heterostructure with ferromagnetic EuO, which is conducting for spin current but insulating for electric current, and KTaO3, we successfully obtained the 2DEGs, which can receive thermally injected spin current directly from EuO and convert the spin current to charge current via inverse Edelstein effect of the interface. Strong dependence of the spin Seebeck coefficient on the layer thickness of EuO is further observed and the propagation length for non-equilibrium magnons in EuO has been determined. The present work demonstrates the great potential of the 2DEGs formed by ferromagnetic oxides for spin caloritronics.

High-Mobility Spin-Polarized Two-Dimensional Electron Gases at EuO/KTaO_{3} Interfaces.

Two-dimensional electron gases (2DEGs) at oxide interfaces, which provide unique playgrounds for emergent phenomena, have attracted increasing attention in recent years. While most of the previous works focused on the 2DEGs at LaAlO_{3}/SrTiO_{3} interfaces, here we report on a new kind of 2DEGs formed between a magnetic insulator EuO and a high-k perovskite KTaO_{3}. The 2DEGs are not only highly conducting, with a maximal Hall mobility of 111.6 cm^{2}/V s at 2 K, but also well spin polarized, showing strongly hysteretic magnetoresistance up to 25 K and well-defined anomalous Hall effect up to 70 K. Moreover, unambiguous correspondences between the hysteretic behaviors of 2DEGs and the EuO layer are captured, suggesting the proximity effect of the latter on the former. This is confirmed by the results of density-functional theory calculations: Through interlayer exchange, EuO drives the neighboring TaO_{2} layer into a ferromagnetic state. The present work opens new avenues for the exploration for high performance spin-polarized 2DEGs at oxide interfaces.

High mobility 2-dimensional electron gas at LaAlO3/SrTiO3 interface prepared by spin coating chemical methods.

Highly mobile 2-dimensional electron gases (2DEGs) at the (001), (011) and (111)-oriented LaAlO3/SrTiO3 (LAO/STO) interfaces are obtained using spin coating chemical method, which is a gentle technique without plasma bombardment of the pulsed laser deposition. As revealed by x-ray diffraction spectrum and x-ray reflectivity analysis, the LAO over layer is epitaxially grown, and has a uniform thickness of ∼15 nm, ∼20 nm and ∼26 nm for (001), (011) and (111) orientations, respectively. The interfaces are well metallic down to 2 K. The carrier mobilities are ∼28 000 cm2 V-1 s-1, ∼22 000 cm2 V-1 s-1 and ∼8300 cm2 V-1 s-1 at 2 K for the (001), (011) and (111) LAO/STO interfaces, respectively, and ∼8 cm2 V-1 s-1, ∼4 cm2 V-1 s-1 and ∼4 cm2 V-1 s-1 at room temperature. The present work shows that the spin coating chemical method is a feasible approach to get high quality 2DEG at both the polar/non-polar and polar/polar interfaces.

Whole-Genome Sequencing for Detecting Antimicrobial Resistance in Nontyphoidal Salmonella.

Laboratory-based in vitro antimicrobial susceptibility testing is the foundation for guiding anti-infective therapy and monitoring antimicrobial resistance trends. We used whole-genome sequencing (WGS) technology to identify known antimicrobial resistance determinants among strains of nontyphoidal Salmonella and correlated these with susceptibility phenotypes to evaluate the utility of WGS for antimicrobial resistance surveillance. Six hundred forty Salmonella of 43 different serotypes were selected from among retail meat and human clinical isolates that were tested for susceptibility to 14 antimicrobials using broth microdilution. The MIC for each drug was used to categorize isolates as susceptible or resistant based on Clinical and Laboratory Standards Institute clinical breakpoints or National Antimicrobial Resistance Monitoring System (NARMS) consensus interpretive criteria. Each isolate was subjected to whole-genome shotgun sequencing, and resistance genes were identified from assembled sequences. A total of 65 unique resistance genes, plus mutations in two structural resistance loci, were identified. There were more unique resistance genes (n = 59) in the 104 human isolates than in the 536 retail meat isolates (n = 36). Overall, resistance genotypes and phenotypes correlated in 99.0% of cases. Correlations approached 100% for most classes of antibiotics but were lower for aminoglycosides and beta-lactams. We report the first finding of extended-spectrum ß-lactamases (ESBLs) (blaCTX-M1 and blaSHV2a) in retail meat isolates of Salmonella in the United States. Whole-genome sequencing is an effective tool for predicting antibiotic resistance in nontyphoidal Salmonella, although the use of more appropriate surveillance breakpoints and increased knowledge of new resistance alleles will further improve correlations.

