dCitrobacter rodentium is a murine intestinal pathogen used as a model for the foodborne human pathogens enterohemorrhagic Escherichia coli and enteropathogenic E. coli. During infection, these pathogens use two-component signal transduction systems to detect and adapt to changing environmental conditions. In E. coli, the CpxRA two-component signal transduction system responds to envelope stress by modulating the expression of a myriad of genes. Quantitative real-time PCR showed that cpxRA was expressed in the colon of C57BL/6J mice infected with C. rodentium. To determine whether CpxRA plays a role during C. rodentium infection, a cpxRA deletion strain was generated and found to have a colonization defect during infection. This defect was independent of an altered growth rate or a defective type III secretion system, and single-copy chromosomal complementation of cpxRA restored virulence. The C. rodentium strains were then tested in C3H/HeJ mice, a lethal intestinal infection model. Mice infected with the ⌬cpxRA strain survived infection, whereas mice infected with the wild-type or complemented strains succumbed to infection. Furthermore, we found that the cpxRA expression level was higher during early infection than at a later time point. Taken together, these data demonstrate that the CpxRA two-component signal transduction system is essential for the in vivo virulence of C. rodentium. In addition, these data suggest that fine-tuned cpxRA expression is important for infection. This is the first study that identifies a C. rodentium two-component transduction system required for pathogenesis. This study further indicates that CpxRA is an interesting target for therapeutics against enteric pathogens.

The PmrAB two-component system of enterobacteria regulates a number of genes whose protein products modify lipopolysaccharide (LPS). The LPS is modified during transport to the bacterial outer membrane (OM). A subset of PmrAB-mediated LPS modifications consists of the addition of phosphoethanolamine (pEtN) to lipid A by PmrC and to the core by CptA. In Salmonella enterica, pEtN modifications have been associated with resistance to polymyxin B and to excess iron. To investigate putative functions of pEtN modifications in Citrobacter rodentium, ⌬pmrAB, ⌬pmrC, ⌬cptA, and ⌬pmrC ⌬cptA deletion mutants were constructed. Compared to the wild type, most mutant strains were found to be more susceptible to antibiotics that must diffuse across the LPS layer of the OM. All mutant strains also showed increased influx rates of ethidium dye across their OM, suggesting that PmrAB-regulated pEtN modifications affect OM permeability. This was confirmed by increased partitioning of the fluorescent dye 1-N-phenylnaphthylamine (NPN) into the OM phospholipid layer of the mutant strains. In addition, substantial release of periplasmic ␤-lactamase was observed for the ⌬pmrAB and ⌬pmrC ⌬cptA strains, indicating a loss of OM integrity. This study attributes a new role for PmrAB-mediated pEtN LPS modifications in the maintenance of C. rodentium OM integrity.

Pseudomonas Quinolone Signal (PQS) probes capture a new binding partner for this signal molecule.

BackgroundThere is an increased risk of death due to drug toxicity after release from incarceration. The purpose of this study was to describe the timing, rate and circumstances of drug toxicity deaths following release from incarceration. This information can be used to help design potential preventive interventions.Methods and FindingsWe reviewed coroner’s files to identify deaths in adults in Ontario between 2006 and 2013 caused by drug toxicity (n = 6,978) and these records were matched with provincial correctional records to identify individuals who died within one year of being released from incarceration (n = 702). Twenty percent (n = 137) of the 702 deaths occurred within one week of release. The majority (77%, n = 538) of deaths after release involved one or more opioids. Of the deaths involving opioids, intervention by another person may have been possible in 318 cases.ConclusionsBetween 2006 and 2013 in Ontario, one in ten drug toxicity deaths in adults occurred within one year of release from provincial incarceration. These findings may help to inform the implemention and assessment of interventions aimed at reducing drug toxicity deaths following release from incarceration.

1IntroductionSince its discovery and initial characterization some 15 years ago by Pesci et al., [1] one particular class of Pseudomonasa eruginosa intercellulars ignaling molecules,t he 4-alkylquinolones (AQs), and the genes involved in the synthesiso ft hese molecules,h ave appeared with refreshing regularity in many studies involving this organism. Herein, we presentahistorical overview of how alkyl quinolones and their signaling pathways were discovered, what these molecules do,w hat gaps remain in our knowledge,a nd how researchers are manipulating AQ signaling for potential therapeutic benefit. Ther eview is not intended to be exhaustive or detailed-the reader is referred to several other excellent monographs for those purposes; [2][3][4] instead, it is intended to providea"taster" of the field and some insights into unresolved questions.ments (las and rhl) of the P. aeruginosa N-acylhomoserine lactone-dependent QS signaling pathways. Herein, we present the discovery and elucidationo fP QS signaling from ah istorical perspective, and also outlines ome of the outstanding research questionst hat still need to be addressed. Finally,w es how how ab etter understanding of the biochemistry underpinning this pathway is leading to the development of new antimicrobial interventions with clear therapeutic potential.Keywords: antimicrobial agents · biological activity · Pseudomonas quinolone signal · quorum sensing · virulence[a] T. Sams