631 research outputs found
Diminished Virulence Of A Sar-lagr- Mutant Of Staphylococcus Aureus In The Rabbit Model Of Endocarditis
Microbial pathogenicity in Staphylococcus aureus is a complex process involving a number of virulence genes that are regulated by global regulatory systems including sar and agr. To evaluate the roles of these two loci in virulence, we constructed sar-lagr- mutants of strains RN6390 and RN450 and compared their phenotypic profiles to the corresponding single sar- and agr- mutants and parents. The secretion of all hemolysins was absent in the sar-lagr- mutants while residual β-hemolysin activity remained in single agr- mutants. The fibronectin binding capacity was significantly diminished in both single sar- mutants and double mutants when compared with parents while the reduction in fibrinogen binding capacity in the double mutants was modest. In the rabbit endocarditis model, there was a significant decrease in both infectivity rates and intravegetation bacterial densities with the double mutant as compared to the parent (RN6390) at 103-106 CFU inocula despite comparable levels of early bacteremia among various challenge groups. Notably, fewer bacteria in the double mutant group adhered to valvular vegetations at 30 min after challenge (106 CFU) than the parent group. These studies suggest that both the sar and agr loci are involved in initial valvular adherence, intravegetation persistence and multiplication of S. aureus in endocarditis.94518151822Waldvogel, F.A., Staphylococcus aureus (1985) Principles and Practice of Infectious Diseases, pp. 1097-1116. , G. L. Mandell, R. G. Douglas, Jr., and J. E. Bennett, editors. John Wiley & Sons, New YorkNeu, H.C., The crisis in antibiotic resistance (1992) Science (Wash. DC), 257, pp. 1064-1072Cohen, M.L., Epidemiology of drug resistance: Implications for a post-antibiotic era (1992) Science (Wash. DC), 257, pp. 1050-1055Easmon, C.S.F., Adlam, C., (1983) Staphylococci and Staphylococcal Infections, pp. 705-740. , Academic Press, New YorkCheung, A.L., Krishnan, M., Jaffe, E.A., Fischetti, V.A., Fibrinogen acts as a bridging molecule in the adherence of Staphylococcus aureus to cultured human endothelial cells (1991) J. Clin. Invest., 87, pp. 2236-2245Herrmann, M., Vaudaux, P.E., Pittet, D., Auckenthaler, R., Lew, P.D., Schumacher Perdreau, F., Peters, G., Waldvogel, F.A., Fibronectin, fibrinogen, and laminin act as mediators of adherence of clinical staphylococcal isolates to foreign material (1988) J. Infect. Dis., 158, pp. 693-701Kuypers, J.M., Proctor, R.A., Reduced adherence to traumatized rat heart valves by a low-fibronectin-binding mutant of Staphylococcus aureus (1989) Infect. Immun., 57, pp. 2306-2312DeRita, V.J., Mekalanos, J.J., Genetic regulation of bacterial virulence (1989) Annu. Rev. Genet., 23, pp. 455-482Kornblum, J., Kreiswirth, B., Projan, S.J., Ross, H., Novick, R.P., Agr: A polycistronic locus regulating exoprotein synthesis in Staphylococcus aureus (1990) Molecular Biology of the Staphylococci, pp. 373-402. , R. P. Novick, editor. VCH Publishers, New YorkNixon, B.T., Ronson, C.W., Ausubel, R.M., Two component regulatory systems responsive to environmental stimuli share strongly conserved domains with the nitrogen assimilation regulatory genes ntrB and btrC (1986) Proc. Natl. Acad. Sci. USA, 83, pp. 7850-7854Smeltzer, M.S., Hart, M.E., Iandolo, J.J., Phenotypic characterization of xpr, a global regulator of extracellular virulence factors in Staphylococcus aureus (1993) Infect. Immun., 61, pp. 919-925Cheung, A.L., Koomey, J.M., Butler, C.A., Projan, S.J., Fischetti, V.A., Regulation of exoprotein expression in Staphylococcus aureus by a locus (sar) distinct from agr (1992) Proc. Natl. Acad. Sci. USA, 89, pp. 6462-6466Cheung, A.L., Yeaman, M., Bayer, A.S., The role of the sar locus of Staphylococcus aureus in the induction of endocarditis in rabbits (1994) Infect. Immun., 62, pp. 1719-1725Vandenesch, F., Kornblum, J., Novick, R.P., A temporal signal, independent of agr, is required for hla but not spa transcription in Staphylococcus aureus (1991) J. Bacteriol., 173, pp. 6313-6320Cheung, A.L., Ying, P., Regulation of α and β hemolysins by the sar locus of Staphylococcus aureus (1994) J. Bacteriol., 176, pp. 580-585Rescei, P., Kreiswirth, B., O'Reilly, M., Schlievert, P., Gruss, A., Novick, R.P., Regulation of exoprotein gene expression in Staphylococcus