Novel gentamicin resistance genes in Campylobacter isolated from humans and retail meats in the USA.

OBJECTIVES: To understand the molecular epidemiology of gentamicin-resistant Campylobacter and investigate aminoglycoside resistance mechanisms. METHODS: One-hundred-and-fifty-one gentamicin-resistant Campylobacter isolates from humans (n = 38 Campylobacter jejuni; n = 41, Campylobacter coli) and retail chickens (n = 72 C. coli), were screened for the presence of gentamicin resistance genes by PCR and subtyped using PFGE. A subset of the isolates (n = 41) was analysed using WGS. RESULTS: Nine variants of gentamicin resistance genes were identified: aph(2″)-Ib, Ic, Ig, If, If1, If3, Ih, aac(6')-Ie/aph(2″)-Ia and aac(6')-Ie/aph(2″)-If2. The aph(2″)-Ib, Ic, If1, If3, Ih and aac(6')-Ie/aph(2″)-If2 variants were identified for the first time in Campylobacter. Human isolates showed more diverse aminoglycoside resistance genes than did retail chicken isolates, in which only aph(2″)-Ic and -Ig were identified. The aph(2″)-Ig gene was only gene shared by C. coli isolates from human (n = 27) and retail chicken (n = 69). These isolates displayed the same resistance profile and similar PFGE patterns, suggesting that contaminated retail chicken was probably the source of human C. coli infections. Human isolates were genetically diverse and generally more resistant than the retail chicken isolates. The most frequent co-resistance was to tetracycline (78/79, 98.7%), followed by ciprofloxacin/nalidixic acid (46/79, 58.2%), erythromycin and azithromycin (36/79, 45.6%), telithromycin (32/79, 40.5%) and clindamycin (18/79, 22.8%). All human and retail meat isolates were susceptible to florfenicol. CONCLUSIONS: This study demonstrated that several new aminoglycoside resistance genes underlie the recent emergence of gentamicin-resistant Campylobacter, and that, in addition to contaminated retail chicken, other sources have also contributed to gentamicin-resistant Campylobacter infections in humans.

WGS accurately predicts antimicrobial resistance in Escherichia coli.

OBJECTIVES: The objective of this study was to determine the effectiveness of WGS in identifying resistance genotypes of MDR Escherichia coli and whether these correlate with observed phenotypes. METHODS: Seventy-six E. coli strains were isolated from farm cattle and measured for phenotypic resistance to 15 antimicrobials with the Sensititre(®) system. Isolates with resistance to at least four antimicrobials in three classes were selected for WGS using an Illumina MiSeq. Genotypic analysis was conducted with in-house Perl scripts using BLAST analysis to identify known genes and mutations associated with clinical resistance. RESULTS: Over 30 resistance genes and a number of resistance mutations were identified among the E. coli isolates. Resistance genotypes correlated with 97.8% specificity and 99.6% sensitivity to the identified phenotypes. The majority of discordant results were attributable to the aminoglycoside streptomycin, whereas there was a perfect genotype-phenotype correlation for most antibiotic classes such as tetracyclines, quinolones and phenicols. WGS also revealed information about rare resistance mechanisms, such as structural mutations in chromosomal copies of ampC conferring third-generation cephalosporin resistance. CONCLUSIONS: WGS can provide comprehensive resistance genotypes and is capable of accurately predicting resistance phenotypes, making it a valuable tool for surveillance. Moreover, the data presented here showing the ability to accurately predict resistance suggest that WGS may be used as a screening tool in selecting anti-infective therapy, especially as costs drop and methods improve.

