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Search Results: 1 - 10 of 8703 matches for " Marie-Therese Khairallah "
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Frequency of conjugative transfer of plasmid-encoded ISEcp1 - blaCTX-M-15 and aac(6')-lb-cr genes in Enterobacteriaceae at a tertiary care center in Lebanon - role of transferases
Mohamad Harajly, Marie-Therese Khairallah, John E Corkill, George F Araj, Ghassan M Matar
Annals of Clinical Microbiology and Antimicrobials , 2010, DOI: 10.1186/1476-0711-9-19
Abstract: Conjugation experiments were done on 53 ESBL-producing and/or fluoroquinolone resistant E. coli and K. pneumoniae and ESBL-producing S. sonnei isolates. Antimicrobial susceptibility testing on parent and transconjugant isolates, and PCR amplifications on plasmid extracts of the resistance-encoding genes: blaCTX-M-15 with the ISEcp1 insertion sequence, the aac(6')-lb-cr and qnrS genes, as well as tra encoding transferases genes were done. Random amplified polymorphic DNA (RAPD) analysis was performed to demonstrate whether conjugative isolates are clonal and whether they are linked epidemiologically to a particular source.Antimicrobial susceptibility testing on transconjugants revealed that 26 out of 53 (49%) ESBL-producing Enterobacteriaceae were able to transfer antimicrobial resistance to the recipients. Transfer of high-level resistance to the transconjugants encoded by the blaCTX-M-15 gene downstream the ISEcp1 insertion sequence against 3rd generation cephalosporins, and of low-level resistance against ciprofloxacin, and variable levels of resistance against aminoglycosides encoded by aac(6')-lb-cr gene, were observed in transconjugants. tra encoding transferase genes were detected exclusively in conjugative isolates.In conclusion, the frequency of transfer of antimicrobial resistance in non clonal Enterobacteriaceae at the tertiary care center by conjugation was 49%. Conjugation occurred in isolates expressing the tra encoding transferase genes. Multiple conjugative strains harboring the plasmid encoded antimicrobial resistant genes were circulating in the medical center. Molecular epidemiology analysis showed that conjugative isolates are neither clonal nor linked to a particular site and transfer of antimicrobial resistance is by horizontal transfer of plasmids.Plasmid-encoded Extended-spectrum β-lactamases (ESBL) are increasingly spreading among Enterobacteriaceae clinical isolates throughout the world due mostly to their presence on highly conjugative plas
Correlation between Group B Streptococcal Genotypes, Their Antimicrobial Resistance Profiles, and Virulence Genes among Pregnant Women in Lebanon
Antoine Hannoun,Marwa Shehab,Marie-Therese Khairallah,Ahmad Sabra,Roland Abi-Rached,Tony Bazi,Khalid A. Yunis,George F. Araj,Ghassan M. Matar
International Journal of Microbiology , 2009, DOI: 10.1155/2009/796512
Abstract: The antimicrobial susceptibility profiles of 76 Streptococcus agalactiae (Group B Streptococci [GBS]) isolates from vaginal specimens of pregnant women near term were correlated to their genotypes generated by Random Amplified Polymorphic DNA analysis and their virulence factors encoding genes cylE, lmb, scpB, rib, and bca by PCR. Based on the distribution of the susceptibility patterns, six profiles were generated. RAPD analysis detected 7 clusters of genotypes. The cylE gene was present in 99% of the isolates, the lmb in 96%, scpB in 94.7%, rib in 33%, and bca in 56.5% of isolates. The isolates demonstrated a significant correlation between antimicrobial resistance and genotype clusters denoting the distribution of particular clones with different antimicrobial resistance profiles, entailing the practice of caution in therapeutic options. All virulence factors encoding genes were detected in all seven genotypic clusters with rib and bca not coexisting in the same genome.
