Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure

We aim to identify and quantify the effects of the satellite distribution around a sample of galaxies in the Catalogue of Isolated Galaxies (CIG), as well as the effects of the Large Scale Structure (LSS) using the SDSS-DR9. To recover the physically bound galaxies we focus on the satellites which are within the escape speed of each CIG galaxy. We also propose a more conservative method using the stacked Gaussian distribution of the velocity difference of the neighbours. The tidal strengths affecting the primary galaxy are estimated to quantify the effects of the local and LSS environments. We also define the projected number density parameter at the 5$^{\rm th}$ nearest neighbour to characterise the LSS around the CIG galaxies. Out of the 386 CIG galaxies considered in this study, at least 340 (88\% of the sample) have no physically linked satellite. Out of the 386 CIG galaxies, 327 (85\% of the sample) have no physical companion within a projected distance of 0.3 Mpc. The CIG galaxies are distributed following the LSS of the local Universe, although presenting a large heterogeneity in their degree of connection with it. A clear segregation appears between early-type CIG galaxies with companions and isolated late-type CIG galaxies. Isolated galaxies are in general bluer, with likely younger stellar populations and rather high star formation with respect to older, redder CIG galaxies with companions. Reciprocally, the satellites are redder and with an older stellar populations around massive early-type CIG galaxies, while they have a younger stellar content around massive late-type CIG galaxies. This suggests that the CIG is composed of a heterogeneous population of galaxies, sampling from old to more recent, dynamical systems of galaxies.Comment: 19 pages, 10 figures, 1 table, accepted for publication in Astronomy & Astrophysic

A permeability-increasing drug synergizes with bacterial efux pump inhibitors and restores susceptibility to antibiotics in multi-drug resistant Pseudomonas aeruginosa strains

Resistance to antibiotics poses a major global threat according to the World Health Organization. Restoring the activity of existing drugs is an attractive alternative to address this challenge. One of the most efficient mechanisms of bacterial resistance involves the expression of efflux pump systems capable of expelling antibiotics from the cell. Although there are efflux pump inhibitors (EPIs) available, these molecules are toxic for humans. We hypothesized that permeability-increasing antimicrobial peptides (AMPs) could lower the amount of EPI necessary to sensitize bacteria to antibiotics that are efflux substrates. To test this hypothesis, we measured the ability of polymyxin B nonapeptide (PMBN), to synergize with antibiotics in the presence of EPIs. Assays were performed using planktonic and biofilm-forming cells of Pseudomonas aeruginosa strains overexpressing the MexAB-OprM efflux system. Synergy between PMBN and EPIs boosted azithromycin activity by a factor of 2,133 and sensitized P. aeruginosa to all tested antibiotics. This reduced several orders of magnitude the amount of inhibitor needed for antibiotic sensitization. The selected antibiotic-EPI-PMBN combination caused a 10 million-fold reduction in the viability of biofilm forming cells. We proved that AMPs can synergize with EPIs and that this phenomenon can be exploited to sensitize bacteria to antibiotics

The AMIGA sample of isolated galaxies XI. A First Look at Isolated Galaxy Colors

The basic properties of galaxies can be affected by both nature (internal processes) or nurture (interactions and effects of environment). Deconvolving the two effects is an important current effort in astrophysics. Observed properties of a sample of isolated galaxies should be largely the result of internal (natural) evolution. It follows that nurture-induced galaxy evolution can only be understood through comparative study of galaxies in different environments. We take a first look at SDSS (g-r) colors of galaxies in the AMIGA sample involving many of the most isolated galaxies in the local Universe. This leads us to simultaneously consider the pitfalls of using automated SDSS colors. We focus on median values for the principal morphological subtypes found in the AMIGA sample (E/S0 and Sb-Sc) and compare them with equivalent measures obtained for galaxies in denser environments. We find a weak tendency for AMIGA spiral galaxies to be redder than objects in close pairs. We find no clear difference when we compare with galaxies in other (e.g. group) environments. However, the (g-r) color of isolated galaxies shows a Gaussian distribution as might be expected assuming nurture-free evolution. We find a smaller median absolute deviation in colors for isolated galaxies compared to both wide and close pairs. The majority of the deviation on median colors for spiral subtypes is caused by a color-luminosity correlation. Surprisingly isolated and non-isolated early-type galaxies show similar (g-r). We see little evidence for a green valley in our sample with most spirals redder than (g-r)=0.7 having spurious colors. The redder colors of AMIGA spirals and lower color dispersions for AMIGA subtypes -compared with close pairs- is likely due to a more passive star formation in very isolated galaxies.Comment: Accepted for publication in A&A. 9 pages, 7 Figures, and 2 tables, one only available onlin

