Defining the sizes of airborne particles that mediate influenza transmission in ferrets

Epidemics and pandemics of influenza are characterized by rapid global spread mediated by non-mutually exclusive transmission modes. The relative significance between contact, droplet, and airborne transmission is yet to be defined, a knowledge gap for implementing evidence-based infection control measures. We devised a transmission chamber that separates virus-laden particles by size and determined the particle sizes mediating transmission of influenza among ferrets through the air. Ferret-to-ferret transmission was mediated by airborne particles larger than 1.5 µm, consistent with the quantity and size of virus-laden particles released by the donors. Onward transmission by donors was most efficient before fever onset and may continue for 5 days after inoculation. Multiple virus gene segments enhanced the transmissibility of a swine influenza virus among ferrets by increasing the release of virus-laden particles into the air. We provide direct experimental evidence of influenza transmission via droplets and fine droplet nuclei, albeit at different efficiency

十字花科黑腐病菌染色體物理圖譜和基因定位

Xanthomonas campestris pv. campestris is a Gram (-) bacterium which has a G+C content of about 65%. It is important in causing black rot in crucifers. In addition, it produces xanthan gum which has high viscosity and is widely used in industry. The purpose of this study was to construct a physical map of strain Xc17 and localize some genes in the physical map. Intact chromosomal DNA was prepared by embedding method, subjected to enzyme digestions with PacI, SpeI and SwaI, respectively, followed by pulsed-field gel electrophoresis running at different parameters to get optimum resolution. The sizes of the fragments were calculated by using lambda II, lambda ladder and yeast chromosomes as markers. During this study, several multi-bands with similar fragment sizes were found in the SpeI-digested samples. These problems are solved by two dimensional PFGE. By calculating the sum of the length of the fragments released by enzyme digestions, the Xc17 genome size was estimated to be 4725 kb. A Tn5 derivative, pUT-Tn5(pfm) CmKm, which carries sites for rare-cut restriction enzymes, including PacI, SpeI and SwaI, was used to mutagenize the Xc17 genes. Different type of mutants were thus obtained, which included Gum-, pigmentation, auxotrophic, protease and secretion mutants. The chromosomal DNAs of these mutant have one more rare cut restriction sites than that of the wild type at sites of Tn5 insertion. After PFGE and hybridization with appropriate probes, the site of Tn5 insertion in a mutant was determined. This in turn represents the location of that gene in the physical map. A combination of partial digestion, two dimensional PFGE, and Tn5 mutant analysis were the strategies employed for SwaI physical mapping. The results thus showed a fragment order WA-WC-WD-WF-WB-WE in the SwaI circular map. In addition, locations for the genes involved in uracil synthesis, a gene cluster required for the synthesis of xanthan gum and the dif site were assigned in physical map of SwaI.十字花科黑腐病菌為革蘭氏陰性菌, 其染色體 DNA 之 G+C 比率約 65 %。 在農業方面， 為引起十字花科黑腐病之病原菌； 另一方面，其產生 之胞外黏多醣黃原膠， 因具有特殊黏性， 在工業上有廣泛之利用價值。 本實驗之主要目的為建立 Xc17 之物理圖譜及把基因定位於物理圖譜上 。 以包埋法製備之完整染色體 DNA 分別以 PacI, SpeI 及 SwaI切割， 並用不同條件進行脈衝電泳 (pulsed-field gel electrophoresis 簡稱 PFGE) 分離, 以求得到最佳之解析度。 各片段之大小經與 size marker (lambda II, lambda ladder and yeast chromosomes) 比較後， 可計算 每一亮帶之大小。 但於 SpeI 切割之情形, 只經一次 PFGE 分離會出現 重疊亮帶。 後來利用第二次脈衝電泳 (two-dimensional PFGE) 把這問 題解決。 同時經過計算後, 估計 Xc17 之基因組大小為 4725 kb。 pUT- Tn5(pfm)CmKm 一為 Tn5 之衍生質體, 其 Tn5 上帶有多個 rare-cut restriction enzyme 切位, 包括 PacI, SpeI 和 SwaI 等。對 Xc17 進 行誘導突變後, 篩選到與 Gum-、 色素、 營養需求、 蛋白質分解和胞外 分泌有關之突變株。 因 Tn5 插入染色體後, 突變株染色體中會比 wild type Xc 多了一些 rare-cut restriction enzyme 切位， 經過 PFGE 和 DNA hybridization 後， 就可知 Tn5插入之位置, 亦即該基因之位置 。綜合 partial digestion, two dimensional PFGE, 及分析 Tn5突變株 之結果, 定出 SwaI 的片段以 WA-WC-WD-WF-WB-WE 之排列,形成環狀物理 圖譜。 同時亦把有關 uracil 合成基因 ,黃原膠合成基因串, 及 dif site (deletion induced filamentation) 之位置定位於 SwaI 物理圖譜 上

oriC Region and Replication Termination Site, dif, of the Xanthomonas campestris pv. campestris 17 Chromosome