Opinion dynamics: inhomogeneous Boltzmann-type equations modelling opinion leadership and political segregation
Bertram Düring,Marie-Therese Wolfram
Physics , 2015,
Abstract: We propose and investigate different kinetic models for opinion formation, when the opinion formation process depends on an additional independent variable, e.g. a leadership or a spatial variable. More specifically, we consider:(i) opinion dynamics under the effect of opinion leadership, where each individual is characterised not only by its opinion, but also by another independent variable which quantifies leadership qualities; (ii) opinion dynamics modelling political segregation in the `The Big Sort', a phenomenon that US citizens increasingly prefer to live in neighbourhoods with politically like-minded individuals. Based on microscopic opinion consensus dynamics such models lead to inhomogeneous Boltzmann-type equations for the opinion distribution. We derive macroscopic Fokker-Planck-type equations in a quasi-invariant opinion limit and present results of numerical experiments.
Genotypes and serotype distribution of macrolide resistant invasive and non- invasive Streptococcus pneumoniae isolates from Lebanon
Nedal Taha, George F Araj, Rima H Wakim, Souha S Kanj, Zeina A Kanafani, Ahmad Sabra, Marie-Therese Khairallah, Farah J Nassar, Marwa Shehab, Maysa Baroud, Ghassan Dbaibo, Ghassan M Matar
Annals of Clinical Microbiology and Antimicrobials , 2012, DOI: 10.1186/1476-0711-11-2
Abstract: Forty four macrolide resistant and 21 macrolide susceptible S. pneumoniae clinical isolates were tested for antimicrobial susceptibility according to CLSI guidelines (2008) and underwent molecular characterization. Serotyping of these isolates was performed by Multiplex PCR-based serotype deduction using CDC protocols. PCR amplification of macrolide resistant erm (encoding methylase) and mef (encoding macrolide efflux pump protein) genes was carried out.Among 44 isolates resistant to erythromycin, 35 were resistant to penicillin and 18 to ceftriaxone. Examination of 44 macrolide resistant isolates by PCR showed that 16 isolates harbored the erm(B) gene, 8 isolates harbored the mef gene, and 14 isolates harbored both the erm(B) and mef genes. There was no amplification by PCR of the erm(B) or mef genes in 6 isolates. Seven different capsular serotypes 2, 9V/9A,12F, 14,19A, 19F, and 23, were detected by multiplex PCR serotype deduction in 35 of 44 macrolide resistant isolates, with 19F being the most prevalent serotype. With the exception of serotype 2, all serotypes were invasive. Isolates belonging to the invasive serotypes 14 and 19F harbored both erm(B) and mef genes. Nine of the 44 macrolide resistant isolates were non-serotypable by our protocols.Macrolide resistance in S. pneumoniae in Lebanon is mainly through target site modification but is also mediated through efflux pumps, with serotype 19F having dual resistance and being the most prevalent and invasive.Streptococcus pneumoniae continues to be a major cause of morbidity and mortality in humans. It is one of the most significant bacterial pathogens causing community acquired infections, most notably pneumonia, otitis media, bacteremia, and meningitis [1,2]. Treatment of pneumococcal infections is becoming difficult due to the high prevalence of penicillin-resistant strains and to the rapid development of resistance to other antimicrobials including macrolides. These drugs are extensively used for the treat
A local version of the Hughes model for pedestrian flow
José A. Carrillo,Stephan Martin,Marie-Therese Wolfram
Physics , 2015,
Abstract: Roger Hughes proposed a macroscopic model for pedestrian dynamics, in which individuals seek to minimize their travel time but try to avoid regions of high density. One of the basic assumptions is that the overall density of the crowd is known to every agent. In this paper we present a modification of the Hughes model to include local effects, namely limited vision, and a conviction towards decision making. The modified velocity field enables smooth turning and temporary waiting behavior. We discuss the modeling in the micro- and macroscopic setting as well as the efficient numerical simulation of either description. Finally we illustrate the model with various numerical experiments and evaluate the behavior with respect to the evacuation time and the overall performance.
