Buoyant microbubbles as alternatives or adjuncts to magnetic bead methods for high-purity cell isolation

Widely used in immunologic applications, magnetic bead systems have significant limitations including cumbersome workflows, generation of high-shear and high-compressive forces during routine use, and limited performance in low and high volume samples. Buoyancy-activated cell sorting (BACS) overcomes these issues by using low-density microbubbles in lieu of magnets and iron beads to perform isolation. Here we report methods for three common uses: removal of extraneous RBCs prior to FACS, isolation of high-purity B lymphocytes from murine spleens, and improvement of a magnetic NK separation system by jointly applying BACS to remove contaminating NKT cells. RBC removal from leukopheresis-derived PBMC was performed with anti-CD235a-conjugated microbubbles. B cell isolation was performed with streptavidin microbubbles and a negative selection cocktail of biotinylated anti-murine antibodies. NK cell isolation was performed on PBMC using Miltenyi human CD56 MicroBeads and an additional purification step using streptavidin microbubbles and an anti-CD3 antibody. Each experiment used Akadeum microbubbles and a one-minute trituration to combine microbubbles with cell suspensions. RBC microbubbles provided 98.3 ± 1.0% removal of RBCs with 11.3 ± 0.9% nonspecific binding. B cells isolated with microbubbles were 91.8 ± 2.8% pure with a yield of 94.2 ± 4.3%. NK purification with magnetic microparticles produced 80.5 ± 0.7% purity. Additional purification with microbubbles increased purity to 90.8 ± 1.3%. Microbubbles are a flexible and simpler alternative to magnetic cell isolation systems, delivering comparable performance and, when used in conjunction with magnetic beads, superior purity.

Rapid, Reproducible, Quantifiable NMR Metabolomics: Methanol and Methanol: Chloroform Precipitation for Removal of Macromolecules in Serum and Whole Blood

Background: Though blood is an excellent biofluid for metabolomics, proteins and lipids present in blood can interfere with 1d-¹H NMR spectra and disrupt quantification of metabolites. Here, we present effective macromolecule removal strategies for serum and whole blood (WB) samples. Methods: A variety of macromolecule removal strategies were compared in both WB and serum, along with tests of ultrafiltration alone and in combination with precipitation methods. Results: In healthy human serum, methanol:chloroform:water extraction with ultrafiltration was compared to methanol precipitation with and without ultrafiltration. Methods were tested in healthy pooled human serum, and in serum from patients with sepsis. Effects of long-term storage at −80 °C were tested to explore the impact of macromolecule removal strategy on serum from different conditions. In WB a variety of extraction strategies were tested in two types of WB (from pigs and baboons) to examine the impact of macromolecule removal strategies on different samples. Conclusions: In healthy human serum methanol precipitation of serum with ultrafiltration was superior, but was similar in recovery and variance to methanol:chloroform:water extraction with ultrafiltration in pooled serum from patients with sepsis. In WB, high quality, quantifiable spectra were obtained with the use of a methanol: chloroform precipitation.

A Cationic Amphiphilic Random Copolymer with pH-Responsive Activity against Methicillin-Resistant Staphylococcus aureus

In this report, we demonstrate the pH-dependent, in vitro antimicrobial activity of a cationic, amphiphilic random copolymer against clinical isolates of drug-resistant Staphylococcus aureus. The polymer was developed toward a long-term goal of potential utility in the treatment of skin infections. The proposed mechanism of action of the polymer is through selectively binding to bacterial membranes and subsequent disruption of the membrane structure/integrity, ultimately resulting in bacterial cell death. The polymer showed bactericidal activity against clinical isolates of methicillin-resistant or vancomycin-intermediate S. aureus. The polymer was effective in killing S. aureus at neutral pH, but inactive under acidic conditions (pH 5.5). The polymer did not exhibit any significant hemolytic activity against human red blood cells or display cytotoxicity to human dermal fibroblasts over a range of pH values (5.5–7.4). These results indicate that the polymer activity was selective against bacteria over human cells. Using this polymer, we propose a new potential strategy for treatment of skin infections using the pH-sensitive antimicrobial polymer agent that would selectively target infections at pH-neutral wound sites, but not the acidic, healthy skin.

Hemodialysis Catheter Heat Transfer for Biofilm Prevention and Treatment

Central line-associated bloodstream infections (CLABSIs) are not easily treated, and many catheters (e.g., hemodialysis catheters) are not easily replaced. Biofilms (the source of infection) on catheter surfaces are notoriously difficult to eradicate. We have recently demonstrated that modest elevations of temperature lead to increased staphylococcal susceptibility to vancomycin and significantly soften the biofilm matrix. In this study, using a combination of microbiological, computational, and experimental studies, we demonstrate the efficacy, feasibility, and safety of using heat as an adjuvant treatment for infected hemodialysis catheters. Specifically, we show that treating with heat in the presence of antibiotics led to additive killing of Staphylococcus epidermidis with similar trends seen for Staphylococcus aureus and Klebsiella pneumoniae. The magnitude of temperature elevation required is relatively modest (45-50°C) and similar to that used as an adjuvant to traditional cancer therapy. Using a custom-designed benchtop model of a hemodialysis catheter, positioned with tip in the human vena cava as well as computational fluid dynamic simulations, we demonstrate that these temperature elevations are likely achievable in situ with minimal increased in overall blood temperature.

Zinc oxide nanoparticle suspensions and layer-by-layer coatings inhibit staphylococcal growth

Despite a decade of engineering and process improvements, bacterial infection remains the primary threat to implanted medical devices. Zinc oxide nanoparticles (ZnO-NPs) have demonstrated antimicrobial properties. Their microbial selectivity, stability, ease of production, and low cost make them attractive alternatives to silver NPs or antimicrobial peptides. Here we sought to (1) determine the relative efficacy of ZnO-NPs on planktonic growth of medically relevant pathogens; (2) establish the role of bacterial surface chemistry on ZnO-NP effectiveness; (3) evaluate NP shape as a factor in the dose-response; and (4) evaluate layer-by-layer (LBL) ZnO-NP surface coatings on biofilm growth. ZnO-NPs inhibited bacterial growth in a shape-dependent manner not previously seen or predicted. Pyramid shaped particles were the most effective and contrary to previous work, larger particles were more effective than smaller particles. Differential susceptibility of pathogens may be related to their surface hydrophobicity. LBL ZnO-NO coatings reduced staphylococcal biofilm burden by >95%. From the Clinical Editor: The use of medical implants is widespread. However, bacterial colonization remains a major concern. In this article, the authors investigated the use of zinc oxide nanoparticles (ZnO-NPs) to prevent bacterial infection. They showed in their experiments that ZnO-NPs significantly inhibited bacterial growth. This work may present a new alternative in using ZnO-NPs in medical devices.