2D Air-Stable Nonlayered Ferrimagnetic FeCr2S4 Crystals Synthesized via Chemical Vapor Deposition.

The discovery of intrinsic 2D magnetic materials has opened up new opportunities for exploring magnetic properties at atomic layer thicknesses, presenting potential applications in spintronic devices. Here a new 2D ferrimagnetic crystal of nonlayered FeCr2S4 is synthesized with high phase purity using chemical vapor deposition. The obtained 2D FeCr2S4 exhibits perpendicular magnetic anisotropy, as evidenced by the out-of-plane/in-plane Hall effect and anisotropic magnetoresistance. Theoretical calculations further elucidate that the observed magnetic anisotropy can be attributed to its surface termination structure. By combining temperature-dependent magneto-transport and polarized Raman spectroscopy characterizations, it is discovered that both the measured Curie temperature and the critical temperature at which a low energy magnon peak disappeared remains constant, regardless of its thickness. Magnetic force microscopy measurements show the flipping process of magnetic domains. The exceptional air-stability of the 2D FeCr2S4 is also confirmed via Raman spectroscopy and Hall hysteresis loops. The robust anisotropic ferrimagnetism, the thickness-independent of Curie temperature, coupled with excellent air-stability, make 2D FeCr2S4 crystals highly attractive for future spintronic devices.

Charge-Transfer-Induced Interfacial Ferromagnetism in Ferromagnet-Free Oxide Heterostructures.

Due to the strong interlayer coupling between multiple degrees of freedom, oxide heterostructures have demonstrated exotic properties that are not shown by their bulk counterparts. One of the most interesting properties is ferromagnetism at the interface formed between "nonferromagnetic" compounds. Here we report on the interfacial ferromagnetic phase induced in the superlattices consisting of the two paramagnetic oxides CaRuO3 (CRO) and LaNiO3 (LNO). By varying the sublayer thickness in the superlattice period, we demonstrate that the ferromagnetic order has been established in both CaRuO3 and LaNiO3 sublayers, exhibiting an identical Curie temperature of ∼75 K. The X-ray absorption spectra suggest a strong charge transfer from Ru to Ni at the interface, triggering superexchange interactions between Ru/Ni ions and giving rise to the emergent ferromagnetic phase. Moreover, the X-ray linear dichroism spectra reveal the preferential occupancy of the d3z2-r2 orbital for the Ru ions and the dx2-y2 orbital for the Ni ions in the heterostructure. This leads to different magnetic anisotropy of the superlattices when they are dominated by CRO or LNO sublayers. This work clearly demonstrates a charge-transfer-induced interfacial ferromagnetic phase in the whole ferromagnet-free oxide heterostructures, offering a feasible way to tailor oxide materials for desired functionalities.

Whole-genome sequencing of gentamicin-resistant Campylobacter coli isolated from U.S. retail meats reveals novel plasmid-mediated aminoglycoside resistance genes.

Aminoglycoside resistance in Campylobacter has been routinely monitored in the United States in clinical isolates since 1996 and in retail meats since 2002. Gentamicin resistance first appeared in a single human isolate of Campylobacter coli in 2000 and in a single chicken meat isolate in 2007, after which it increased rapidly to account for 11.3% of human isolates and 12.5% of retail isolates in 2010. Pulsed-field gel electrophoresis analysis indicated that gentamicin-resistant C. coli isolates from retail meat were clonal. We sequenced the genomes of two strains of this clone using a next-generation sequencing technique in order to investigate the genetic basis for the resistance. The gaps of one strain were closed using optical mapping and Sanger sequencing, and this is the first completed genome of C. coli. The two genomes are highly similar to each other. A self-transmissible plasmid carrying multiple antibiotic resistance genes was revealed within both genomes, carrying genes encoding resistance to gentamicin, kanamycin, streptomycin, streptothricin, and tetracycline. Bioinformatics analysis and experimental results showed that gentamicin resistance was due to a phosphotransferase gene, aph(2")-Ig, not described previously. The phylogenetic relationship of this newly emerged clone to other Campylobacter spp. was determined by whole-genome single nucleotide polymorphisms (SNPs), which showed that it clustered with the other poultry isolates and was separated from isolates from livestock.