aureus by agr (1986) Mol. & Gen. Genet., 202, pp. 58-61Fröman, G., Switalski, L., Speziale, P., Höök, M., Isolation and characterization of a fibronectin receptor from Staphylococcus aureus (1987) J. Biol. Chem., 262, pp. 6564-6571Lantz, M., Allen, R.D., Bounelis, P., Switalski, L.M., Höök, M., Bacteroides gingivalis and Bacteroides intermedius recognize different sites on human fibrinogen (1990) J. Bacteriol., 172, pp. 716-726Yeaman, M.R., Sullam, P.M., Dazin, P.F., Norman, D.C., Bayer, A.S., Characterization of Staphylococcus aureus-platelet binding by quantitative flow cytometric analysis (1992) J. Infect. Dis., 166, pp. 65-73Clawson, C.C., White, J.G., Herzberg, M.C., Platelet interaction with bacteria. VI. Contrasting the role of fibrinogen and fibronectin (1980) Am. J. Hematol., 9, pp. 43-53Yeaman, M.R., Norman, D.C., Bayer, A.S., Staphylococcus aureus susceptibility to thrombin-induced platelet microbicidal protein is independent of platelet adherence and aggregation in vitro (1992) Infect. 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Bacteriol., 176, pp. 4168-4172Scheld, W.M., Strunk, R.W., Balian, G., Calderone, R.A., Microbial adhesion to fibronectin in vitro correlates with production of endocarditis in rabbits (1985) Proc. Soc. Exp. Biol. Med., 180, pp. 474-482Durack, D.T., Beeson, P.B., Pathogenesis of infective endocarditis (1980) Infective Endocarditis, pp. 1-53. , S. H. Rahimtoola, editor. Grune and Stratton, Inc., New YorkJaffe, E., Cell biology of endothelial cells (1987) Hum. Pathol., 18, pp. 234-239Lopes, J.D., Reis, M.D., Bretani, R.R., Presence of laminin receptors in Staphylococcus aureus (1985) Science (Wash. DC), 229, pp. 275-277Patti, J.M., Bremell, T., Krajewska-Paetrasik, D., Adelnour, A., Tarkowski, A., Ryden, C., Höök, M., The Staphylococcus aureus collagen adhesin is a virulence determinant in experimental septic arthritis Infect. Immun., 62, pp. 152-161Herrmann, M., Suchard, S.J., Boxer, L.A., Waldvogel, F.A., Lew, P.D., Thrombospondin binds to Staphylococcus aureus and promotes staphylococcal adhesion to surfaces (1991) Infect. Immun., 59, pp. 279-288Bhakdi, S., Muhly, M., Mannhardt, U., Hugo, F., Klapettek, K., Muller-Eckhardt, C., Roka, L., Staphylococcal α-toxin promotes blood coagulation via attack on human platelets (1988) J. Exp. Med., 168, pp. 527-542Suttorp, N., Hessz, T., Seeger, W., Wilke, A., Koob, R., Lutz, F., Drenckhahn, D., Bacterial exotoxins and endothelial permeability for water and albumin in vitro (1988) Am. J. Physiol., 255, pp. C368Novick, R.P., Genetic systems in staphylococci (1991) Methods Enzymol., 204, pp. 587-636O'Reilly, M., De Azavedo, J.C.S., Kennedy, S., Foster, T.J., Inactivation of the alpha-hemolysin of Staphylococcus aureus 8325-4 by site directed mutagenesis and studies on the expression of its haemolysins (1986) Microb. 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The complete chloroplast genome of pearl millet (Pennisetum glaucum (L.) R. Br.) and comparative analysis within the family poaceae
The complete chloroplast (cp) genome sequence of Pearl millet (Pennisetum glaucum [L.] R. Br.), an important grain and forage crop in the family Poaceae, is reported in this study. The complete cp genome sequence of P. glaucum is 138,172 bp in length with 38.6% overall GC content and exhibits a typical quadripartite structure comprising one pair of inverted repeat (IR) regions (22,275 bp) separated by a small single-copy (SSC) region (12,409 bp) and a large single-copy (LSC) region (81,213). The P. glaucum cp genome encodes 110 unique genes, 76 of which are protein-coding genes, 4 ribosomal RNA (rRNA) genes, 30 transfer RNA (tRNA) genes and 18 duplicated genes in the IR region. Nine genes contain one or two introns. Whole genome alignments of cp genome were performed for genome-wide comparison. Locally collinear blocks (LCBs) identified among the cp genomes showed that they were well conserved with respect to gene organization and order. This newly determined cp genome sequence of P. glaucum will provide valuable information for the future breeding programs of valuable cereal crops in the family Poaceae
Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations
The infrared behaviour of the medium modified gluon propagator in
non-equilibrium situations is studied in the covariant gauge using the
Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic
