Molecular bases determining daptomycin resistance-mediated re-sensitization to β-lactams ("see-saw effect") in MRSA

Antimicrobial resistance is recognized as one of the principal threats to public health worldwide, yet the problem is increasing. Methicillin-resistant Staphylococcus aureus (MRSA) are among the most difficult to treat in clinical settings due to the resistance to nearly all available antibiotics. The cyclic anionic lipopeptide antibiotic Daptomycin (DAP) is the clinical mainstay of anti-MRSA therapy. Decreased susceptibility to DAP (DAPR) reported in MRSA is frequently accompanied with a paradoxical decrease in β-lactam resistance, a process known as the "see-saw" effect. Despite the observed discordance in resistance phenotypes, the combination of DAP/β-lactams has been proven clinically effective for the prevention and treatment of infections due to DAPR-MRSA strains. However, the mechanisms underlying the interactions between DAP and β-lactams are largely unknown. Herein, we studied the role of DAP-induced mutated mprF in β-lactam sensitization and its involvement in the effective killing by the DAP/OXA combination. DAP/OXA-mediated effects resulted in cell-wall perturbations including changes in peptidoglycan (PG) insertion, penicillin-binding protein 2 (PBP2) delocalization and reduced membrane amounts of penicillin-binding protein 2a (PBP2a) contents despite increased transcription of mecA through mec regulatory elements. We have found that the VraSR sensor-regulator is a key component of DAP resistance, triggering mutated mprF-mediated cell membrane (CM) modifications and resulting in impairment of PrsA location and chaperone functions, both essentials for PBP2a maturation, the key determinant of β-lactam resistance. These observations provide first time evidence that synergistic effects between DAP and β-lactams involve PrsA post-transcriptional regulation of CM-associated PBP2a

Efeitos de giberelinas no desenvolvimento do algodoeiro (Gossypium hirsutum L. cv.'IAC-RM3')

Seedlings of cotton were treated 19 days after the sowing with gibberellins at concentrations of 2, 20 and 200 ppm and the check to verify The effect of the compound on the growth of the plant. The experiment was done under greenhouse conditions in 1974. The main proposal of this work is to study the variation of plant height, net assimilation rate, relative growth rate and the leaf area ratio with application of gibberellins. The growth regulator at concentrations of 2, 20 and 200 ppm increased plant height, respectively in 27, 48 and 65% when compared to the control. Application of gibberellins at concentrations of 2 and 20 ppm promotes increase in the net assimilation rate and in the leaf area ratio of cotton. The relative growth rate was superior in the plots that received gibberelins at concentrations of 2, 20 and 200 ppm. It was verified that gibberellins at 200 ppm has a tendency to promote reduction in the net assimilation rate and slight variation in the leaf area ratio in relation to check.Verificou-se o efeito de giberelinas, quando aplicada sob a forma de pulverização das plântulas, no desenvolvimento do algodoeiro cultivar 'IAC-RM3' em condições de casa-de-vegetação. Estudaram-se as concentrações de 0, 2, 20 e 200 ppm do regulador de crescimento; sendo que os tratamentos aumentaram a altura das plantas em 27, 48 e 65%, com relação ao controle. Aplicações de giberelinas nas dosagens de 2 e 20 ppm promoveram aumento na TAL e na RAF do algodoeiro. A TCR foi superior nas plantas tratadas com giberelinas. Verificou-se ainda que giberelinas a 200 ppm promove redução na TAL e variação mínima na RAF, com relação ao controle

Role of Network Topology in the Synchronization of Power Systems

We study synchronization dynamics in networks of coupled oscillators with bimodal distribution of natural frequencies. This setup can be interpreted as a simple model of frequency synchronization dynamics among generators and loads working in a power network. We derive the minimum coupling strength required to ensure global frequency synchronization. This threshold value can be efficiently found by solving a binary optimization problem, even for large networks. In order to validate our procedure, we compare its results with numerical simulations on a realistic network describing the European interconnected high-voltage electricity system, finding a very good agreement. Our synchronization threshold can be used to test the stability of frequency synchronization to link removals. As the threshold value changes only in very few cases when aplied to the European realistic network, we conclude that network is resilient in this regard. Since the threshold calculation depends on the local connectivity, it can also be used to identify critical network partitions acting as synchronization bottlenecks. In our stability experiments we observe that when a link removal triggers a change in the critical partition, its limits tend to converge to national borders. This phenomenon, which can have important consequences to synchronization dynamics in case of cascading failure, signals the influence of the uncomplete topological integration of national power grids at the European scale.Comment: The final publication is available at http://www.epj.org (see http://www.springerlink.com/content/l22k574x25u6q61m/

