132,017 research outputs found
Genetic and Functional Analyses of Virulence Potential of an Escherichia coli O157:H7 Strain Isolated From Super-Shedder Cattle
Shiga toxin (Stx)-producing Escherichia coli (STEC) O157:H7 is an enteric pathogen that causes life-threatening disease in humans, with cattle being major natural reservoirs. A group of STEC O157:H7 with a dramatic combination of high virulence potentials and super-shedder bovine origin have been isolated. Here, an STEC O157:H7 isolate, JEONG-1266, was analyzed by comparative genomics, stx genotyping, and phenotypic analyses. The phylogenetic typing and whole-genome comparison consistently showed that JEONG-1266 is genetically close to EC4115 (one of 2006 Spinach outbreak isolates) and SS17 (an isolate from super-shedder cattle) strains, all of which belong to lineage I/II and Clade 8. Both lineage I/II and Clade 8 are known to be mostly associated with clinical strains with high virulence and severe clinical symptoms. Further, JEONG-1266, like EC4115 and SS17, harbors stx2a/stx2c genes, and carries Stx-encoding prophages, specifically the φstx2a-γ subtype. Possession of the φstx2a-γ subtype of Stx-encoding prophages and production of Stx2a have been shown to be a key signature associated with hypervirulent STEC O157:H7 strains. In silico virulence typing elucidated JEONG- 1266, EC4115, and SS17 shared a highly conserved profile of key virulence genes at the nucleotide sequence level. Consistently, phenotypic data showed that JEONG-1266 expressed a high level of Stx2 toxins and had the full capacity of adhesion in vitro. Taken together, our study suggests that JEONG-1266 may represent an emerging STEC O157:H7 group, which are hypervirulent strains that originate from super-shedders, that can be a threat to food safety and public health
Green-Schwarz superstring on doubled-yet-gauged spacetime
We construct a world-sheet action for Green-Schwarz superstring in terms of
doubled-yet-gauged spacetime coordinates. For an arbitrarily curved NS-NS
background, the action possesses T-duality,
Lorentz symmetry, coordinate gauge
symmetry, spacetime doubled-yet-gauged diffeomorphisms, world-sheet
diffeomorphisms and Weyl symmetry. Further, restricted to flat backgrounds, it
enjoys maximal spacetime supersymmetry and kappa-symmetry. After the auxiliary
coordinate gauge symmetry potential being integrated out, our action can
consistently reduce to the original undoubled Green-Schwarz action. Thanks to
the twofold spin groups, the action is unique: it is specific choices of the
NS-NS backgrounds that distinguish IIA or IIB, as well as lead to
non-Riemannian or non-relativistic superstring a la Gomis-Ooguri which might
deserve the nomenclature, type IIC.Comment: 1+27 pages. No figure. v2) Wess-Zumino term identified, More Refs. To
be published in JHE
Stringy Gravity: Solving the Dark Problems at `short' distance
Dictated by Symmetry Principle, string theory predicts not General Relativity
but its own gravity which assumes the entire closed string massless sector to
be geometric and thus gravitational. In terms of , i.e. the
dimensionless radial variable normalized by mass, Stringy Gravity agrees with
General Relativity toward infinity, but modifies it at short distance. At far
short distance, gravitational force can be even repulsive. These may solve the
dark matter and energy problems, as they arise essentially from small
observations: long distance divided by much heavier mass. We address the
pertinent differential geometry for Stringy Gravity, stringy Equivalence
Principle, stringy geodesics and the minimal coupling to the Standard Model. We
highlight the notion of `doubled-yet-gauged' coordinate system, in which a
gauge orbit corresponds to a single physical point and proper distance is
defined between two gauge orbits by a path integral.Comment: 8 pages, 2 figures. Invited plenary talk at Joint Conference of
ICGAC-XIII and IK15, 3-7 July 201
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