screening mass is non-zero at the one loop level whenever the initial gluon
distribution function is non isotropic with the assumption that the
distribution function of the gluon is not divergent at zero transverse
momentum. For isotropic gluon distribution functions, such as those describing
local equilibrium, the magnetic mass at one loop level is zero which is
consistent with finite temperature field theory results. Assuming that a
reasonable initial gluon distribution function can be obtained from a
perturbative QCD calculation of minijets, we determine these out of equilibrium
values for the initial magnetic and Debye screening masses at energy densities
appropriate to RHIC and LHC. We also compare the magnetic masses obtained here
with those obtained using finite temperature lattice QCD methods at similar
temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys.
Rev.
Special relativity constraints on the effective constituent theory of hybrids
We consider a simplified constituent model for relativistic
strong-interaction decays of hybrid mesons. The model is constructed using
rules of renormalization group procedure for effective particles in light-front
quantum field theory, which enables us to introduce low-energy phenomenological
parameters. Boost covariance is kinematical and special relativity constraints
are reduced to the requirements of rotational symmetry. For a hybrid meson
decaying into two mesons through dissociation of a constituent gluon into a
quark-anti-quark pair, the simplified constituent model leads to a rotationally
symmetric decay amplitude if the hybrid meson state is made of a constituent
gluon and a quark-anti-quark pair of size several times smaller than the
distance between the gluon and the pair, as if the pair originated from one
gluon in a gluonium state in the same effective theory.Comment: 11 pages, 5 figure
Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime
Numerical simulations are used to study how fiber supercontinuum generation
seeded by picosecond pulses can be actively controlled through the use of input
pulse modulation. By carrying out multiple simulations in the presence of
noise, we show how tailored supercontinuum Spectra with increased bandwidth and
improved stability can be generated using an input envelope modulation of
appropriate frequency and depth. The results are discussed in terms of the
non-linear propagation dynamics and pump depletion.Comment: Aspects of this work were presented in Paper ThJ2 at OECC/ACOFT 2008,
Sydney Australia 7-10 July (2008). Journal paper submitted for publication 30
July 200
Wave Function Based Characteristics of Hybrid Mesons
We propose some extensions of the quark potential model to hybrids, fit them
to the lattice data and use them for the purpose of calculating the masses,
root mean square radii and wave functions at the origin of the conventional and
hybrid charmonium mesons. We treat the ground and excited gluonic field between
a quark and an antiquark as in the Born-Oppenheimer expansion, and use the
shooting method to numerically solve the required Schrdinger
equation for the radial wave functions; from these wave functions we calculate
the mesonic properties. For masses we also check through a Crank Nichelson
discretization. For hybrid charmonium mesons, we consider the exotic quantum
number states with and . We also compare
our results with the experimentally observed masses and theoretically predicted
results of the other models. Our results have implications for scalar form
factors, energy shifts, magnetic polarizabilities, decay constants, decay
widths and differential cross sections of conventional and hybrid mesons.Comment: 13 pages, 6 figures, Erratum is submitted to EPJ
Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter
We apply the closed-time path integral formalism to study the medium effects
of non-equilibrium gluon matter. We derive the medium modified resummed gluon
propagator to the one loop level in non-equilibrium in the covariant gauge. The
gluon propagator we derive can be used to remove the infrared divergences in
the secondary parton collisions to study thermalization of minijet parton
plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification,
reference adde
Serotype, mating type and ploidy of Cryptococcus neoformans strains isolated from patients in Brazil
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