Sensing Gram-negative bacteria: a phylogenetic perspective.

Gram-negative bacteria represent a major group of pathogens that infect all eukaryotes from plants to mammals. Gram-negative microbe-associated molecular patterns include lipopolysaccharides and peptidoglycans, major immunostimulatory determinants across phyla. Recent advances have furthered our understanding of Gram-negative detection beyond the well-defined pattern recognition receptors such as TLR4. A B-type lectin receptor for LPS and Lysine-motif containing receptors for peptidoglycans were recently added to the plant arsenal. Caspases join the ranks of mammalian cytosolic immune detectors by binding LPS, and make TLR4 redundant for septic shock. Fascinating bacterial evasion mechanisms lure the host into tolerance or promote inter-bacterial competition. Our review aims to cover recent advances on bacterial messages and host decoding systems across phyla, and highlight evolutionarily recurrent strategies.

Gram-negative flagella glycosylation

Protein glycosylation had been considered as an eccentricity of a few bacteria. However, through advances in analytical methods and genome sequencing, it is now established that bacteria possess both N-linked and O-linked glycosylation pathways. Both glycosylation pathways can modify multiple proteins, flagellins from Archaea and Eubacteria being one of these. Flagella O-glycosylation has been demonstrated in many polar flagellins from Gram-negative bacteria and in only the Gram-positive genera Clostridium and Listeria. Furthermore, O-glycosylation has also been demonstrated in a limited number of lateral flagellins. In this work, we revised the current advances in flagellar glycosylation from Gram-negative bacteria, focusing on the structural diversity of glycans, the O-linked pathway and the biological function of flagella glycosylation.

Separação de espectros simulados e de luminescência total através do método generalizado de anulação do posto (GRAM)

A multivariate curve resolution method, "GENERALIZED RANK ANNIHILATION METHOD (GRAM)", is discussed and tested with simulated and experimental data. The analysis of simulated data provides general guidelines concerning the condition for uniqueness of a solution for a given problem. The second-order emission-excitation spectra of human and animal dental calculus deposits were used as an experimental data to estimate the performance of the above method. Three porphyrinic spectral profiles, for both human and cat, were obtained by the use of GRAM.

Convergent Approaches for the Synthesis of the Anti-tumoral Peptide, Kahalalide F. Study of Orthogonal Protecting Groups

Kahalalide compounds are peptides that are isolated from a Hawaiian herbivorous marine species of mollusc, Elysia rufescens, and its diet, the green alga Bryopsis sp. Kahalalide F and its synthetic analogues are the most promising compounds of the Kahalalide family because they show anti-tumoral activity. Linear solid-phase syntheses of Kahalalide F have been reported. Here we describe several new improved synthetic routes based on convergent approaches with distinct orthogonal protection schemes for the preparation of Kahaladide analogues. These strategies allow a better control and characterization of the intermediates because more reactions are performed in solution. Five derivatives of Kahalalide F were synthesized using several convergent approaches.

Nonlinear principal and canonical directions from continuous extensions of multidimensional scaling

A continuous random variable is expanded as a sum of a sequence of uncorrelated random variables. These variables are principal dimensions in continuous scaling on a distance function, as an extension of classic scaling on a distance matrix. For a particular distance, these dimensions are principal components. Then some properties are studied and an inequality is obtained. Diagonal expansions are considered from the same continuous scaling point of view, by means of the chi-square distance. The geometric dimension of a bivariate distribution is defined and illustrated with copulas. It is shown that the dimension can have the power of continuum.

Orthogonal function method in modelling paper web quality variation

This work is devoted to the analysis of signal variation of the Cross-Direction and Machine-Direction measurements from paper web. The data that we possess comes from the real paper machine. Goal of the work is to reconstruct the basis weight structure of the paper and to predict its behaviour to the future. The resulting synthetic data is needed for simulation of paper web. The main idea that we used for describing the basis weight variation in the Cross-Direction is Empirical Orthogonal Functions (EOF) algorithm, which is closely related to Principal Component Analysis (PCA) method. Signal forecasting in time is based on Time-Series analysis. Two principal mathematical procedures that we used in the work are Autoregressive-Moving Average (ARMA) modelling and Ornstein–Uhlenbeck (OU) process.

