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Biomedical subjects

Mark Roberts

Publications and source records attributed to Mark Roberts.

At least 19 recordsLinked to original sources
PubMed2007

Role of the alternative sigma factors sigmaE and sigmaS in survival of Salmonella enterica serovar Typhimurium during starvation, refrigeration and osmotic shock.

The ability of Salmonella enterica serovar Typhimurium to survive environmental stress requires specific, coordinated, responses, which induce resistance to the stress condition. This study investigated the relative contribution of sigmaE and sigmaS, the sigma factors regulating extracytoplasmic and general stress response functions, respectively, to survival at low temperature and also in media of differing osmotic strength, conditions relevant to food preservation. To determine if low-temperature storage is a signal for sigmaE- and sigmaS-mediated survival, the ability of S. Typhimurium rpoE, rpoS and rpoE/rpoS mutants to survive in a saline starvation-survival model at a refrigeration temperature (4.5 degrees C) was examined. Under these conditions, the rpoE mutant was significantly (P<0.05) compromised compared to the parent and to an rpoS mutant. The double mutant in rpoE and rpoS displayed a cumulative defect in survival. In hyperosmotic environments (low aw) containing 6 % NaCl and at refrigeration temperature, both sigma factors were important for maximum survival but sigmaS played the dominant role. Analysis of the metabolic activity of starved populations at 4.5 and 37 degrees C revealed significantly (P<0.001) elevated electron-transport system activity in mutants in rpoE and rpoS, indicating a role for sigmaE- and sigmaS-regulated genes in maintaining energy homeostasis. Together these data demonstrate that sigmaE and sigmaS are important for survival of S. Typhimurium in conditions encountered during food processing and that the relative contribution of sigmaE and sigmaS is critically dependent on the precise nature of the stress.

Bacterial Proteins↗
PubMed2006

An event-related potential component sensitive to images of the human body.

One of the critical functions of vision is to provide information about other individuals. Neuroimaging experiments examining the cortical regions that analyze the appearance of other people have found partially overlapping networks that respond selectively to human faces and bodies. In event-related potential (ERP) studies, faces systematically elicit a negative component peaking 170 ms after presentation - the N170. To characterize the electrophysiological response to human bodies, we compared the ERPs elicited by faces, bodies and various control stimuli. In Experiment 1, a comparison of ERPs elicited by faces, bodies, objects and places showed that pictures of the human body (without the head) elicit a negative component peaking at 190 ms (an N190). While broadly similar to the N170, the N190 differs in both spatial distribution and amplitude from the N1 components elicited by faces, objects and scenes and peaks significantly later than the N170. The difference between N190 and N170 was further supported using topographic analyses of ERPs and source localization techniques. A unique, stable map topography was found to characterize human bodies between 130 and 230 ms. In Experiment 2, we tested the four conditions from Experiment 1, as well as intact and scrambled silhouettes and stick figures of the human body. We found that intact silhouettes and stick figures elicited significantly greater N190 amplitudes than their scrambled counterparts. Thus, the N190 generalizes to some degree to schematic depictions of the human form. Overall, our findings are consistent with intertwined, but functionally distinct, neural representations of the human face and body.

Adult↗
PubMed2006

Patterning organic semiconductors using "dry" poly(dimethylsiloxane) elastomeric stamps for thin film transistors.

This communication demonstrates a method of transferring unreacted low molecular weight (LMW) siloxane oligomers from freshly prepared "dry" PDMS stamps for patterning organic semiconductors and conducting polymers into functional devices via selective wetting. The semiconductors were patterned onto the modified surfaces via dip-coating with well-resolved feature sizes as small as 1 mum. Functional transistor arrays exhibited field-effect mobilities as high as 0.07 cm2/Vs. The proposed printing method eliminates the need to ink SAMs for fabricating patterns and results in a simple, fast, and highly reproducible method of patterning organic semiconductors from solution. The method herein also produced a flexible transistor composed of patterned PEDOT source-drain electrodes.

Journal Article↗
PubMed2006

Pushing the envelope: extracytoplasmic stress responses in bacterial pathogens.

