Increased human pathogenic potential of Escherichia coli from polymicrobial urinary tract infections in comparison to isolates from monomicrobial culture samples

The current diagnostic standard procedure outlined by the Health Protection Agency for urinary tract infections (UTIs) in clinical laboratories does not report bacteria isolated from samples containing three or more different bacterial species. As a result many UTIs go unreported and untreated, particularly in elderly patients, where polymicrobial UTI samples are especially prevalent. This study reports the presence of the major uropathogenic species in mixed culture urine samples from elderly patients, and of resistance to front-line antibiotics, with potentially increased levels of resistance to ciprofloxacin and trimethoprim. Most importantly, the study highlights that Escherichia coli present in polymicrobial UTI samples are statistically more invasive (P<0.001) in in vitro epithelial cell infection assays than those isolated from monomicrobial culture samples. In summary, the results of this study suggest that the current diagnostic standard procedure for polymicrobial UTI samples needs to be reassessed, and that E. coli present in polymicrobial UTI samples may pose an increased risk to human health

Separation of long DNA chains using non-uniform electric field: a numerical study

We study migration of DNA molecules through a microchannel with a series of electric traps controlled by an ac electric field. We describe the motion of DNA based on Brownian dynamics simulations of a beads-spring chain. Our simulation demonstrates that the chain captured by an electrode escapes from the binding electric field due to thermal fluctuation. We find that the mobility of chain would depend on the chain length; the mobility sharply increases when the length of a chain exceeds a critical value, which is strongly affected by the amplitude of the applied ac field. Thus we can adjust the length regime, in which this microchannel well separates DNA molecules, without changing the structure of the channel. We also present a theoretical insight into the relation between the critical chain length and the field amplitude.Comment: 12 pages, 9 figure

Measurement of correlations between low-frequency vibrational modes and particle rearrangements in quasi-two-dimensional colloidal glasses

We investigate correlations between low-frequency vibrational modes and rearrangements in two-dimensional colloidal glasses composed of thermosensitive microgel particles which readily permit variation of sample packing fraction. At each packing fraction, the particle displacement covariance matrix is measured and used to extract the vibrational spectrum of the "shadow" colloidal glass (i.e., the particle network with the same geometry and interactions as the sample colloid but absent damping). Rearrangements are induced by successive, small reductions in packing fraction. The experimental results suggest that low-frequency quasi-localized phonon modes in colloidal glasses, i.e., modes that present low energy barriers for system rearrangements, are spatially correlated with rearrangements in this thermal system

A five year record of high-frequency in situ measurements of non-methane hydrocarbons at Mace Head, Ireland

Continuous high-frequency in situ measurements of a range of non-methane hydrocarbons have been made at Mace Head since January 2005. Mace Head is a background Northern Hemispheric site situated on the eastern edge of the Atlantic. Five year measurements (2005–2009) of six C&lt;sub&gt;2&lt;/sub&gt;–C&lt;sub&gt;5&lt;/sub&gt; non-methane hydrocarbons have been separated into baseline Northern Hemispheric and European polluted air masses, among other sectors. Seasonal cycles in baseline Northern Hemispheric air masses and European polluted air masses arriving at Mace Head have been studied. Baseline air masses show a broad summer minima between June and September for shorter lived species, longer lived species show summer minima in July/August. All species displayed a winter maxima in February. European air masses showed baseline elevated mole fractions for all non-methane hydrocarbons. Largest elevations (of up to 360 ppt for ethane maxima) from baseline data were observed in winter maxima, with smaller elevations observed during the summer. Analysis of temporal trends using the Mann-Kendall test showed small (&lt;6 % yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) but statistically significant decreases in the butanes and &lt;i&gt;i&lt;/i&gt;-pentane between 2005 and 2009 in European air. No significant trends were found for any species in baseline air

A Neutral Polyampholyte in an ionic solution

The behavior of a neutral polyampholyte ($PA$) chain with $N$ monomers, in an ionic solution, is analyzed in the framework of the full Debye-H$\ddot u$ckel-Bjerrum-Flory $(DHBjF)$ theory. A $PA$ chain, that in addition to the neutral monomers, also contains an equal number of positively and negatively charged monomers, is dissolved in an ionic solution. For \underline{high} concentrations of salt and at high temperatures, the $PA$ exists in an extended state. As the temperature is decreased, the electrostatic energy becomes more relevant and at a $T=T_{\theta}$ the system collapses into a dilute globular state, or microelectrolyte. This state contains a concentration of salt higher than the surrounding medium. As the temperature is decreased even further, association between the monomers of the polymer and the ions of the salt becomes relevant and there is a crossover from this globular state to a low temperature extended state. For \underline{low} densities of salt, the system is collapsed for almost all temperatures and exhibits a first-order phase transition to an extended state at an unphysical low temperature.Comment: 10 pages, Revtex with epsf, 9 Postscript figures. Submitted to PR

