192 research outputs found

    Protease treatment affects both invasion ability and biofilm formation in Listeria monocytogenes

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    Listeria monocytogenes is a notably invasive bacterium associated with life-threatening food-borne disease in humans. Several surface proteins have been shown to be essential in the adhesion of L. monocytogenes, and in the subsequent invasion of phagocytes. Because the control of the invasion of host cells by Listeria could potentially hinder its spread in the infected host, we have examined the effects of a protease treatment on the ability of L. monocytogenes to form biofilms and to invade tissues. We have chosen serratiopeptidase (SPEP), an extracellular metalloprotease produced by Serratia marcescens that is already widely used as an anti-inflammatory agent, and has been shown to modulate adhesin expression and to induce antibiotic sensitivity in other bacteria. Treatment of L. monocytogenes with sublethal concentrations of SPEP reduced their ability to form biofilms and to invade host cells. Zymograms of the treated cells revealed that Ami4b autolysin, internalinB, and ActA were sharply reduced. These cell-surface proteins are known to function as ligands in the interaction between these bacteria and their host cells, and our data suggest that treatment with this natural enzyme may provide a useful tool in the prevention of the initial adhesion of L. monocytogenes to the human gu

    Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV

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    A search for charginos nearly mass-degenerate with the lightest supersymmetric particle is performed using the 176 pb^-1 of data collected at 189 GeV in 1998 with the L3 detector. Mass differences between the chargino and the lightest supersymmetric particle below 4 GeV are considered. The presence of a high transverse momentum photon is required to single out the signal from the photon-photon interaction background. No evidence for charginos is found and upper limits on the cross section for chargino pair production are set. For the first time, in the case of heavy scalar leptons, chargino mass limits are obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference

    Formation of the ηc\eta_c in Two-Photon Collisions at LEP

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    The two-photon width Γγγ\Gamma_{\gamma\gamma} of the ηc\eta_c meson has been measured with the L3 detector at LEP. The ηc\eta_c is studied in the decay modes π+ππ+π\pi^+\pi^-\pi^+\pi^-, π+π\pi^+\pi^-K+^+K^-, Ks0_s^0K±π^\pm\pi^\mp, K+^+Kπ0^-\pi^{0}, π+πη\pi^+\pi^-\eta, π+πη\pi^+\pi^-\eta', and ρ+ρ\rho^+\rho^- using an integrated luminosity of 140 pb1^{-1} at s91\sqrt{s} \simeq 91 GeV and of 52 pb1^{-1} at s183\sqrt{s} \simeq 183 GeV. The result is Γγγ(ηc)=6.9±1.7(stat.)±0.8(sys.)±2.0\Gamma_{\gamma\gamma}(\eta_c) = 6.9 \pm 1.7 (stat.) \pm 0.8 (sys.) \pm 2.0(BR) keV. The Q2Q^2 dependence of the ηc\eta_c cross section is studied for Q2<9Q^2 < 9 GeV2^{2}. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a ρ\rho-pole. In addition, a signal of 29±1129 \pm 11 events is observed at the χc0\chi_c0 mass. Upper limits for the two-photon widths of the χc0\chi_c0, χc2\chi_c2, and ηc\eta_c' are also given

    K0s K0s Final State in Two-Photon Collisions and Implications for Glueballs

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    The K0s K0s final state in two-photon collisions is studied with the L3 detector at LEP. The mass spectrum is dominated by the formation of the f_2'(1525) tensor meson in the helicity-two state with a two-photon width times the branching ratio into K Kbar of 76 +- 6 +- 11 eV. A clear signal for the formation of the f_J(1710) is observed and it is found to be dominated by the spin-two helicity-two state. No resonance is observed in the mass region around 2.2 GeV and an upper limit of 1.4 eV at 95% C.L. is derived for the two-photon width times the branching ratio into K0s K0s for the glueball candidate xi(2230)

    Direct Observation of Longitudinally Polarised W Bosons

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    The three different helicity states of W bosons, produced in the reaction e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of the scattering angle between the W- and the direction of the e- beam. The analysis demonstrates that W bosons are produced with all three helicities, the longitudinal and the two transverse states. Combining the results from the two center-of-mass energies and with leptonic and hadronic W decays, the fraction of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.) +/- 0.016(syst.) in agreement with the expectation from the Standard Model

    Study of Z Boson Pair Production in e^+e^- Interactions at \sqrt{s}=192 - 202 GeV

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    The cross section for the production of Z boson pairs is measured using the data collected by the L3 detector at LEP in 1999 in e^+e^- collisions at centre-of-mass energies ranging from 192 GeV up to 202 GeV. Events in all the visible final states are selected, measuring the cross section of this process. The special case of final states containing b quarks is also investigated. All results are in agreement with the Standard Model predictions

    Search for Scalar Leptons in e+e- collisions at \sqrt{s}=189 GeV

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    We report the result of a search for scalar leptons in e+e- collisions at 189 GeV centre-of-mass energy at LEP. No evidence for such particles is found in a data sample of 176 pb^{-1}. Improved upper limits are set on the production cross sections for these new particles. New exclusion contours in the parameter space of the Minimal Supersymmetric Standard Model are derived, as well as new lower limits on the masses of these supersymmetric particles. Under the assumptions of common gaugino and scalar masses at the GUT scale, we set an absolute lower limit on the mass of the lightest scalar electron of 65.5 Ge
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