Symbolic Derivation of Mean-Field PDEs from Lattice-Based Models
Christoph Koutschan,Helene Ranetbauer,Georg Regensburger,Marie-Therese Wolfram
Physics , 2015,
Abstract: Transportation processes, which play a prominent role in the life and social sciences, are typically described by discrete models on lattices. For studying their dynamics a continuous formulation of the problem via partial differential equations (PDE) is employed. In this paper we propose a symbolic computation approach to derive mean-field PDEs from a lattice-based model. We start with the microscopic equations, which state the probability to find a particle at a given lattice site. Then the PDEs are formally derived by Taylor expansions of the probability densities and by passing to an appropriate limit as the time steps and the distances between lattice sites tend to zero. We present an implementation in a computer algebra system that performs this transition for a general class of models. In order to rewrite the mean-field PDEs in a conservative formulation, we adapt and implement symbolic integration methods that can handle unspecified functions in several variables. To illustrate our approach, we consider an application in crowd motion analysis where the dynamics of bidirectional flows are studied. However, the presented approach can be applied to various transportation processes of multiple species with variable size in any dimension, for example, to confirm several proposed mean-field models for cell motility.
Individual based and mean-field modelling of direct aggregation
Martin Burger,Jan Haskovec,Marie-Therese Wolfram
Physics , 2011,
Abstract: We introduce two models of biological aggregation, based on randomly moving particles with individual stochasticity depending on the perceived average population density in their neighbourhood. In the first-order model the location of each individual is subject to a density-dependent random walk, while in the second-order model the density-dependent random walk acts on the velocity variable, together with a density-dependent damping term. The main novelty of our models is that we do not assume any explicit aggregative force acting on the individuals; instead, aggregation is obtained exclusively by reducing the individual stochasticity in response to higher perceived density. We formally derive the corresponding mean-field limits, leading to nonlocal degenerate diffusions. Then, we carry out the mathematical analysis of the first-order model, in particular, we prove the existence of weak solutions and show that it allows for measure-valued steady states. We also perform linear stability analysis and identify conditions for pattern formation. Moreover, we discuss the role of the nonlocality for well-posedness of the first-order model. Finally, we present results of numerical simulations for both the first- and second-order model on the individual-based and continuum levels of description.
On a Boltzmann type price formation model
Martin Burger,Luis Caffarelli,Peter Markowich,Marie-Therese Wolfram
Mathematics , 2013, DOI: 10.1098/rspa.2013.0126
Abstract: In this paper we present a Boltzmann type price formation model, which is motivated by a parabolic free boundary model for the evolution of the prize presented by Lasry and Lions in 2007. We discuss the mathematical analysis of the Boltzmann type model and show that its solutions converge to solutions of the model by Lasry and Lions as the transaction rate tends to infinity. Furthermore we analyse the behaviour of the initial layer on the fast time scale and illustrate the price dynamics with various numerical experiments.
Socio-economic applications of finite state mean field games
Diogo A. Gomes,Roberto M. Velho,Marie-Therese Wolfram
Mathematics , 2014, DOI: 10.1098/rsta.2013.0405
Abstract: In this paper we present different applications of finite state mean field games to socio-economic sciences. Examples include paradigm shifts in the scientific community or the consumer choice behaviour in the free market. The corresponding finite state mean field game models are hyperbolic systems of partial differential equations, for which we present and validate different numerical methods. We illustrate the behaviour of solutions with various numerical experiments, which show interesting phenomena like shock formation. Hence we conclude with an investigation of the shock structure in the case of two-state problems.
Dual two-state mean-field games
Diogo A. Gomes,Roberto M. Velho,Marie-Therese Wolfram
Mathematics , 2014,
Abstract: In this paper, we consider two-state mean-field games and its dual formulation. We then discuss numerical methods for these problems. Finally, we present various numerical experiments, exhibiting different behaviours, including shock formation, lack of invertibility, and monotonicity loss.
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