Artificial biofilms establish the role of matrix interactions in staphylococcal biofilm assembly and disassembly

We demonstrate that the microstructural and mechanical properties of bacterial biofilms can be created through colloidal self-assembly of cells and polymers, and thereby link the complex material properties of biofilms to well understood colloidal and polymeric behaviors. This finding is applied to soften and disassemble staphylococcal biofilms through pH changes. Bacterial biofilms are viscoelastic, structured communities of cells encapsulated in an extracellular polymeric substance (EPS) comprised of polysaccharides, proteins, and DNA. Although the identity and abundance of EPS macromolecules are known, how these matrix materials interact with themselves and bacterial cells to generate biofilm morphology and mechanics is not understood. Here, we find that the colloidal self-assembly of Staphylococcus epidermidis RP62A cells and polysaccharides into viscoelastic biofilms is driven by thermodynamic phase instability of EPS. pH conditions that induce phase instability of chitosan produce artificial S. epidermidis biofilms whose mechanics match natural S. epidermidis biofilms. Furthermore, pH-induced solubilization of the matrix triggers disassembly in both artificial and natural S. epidermidis biofilms. This pH-induced disassembly occurs in biofilms formed by five additional staphylococcal strains, including three clinical isolates. Our findings suggest that colloidal self-assembly of cells and matrix polymers produces biofilm viscoelasticity and that biofilm control strategies can exploit this mechanism.

Effects of temperature on the morphological, polymeric, and mechanical properties of Staphylococcus epidermidis bacterial biofilms

Changes in temperature were found to affect the morphology, cell viability, and mechanical properties of Staphylococcus epidermidis bacterial biofilms. S. epidermidis biofilms are commonly associated with hospital-acquired medical device infections. We observed the effect of heat treatment on three physical properties of the biofilms: the bacterial cell morphology and viability, the polymeric properties of the extracellular polymeric substance (EPS), and the rheological properties of the bulk biofilm. After application of a 1 h heat treatment at 45 °C, cell reproduction had ceased, and at 60 °C, cell viability was significantly reduced. Size exclusion chromatography was used to fractionate the extracellular polymeric substance (EPS) based on size. Chemical analysis of each fraction showed that the relative concentrations of the polysaccharide, protein, and DNA components of the EPS were unchanged by the heat treatment at 45 and 60 °C. The results suggest that the EPS molecular constituents are not significantly degraded by the temperature treatment. However, some aggregation on the scale of 100 nm was found by dynamic light scattering at 60 °C. Finally, relative to control biofilms maintained at 37 °C, we observed an order of magnitude reduction in the biofilm yield stress after 60 °C temperature treatment. No such difference was found for treatment at 45 °C. From these results, we conclude that the yield stress of bacterial biofilms is temperature-sensitive and that this sensitivity is correlated with cell viability. The observed significant decrease in yield stress with temperature suggests a means to weaken the mechanical integrity of S. epidermidis biofilms with applications in areas such as the treatment of biofilm-infected medical devices.

Elasticity of microscale volumes of viscoelastic soft matter by cavitation rheometry

Measurement of the elastic modulus of soft, viscoelastic liquids with cavitation rheometry is demonstrated for specimens as small as 1 μl by application of elasticity theory and experiments on semi-dilute polymer solutions. Cavitation rheometry is the extraction of the elastic modulus of a material, E, by measuring the pressure necessary to create a cavity within it [J. A. Zimberlin, N. Sanabria-DeLong, G. N. Tew, and A. J. Crosby, Soft Matter 3, 763-767 (2007)]. This paper extends cavitation rheometry in three ways. First, we show that viscoelastic samples can be approximated with the neo-Hookean model provided that the time scale of the cavity formation is measured. Second, we extend the cavitation rheometry method to accommodate cases in which the sample size is no longer large relative to the cavity dimension. Finally, we implement cavitation rheometry to show that the theory accurately measures the elastic modulus of viscoelastic samples with volumes ranging from 4 ml to as low as 1 μl.

Sticky surface: sphere-sphere adhesion dynamics

We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluid-immersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive/repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e. non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favours large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g→1) and in a neutral solution with no dissolved salts.

Multilocus Sequence Typing for Interpreting Blood Isolates of Staphylococcus epidermidis

Staphylococcus epidermidis is an important cause of nosocomial infection and bacteremia. It is also a common contaminant of blood cultures and, as a result, there is frequently uncertainty as to its diagnostic significance when recovered in the clinical laboratory. One molecular strategy that might be of value in clarifying the interpretation of S. epidermidis identified in blood culture is multilocus sequence typing. Here, we examined 100 isolates of this species (50 blood isolates representing true bacteremia, 25 likely contaminant isolates, and 25 skin isolates) and the ability of sequence typing to differentiate them. Three machine learning algorithms (classification regression tree, support vector machine, and nearest neighbor) were employed. Genetic variability was substantial between isolates, with 44 sequence types found in 100 isolates. Sequence types 2 and 5 were most commonly identified. However, among the classification algorithms we employed, none were effective, with CART and SVM both yielding only 73% diagnostic accuracy and nearest neighbor analysis yielding only 53% accuracy. Our data mirror previous studies examining the presence or absence of pathogenic genes in that the overlap between truly significant organisms and contaminants appears to prevent the use of MLST in the clarification of blood cultures recovering S. epidermidis.

Characterization of a reverse-phase perfluorocarbon emulsion for the pulmonary delivery of tobramycin

BACKGROUND

Aerosolized delivery of antibiotics is hindered by poor penetration within distal and plugged airways. Antibacterial perfluorocarbon ventilation (APV) is a proposed solution in which the lungs are partially or totally filled with perfluorocarbon (PFC) containing emulsified antibiotics. The purpose of this study was to evaluate emulsion stability and rheological, antibacterial, and pharmacokinetic characteristics.

METHODS

This study examined emulsion aqueous droplet diameter and number density over 24 hr and emulsion and neat PFC viscosity and surface tension. Additionally, Pseudomonas aeruginosa biofilm growth was measured after 2-hr exposure to emulsion with variable aqueous volume percentages (0.25, 1, and 2.5%) and aqueous tobramycin concentrations (Ca=0.4, 4, and 40 mg/mL). Lastly, the time course of serum and pulmonary tobramycin concentrations was evaluated following APV and conventional aerosolized delivery of tobramycin in rats.

RESULTS

The initial aqueous droplet diameter averaged 1.9±0.2 μm with little change over time. Initial aqueous droplet number density averaged 3.5±1.7×10(9) droplets/mL with a significant (p<0.01) decrease over time. Emulsion and PFC viscosity were not significantly different, averaging 1.22±0.03×10(-3) Pa·sec. The surface tensions of PFC and emulsion were 15.0±0.1×10(-3) and 14.6±0.6×10(-3) N/m, respectively, and the aqueous interfacial tensions were 46.7±0.3×10(-3) and 26.9±11.0×10(-3) N/m (p<0.01), respectively. Biofilm growth decreased markedly with increasing Ca and, to a lesser extent, aqueous volume percentage. Tobramycin delivered via APV yielded 2.5 and 10 times larger pulmonary concentrations at 1 and 4 hr post delivery, respectively, and significantly (p<0.05) lower serum concentrations compared with aerosolized delivery.

CONCLUSIONS

The emulsion is bactericidal, retains the rheology necessary for pulmonary delivery, is sufficiently stable for this application, and results in increased pulmonary retention of the antibiotic.