Despite being nutrient rich, the tissues and fluids of vertebrates are hostile to microorganisms, and most bacteria that attempt to take advantage of this environment are rapidly eliminated by host defences. Pathogens have evolved various means to promote their survival in host tissues, including stress responses that enable bacteria to sense and adapt to adverse conditions. Many different stress responses have been described, some of which are responsive to one or a small number of cues, whereas others are activated by a broad range of insults. The surface layers of pathogenic bacteria directly interface with the host and can bear the brunt of the attack by the host armoury. Several stress systems that respond to perturbations in the microbial cell outside of the cytoplasm have been described and are known collectively as extracytoplasmic or envelope stress responses (ESRs). Here, we review the role of the ESRs in the pathogenesis of Gram-negative bacterial pathogens.

Adaptation, Physiological↗
PubMed2006

Identification of the sigmaE regulon of Salmonella enterica serovar Typhimurium.

The extracytoplasmic function sigma factor, sigma(E), has been shown to play a critical role in virulence of Salmonella enterica serovar Typhimurium (S. Typhimurium). The previously optimized two-plasmid system has been used to identify S. Typhimurium promoters recognized by RNA polymerase containing sigma(E). This method allowed identification of 34 sigma(E)-dependent promoters that direct expression of 62 genes in S. Typhimurium, 23 of which (including several specific for S. Typhimurium) have not been identified previously to be dependent upon sigma(E) in Escherichia coli. The promoters were confirmed in S. Typhimurium and transcriptional start points of the promoters were determined by S1-nuclease mapping. All the promoters contained sequences highly similar to the consensus sequence of sigma(E)-dependent promoters. The identified genes belonging to the S. Typhimurium sigma(E)-regulon encode proteins involved in primary metabolism, DNA repair systems and outer-membrane biogenesis, and regulatory proteins, periplasmic proteases and folding factors, proposed lipoproteins, and inner- and outer-membrane proteins with unknown functions. Several of these sigma(E)-dependent genes have been shown to play a role in virulence of S. Typhimurium.

Base Sequence↗
PubMed2006

Characterization of the sigmaE-dependent rpoEp3 promoter of Salmonella enterica serovar Typhimurium.

Using a two-plasmid system, we recently identified sigma(E)-dependent promoters directing expression of the sigma(E) regulon genes in Salmonella enterica serovar Typhimurium (S. Typhimurium). Comparison of the promoters revealed a consensus sequence almost identical to the sigma(E)-dependent rpoEp3 promoter directing expression of rpoE. This two-plasmid system was previously optimized to identify nucleotides critical for the rpoEp3 promoter activity. However, two highly conserved nucleotides in the sigma(E) consensus sequence were not identified by this screening. In the present study, we have improved the two-plasmid screening system using a new optimized error-prone PCR mutagenesis. Together with site-directed mutagenesis, we further identified nucleotides critical for activity of the rpoEp3 promoter and quantified the effect of the particular mutation upon promoter activity. All the identified critical nucleotides of the rpoEp3 promoter (in capital) were located in the -35 (ggAACtt) and -10 (gTCtaA) regions and corresponded to the most conserved nucleotides in the sigma(E) consensus sequence. The expression of the wild-type and mutated rpoEp3 promoters was confirmed in S. Typhimurium and was found to exhibit a different pattern of sigma(E) activation compared with Escherichia coli, with a peak rpoEp3 promoter activity in early stationary phase followed by a decrease in late stationary phase.

Amino Acid Sequence↗
PubMed2006

Drug-related hospitalizations in a tertiary care internal medicine service of a Canadian hospital: a prospective study.