Nonlinear Elasticity of Single Collapsed Polyelectrolytes

Nonlinear elastic responses of short and stiff polyelectrolytes are investigated by dynamic simulations on a single molecule level. When a polyelectrolyte condensate undergoes a mechanical unfolding, two types of force-extension curves, i.e., a force plateau and a stick-release pattern, are observed depending on the strength of the electrostatic interaction. We provide a physical interpretation of such force-extension behavior in terms of intramolecular structures of the condensates. We also describe a charge distribution of condensed counterions onto a highly stretched polyelectrolyte, which clarifies a formation of one-dimensional strongly correlated liquid at large Coulomb coupling regime where a stick-release pattern is observed. These findings may provide significant insights into the relationship between a molecular elasticity and a molecular mechanism of like-charge attractions observed in a wide range of charged biopolymer systems.Comment: 5pages, 5figure

Polyelectrolyte Persistence Length: Attractive Effect of Counterion Correlations and Fluctuations

The persistence length of a single, strongly charged, stiff polyelectrolyte chain is investigated theoretically. Path integral formulation is used to obtain the effective electrostatic interaction between the monomers. We find significant deviations from the classical Odijk, Skolnick and Fixman (OSF) result. An induced attraction between monomers is due to thermal fluctuations and correlations between bound counterions. The electrostatic persistence length is found to be smaller than the OSF value and indicates a possible mechanical instability (collapse) for highly charged polyelectrolytes with multivalent counterions. In addition, we calculate the amount of condensed counterions on a slightly bent polyelectrolyte. More counterions are found to be adsorbed as compared to the Manning condensation on a cylinder.Comment: 5 pages, 1 ps figur

Roles of Candida albicans Mig1 and Mig2 in glucose repression, pathogenicity traits, and SNF1 essentiality.

Metabolic adaptation is linked to the ability of the opportunistic pathogen Candida albicans to colonize and cause infection in diverse host tissues. One way that C. albicans controls its metabolism is through the glucose repression pathway, where expression of alternative carbon source utilization genes is repressed in the presence of its preferred carbon source, glucose. Here we carry out genetic and gene expression studies that identify transcription factors Mig1 and Mig2 as mediators of glucose repression in C. albicans. The well-studied Mig1/2 orthologs ScMig1/2 mediate glucose repression in the yeast Saccharomyces cerevisiae; our data argue that C. albicans Mig1/2 function similarly as repressors of alternative carbon source utilization genes. However, Mig1/2 functions have several distinctive features in C. albicans. First, Mig1 and Mig2 have more co-equal roles in gene regulation than their S. cerevisiae orthologs. Second, Mig1 is regulated at the level of protein accumulation, more akin to ScMig2 than ScMig1. Third, Mig1 and Mig2 are together required for a unique aspect of C. albicans biology, the expression of several pathogenicity traits. Such Mig1/2-dependent traits include the abilities to form hyphae and biofilm, tolerance of cell wall inhibitors, and ability to damage macrophage-like cells and human endothelial cells. Finally, Mig1 is required for a puzzling feature of C. albicans biology that is not shared with S. cerevisiae: the essentiality of the Snf1 protein kinase, a central eukaryotic carbon metabolism regulator. Our results integrate Mig1 and Mig2 into the C. albicans glucose repression pathway and illuminate connections among carbon control, pathogenicity, and Snf1 essentiality

The Search for Intergalactic Hydrogen Clouds in Voids

I present the results of a search for intergalactic hydrogen clouds in voids. Clouds are detected by their HI LyA absorption lines in the HST spectra of low-redshift AGN. The parameter with which the environments of clouds are characterized is the tidal field, which places a lower limit on the cloud mass-density which is dynamically stable against disruption. Galaxy redshift catalogs are used to sum the tidal fields along the lines of sight, sorting clouds according to tidal field upper, or lower limits. The analytical methodology employed is designed to detect gas clouds whose expansion following reionization is restrained by dark matter perturbations. End-products are the cloud equivalent width distribution functions (EWDF) of catalogs formed by sorting clouds according to various tidal field upper, or lower limits. Cumulative EWDFs are steep in voids (S ~ -1.5 \pm 0.2), but flatter in high tidal field zones (S ~ -0.5 \pm 0.1). Most probable cloud Doppler parameters are ~30 km/s in voids and ~60 km/s in proximity to galaxies. In voids, the cumulative line density at low EW (~ 15 mA) is ~ 500 per unit redshift. The void filling factor is found to be 0.87 <= f_v <= 0.94. The void EWDF is remarkably uniform over this volume, with a possible tendency for more massive clouds to be in void centers. The size and nature of the void cloud population suggested by this study is completely unanticipated by the results of published 3-D simulations, which predict that most clouds are in filamentary structures around galaxy concentrations, and that very few observable absorbers would lie in voids. Strategies for modeling this population are briefly discussed.Comment: 21 pages, 19 figures, apjemulate style, to appear in ApJ vol. 57