Role of environmental and antibiotic stress on Staphylococcus epidermidis biofilm microstructure

Cellular clustering and separation of Staphylococcus epidermidis surface adherent biofilms were found to depend significantly on both antibiotic and environmental stress present during growth under steady flow. Image analysis techniques common to colloidal science were applied to image volumes acquired with high-resolution confocal laser scanning microscopy to extract spatial positions of individual bacteria in volumes of size ~30 × 30 × 15 μm(3). The local number density, cluster distribution, and radial distribution function were determined at each condition by analyzing the statistics of the bacterial spatial positions. Environmental stressors of high osmotic pressure (776 mM NaCl) and sublethal antibiotic dose (1.9 μg/mL vancomycin) decreased the average bacterial local number density 10-fold. Device-associated bacterial biofilms are frequently exposed to these environmental and antibiotic stressors while undergoing flow in the bloodstream. Characteristic density phenotypes associated with low, medium, and high local number densities were identified in unstressed S. epidermidis biofilms, while stressed biofilms contained medium- and low-density phenotypes. All biofilms exhibited clustering at length scales commensurate with cell division (~1.0 μm). However, density phenotypes differed in cellular connectivity at the scale of ~6 μm. On this scale, nearly all cells in the high- and medium-density phenotypes were connected into a single cluster with a structure characteristic of a densely packed disordered fluid. However, in the low-density phenotype, the number of clusters was greater, equal to 4% of the total number of cells, and structures were fractal in nature with d(f) =1.7 ± 0.1. The work advances the understanding of biofilm growth, informs the development of predictive models of transport and mechanical properties of biofilms, and provides a method for quantifying the kinetics of bacterial surface colonization as well as biofilm fracture and fragmentation.

Molar mass, entanglement, and associations of the biofilm polysaccharide of Staphylococcus epidermidis

Biofilms are microbial communities that are characterized by the presence of a viscoelastic extracellular polymeric substance (EPS). Studies have shown that polysaccharides, along with proteins and DNA, are a major constituent of the EPS and play a dominant role in mediating its microstructure and rheological properties. Here, we investigate the possibility of entanglements and associative complexes in solutions of extracellular polysaccharide intercellular adhesin (PIA) extracted from Staphylococcus epidermidis biofilms. We report that the weight average molar mass and radius of gyration of PIA isolates are 2.01×10(5)±1200 g/mol and 29.2±1.2 nm, respectively. The coil overlap concentration, c*, was thus determined to be (32±4)×10(-4) g/mL. Measurements of the in situ concentration of PIA (cPIA,biofilm) was found to be (10±2)×10(-4) g/mL.Thus, cPIA,biofilm Collapse

Key Words

• staphylococcus epidermidis
• biofilm
• entangled polymers
• polysaccharide-protein complex
• extracellular polysaccharides
• static light scattering

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MESH Headings

• Animals
• Bacterial Adhesion
• Biofilms/growth & development
• Carbohydrate Conformation
• Cattle
• Elasticity
• Hydrogen Bonding
• Hydrogen-Ion Concentration
• Polysaccharides, Bacterial/chemistry
• Polysaccharides, Bacterial/isolation & purification
• Protein Binding
• Serum Albumin, Bovine/chemistry
• Staphylococcus epidermidis/chemistry
• Static Electricity
• Viscosity

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Grants

• R01 GM069438 NIGMS NIH HHS
• R01 GM081702 NIGMS NIH HHS
• GM-069438 NIGMS NIH HHS

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Spatiotemporal dynamics of complement C5a production within bacterial extracellular polymeric substance

Opsonization and anaphylatoxin production are early events in the innate response to bacterial pathogens. Opsonization alone is frequently not lethal and production of anaphy-latoxins, especially C5a, allows for recruitment of cellular defenses. Complement biochemistry is extensively studied and computational models have been reported previously. However, a critical feature of complement-mediated attack is its spatial dependence: diffusion of mediators into and away from a bacterium is central to understanding C5a generation. Spatial dependence is especially important in biofilms, where diffusion limitation is crucial to bacterial counterdefense. Here we develop a model of opsonization and C5a production in the presence of a common blood-borne pathogen, Staphylococcus epidermidis. Our results indicate that when complement attacks a single cell, diffusion into the extracellular polymeric substance (EPS) is complete within 10 ms and that production of C5a peaks over the next 15 min. When longer diffusion lengths (as in an EPS-rich biofilm) are incorporated, diffusion limitation appears such that the intensity and duration of C5a production is increased. However, the amount of C5a produced under several likely clinical scenarios where single cells or sparse biofilms are present is below the kD of the C5a receptor suggesting that complement activation by a single bacterium may be difficult to detect when diffusion is taken into account.

In situ rheology of Staphylococcus epidermidis bacterial biofilms

We developed a method to grow Staphylococcus epidermidis bacterial biofilms and characterize their rheological properties in situ in a continuously fed bioreactor incorporated into a parallel plate rheometer. The temperature and shear rates of growth modeled bloodstream conditions, a common site of S. epidermidis infection. We measured the linear elastic (G') and viscous moduli (G″) of the material using small-amplitude oscillatory rheology and the yield stress using non-linear creep rheology. We found that the elastic and viscous moduli of the S. epidermidis biofilm were 11 ± 3 Pa and 1.9 ± 0.5 Pa at a frequency of 1 Hz (6.283 rad per s) and that the yield stress was approximately 20 Pa. We modeled the linear creep response of the biofilm using a Jeffreys model and found that S. epidermidis has a characteristic relaxation time of approximately 750 seconds and a linear creep viscosity of 3000 Pa s. The effects on the linear viscoelastic moduli of environmental stressors, such as NaCl concentration and extremes of temperature, were also studied. We found a non-monotonic relationship between moduli and NaCl concentrations, with the stiffest material properties found at human physiological concentrations (135 mM). Temperature dependent rheology showed hysteresis in the moduli when heated and cooled between 5 °C and 60 °C. Through these experiments, we demonstrated that biofilms are rheologically complex materials that can be characterized by a combination of low modulus (~10 Pa), long relaxation time (~103 seconds), and a finite yield stress (20 Pa). This suggests that biofilms should be viewed as soft viscoelastic solids whose properties are determined in part by local environmental conditions. The in situ growth method introduced here can be adapted to a wide range of biofilm systems and applied over a broad spectrum of rheological and environmental conditions because the technique minimizes the risk of irreversible, non-linear deformation of the microbial specimen before analysis.

Prospective comparison of live evaluation and video review in the evaluation of operator performance in a pediatric emergency airway simulation

INTRODUCTION

Real-time assessment of operator performance during procedural simulation is a common practice that requires undivided attention by 1 or more reviewers, potentially over many repetitions of the same case.

OBJECTIVE

To determine whether reviewers display better interrater agreement of procedural competency when observing recorded, rather than live, performance; and to develop an assessment tool for pediatric rapid sequence intubation (pRSI).

METHODS

A framework of a previously established Objective Structured Assessment of Technical Skills (OSATS) tool was modified for pRSI. Emergency medicine residents (postgraduate year 1-4) were prospectively enrolled in a pRSI simulation scenario and evaluated by 2 live raters using the modified tool. Sessions were videotaped and reviewed by the same raters at least 4 months later. Raters were blinded to their initial rating. Interrater agreement was determined by using the Krippendorff generalized concordance method.

RESULTS

Overall interrater agreement for live review was 0.75 (95% confidence interval [CI], 0.72-0.78) and for video was 0.79 (95% CI, 0.73-0.82). Live review was significantly superior to video review in only 1 of the OSATS domains (Preparation) and was equivalent in the other domains. Intrarater agreement between the live and video evaluation was very good, greater than 0.75 for all raters, with a mean of 0.81 (95% CI, 0.76-0.85).