Giant Exchange-Bias-Like Effect at Low Cooling Fields Induced by Pinned Magnetic Domains in Y2 NiIrO6 Double Perovskite.

Exchange bias (EB) is highly desirable for widespread technologies. Generally, conventional exchange-bias heterojunctions require excessively large cooling fields for sufficient bias fields, which are generated by pinned spins at the interface of ferromagnetic and antiferromagnetic layers. It is crucial for applicability to obtain considerable exchange-bias fields with minimum cooling fields. Here, an exchange-bias-like effect is reported in a double perovskite, Y2 NiIrO6 , which shows long-range ferrimagnetic ordering below 192 K. It displays a giant bias-like field of 1.1 T with a cooling field of only 15 Oe at 5 K. This robust phenomenon appears below 170 K. This fascinating bias-like effect is the secondary effect of the vertical shifts of the magnetic loops, which is attributed to the pinned magnetic domains due to the combination of strong spin-orbit coupling on Ir, and antiferromagnetically coupled Ni- and Ir-sublattices. The pinned moments in Y2 NiIrO6 are present throughout the full volume, not just at the interface as in conventional bilayer systems.

Comparative genomic analysis of Vibrio parahaemolyticus: serotype conversion and virulence.

BACKGROUND: Vibrio parahaemolyticus is a common cause of foodborne disease. Beginning in 1996, a more virulent strain having serotype O3:K6 caused major outbreaks in India and other parts of the world, resulting in the emergence of a pandemic. Other serovariants of this strain emerged during its dissemination and together with the original O3:K6 were termed strains of the pandemic clone. Two genomes, one of this virulent strain and one pre-pandemic strain have been sequenced. We sequenced four additional genomes of V. parahaemolyticus in this study that were isolated from different geographical regions and time points. Comparative genomic analyses of six strains of V. parahaemolyticus isolated from Asia and Peru were performed in order to advance knowledge concerning the evolution of V. parahaemolyticus; specifically, the genetic changes contributing to serotype conversion and virulence. Two pre-pandemic strains and three pandemic strains, isolated from different geographical regions, were serotype O3:K6 and either toxin profiles (tdh+, trh-) or (tdh-, trh+). The sixth pandemic strain sequenced in this study was serotype O4:K68. RESULTS: Genomic analyses revealed that the trh+ and tdh+ strains had different types of pathogenicity islands and mobile elements as well as major structural differences between the tdh pathogenicity islands of the pre-pandemic and pandemic strains. In addition, the results of single nucleotide polymorphism (SNP) analysis showed that 94% of the SNPs between O3:K6 and O4:K68 pandemic isolates were within a 141 kb region surrounding the O- and K-antigen-encoding gene clusters. The "core" genes of V. parahaemolyticus were also compared to those of V. cholerae and V. vulnificus, in order to delineate differences between these three pathogenic species. Approximately one-half (49-59%) of each species' core genes were conserved in all three species, and 14-24% of the core genes were species-specific and in different functional categories. CONCLUSIONS: Our data support the idea that the pandemic strains are closely related and that recent South American outbreaks of foodborne disease caused by V. parahaemolyticus are closely linked to outbreaks in India. Serotype conversion from O3:K6 to O4:K68 was likely due to a recombination event involving a region much larger than the O-antigen- and K-antigen-encoding gene clusters. Major differences between pathogenicity islands and mobile elements are also likely driving the evolution of V. parahaemolyticus. In addition, our analyses categorized genes that may be useful in differentiating pathogenic Vibrios at the species level.

Recent clonal origin of cholera in Haiti.

Altered El Tor Vibrio cholerae O1, with classical cholera toxin B gene, was isolated from 16 patients with severe diarrhea at St. Mark's Hospital, Arbonite, Haiti, <3 weeks after onset of the current cholera epidemic. Variable-number tandem-repeat typing of 187 isolates showed minimal diversity, consistent with a point source for the epidemic.

Web-accessible database of hsp65 sequences from Mycobacterium reference strains.