Development of a tight-binding potential for bcc-Zr. Application to the study of vibrational properties

We present a tight-binding potential based on the moment expansion of the density of states, which includes up to the fifth moment. The potential is fitted to bcc and hcp Zr and it is applied to the computation of vibrational properties of bcc-Zr. In particular, we compute the isothermal elastic constants in the temperature range 1200K < T < 2000K by means of standard Monte Carlo simulation techniques. The agreement with experimental results is satisfactory, especially in the case of the stability of the lattice with respect to the shear associated with C'. However, the temperature decrease of the Cauchy pressure is not reproduced. The T=0K phonon frequencies of bcc-Zr are also computed. The potential predicts several instabilities of the bcc structure, and a crossing of the longitudinal and transverse modes in the (001) direction. This is in agreement with recent ab initio calculations in Sc, Ti, Hf, and La.Comment: 14 pages, 6 tables, 4 figures, revtex; the kinetic term of the isothermal elastic constants has been corrected (Eq. (4.1), Table VI and Figure 4

Migrant mortality from diabetes mellitus across Europe: the importance of socio-economic change

The first objective of this study was to determine and quantify variations in diabetes mortality by migrant status in different European countries. The second objective was to investigate the hypothesis that diabetes mortality is higher in migrant groups for whom the country of residence (COR) is more affluent than the country of birth (COB). We obtained mortality data from 7 European countries. To assess migrant diabetes mortality, we used direct standardization and Poisson regression. First, migrant mortality was estimated for each country separately. Then, we merged the data from all mortality registers. Subsequently, to examine the second hypothesis, we introduced gross domestic product (GDP) per capita of COB in the models, as an indicator of socio-economic circumstances. The overall pattern shows higher diabetes mortality in migrant populations compared to local-born populations. Mortality rate ratios (MRRs) were highest in migrants originating from either the Caribbean or South Asia. MRRs for the migrant population as a whole were 1.9 (95% CI 1.8–2.0) and 2.2 (95% CI 2.1–2.3) for men and women respectively. We furthermore found a consistently inverse association between GDP of COB and diabetes mortality. Most migrant groups have higher diabetes mortality rates than the local-born populations. Mortality rates are particularly high in migrants from North Africa, the Caribbean, South Asia or low-GDP countries. The inverse association between GDP of COB and diabetes mortality suggests that socio-economic change may be one of the key aetiological factors

The effect of pressure and guanidine hydrochloride on azurins mutated in the hydrophobic core

The unfolding of the blue-copper protein azurin from Pseudomonas aeruginosa by guanidine hydrochloride, under nonreducing conditions, has been studied by fluorescence techniques and circular dichroism. The denaturation transition may be fitted by a simple two-state model. The total free energy change from the native to the unfolded state was 9.4 ± 0.4 kcal·mol-1, while a lower value (6.4 ± 0.4 kcal·mol-1) was obtained for the metal depleted enzyme (apo-azurin) suggesting that the copper atom plays an important stabilization role. Azurin and apo-azurin were practically unaffected by hydrostatic pressure up to 3000 bar. Site-directed mutagenesis has been used to destabilize the hydrophobic core of azurin. In particular either hydrophobic residue Ile7 or Phe110 has been substituted with a serine. The free energy change of unfolding by guanidinium hydrochloride, resulted to be 5.8 ± 0.3 kcal·mol-1 and 4.8 ± 0.3 kcal·mol-1 for Ile7Ser and Phe110Ser, respectively, showing that both mutants are much less stable than the wild-type protein. The mutated apoproteins could be reversible denatured even by high pressure, as demonstrated by steady-state fluorescence measurements. The change in volume associated to the pressure-induced unfolding was estimated to be -24 mL·mol-1 for 11e7Ser and -55 mL·mol-1 for Phe110Ser. These results show that the tight packing of the hydrophobic residues that characterize the inner structure of azurin is fundamental for the protein stability. This suggests that the proper assembly of the hydrophobic core is one of the earliest and most crucial event in the folding process, bearing important implication for de novo design of proteins