CONCLUSION

The modified OSATS assessment tool demonstrated some evidence of validity in discriminating among levels of resident experience and high interreviewer reliability. With this tool, intrareviewer reliability was high between live and 4-months' delayed video review of the simulated procedure, which supports feasibility of delayed video review in resident assessment.

Early development of bacterial community diversity in emergently placed urinary catheters

BACKGROUND

Approximately 25% of hospitalized patients have a urinary catheter, and catheter associated urinary tract infection is the most common nosocomial infection in the US, causing >1 million cases/year. However, the natural history of the biofilms that rapidly form on urinary catheters and lead to infection is not well described.

FINDINGS

We characterized the dynamics of catheter colonization among catheters collected from 3 women and 5 men in a trauma burn unit with different indwelling times using TRFLP and culture. All patients received antibiotic therapy.

RESULTS

Colony-forming units increased along the extraluminal catheter surface from the catheter balloon to the urethra, but no trend was apparent for the intraluminal surface. This suggests extraluminal bacteria come from periurethral communities while intraluminal bacteria are introduced via the catheter or already inhabit the urine/bladder. Richness of operational taxonomic units (OTUs) increased over time on the intraluminal surface, but was constant extraluminally.

CONCLUSIONS

OTU community composition was explained best by time rather than axial location or surface. Our results suggest that catheter colonization can be very dynamic, and possibly have a predictable succession.

Multicellularity and antibiotic resistance in Klebsiella pneumoniae grown under bloodstream-mimicking fluid dynamic conditions

BACKGROUND

While the importance of fluid dynamical conditions is well recognized in the growth of biofilms, their role during bacteremia is unknown. We examined the impact of physiological fluid shear forces on the development of multicellular aggregates of Klebsiella pneumoniae.

METHODS

Wild-type and O-antigen or capsular mutants of K. pneumoniae were grown as broth culture in a Taylor-Couette flow cell configured to provide continuous shear forces comparable to those encountered in the human arterial circulation (ie, on the order of 1.0 Pa). The size distribution and antibiotic resistance of aggregates formed in this apparatus were determined, as was their ability to persist in the bloodstream of mice following intravenous injection.

RESULTS

Unlike growth in shaking flasks, bacteria grown in the test apparatus readily formed aggregates, a phenotype largely absent in capsular mutants and to a lesser degree in O-antigen mutants. Aggregates were found to persist in the bloodstream of mice. Importantly, organisms grown under physiological shear were found to have an antibiotic resistance phenotype intermediate between that of fully planktonic and biofilm states.

CONCLUSIONS

When grown under intravascular-magnitude fluid dynamic conditions, K. pneumoniae spontaneously develops into multicellular aggregates that are capable of persisting in the circulation and exhibit increased antibiotic resistance.

A prospective study of central venous catheters placed in a tertiary care Emergency Department: indications for use, infectious complications, and natural history

Despite successful efforts to improve overall central line-associated bloodstream infections (CLABSI) rates, little is known about CLABSI rates or even central venous catheter insertion practices in the Emergency Department. We sought to determine the baseline CLABSI rate for Emergency Department-inserted central venous catheters and to describe indications for placement, duration of use, and the natural history of these devices.

Diabetes is not associated with increased mortality in emergency department patients with sepsis

STUDY OBJECTIVE

Despite its high prevalence, the influence of diabetes on outcomes of emergency department (ED) patients with sepsis remains undefined. Our aim is to investigate the association of diabetes and initial glucose level with mortality in patients with suspected infection from the ED.

METHODS

Three independent, observational, prospective cohorts from 2 large US tertiary care centers were studied. We included patients admitted to the hospital from the ED with suspected infection. We investigated the association of diabetes and inhospital mortality within each cohort separately and then overall with logistic regression and generalized estimating equations adjusted for age, sex, disease severity, and sepsis syndrome. We also tested for an interaction between diabetes and hyperglycemia/hypoglycemia.

RESULTS

A total of 7,754 patients were included. The mortality rate was 4.3% (95% confidence interval [CI] 3.9% to 4.8%) and similar in diabetic and nondiabetic patients (4.1% versus 4.4%; absolute risk difference 0.4%; 95% CI -0.7% to 1.4%). There was no significant association between diabetes and mortality in adjusted analysis (odds ratio [OR] overall 0.85; 95% CI 0.71 to 1.01). Diabetes significantly modified the effect of hyperglycemia and hypoglycemia with mortality; initial glucose levels greater than 200 mg/dL were associated with higher mortality in nondiabetic patients (OR 2.1; 95% CI 1.4 to 3.0) but not in diabetic patients (OR 1.0; 95% CI 0.2 to 4.7), whereas glucose levels less than 100 mg/dL were associated with higher mortality mainly in the diabetic population (OR 2.3; 95% CI 1.6 to 3.3) and to a lesser extent in nondiabetic patients (OR 1.1; 95% CI 1.03 to 1.14).

CONCLUSION

We found no evidence for a harmful association of diabetes and mortality in patients across different sepsis severities. High initial glucose levels were associated with adverse outcomes in the nondiabetic population only. Further investigation is warranted to determine the mechanism for these effects.

Early career academic productivity among emergency physicians with R01 grant funding

OBJECTIVES

The objective was to describe the early academic career activities of emergency physician (EP) scientists with recent Research Project Grant Program (R01) grant funding from the National Institutes of Health (NIH).

METHODS

The curricula vitae of all EP scientists in the United States currently funded by the NIH were analyzed for evidence of advanced research training and frequency and type of publication and grant writing. Each investigator was surveyed for demographic features and estimation of protected time during their early career development.

RESULTS

Eighteen investigators were identified. The median length of time from completion of residency to receipt of their first R01 grant was 11 years (interquartile range [IQR] = 11 to 15 years), and the median age of investigators at the time of this award was 43 years (IQR = 39 to 47 years). At the time of their award, researchers were publishing five peer-reviewed manuscripts a year (IQR = 1 to 8 manuscripts) and had already received considerable external funding. Ninety-four percent of those studied had pursued a research fellowship, an advanced degree, or an NIH K-award following residency.

CONCLUSIONS

For EPs, receipt of an R01 from the NIH requires more than a decade of work following the completion of training. This period is characterized by pursuit of advanced research training, active and accelerating publication and collaboration, and acquisition of smaller extramural grants.

Prospective trial of real-time electronic surveillance to expedite early care of severe sepsis

STUDY OBJECTIVE

An automated, real-time electronic medical record query and caregiver notification system was developed and examined for its utility in improving sepsis care. We hypothesize that the algorithm will increase the rate and timeliness of sampling of blood lactate and blood cultures, performance of chest radiography, and provision of antibiotics.

METHODS

A before-and-after, prospective study with consecutive enrollment examined an algorithm that automatically identified adult patients accumulating 2 or more systemic inflammatory response syndrome (SIRS) criteria and 2 or more blood pressure measurements less than or equal to 90 mm Hg during their emergency department (ED) stay. In phase 1, the system collected information but did not alert caregivers. In phase 2, caregivers were notified by alphanumeric paging and a text entry into the electronic medical record of the patients' potential illness and were provided with specific recommendations.