Unveiling the environment and faint features of the isolated galaxy CIG 96 with deep optical and HI observations

Asymmetries in HI in galaxies are often caused by the interaction with close companions, making isolated galaxies an ideal framework to study secular evolution. The AMIGA project has demonstrated that isolated galaxies show the lowest level of asymmetry in their HI integrated profiles, yet some present significant asymmetries. CIG 96 (NGC 864) is a representative case reaching a 16% level. Our aim is to investigate the HI asymmetries of this spiral galaxy and what processes have triggered the star-forming regions observed in the XUV pseudoring. We performed deep optical observations at CAHA 1.23m, 2.2m and VST telescopes. We reach surface brightness (SB) limits of mu_2.2m = 27.5 mag arcsec-2 (Cous R) and mu_VST = 28.7mag arcsec-2 (r) that show the XUV pseudoring of the galaxy in detail. Additionally, a wavelet filtering of the HI data cube from our deep observations with E/VLA telescope allowed us to reach a column density of N_HI = 8.9x10^18 cm -2 (5sigma) (28"x28" beam), lower than in any isolated galaxy. We confirm that the HI extends farther than 4xr_25 in all directions. Furthermore, we detect for the first time two gaseous structures (10^6 Msol) in the outskirts. The g-r colour index image from 1.23m shows extremely blue colours in certain regions of the pseudoring where N_HI>8.5x10^20 cm-2 , whereas the rest show red colours. Galactic cirrus contaminate the field, setting an unavoidable detection limit at 28.5mag arcsec-2 (r). We detect no stellar link within 1degx1deg or gaseous link within 40'x40' between CIG 96 and any companion. The isolation criteria rule out interactions with other similar-sized galaxies for at least 2.7Gyr. Using existing stellar evolution models, the age of the pseudoring is estimated at 1Gyr or older. Undetected previously accreted companions and cold gas accretion remain as the main hypothesis to explain the optical pseudoring and HI features of CIG 96.Comment: 23 pages, 18 figures, 4 table

Factors affecting the establishment of the invasive crayfish Procambarus clarkii (Crustacea, Decapoda) in the Mediterranean rivers of the northeastern Iberian Peninsula

It is essential to find the combination of factors associated with ecosystem invasibility, as this forms part of basic knowledge on biological invasions and provides important information to guide management and conservation decisions. We surveyed 325 sampling sites in Catalonia to investigate relationships between crayfish presence and a series of biotic and abiotic factors, including fish abundance and species richness, geographical features, and water mineralization and eutrophication. Abiotic data provided by 29 environmental variables were studied by principal-components analysis. We then used a combination of three statistical approaches (comparison of average scores, general linear mixed models, and hierarchical partitioning analysis) to determine the potential relationship between crayfish occurrence and predictors. Our findings seem to indicate that the presence of crayfish was associated with geographical features, water mineralization and eutrophication, and the introduction of non-indigenous fish species to Catalonia. Our results also suggest that re-establishment of the natural hydrology of Mediterranean streams could hinder the spread of Procambarus clarkii. This, combined with preservation of headwater streams and attempts at local extirpation of P. clarkii, would favour native species and, potentially, enable the successful reintroduction of the native white-clawed crayfish (Austropotamobius pallipes species complex)

Potenciación de antibióticos, inhibidores de betalactamasas y bombas de expulsión mediante péptidos antimicrobianos en bacterias gramnegativas multiresistentes