Perfil de susceptibilidade a antimicrobianos em amostras de cocos Gram-positivos, catalase negativos, isoladas de mastite subclínica bubalina

Estudou-se o perfil de susceptibilidade a antimicrobianos em cocos Gram-positivos catalase negativos (21 amostras de Lactococcus garvieae e 6 de Enterococcus gallinarum), isoladas do leite de fêmeas com mastite subclínica e pertencentes a uma população composta por seis rebanhos bubalinos localizados no Estado do Rio de Janeiro. O teste utilizado foi o da difusão de discos em agar Müller Hinton, segundo recomendações do National Committee for Clinical Laboratory Standards - NCCLS, tendo sido testados discos com ampicilina (10mg), cefalotina (30mg), cefotaxima (30mg), cefoxitina (30mg), cloranfenicol (30mg), eritromicina (15mg), gentamicina (10mg), nitrofurantoína (300mg), norfloxacina (10mg), penicilina (10 UI), tetraciclina (30mg) e vancomicina (30mg). Os resultados evidenciaram que em se tratando de Lactococcus garvieae, o antimicrobiano mais eficiente foi o nitrofurantoína com 85,71% de sensibilidade, seguido da cefotaxima (61,90%), vancomicina (52,38%), norfloxacina (47,62%) e cefalotina (47,62%). A maior resistência foi desenvolvida frente a penicilina e ampicilina, com 95,24% de resistênciapara os dois antimicrobianos testados. O perfil de susceptibilidade desenvolvido pelas amostras de Enterococcus gallinarum, mostrou baixa sensibilidade frente aos antimicrobianos testados, onde os maiores índices foram observados frente eritromicina e gentamicina, com 33,34% de sensibilidade para ambos; quanto à resistência desenvolvida, foi possível observar 100% de resistência com relação a vancomicina e tetraciclina, seguindo-se cloranfenicol, penicilina, ampicilina, cefoxitina, cefalotina, cefotaxima, norfloxacina e nitrofurantoína, todas evidenciando uma resistência de 83,33% das amostras testadas.

Bastonetes Gram-negativos aeróbios e anaeróbios facultativos no fluido ruminal de bovinos de corte alimentados em pastagem lignificada e em novilhos com acidose ruminal

Resumo: Objetivou-se analisar a população de bastonetes Gram negativos aeróbios e anaeróbios facultativas no suco ruminal bovinos zebuínos de diferentes categorias, alimentados em pastagem tropical, e de novilhos alimentados com alto teor de grão e sem volumosos. Foram coletados fluido ruminal de 32 vacas, 50 novilhos e 50 bezerros alimentadas em pastagem de Brachiaria spp. e de 20 novilhos com acidose ruminal. Após diluições decimais, amostras foram inoculadas em placas contendo ágar MacConkey a 39°C. Para a identificação dos gêneros mais frequentes foram utilizadas provas bioquímicas. A concentração dessas bactérias não diferiu no ambiente ruminal de vacas, novilhos e bezerros de corte alimentados com pastagem tropical lignificada. Os gêneros mais frequentemente identificados para esses animais foram Escherichia, Enterobacter e Klebsiella. Novilhos alimentados sem volumoso e com acidose apresentaram maior taxa de detecção e maior população dessas bactérias no ambiente ruminal (>6 log/ml) quando comparados aos novilhos alimentados somente em pastagem. A espécie Escherichia coli foi predominante entre as bactérias isoladas do fluido ruminal de novilhos alimentados com dieta com alta concentração de grãos e com acidose (p<0,01). Constatou-se que em bovinos de corte, criados em pastagem tropical lignificada, a população desses microrganismos é baixa no ambiente ruminal e com maior diversidade de gêneros bacterianos. Entretanto em novilhos confinados e alimentos sem volumoso, apresentando acidose ruminal subaguda, ocorre desequilíbrio populacional com aumento da população de E. coli.

Excessive functions, Appell polynomials and optimal stopping

The main topic of the thesis is optimal stopping. This is treated in two research articles. In the first article we introduce a new approach to optimal stopping of general strong Markov processes. The approach is based on the representation of excessive functions as expected suprema. We present a variety of examples, in particular, the Novikov-Shiryaev problem for Lévy processes. In the second article on optimal stopping we focus on differentiability of excessive functions of diffusions and apply these results to study the validity of the principle of smooth fit. As an example we discuss optimal stopping of sticky Brownian motion. The third research article offers a survey like discussion on Appell polynomials. The crucial role of Appell polynomials in optimal stopping of Lévy processes was noticed by Novikov and Shiryaev. They described the optimal rule in a large class of problems via these polynomials. We exploit the probabilistic approach to Appell polynomials and show that many classical results are obtained with ease in this framework. In the fourth article we derive a new relationship between the generalized Bernoulli polynomials and the generalized Euler polynomials.