RESULTS

Patients (33,460) were screened during 6 months; 398 patients activated the system, including 184 (46%) appropriately identified as severely septic. The algorithm had a 54% positive predictive value and 99% negative predictive value in detecting severe infection with acute organ dysfunction. The median time for patients to accumulate SIRS and blood pressure criteria was 152 minutes (interquartile range [IQR] 71 to 284 minutes), underscoring the dynamic nature of diagnosing critical illness in the emergency setting and the need for detection algorithms to repeatedly assess patients during their evaluation. After implementation, 2 interventions were performed more frequently, chest radiograph before admission (odds ratio 3.2; 95% confidence interval 1.1 to 9.5) and collection of blood cultures (odds ratio 2.9; 95% confidence interval 1.1 to 7.7). Only blood culture testing was performed significantly faster in the presence of decision support (median time to culture before intervention 86 minutes, IQR 31, 296 minutes; median time to culture after intervention 81 minutes, IQR 37, 245 minutes; P=.032 by Cox proportional hazards modeling). The predominant shortcoming of the strategy was failing to detect severely septic cases before caregivers.

CONCLUSION

An automated algorithm for detecting potential sepsis increased the frequency and timeliness of some ED interventions for severe sepsis. Future efforts need to identify patient features present earlier in ED evaluation than SIRS and hypotension.

Complement activation in emergency department patients with severe sepsis

OBJECTIVES

This study assessed the extent and mechanism of complement activation in community-acquired sepsis at presentation to the emergency department (ED) and following 24 hours of quantitative resuscitation.

METHODS

A prospective pilot study of patients with severe sepsis and healthy controls was conducted among individuals presenting to a tertiary care ED. Resuscitation, including antibiotics and therapies to normalize central venous and mean arterial pressure (MAP) and central venous oxygenation, was performed on all patients. Serum levels of Factor Bb (alternative pathway), C4d (classical and mannose-binding lectin [MBL] pathway), C3, C3a, and C5a were determined at presentation and 24 hours later among patients.

RESULTS

Twenty patients and 10 healthy volunteer controls were enrolled. Compared to volunteers, all proteins measured were abnormally higher among septic patients (C4d 3.5-fold; Factor Bb 6.1-fold; C3 0.8-fold; C3a 11.6-fold; C5a 1.8-fold). Elevations in C5a were most strongly correlated with alternative pathway activation. Surprisingly, a slight but significant inverse relationship between illness severity (by sequential organ failure assessment [SOFA] score) and C5a levels at presentation was noted. Twenty-four hours of structured resuscitation did not, on average, affect any of the mediators studied.

CONCLUSIONS

Patients with community-acquired sepsis have extensive complement activation, particularly of the alternative pathway, at the time of presentation that was not significantly reversed by 24 hours of aggressive resuscitation.

Dynamics of human complement-mediated killing of Klebsiella pneumoniae

With an in vitro system that used a luminescent strain of Klebsiella pneumoniae to assess bacterial metabolic activity in near-real-time, we investigated the dynamics of complement-mediated attack in healthy individuals and in patients presenting to the emergency department with community-acquired severe sepsis. A novel mathematical/statistical model was developed to simplify light output trajectories over time into two fitted parameters, the rate of complement activation and the delay from activation to the onset of killing. Using Factor B-depleted serum, the alternative pathway was found to be the primary bactericidal effector: In the absence of B, C3 opsonization as measured by flow cytometry did not progress and bacteria proliferated near exponentially. Defects in bacterial killing were easily demonstrable in patients with severe sepsis compared with healthy volunteers. In most patients with sepsis, the rate of activation was higher than in normal subjects but was associated with a prolonged delay between activation and bacterial killing (P < 0.05 for both). Theoretical modeling suggested that this combination of accentuated but delayed function should allow successful bacterial killing but with significantly greater complement activation. The use of luminescent bacteria allowed for the development of a novel and powerful tool for assessing complement immunology for the purposes of mechanistic study and patient evaluation.

Accuracy of non-contact infrared thermometry versus rectal thermometry in young children evaluated in the emergency department for fever

OBJECTIVE

We evaluated the accuracy of a non-contact infrared thermometer compared with a rectal thermometer.

METHODS

Two hundred patients, ages 1 month to 4 years, were included in the study. Each child underwent contemporaneous standard rectal thermometry and mid forehead non-contact infrared thermometry. Clinical features, including chief complaint, recently administered antipyretic agents, and ambient temperature at the time of measurement, were included.

ANALYSIS

Linear models were used to compare agreement between the 2 techniques, as well as to determine bias of infrared thermometry at different rectal temperatures. Multivariate linear models were used to evaluate the impact of clinical variables and ambient temperature.

RESULTS

A linear relationship between rectal and infrared temperature measurements was observed; however, the coefficient of determination (r(2)) value between was only 0.48 (P < 0.01). Infrared thermometry tended to overestimate the temperature of afebrile children and underestimate the temperature of febrile patients (P < .01). Ambient temperature and child age did not affect the accuracy of the device.

CONCLUSION

In this study, non-contact infrared thermometry did not sufficiently agree with rectal thermometer to indicate its routine use.

Flexible microfluidic device for mechanical property characterization of soft viscoelastic solids such as bacterial biofilms

We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by the application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis with an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and the transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young's moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102-105 Pa. The flexible microfluidic rheometer addresses the need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food, and consumer products. It requires only 200 pL of the test specimen.

Antibacterial properties of an iron-based hemostatic agent in vitro and in a rat wound model

OBJECTIVES

Topical hemostatic agents are currently employed on the battlefield for control of major hemorrhage and have potential for use in civilian settings. Some of these compounds may also be antibacterial. Given the behavior of these compounds, the purpose of this study was to assess the potential antibacterial properties of an iron oxyacid-based topical hemostatic agent against three problematic species of wound-contaminating microorganisms: Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and methicillin-resistant Staphylococcus epidermidis.

METHODS

Bacteria were treated in vitro with the test powder for 30 minutes and then assessed for viability. Long-term (8-hour) inhibition of bacterial growth was also examined. In vivo, a rat full-thickness 1-cm(2) skin wound was studied. Wounds were contaminated, treated, and then quantitatively cultured 24 hours later.

RESULTS

The lethal dose for 99% of the organisms (LD(99)) for the compound against each organism ranged from 0.89 (+/-0.28) to 4.77 (+/-0.66) mg/mL (p < 0.05). The compound produced sustained inhibition over 8 hours at both 1 and 5 mg/mL (p < 0.05 for each), for P. aeruginosa, S. epidermidis, and S. aureus. In vivo, activity was noted against only P. aeruginosa, with the largest magnitude reduction being on the order of 3-log colony-forming units (CFU; p < 0.01).

CONCLUSIONS

The iron-based agent studied possesses significant in vitro and lesser in vivo antibacterial effects. Further optimization of the delivery, dosing, and evaluation of this agent in a larger animal model with more humanlike skin structures may reveal important wound effects beyond control of bleeding.

Factors associated with survival in infants with congenital diaphragmatic hernia requiring extracorporeal membrane oxygenation: a report from the Congenital Diaphragmatic Hernia Study Group

OBJECTIVE

To identify factors associated with survival in patients with congenital diaphragmatic hernia (CDH) treated with extracorporeal membrane oxygenation (ECMO).