Resistance to antibiotics poses a “major global threat” to public health according to World Health Organization. The increasing emergence of bacterial clones insensitive to these drugs greatly limits the therapeutic options for infectious diseases and highlights the urgent need to develop novel treatments effective against these organisms. In the present work, we demonstrated that subinhibitory concentrations of certain antimicrobial peptides can neutralize several antibiotic resistance mechanisms expressed by Gramnegative multi-drug resistant pathogens such as Klebsiella pneumoniae and Pseudomonas aeruginosa (“ESKAPE” pathogens) and Escherichia coli. This enhancement of antibiotic activity resulted in the sensitization of these organisms to several antibiotic classes. We hypothesized that antimicrobial peptides could potentiate the activity of inhibitors of either β-lactamases or antibiotic efflux pump systems and sensitize bacteria to antibiotics substrate of those resistance mechanisms. To test this hypothesis we measured the ability of peptides to synergize with those antibiotics in the presence of selected inhibitors of those systems. As peptides, we used the nonapeptides of polymyxin B and polymyxin E (PMBN and PMEN), as well as a peptide library derived from human lactoferricin with improved bacterial permeabilizing activity and very low toxicity towards human cells. To characterize the antimicrobial efficiency of the combinations, we used an array of techniques including conventional MIC/MBC testing, checkerboard analysis, growth kinetics, killing curves, and anti-biofilm activity against biofilms measured by confocal microscopy and viable counts on biofilms grown under static (on microplates) and dynamic (in a CDC-reactor) flow regimes. Using planktonic cultures, we demonstrated that, PMBN was able to greatly enhance the activity of several (i) β-lactamase inhibitors in a β-lactamase AmpC overproducing P. aeruginosa strain (potentiating the activity of amoxicillin, ampicillin, ticarcillin, piperacillin and ceftazidime), (ii) β-lactamase inhibitors in ESBL-producing Enterobacteriaceae strains (sensitizing them to ampicillin, amoxicillin, ticarcillin and piperacillin) and (iii) efflux pump inhibitors in a MexAB-OprM pump P. aeruginosa overproducing strain (enhancing the activity of aztreonam, ceftazidime, doxycycline, levofloxacin, piperacillin and azithromycin). In addition, all the triple combinations selected were able to cause a 10- 100 million fold reduction in the viability of biofilm forming cells. Finally, we showed that these antimicrobial peptides can potentiate not only resistance mechanism inhibitors (β-lactamases and efflux pumps), but they can also enhance the activity of several antibiotics that specifically target Gram-positive bacteria (i.e. vancomycin), sensitizing P. aeruginosa, E. coli and K. pneumoniae to them. This strategy allows the use of these combinations as empirical therapy with a broad spectrum of activity

Potenciación de antibióticos, inhibidores de betalactamasas y bombas de expulsión mediante péptidos antimicrobianos en bacterias gramnegativas multiresistentes

Resistance to antibiotics poses a “major global threat” to public health according to World Health Organization. The increasing emergence of bacterial clones insensitive to these drugs greatly limits the therapeutic options for infectious diseases and highlights the urgent need to develop novel treatments effective against these organisms. In the present work, we demonstrated that subinhibitory concentrations of certain antimicrobial peptides can neutralize several antibiotic resistance mechanisms expressed by Gramnegative multi-drug resistant pathogens such as Klebsiella pneumoniae and Pseudomonas aeruginosa (“ESKAPE” pathogens) and Escherichia coli. This enhancement of antibiotic activity resulted in the sensitization of these organisms to several antibiotic classes. We hypothesized that antimicrobial peptides could potentiate the activity of inhibitors of either β-lactamases or antibiotic efflux pump systems and sensitize bacteria to antibiotics substrate of those resistance mechanisms. To test this hypothesis we measured the ability of peptides to synergize with those antibiotics in the presence of selected inhibitors of those systems. As peptides, we used the nonapeptides of polymyxin B and polymyxin E (PMBN and PMEN), as well as a peptide library derived from human lactoferricin with improved bacterial permeabilizing activity and very low toxicity towards human cells. To characterize the antimicrobial efficiency of the combinations, we used an array of techniques including conventional MIC/MBC testing, checkerboard analysis, growth kinetics, killing curves, and anti-biofilm activity against biofilms measured by confocal microscopy and viable counts on biofilms grown under static (on microplates) and dynamic (in a CDC-reactor) flow regimes. Using planktonic cultures, we demonstrated that, PMBN was able to greatly enhance the activity of several (i) β-lactamase inhibitors in a β-lactamase AmpC overproducing P. aeruginosa strain (potentiating the activity of amoxicillin, ampicillin, ticarcillin, piperacillin and ceftazidime), (ii) β-lactamase inhibitors in ESBL-producing Enterobacteriaceae strains (sensitizing them to ampicillin, amoxicillin, ticarcillin and piperacillin) and (iii) efflux pump inhibitors in a MexAB-OprM pump P. aeruginosa overproducing strain (enhancing the activity of aztreonam, ceftazidime, doxycycline, levofloxacin, piperacillin and azithromycin). In addition, all the triple combinations selected were able to cause a 10- 100 million fold reduction in the viability of biofilm forming cells. Finally, we showed that these antimicrobial peptides can potentiate not only resistance mechanism inhibitors (β-lactamases and efflux pumps), but they can also enhance the activity of several antibiotics that specifically target Gram-positive bacteria (i.e. vancomycin), sensitizing P. aeruginosa, E. coli and K. pneumoniae to them. This strategy allows the use of these combinations as empirical therapy with a broad spectrum of activity