Factors associated with bacteremia due to multidrug-resistant Gram-negative bacilli in hematopoietic stem cell transplant recipients

The epidemiology of bacteremia developing during neutropenia has changed in the past decade, with the re-emergence of Gram-negative (GN) bacteria and the development of multidrug resistance (MDR) among GN bacteria. We conducted a case-control study in order to identify factors associated with bacteremia due to multidrug-resistant Gram-negative (MDRGN) isolates in hematopoietic stem cell transplant recipients. Ten patients with MDRGN bacteremia were compared with 44 patients with GN bacteremia without MDR. Bacteremia due to Burkholderia or Stenotrophomonas sp was excluded from analysis (3 cases), because the possibility of intrinsical resistance. Infection due to MDRGN bacteria occurred in 2.9% of 342 hematopoietic stem cell transplant recipients. Klebsiella pneumoniae was the most frequent MDRGN (4 isolates), followed by Pseudomonas aeruginosa (3 isolates). Among non-MDRGN, P. aeruginosa was the most frequent agent (34%), followed by Escherichia coli (30%). The development of GN bacteremia during the empirical treatment of febrile neutropenia (breakthrough bacteremia) was associated with MDR (P < 0.001, odds ratio = 32, 95% confidence interval = 5_190) by multivariate analysis. Bacteremia due to MDRGN bacteria was associated with a higher death rate by univariate analysis (40 vs 9%; P = 0.03). We were unable to identify risk factors on admission or at the time of the first fever, but the occurrence of breakthrough bacteremia was strongly associated with MDRGN bacteria. An immediate change in the antibiotic regimen in such circumstances may improve the prognosis of these patients.

X-ray diffraction of a gram-negative bacterial membrane mimetic

This thesis applies x-ray diffraction to measure he membrane structure of lipopolysaccharides and to develop a better model of a LPS bacterial melilbrane that can be used for biophysical research on antibiotics that attack cell membranes. \iVe ha'e Inodified the Physics department x-ray machine for use 3.'3 a thin film diffractometer, and have lesigned a new temperature and relative humidity controlled sample cell.\Ve tested the sample eel: by measuring the one-dimensional electron density profiles of bilayers of pope with 0%, 1%, 1G :VcJ, and 100% by weight lipo-polysaccharide from Pse'udo'lTwna aeTuginosa. Background VVe now know that traditional p,ntibiotics ,I,re losing their effectiveness against ever-evolving bacteria. This is because traditional antibiotic: work against specific targets within the bacterial cell, and with genetic mutations over time, themtibiotic no longer works. One possible solution are antimicrobial peptides. These are short proteins that are part of the immune systems of many animals, and some of them attack bacteria directly at the membrane of the cell, causing the bacterium to rupture and die. Since the membranes of most bacteria share common structural features, and these featuret, are unlikely to evolve very much, these peptides should effectively kill many types of bacteria wi Lhout much evolved resistance. But why do these peptides kill bacterial cel: '3 , but not the cells of the host animal? For gramnegative bacteria, the most likely reason is that t Ileir outer membrane is made of lipopolysaccharides (LPS), which is very different from an animal :;ell membrane. Up to now, what we knovv about how these peptides work was likely done with r !10spholipid models of animal cell membranes, and not with the more complex lipopolysa,echaricies, If we want to make better pepticies, ones that we can use to fight all types of infection, we need a more accurate molecular picture of how they \vork. This will hopefully be one step forward to the ( esign of better treatments for bacterial infections.

Prime Rational Functions and Integral Polynomials

Let f(x) be a complex rational function. In this work, we study conditions under which f(x) cannot be written as the composition of two rational functions which are not units under the operation of function composition. In this case, we say that f(x) is prime. We give sufficient conditions for complex rational functions to be prime in terms of their degrees and their critical values, and we derive some conditions for the case of complex polynomials. We consider also the divisibility of integral polynomials, and we present a generalization of a theorem of Nieto. We show that if f(x) and g(x) are integral polynomials such that the content of g divides the content of f and g(n) divides f(n) for an integer n whose absolute value is larger than a certain bound, then g(x) divides f(x) in Z[x]. In addition, given an integral polynomial f(x), we provide a method to determine if f is irreducible over Z, and if not, find one of its divisors in Z[x].

Surface display of proteins by Gram-negative bacterial autotransporters

Affiliation: Faculté de Médecine Vétérinaire, Université de Montréal