METHODS

We retrospectively analyzed the data on 3100 patients with CDH in the Congenital Diaphragmatic Hernia Study Group from 82 participating pediatric surgical centers (1995-2004). Covariates considered included prenatal and perinatal clinical information, specifics of surgical repair, and the duration of extracorporeal support.

RESULT

Nine hundred seven patients from the registry were identified as having been both managed with ECMO and undergone attempted surgical repair. The survival rate for the entire Congenital Diaphragmatic Hernia Study Group registry was 67% and 61% for those receiving ECMO in whom repair was attempted (P < .001). Among ECMO-treated children, survivors had a greater estimated gestational age (38 +/- 2 vs 37 +/- 2 weeks; P < .01), greater birth weights (3.2 +/- 0.5 vs 2.9 +/- 0.5 kg; P < .001), were less often prenatally diagnosed (53% vs 63%; P < .01), and were on ECMO for a shorter period of time (9 +/- 5 vs 12 +/- 5 days; P < .001). In logistic regression models, therapy-related variables, including the duration of ECMO, the nature of diaphragmatic repair, and the type of abdominal closure and certain comorbidities, particularly the presence of a concomitant severe cardiac abnormality, were independently associated with outcome.

CONCLUSION

Our model identifies a group of pre-surgical and postsurgical parameters that predict survival rate in patients with CDH on ECMO support. This model was derived from the retrospective data from a large database and will need to be prospectively tested.

Forecasting models of emergency department crowding

OBJECTIVES

The authors investigated whether models using time series methods can generate accurate short-term forecasts of emergency department (ED) bed occupancy, using traditional historical averages models as comparison.

METHODS

From July 2005 through June 2006, retrospective hourly ED bed occupancy values were collected from three tertiary care hospitals. Three models of ED bed occupancy were developed for each site: 1) hourly historical average, 2) seasonal autoregressive integrated moving average (ARIMA), and 3) sinusoidal with an autoregression (AR)-structured error term. Goodness of fits were compared using log likelihood and Akaike's Information Criterion (AIC). The accuracies of 4- and 12-hour forecasts were evaluated by comparing model forecasts to actual observed bed occupancy with root mean square (RMS) error. Sensitivity of prediction errors to model training time was evaluated, as well.

RESULTS

The seasonal ARIMA outperformed the historical average in complexity adjusted goodness of fit (AIC). Both AR-based models had significantly better forecast accuracy for the 4- and the 12-hour forecasts of ED bed occupancy (analysis of variance [ANOVA] p < 0.01), compared to the historical average. The AR-based models did not differ significantly from each other in their performance. Model prediction errors did not show appreciable sensitivity to model training times greater than 7 days.

CONCLUSIONS

Both a sinusoidal model with AR-structured error term and a seasonal ARIMA model were found to robustly forecast ED bed occupancy 4 and 12 hours in advance at three different EDs, without needing data input beyond bed occupancy in the preceding hours.

Real-time identification of serious infection in geriatric patients using clinical information system surveillance

OBJECTIVES

To develop and characterize an automated syndromic surveillance mechanism for early identification of older emergency department (ED) patients with possible life-threatening infection.

DESIGN

Prospective, consecutive-enrollment, single-site observational study.

SETTING

A large university medical center with an annual ED census of 75,273.

PARTICIPANTS

Patients aged 70 and older admitted to the ED and having two or more systemic inflammatory response syndrome (SIRS) criteria during their ED stay.

MEASUREMENTS

A search algorithm was developed to screen the census of the ED through its clinical information system. A study coordinator confirmed all patients electronically identified as having a probable infectious explanation for their visit.

RESULTS

Infection accounted for 28% of ED and 34% of final hospital diagnoses. Identification using the software tool alone carried a 1.63 relative risk of infection (95% confidence interval CI51.09-2.44) compared with other ED patients sufficiently ill to require admission. Follow-up confirmation by a study coordinator increased the risk to 3.06 (95% CI52.11-4.44). The sensitivity of the strategy overall wasmodest (14%), but patients identified were likely to have an infectious diagnosis (specificity 598%). The most common SIRS criterion triggering the electronic notification was the combination of tachycardia and tachypnea.

CONCLUSION

A simple clinical informatics algorithm can detect infection in elderly patients in real time with high specificity. The utility of this tool for research and clinical care may be substantial.

In vitro and in silico analysis of annexin V binding to lymphocytes as a biomarker in emergency department sepsis studies

BACKGROUND

Peripheral blood lymphocyte apoptosis is a recognized feature of serious infection and sepsis and can be easily quantified by flow cytometric measurement of annexin V binding to the cell surface. Use of apoptosis as a biomarker in emergency department (ED) studies of sepsis is potentially difficult because of sample processing requirements and limited availability of a research cytometer with which to measure patient samples.

OBJECTIVES

To assess, in vitro and in simulation, the relationship between sample stability, timing of patient enrollment, and diagnostic performance of a flow cytometric assay for sepsis in patients evaluated in EDs.

METHODS

Assuming any clinical trial would require daily sample batching, the authors measured the stability of lymphocyte samples over time, noting the rate at which annexin V-negative cells became positive as ED processing delays increased. With these data, they then optimized a study design that could evaluate lymphocyte apoptosis as a sepsis biomarker by using a series of Monte Carlo-based simulated clinical trials.

RESULTS

The authors found that annexin V-negative lymphocytes become positive during storage delays that would be encountered in an ED sepsis trial. The extent of this deterioration was least among cells left as whole blood at room temperature until just before analysis or when lymphocytes were isolated early and stored in culture media at 4 degrees C until analysis. When the expected rate of sample deterioration was considered in simulated clinical trials, an inverse relationship was found between the rate at which patients are enrolled and the best achievable receiver operating characteristic curve a study could produce.

CONCLUSIONS

Peripheral blood samples being analyzed for lymphocyte apoptosis degrade at a rate relevant to the design of ED trials of sepsis. Because of sample processing delays inherent in studying unscheduled septic patients, the performance of annexin V binding as a biomarker for sepsis can approach, but not be expected to exceed, its performance in a comparable intensive care unit-based study.

Lipopolysaccharide O-antigen promotes persistent murine bacteremia

Bacteremia is a common complication of pneumonia with Klebsiella pneumoniae. In the previous work, we have shown that the lipopolysaccharide (LPS) O-antigen in K. pneumoniae O1:K2 contributes to lethality during pneumonia in part by promoting bacteremia. In the current work, we studied an O-antigen-deficient K. pneumoniae strain to further evaluate this polysaccharide's role in bloodstream infection. Cultured macrophage and murine bacteremia models were studied. In vitro, O-antigen-deficient bacteria, compared with wild-type organisms, were stronger activators of the murine alveolar macrophage cell line MH-S as assessed by nuclear localization of RelA/p65 and by secretion of cytokines and chemokines. O-antigen-deficient Klebsiellae were also more susceptible to killing by murine neutrophils. In vivo, the absence of O-antigen allowed more rapid and complete clearance of bacteria from the bloodstream, liver, and spleen after intravenous injection in mice. Survival was also greater among animals infected with bacteria missing the O-antigen. Gene expression profiling (via reverse transcriptase-polymerase chain reaction of 84 inflammatory mediator complementary DNA) revealed that by 24 h postinfection, the livers and spleens of animals infected with O-antigen-deficient organisms had significantly downregulated cytokine and chemokine expression compared with wild-type infected animals. The O-antigen surface carbohydrate of O1:K2 serotype K. pneumoniae appears to contribute to bacterial virulence by lessening the activation of macrophages, conveying resistance to killing by neutrophils, and by promoting persistent infection in the blood, liver, and spleen after the onset of bacteremia.