STUDY OBJECTIVES: To determine the frequency, severity, preventability, and classification of adverse drug events resulting in hospitalization, and to identify any patient, prescriber, drug, and system factors associated with these events. DESIGN: Prospective, observational study. SETTING: Internal medicine service of a large tertiary care hospital in Canada. PATIENTS: A total of 565 consecutive adult patients admitted to the hospital during a 12-week period. MEASUREMENTS AND MAIN RESULTS: A patient's hospitalization was defined as drug related if it was directly related to one of eight predefined classifications; severity and preventability of the hospitalization were also assessed. Multivariate logistic regression analysis was used to evaluate patient, prescriber, drug, and system factors associated with drug-related hospitalizations. The frequency of drug-related hospitalization was 24.1% (95% confidence interval [CI] 20.6-27.8%), of which 72.1% (95% CI 63.7-79.4%) were deemed preventable. Severity was classified as mild, moderate, severe, and fatal in 8.1% (95% CI 4.1-14.0%), 83.8% (95% CI 76.5-89.6%), 7.4% (95% CI 3.6-13.1%), and 0.7% (95% CI 0.0-4.0%), respectively, of the hospitalizations. The most common classifications of drug-related hospitalization were adverse drug reactions (35.3% [95% CI 27.3-43.9%]), improper drug selection (17.6% [95% CI 11.6-25.1%]), and noncompliance (16.2% [95% CI 10.4-23.5%]). No independent risk factors for drug-related hospitalization were identified with regression modeling. CONCLUSION: Approximately 25% of patients in our study were hospitalized for drug-related causes; over 70% of these causes were deemed preventable. Drug-related hospitalization is a significant problem that merits further research and intervention.

Aged↗
PubMed2005

Implementation and outcomes of commercial disease management programs in the United States: the disease management outcomes consolidation survey.

Despite widespread adoption of disease management (DM) programs by US health plans, gaps remain in the evidence for their benefit. The Disease Management Outcomes Consolidation Survey was designed to gather data on DM programs for commercial health plans, to assess program success and DM effectiveness. The questionnaire was mailed to 292 appropriate health plan contacts; 26 plans covering more than 14 million commercial members completed and returned the survey. Respondents reported that DM plays a significant and increasing role in their organizations. Key reasons for adopting DM were improving clinical outcomes, reducing medical costs and utilization, and improving member satisfaction. More respondents were highly satisfied with clinical results than with utilization or cost outcomes of their programs (46%, 17%, and 13%, respectively). Detailed results were analyzed for 57 DM programs with over 230,000 enrollees. Most responding plans offered DM programs for diabetes and asthma, with return on investment (ROI) ranging from 0.16:1 to 4:1. Weighted by number of enrollees per DM program, average ROI was 2.56:1 for asthma (n = 1,136 enrollees) and 1.98:1 for diabetes (n = 25,364). Most (but not all) respondents reported reduced hospital admissions, increasing rates of preventive care, and improved clinical measures. Few respondents provided detailed information about DM programs for other medical conditions, but most that did reported positive outcomes. Lack of standardized methodology was identified as a major barrier to in-house program evaluation. Although low response rate precluded drawing many general conclusions, a clear need emerged for more rigorous evaluation methods and greater standardization of outcomes measurement.

Disease Management↗
PubMed2005

Effect of inactivation of degS on Salmonella enterica serovar typhimurium in vitro and in vivo.

The alternative sigma factor (RpoE sigma(E)) enables Salmonella enterica serovar Typhimurium to adapt to stressful conditions, such as oxidative stress, nutrient deprivation, and growth in mammalian tissues. Infection of mice by Salmonella serovar Typhimurium also requires sigma(E). In Escherichia coli, activation of the sigma(E) pathway is dependent on proteolysis of the anti-sigma factor RseA and is initiated by DegS. DegS is also important in order for E. coli to cause extraintestinal infection in mice. We constructed a degS mutant of the serovar Typhimurium strain SL1344 and compared its behavior in vitro and in vivo with those of its wild-type (WT) parent and an isogenic rpoE mutant. Unlike E. coli degS strains, the Salmonella serovar Typhimurium degS strain grew as well as the WT strain at 42 degrees C. The degS mutant survived very poorly in murine macrophages in vitro and was highly attenuated compared with the WT strain for both the oral and parenteral routes of infection in mice. However, the degS mutant was not as attenuated as the serovar Typhimurium rpoE mutant: 100- to 1,000-fold more degS bacteria than rpoE bacteria were present in the livers and spleens of mice 24 h after intraperitoneal challenge. In most assays, the rpoE mutant was more severely affected than the degS mutant and a sigma(E)-dependent reporter gene was more active in the degS mutant than the rpoE strain. These findings indicate that degS is important for activation of the sigma(E) pathway in serovar Typhimurium but that alternative pathways for sigma(E) activation probably exist.