Mycobacteria include a large number of pathogens. Identification to species level is important for diagnoses and treatments. Here, we report the development of a Web-accessible database of the hsp65 locus sequences (http://msis.mycobacteria.info) from 149 out of 150 Mycobacterium species/subspecies. This database can serve as a reference for identifying Mycobacterium species.

Multiple-genome comparison reveals new loci for Mycobacterium species identification.

To identify loci useful for species identification and to enhance our understanding of the population structure and genetic variability of the genus Mycobacterium, we conducted a multiple-genome comparison of a total of 27 sequenced genomes in the suborder of Corynebacterineae (18 from the Mycobacterium genus, 7 from the Corynebacterium genus, 1 each from the Nocardia and Rhodococcus genera). Our study revealed 26 informative loci for species identification in Mycobacterium. The sequences from these loci were used in a phylogenetic analysis to infer the evolutionary relations of the 18 mycobacterial genomes. Among the loci that we identified, rpoBC, dnaK, and hsp65 were amplified from 29 ATCC reference strains and 17 clinical isolates and sequenced. The phylogenetic trees generated from these loci show similar topologies. The newly identified dnaK locus is more discriminatory and more robust than the widely used hsp65 locus. The length-variable rpoBC locus is the first intergenic locus between two protein-encoding genes being used for mycobacterial species identification. A multilocus sequence analysis system including the rpoBC, dnaK, and hsp65 loci is a robust tool for accurate identification of Mycobacterium species.

Infinite-layer/perovskite oxide heterostructure-induced high-spin states in SrCuO2/SrRuO3 bilayer films.

Heterostructures composed of dissimilar oxides with different properties offer opportunities to develop emergent devices with desired functionalities. A key feature of oxide heterostructures is interface electronics and orbital reconstructions. Here, we combined infinite-layered SrCuO2 and perovskite SrRuO3 into heterostructures. A rare high spin state as large as 3.0 µB f.u-1 and an increase in Curie temperature by 12 K are achieved in an ultrathin SrRuO3 film capped by a SrCuO2 layer. Atomic-scale lattice imaging shows the uniform CuO2-plane-to-RuO5-pyramid connection at the interface, where the regularly arranged RuO5 pyramids were elongated along the out-of-plane direction. As revealed by theoretical calculations and spectral analysis, these features finally result in an abnormally high spin state of the interfacial Ru ions with highly polarized eg orbitals. The present work demonstrates that oxygen coordination engineering at the infinite-layer/perovskite oxide interface is a promising approach towards advanced oxide electronics.

Genetic analysis of the capsule polysaccharide (K antigen) and exopolysaccharide genes in pandemic Vibrio parahaemolyticus O3:K6.

BACKGROUND: Pandemic Vibrio parahaemolyticus has undergone rapid changes in both K- and O-antigens, making detection of outbreaks more difficult. In order to understand these rapid changes, the genetic regions encoding these antigens must be examined. In Vibrio cholerae and Vibrio vulnificus, both O-antigen and capsular polysaccharides are encoded in a single region on the large chromosome; a similar arrangement in pandemic V. parahaemolyticus would help explain the rapid serotype changes. However, previous reports on "capsule" genes are controversial. Therefore, we set out to clarify and characterize these regions in pandemic V. parahaemolyticus O3:K6 by gene deletion using a chitin based transformation strategy. RESULTS: We generated different deletion mutants of putative polysaccharide genes and examined the mutants by immuno-blots with O and K specific antisera. Our results showed that O- and K-antigen genes are separated in V. parahaemolyticus O3:K6; the region encoding both O-antigen and capsule biosynthesis in other vibrios, i.e. genes between gmhD and rjg, determines the K6-antigen but not the O3-antigen in V. parahaemolyticus. The previously identified "capsule genes" on the smaller chromosome were related to exopolysaccharide synthesis, not K-antigen. CONCLUSION: Understanding of the genetic basis of O- and K-antigens is critical to understanding the rapid changes in these polysaccharides seen in pandemic V. parahaemolyticus. This report confirms the genetic location of K-antigen synthesis in V. parahaemolyticus O3:K6 allowing us to focus future studies of the evolution of serotypes to this region.