The role of complement C3 in intracerebral hemorrhage-induced brain injury

Activation of the complement cascade contributes to brain injury after intracerebral hemorrhage (ICH). However, a recent study found that complement C5 deficient mice had enhanced ICH-induced brain injury. The present study, therefore, investigated the role of complement C3 (which is upstream from C5) in ICH. Male complement C3 deficient and sufficient mice had an intracerebral infusion of 30-muL autologous whole blood. The mice were killed and the brains were sampled for edema, Western blotting, immunohistochemistry and histologic analysis. Behavioral tests including forelimb use asymmetry test and corner turn were also performed before and after ICH. Compared to complement C3 sufficient mice, C3 deficient mice had less brain edema, lower hemeoxygenase-1 levels, less microglia activation and neutrophil infiltration around the clot after ICH. In addition, the C3-deficient mice had less ICH-induced forelimb use asymmetry deficits compared with C3-sufficient mice. These results suggest complement activation may affect heme metabolism and the inflammatory response after ICH suggesting that complement C3 is an important factor causing ICH-induced brain injury.

Generation of C5a in the absence of C3: a new complement activation pathway

Complement-mediated tissue injury in humans occurs upon deposition of immune complexes, such as in autoimmune diseases and acute respiratory distress syndrome. Acute lung inflammatory injury in wild-type and C3-/- mice after deposition of IgG immune complexes was of equivalent intensity and was C5a dependent, but injury was greatly attenuated in Hc-/- mice (Hc encodes C5). Injury in lungs of C3-/- mice and C5a levels in bronchoalveolar lavage (BAL) fluids from these mice were greatly reduced in the presence of antithrombin III (ATIII) or hirudin but were not reduced in similarly treated C3+/+ mice. Plasma from C3-/- mice contained threefold higher levels of thrombin activity compared to plasma from C3+/+ mice. There were higher levels of F2 mRNA (encoding prothrombin) as well as prothrombin and thrombin protein in liver of C3-/- mice compared to C3+/+ mice. A potent solid-phase C5 convertase was generated using plasma from either C3+/+ or C3-/- mice. Human C5 incubated with thrombin generated C5a that was biologically active. These data suggest that, in the genetic absence of C3, thrombin substitutes for the C3-dependent C5 convertase. This linkage between the complement and coagulation pathways may represent a new pathway of complement activation.

Harmful and protective roles of neutrophils in sepsis

The current studies demonstrate protective and harmful effects of neutrophils (PMN) during experimental sepsis after cecal ligation and puncture (CLP). It is known that CLP induces signaling defects in blood PMN. When PMN were depleted 12 h after CLP, there were dramatic reductions in levels of bacteremia, evidence for reduced liver and renal dysfunction, sharp reductions in serum levels of cytokines (IL-1beta, IL-6, IL-10, TNF-alpha, and IL-2), and improved survival. In contrast, PMN depletion before CLP resulted in substantial increases in bacteremia and no evidence for attenuation of liver and renal failure dysfunction. These data suggest that at the onset of sepsis, PMN are important in regulating the levels of bacteremia, whereas after the onset of sepsis, as they lose innate immune functions, their presence is associated with higher levels of bacteremia and intensified organ dysfunction.

Intracerebral hemorrhage in complement C3-deficient mice

The complement cascade is activated and contributes to brain damage after intracerebral hemorrhage (ICH). The present study investigated ICH-induced brain damage in complement C3-deficient mice. This study was divided into 2 parts. Male C3-deficient and C3-sufficient mice received an infusion of 30-microl autologous whole blood into the right basal ganglia. In the first part of our study, mice were killed 3 days later for brain water content measurement. Behavioral assessments including forelimb use asymmetry and corner turn tests were also preformed before and after ICH. In the second part of the study, brain heme oxygenase-1 (HO-1) was measured by Western blot analysis and immunohistochemistry 3 days after the infusion. We found that brain water content in the ipsilateral basal ganglia 3 days after ICH was less in C3-deficient mice compared to C3-sufficient mice (p < 0.05). The C3-deficient mice had reduced ICH-induced forelimb use asymmetry deficits compared with C3-sufficient mice (p < 0.05), although there was no significant difference in the corner turn test score. Western blot analysis showed that HO-1 contents were significantly lower in C3-deficient mice (day 3: 2024 +/- 560 vs. 5140 +/- 1151 pixels in the C3-sufficient mice, p < 0.05). We conclude that ICH causes less brain edema and behavioral deficits in complement C3-deficient mice. These results suggest that complement C3 is a key factor contributing to brain injury following ICH.

Acute respiratory infection with mouse adenovirus type 1

Studies of the pathogenesis of adenovirus respiratory disease are limited by the strict species-specificity of the adenoviruses. Following intranasal inoculation of adult C57BL/6 mice with mouse adenovirus type 1 (MAV-1), we detected MAV-1 early region 3 (E3) and hexon gene expression in the lungs at 7 days post-infection (dpi). We detected MAV-1 E3 protein in the respiratory epithelium at 7 dpi. We did not detect viral mRNA or protein at 14 dpi, but MAV-1 DNA was detected by PCR at 21 dpi. Chemokine transcript levels increased between 7 and 14 dpi in the lungs of infected mice. MAV-1 infection induced a patchy cellular infiltrate in lungs at 7 and 14 dpi. This is the first report demonstrating the presence of MAV-1 in the respiratory epithelium of infected mice and describing chemokine responses in the lung induced by MAV-1 respiratory infection. MAV-1 infection of mice has the potential to serve as a model for inflammatory changes seen in human adenovirus respiratory disease.

Dynamics of intrapulmonary bacterial growth in a murine model of repeated microaspiration

To study the change in intrapulmonary bacterial growth rate over time during Gram-negative pneumonia, a two-hit model of recurrent bacterial aspiration was developed in mice. A mutant of Klebsiella pneumoniae was isolated that could be distinguished from the wild type when cultured on appropriate media. These strains were intranasally administered, 4 h apart, to mice whose lungs were quantitatively cultured 24 h later. The relative burden of each aspirated inoculum was determined, and, using the administered dose and the number of bacteria from each inoculum present at the end of the experiment, first-order growth constants for each inoculum were calculated. Results indicate that after an initial aspiration of this organism, subsequently aspirated bacteria proliferate more slowly. When two aspirations occurred 4 h apart, the bacteria aspirated first represented 96% of total lung burden at 24 h. The growth constant of the second inoculum was related to the magnitude of the first inoculum in an inverse, nonlinear fashion. When parallel experiments were performed in complement C3-deficient mice, no suppression of the second inoculum was noted, suggesting that early upregulation of antibacterial activity in the lung is a C3-mediated event.

Complement C5 and early oxygen kinetics during murine sepsis

OBJECTIVES

Changes in oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) are common but poorly understood features of sepsis. The authors studied the role of complement C5 in the development of abnormal oxygen kinetics during sepsis in mice, arguing that as a pro-inflammatory event, complement activation might exacerbate disturbances in oxygen use during abdominal sepsis.