A 13-kb DNA fragment containing oriC and the flanking genes thdF, orf900, yidC, rnpA, rpmH, oriC, dnaA, dnaN, recF, and gyrB was cloned from the gram-negative plant pathogen Xanthomonas campestris pv. campestris 17. These genes are conserved in order with other eubacterial oriC genes and code for proteins that share high degrees of identity with their homologues, except for orf900, which has a homologue only in Xylella fastidiosa. The dnaA/dnaN intergenic region (273 bp) identified to be the minimal oriC region responsible for autonomous replication has 10 pure AT clusters of four to seven bases and only three consensus DnaA boxes. These findings are in disagreement with the notion that typical oriCs contain four or more DnaA boxes located upstream of the dnaA gene. The X. campestris pv. campestris 17 attB site required for site-specific integration of cloned fragments from filamentous phage φLf replicative form DNA was identified to be a dif site on the basis of similarities in nucleotide sequence and function with the Escherichia coli dif site required for chromosome dimer resolution and whose deletion causes filamentation of the cells. The oriC and dif sites were located at 12:00 and 6:00, respectively, on the circular X. campestris pv. campestris 17 chromosome map, similar to the locations found for E. coli sites. Computer searches revealed the presence of both the dif site and XerC/XerD recombinase homologues in 16 of the 42 fully sequenced eubacterial genomes, but eight of the dif sites are located far away from the 6:00 point instead of being placed opposite the cognate oriC. The differences in the relative position suggest that mechanisms different from that of E. coli may participate in the control of chromosome replication

Neutralizing Monoclonal Antibodies That Target the Spike Receptor Binding Domain Confer Fc Receptor-Independent Protection against SARS-CoV-2 Infection in Syrian Hamsters

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein is the main target for neutralizing antibodies. These antibodies can be elicited through immunization or passively transferred as therapeutics in the form of convalescent-phase sera or monoclonal antibodies (MAbs)

CD44+ Cancer Stem-Like Cells in EBV-Associated Nasopharyngeal Carcinoma

<div><p>Nasopharyngeal carcinoma (NPC) is a unique EBV-associated epithelial malignancy, showing highly invasive and metastatic phenotype. Despite increasing evidence demonstrating the critical role of cancer stem-like cells (CSCs) in the maintenance and progression of tumors in a variety of malignancies, the existence and properties of CSC in EBV-associated NPC are largely unknown. Our study aims to elucidate the presence and role of CSCs in the pathogenesis of this malignant disease. Sphere-forming cells were isolated from an EBV-positive NPC cell line C666-1 and its tumor-initiating properties were confirmed by <em>in vitro</em> and <em>in vivo</em> assays. In these spheroids, up-regulation of multiple stem cell markers were found. By flow cytometry, we demonstrated that both CD44 and SOX2 were overexpressed in a majority of sphere-forming C666-1 cells. The CD44+SOX2+ cells was detected in a minor population in EBV-positive xenografts and primary tumors and considered as potential CSC in NPC. Notably, the isolated CD44+ NPC cells were resistant to chemotherapeutic agents and with higher spheroid formation efficiency, showing CSC properties. On the other hand, microarray analysis has revealed a number of differentially expressed genes involved in transcription regulation (e.g. <em>FOXN4</em>, <em>GLI1</em>), immune response (<em>CCR7</em>, <em>IL8</em>) and transmembrane transport (e.g. <em>ABCC3</em>, <em>ABCC11</em>) in the spheroids. Among these genes, increased expression of CCR7 in CD44+ CSCs was confirmed in NPC xenografts and primary tumors. Importantly, blocking of CCR7 abolished the sphere-forming ability of C666-1 <em>in vitro</em>. Expression of CCR7 was associated with recurrent disease and distant metastasis. The current study defined the specific properties of a CSC subpopulation in EBV-associated NPC. Our findings provided new insights into developing effective therapies targeting on CSCs, thereby potentiating treatment efficacy for NPC patients.</p> </div

In vivo tumorigenic capacity of sphere-forming cells and unselected parental cells of C666-1 in nude mice.

<p>N/A – data not available.</p