Animals↗
PubMed2004

Intranasal immunisation against tetanus with an attenuated Bordetella bronchiseptica vector expressing FrgC: improved immunogenicity using a Bvg-regulated promoter to express FrgC.

Mice were immunised intranasally with live Bordetella bronchiseptica aroA strains possessing plasmids encoding fragment C (FrgC) of tetanus toxin. FrgC was expressed either from a constitutive tac promoter (strain GVB120) or the Bvg-dependent fhaB promoter (strain GVB1543). Serum anti-FrgC antibody titres were detected in all mice immunised with GVB1543 and GVB120 but the average titres were higher and the responses to FrgC were more consistent in GVB1543 immunised animals. This was reflected in the protective immunity conferred by the different strains: 100% of GVB1543 immunised mice were protected against tetanus toxin challenge whereas only 60% of animals immunised with GVB120 survived tetanus challenge. Viability of the B. bronchiseptica vector strain was shown to be critical to its efficacy as a vector for FrgC.

Adhesins, Bacterial↗
PubMed2004

Identification of nucleotides critical for activity of the sigmaE-dependent rpoEp3 promoter in Salmonella enterica serovar Typhimurium.

We previously described a two-plasmid system for the identification of promoters recognized by Salmonella enterica serovar Typhimurium (S. Typhimurium) sigmaE. The S. Typhimurium sigmaE-dependent rpoEp3 promoter was active in the E. coli two-plasmid system only after arabinose-induced expression of S. Typhimurium rpoE. In the present study, we have exploited this two-plasmid system for the identification of nucleotides critical for activity of the rpoEp3 promoter. A library of randomly mutated DNA fragments containing the rpoEp3 promoter was cloned upstream of a lacZalpha reporter gene and screened for activity in the presence of S. Typhimurium sigmaE. The clones exhibiting reduced LacZ activity were sequenced to identify the mutations. The activity of the mutated rpoEp3 promoters were studied further using a luciferase-based promoter-probe plasmid. All of the important nucleotides of the rpoEp3 promoter (in capital) were located in the -35 (ggAActt) and -10 (TctaA) regions. The critical nucleotides were also the most conserved in known sigmaE-dependent promoters. The study also revealed the importance of the 16-bp spacing between -10 and -35 region, as reducing the spacing to 15-bp greatly reduced activity of the promoter. This method should be generally applicable for the identification of important nucleotides in the cognate promoters of other sigma factors.

Artificial Gene Fusion↗
PubMed2004

The patient experience in emergency departments: a review of the literature.

This paper analyses the literature on the patient experience within emergency departments. We identify six themes within the literature: waiting times, communication, cultural aspects of care, pain, the environment and dilemmas in accessing the patient experience. Overall, the literature has a North American bias and is largely quantitative in approach. Although levels of patient satisfaction are high, a number of issues arise within the review, which suggest areas where quality of care could improve. We also identify the problematic nature of accessing the patient experience and suggest future areas for researchers to explore.

Adult↗
PubMed2004

Effect of inactivation of the HtrA-like serine protease DegQ on the virulence of Salmonella enterica serovar Typhimurium in mice.

DegQ is a serine protease that is highly homologous to HtrA, an important virulence determinant of Salmonella enterica serovar Typhimurium. We examined if DegQ is involved in serovar Typhimurium pathogenesis. A serovar Typhimurium degQ mutant was as virulent as the wild-type strain in mice. However, a serovar Typhimurium htrA degQ mutant survived less well in murine organs, particularly in the liver, than a serovar Typhimurium htrA mutant. DegQ is not essential for serovar Typhimurium pathogenesis but may play a small role during salmonella growth at systemic sites.