METHODS

An open-circuit indirect calorimeter was used to measure VO(2), VCO(2), and respiratory exchange ratio during a seven-day median lethal dose (LD(50)) murine cecal ligation and puncture (CLP) model.

RESULTS

CLP produced significant changes in oxygen kinetics within three hours of onset, although when the animals were stratified by seven-day survival, no difference in these abnormalities was seen between the survivors and the nonsurvivors. Genetic deficiency of C5 did not ameliorate the changes in oxygen utilization. Rather, the C5-deficient mice experienced more severe abnormalities in oxygen kinetics and greater mortality. Treating animals with anti-C5a antibodies at the time of injury had little effect on oxygen kinetics, indicating that C5b, rather than C5a, was predominantly acting to protect the mice during the first 24 hours of illness.

CONCLUSIONS

These findings indicate that the primary contribution of C5 to oxygen kinetics during sepsis is salutary through the host defense conveyed by generation of C5b, rather than detrimental by worsening oxygen utilization via pro-inflammatory mechanisms.

The Klebsiella pneumoniae O antigen contributes to bacteremia and lethality during murine pneumonia

Bacterial surface carbohydrates are important pathogenic factors in gram-negative pneumonia infections. Among these factors, O antigen has been reported to protect pathogens against complement-mediated killing. To examine further the role of O antigen, we insertionally inactivated the gene encoding a galactosyltransferase necessary for serotype O1 O-antigen synthesis (wbbO) from Klebsiella pneumoniae 43816. Analysis of the mutant lipopolysaccharide by sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed the absence of O antigen. In vitro, there were no detectable differences between wild-type K. pneumoniae and the O-antigen-deficient mutant in regard to avid binding by murine complement C3 or resistance to serum- or whole-blood-mediated killing. Nevertheless, the 72-h 50% lethal dose of the wild-type strain was 30-fold greater than that of the mutant (2 x 10(3) versus 6 x 10(4) CFU) after intratracheal injection in ICR strain mice. Despite being less lethal, the mutant organism exhibited comparable intrapulmonary proliferation at 24 h compared to the level of the wild type. Whole-lung chemokine expression (CCL3 and CXCL2) and bronchoalveolar inflammatory cell content were also similar between the two infections. However, whereas the wild-type organism produced bacteremia within 24 h of infection in every instance, bacteremia was not seen in mutant-infected mice. These results suggest that during murine pneumonia caused by K. pneumoniae, O antigen contributes to lethality by increasing the propensity for bacteremia and not by significantly changing the early course of intrapulmonary infection.

Murine complement interactions with Pseudomonas aeruginosa and their consequences during pneumonia

Complement is necessary for defense against lung infection with Pseudomonas aeruginosa in mice. We studied in vitro interactions between complement and P. aeruginosa and in vivo effects of complement depletion to better understand this relationship. In vitro, P. aeruginosa strain UI-18 was resistant to killing by mouse serum. However, C3 opsonized the organism (via the alternative and mannose binding lectin [MBL] pathways), and C5 convertase activity on the bacterial surface was demonstrated. In vivo, compared with normal mice, complement-deficient mice experienced higher mortality and failed to sterilize their bronchoalveolar space within 24 h of inoculation. These changes did not seem to be a result of decreased inflammation because complement-deficient mice had normal neutrophil recruitment, greater lung myeloperoxidase content, and, by 24 h, a 35-fold higher level of the CXC chemokine KC. Lung static pressure-volume curves were abnormal in infected animals but were significantly more so in complement deficient mice. These data indicate that although P. aeruginosa is resistant to serum killing, C3 opsonization and C5 convertase assembly occur on its surface. This interaction in vivo plays a central role in host survival beyond just recruitment and activation of phagocytes and may serve to limit the inflammatory response to and tissue injury resulting from bacterial infection.

Status report: Development of emergency medicine research since the Macy Report

In Williamsburg, VA, April 17 to 20, 1994, the Josiah Macy, Jr. Foundation sponsored a conference entitled "The Role of Emergency Medicine in the Future of American Medical Care," a report on which was published in Annals in 1995. This report promulgated recommendations for the development and enhancement of academic departments of emergency medicine and a conference to develop an agenda for research in emergency medicine. The American College of Emergency Physicians' Research Committee, along with several ad hoc members, presents updates in several of the areas addressed by the Macy Report and subsequent conferences, as a status report for the development of emergency medicine research as a whole, as of late 2002.

Inhibition of prostaglandin synthesis during polystyrene microsphere-induced pulmonary embolism in the rat

Our objective was to test the effect of inhibition of thromboxane synthase versus inhibition of cyclooxygenase (COX)-1/2 on pulmonary gas exchange and heart function during simulated pulmonary embolism (PE) in the rat. PE was induced in rats via intrajugular injection of polystyrene microspheres (25 micro m). Rats were randomized to one of three posttreatments: 1) placebo (saline), 2) thromboxane synthase inhibition (furegrelate sodium), or 3) COX-1/2 inhibition (ketorolac tromethamine). Control rats received no PE. Compared with controls, placebo rats had increased thromboxane B(2) (TxB(2)) in bronchoalveolar lavage fluid and increased urinary dinor TxB(2). Furegrelate and ketorolac treatments reduced TxB(2) and dinor TxB(2) to control levels or lower. Both treatments significantly decreased the alveolar dead space fraction, but neither treatment altered arterial oxygenation compared with placebo. Ketorolac increased in vivo mean arterial pressure and ex vivo left ventricular pressure (LVP) and right ventricular pressure (RVP). Furegrelate improved RVP but not LVP. Experimental PE increased lung and systemic production of TxB(2). Inhibition at the COX-1/2 enzyme was equally as effective as inhibition of thromboxane synthase at reducing alveolar dead space and improving heart function after PE.

Segmental hemodynamics during partial liquid ventilation in isolated rat lungs

Partial liquid ventilation (PLV) is a means of ventilatory support in which gas ventilation is carried out in a lung partially filled with a perfluorocarbon liquid capable of supporting gas exchange. Recently, this technique has been proposed as an adjunctive therapy for cardiac arrest, during which PLV with cold perfluorocarbons might rapidly cool the intrathoracic contents and promote cerebral protective hypothermia while not interfering with gas exchange. A concern during such therapy will be the effect of PLV on pulmonary hemodynamics during very low blood flow conditions. In the current study, segmental (i.e. precapillary, capillary, and postcapillary) hemodynamics were studied in the rat lung using a standard isolated lung perfusion system at a flow rate of 6 ml/min ( approximately 5% normal cardiac output). Lungs received either gas ventilation or 5 or 10 ml/kg PLV. Segmental pressures and vascular resistances were determined, as was transcapillary fluid flux. The relationship between individual hemodynamic parameters and PLV dose was examined using linear regression, with n=5 in each study group. PLV at both the 5 and 10 ml/kg dose produced no detectable changes in pulmonary blood flow or in transcapillary fluid flux (all R(2) values<0.20).

CONCLUSION

In an isolated perfused lung model of low flow conditions, normal segmental hemodynamic behavior was preserved during liquid ventilation. These data support further investigation of this technique as an adjunct to cardiopulmonary resuscitation.