Comprehensive Molecular Dissection of Dermatophilus congolensis Genome and First Observation of tet(Z) Tetracycline Resistance

Dermatophilus congolensis is a bacterial pathogen mostly of ruminant livestock in the tropics/subtropics and certain temperate climate areas. It causes dermatophilosis, a skin disease that threatens food security by lowering animal productivity and compromising animal health and welfare. Since it is a prevalent infection in ruminants, dermatophilosis warrants more research. There is limited understanding of its pathogenicity, and as such, there is no registered vaccine against D. congolensis. To better understanding the genomics of D. congolensis, the primary aim of this work was to investigate this bacterium using whole-genome sequencing and bioinformatic analysis. D. congolensis is a high GC member of the Actinobacteria and encodes approximately 2527 genes. It has an open pan-genome, contains many potential virulence factors, secondary metabolites and encodes at least 23 housekeeping genes associated with antimicrobial susceptibility mechanisms and some isolates have an acquired antimicrobial resistance gene. Our isolates contain a single CRISPR array Cas type IE with classical 8 Cas genes. Although the isolates originate from the same geographical location there is some genomic diversity among them. In conclusion, we present the first detailed genomic study on D. congolensis, including the first observation of tet(Z), a tetracycline resistance-conferring gene.     

Synthesis of β‐Lactams by 4‐exo‐tet Cyclization Process Induced by Electrogenerated Cyanomethyl Anion,Part 2:[1] Stereochemical Implications

An efficient electrochemically induced synthesis of chiral cis β‐lactams has been described, via deprotonation of chiral amides containing an acidic methylene group and a bromine atom as leaving group and bearing a chiral auxiliary or amine function. The electrogenerated base – cyanomethyl anion – is easily obtained by galvanostatic reduction of acetonitrile‐tetraethylammonium hexafluorophosphate solutions under very mild conditions. The yields are high and the cis‐diastereoselection complete. The use of starting chiral amides has allowed in many cases the preparation of the most abundant isomer in a pure form.     

When emulsification meets self-assembly: The role of emulsification in directing block copolymer assembly

Emulsification is used to generate spherical particles or droplets of immiscible liquids, while block copolymer self-assembly yields a wide variety of nanostructures. The combination of these two methodologies can yield a variety of structures that would not be otherwise observed. The emulsification/solvent evaporation process provides a powerful means to direct block copolymer assembly. Various factors arising from the emulsification can direct the block copolymer assembly, such as confinement effects, interfacial tension, as well as other conditions. In this review, various emulsification techniques are discussed, such as oil-in-water emulsions, double emulsions, as well as the use of microfluidic devices. While emulsification-induced self-assembly may be used to control internal morphologies as well as overall shapes of particles, it also lends a convenient method for controlling surface structures. Examples of exotic structures that may be obtained through the use of these techniques will be described. Also, ways in which morphologies may be controlled using these methods will be discussed.     

Quantity of the tetracycline resistance gene tet(M) differs substantially between meat at slaughterhouses and at retail

Abstract: Concentrations of the tetracycline resistance gene tet(M) per square centimeter were assessed in meat from the slaughterhouse (n = 100) and from retail (n = 100) by real‐time quantitative PCR. The study revealed a substantial contamination of retail meat with the tetracycline resistance gene tet(M), with a mean of 4.34 log copies per cm² fasces in chicken and 5.58 log copies per cm² fasces in pork. Quantitative resistance gene analysis provides an interesting tool for risk assessment and is becoming increasingly important. For both chicken and pork, tet(M) concentrations were significantly higher in meat at retail, compared to meat at slaughter. Cultural investigations revealed substantial differences in the prevalence of listeria and enterococci, and of E. coli and coliforms, between meat at slaughter (n = 500) and at retail (n = 500). However, the differences in the prevalence of 2 investigated groups of potential tet(M)‐carriers (enterococci, listeria) could not sufficiently explain the differences in tet(M) concentrations, since increasing concentrations of tet(M) were accompanied by decreasing prevalences of these potential tet(M)‐carriers. The percentage of tetracycline susceptible indicator bacteria (E. faecalis, E. coli) did not differ between meat at slaughter and meat at retail. Higher concentrations of tet(M) at retail might correlate with the proliferation of other genera than enterococci and listeria, but there is also a reason to discuss whether secondary contaminants might carry tet(M) more often than the primary flora of meat. Practical Application: We successfully applied the direct quantitative monitoring of resistance genes in meat, which generally might aid as a useful and rapid additional tool for risk assessment. We know that bacteria provide a large pool of resistance genes, which are widely shared between each other—the larger the pool is, the more genes might be exchanged. Thus, in terms of resistance gene monitoring, we should sometimes overcome the restricted view on single bacteria and look at the gene pool, instead.     

Development of an optimized expression system for the screening of antibody libraries displayed on the Escherichia coli surface

Polypeptide library screening technologies are critically dependentupon the characteristics of the expression system employed.A comparative analysis of the lpp–lac, tet and araBAD promoterswas performed to determine the importance of tight regulationand expression level in library screening applications. Thesurface display of single-chain antibody (scFv) in Escherichiacoli as an Lpp–OmpA' fusion was monitored using a fluorescentlytagged antigen in conjunction with flow cytometry. In contrastto the lpp–lac promoter, both tet and araBAD promoterscould be tightly repressed. Tight regulation was found to beessential for preventing rapid depletion of library clones expressingfunctional scFv and thus for maintaining the initial librarydiversity. Induction with subsaturating inducer concentrationsyielded mixed populations of uninduced and fully induced cellsfor both the tet and araBAD expression systems. In contrast,homogeneous expression levels were obtained throughout the populationusing saturating inducer concentrations and could be adjustedby varying the induction time and plasmid copy number. Underoptimal induction conditions for the araBAD system, proteinexpression did not compromise either cell viability or librarydiversity. This expression system was used to screen a libraryof random scFv mutants specific for digoxigenin for clones exhibitingimproved hapten dissociation kinetics. Thus, an expression systemhas been developed which allows library diversity to be preservedand is generally applicable to the screening of E.coli surfacedisplayed libraries.     

整体汽缸盖疲劳试验研究

该文介绍了应用结构试验系统中内压试验系统对整体铝缸盖进行应力测量及使劳试验的方法。通过对缸盖的电测、疲劳试验结果分析，找出了此种整体铝缸盖的薄弱环节及整体刚度问题，为缸盖的改进设计提供了依据。