Animals↗
PubMed2004

Role of the two-component regulator CpxAR in the virulence of Salmonella enterica serotype Typhimurium.

The CpxAR (Cpx) two-component regulator controls the expression of genes in response to a variety of environmental cues. The Cpx regulator has been implicated in the virulence of several gram-negative pathogens, although a role for Cpx in vivo has not been demonstrated directly. Here we investigate whether positive or negative control of gene expression by Cpx is important for the pathogenesis of Salmonella enterica serotype Typhimurium. The Cpx signal pathway in serotype Typhimurium was disrupted by insertional inactivation of the cpxA and cpxR genes. We also constitutively activated the Cpx pathway by making an internal in-frame deletion in cpxA (a cpxA* mutation). Activation of the Cpx pathway inhibited induction of the envelope stress response pathway controlled by the alternative sigma factor sigma(E) (encoded by rpoE). Conversely, the Cpx pathway was highly up-regulated (>40-fold) in a serotype Typhimurium rpoE mutant. The cpxA* mutation, but not the cpxA or the cpxR mutation, significantly reduced the capacity of serotype Typhimurium to adhere to and invade eucaryotic cells, although intracellular replication was not affected. The cpxA and cpxA* mutations significantly impaired the ability of serotype Typhimurium to grow in vivo in mice. To our knowledge, this is the first demonstration that the Cpx system is important for a bacterial pathogen in vivo.

Animals↗
PubMed2003

Familiar words capture the attention of 11-month-olds in less than 250 ms.

The capacity of human infants to discriminate contrasting speech sounds specializes to the native language by the end of the first year of life, when the first signs of word recognition have also been found, using behavioural measures. The extent of voluntary attentional involvement in such word recognition has not been explored, however, nor do we know what its neural time-course may be. Here we demonstrate that 11-month-old children shift their attention automatically to familiar words within 250 ms of presentation onset by measuring event-related potentials elicited by familiar and unfamiliar words. A significant modulation of the first negative peak (N200), known to index implicit change detection in adults, was induced by word familiarity in the infants.

Acoustic Stimulation↗
PubMed2003

Prevention and suppression of metal packing fires.

Structured packing has been widely used because of large surface area that makes possible columns with high capacity and efficiency. The large surface area also contributes to fire hazards because of hydrocarbon deposits that can easily combust and promote combustion of the thin metal packing materials. Materials of high surface area that can fuel fires include reactive metals, such as titanium, and materials that are not considered combustible, such as stainless steel. Column design and material selection for packing construction is discussed together with employee training and practices for safe column maintenance and operations. Presented also are methods and agents for suppression of metal fires. Guidance for prevention and suppression of metal fires is related to incidents involving packing fires in columns.

Explosions↗
PubMed2003

Transcriptional analysis of the rpoE gene encoding extracytoplasmic stress response sigma factor sigmaE in Salmonella enterica serovar Typhimurium.

The rpoE gene of Salmonella enterica serovar Typhimurium (S. Typhimurium), which encodes the extracytoplasmic stress response sigma factor sigmaE, is critically important for the virulence of S. Typhimurium. We analysed expression of rpoE by wild-type and mutant bacteria grown in different conditions by S1-nuclease mapping using RNA, and using in vivo reporter gene fusions. Three promoters, rpoEp1, rpoEp2 and rpoEp3, were located upstream of the S. Typhimurium rpoE gene. The promoters were differentially expressed during growth and under several stress conditions including cold shock. Expression from the rpoEp3 promoter was absent in an S. Typhimurium rpoE mutant, demonstrating its dependence upon sigmaE. The level of mRNA corresponding to rpoEp3 was also higher in a cpxR mutant, indicating a negative regulation of the promoter by the Cpx system. Using this rpoE-dependent promoter, we optimised a two-plasmid system for identification of promoters recognised by S. Typhimurium sigmaE. The rpoEp3 promoter was active in the Escherichia coli two-plasmid system and has an identical transcription start point as in S. Typhimurium but only after induction of S. Typhimurium rpoE expression.

Artificial Gene Fusion↗