ß-Variational autoencoders and transformers for reduced-order modelling of fluid flows.

Variational autoencoder architectures have the potential to develop reduced-order models for chaotic fluid flows. We propose a method for learning compact and near-orthogonal reduced-order models using a combination of a ß-variational autoencoder and a transformer, tested on numerical data from a two-dimensional viscous flow in both periodic and chaotic regimes. The ß-variational autoencoder is trained to learn a compact latent representation of the flow velocity, and the transformer is trained to predict the temporal dynamics in latent-space. Using the ß-variational autoencoder to learn disentangled representations in latent-space, we obtain a more interpretable flow model with features that resemble those observed in the proper orthogonal decomposition, but with a more efficient representation. Using Poincaré maps, the results show that our method can capture the underlying dynamics of the flow outperforming other prediction models. The proposed method has potential applications in other fields such as weather forecasting, structural dynamics or biomedical engineering.

The effect of gender dyads on the quality of narrative assessments of general surgery trainees.

BACKGROUND: Prior studies have shown that gender can influence how learners are assessed and the feedback they receive. We investigated the quality of faculty narrative comments in general surgery trainee evaluation using trainee-assessor gender dyads. METHODS: Narrative assessments of surgical trainees at the University of British Columbia were collected and rated using the McMaster Narrative Comment Rating Scale (MNCRS). Variables from the MNCRS were inputted into a generalized linear mixed model to explore the impact of gender dyads on the quality of narrative feedback. RESULTS: 2,469 assessments were collected. Women assessors tended to give higher-quality comments (p's < 0.05) than men assessors. Comments from men assessors to women trainees were significantly more positive than comments from men assessors to men trainees (p = 0.02). Men assessors also tended to give women trainees more reinforcing than corrective comments than to men trainees (p < 0.01). CONCLUSIONS: There are significant differences in the quality of faculty feedback to trainees by gender dyads. A range of solutions to improve and reduce differences in feedback quality are discussed.

Integrating multi-fidelity blood flow data with reduced-order data assimilation.

High-fidelity patient-specific modeling of cardiovascular flows and hemodynamics is challenging. Direct blood flow measurement inside the body with in-vivo measurement modalities such as 4D flow magnetic resonance imaging (4D flow MRI) suffer from low resolution and acquisition noise. In-vitro experimental modeling and patient-specific computational fluid dynamics (CFD) models are subject to uncertainty in patient-specific boundary conditions and model parameters. Furthermore, collecting blood flow data in the near-wall region (e.g., wall shear stress) with experimental measurement modalities poses additional challenges. In this study, a computationally efficient data assimilation method called reduced-order modeling Kalman filter (ROM-KF) was proposed, which combined a sequential Kalman filter with reduced-order modeling using a linear model provided by dynamic mode decomposition (DMD). The goal of ROM-KF was to overcome low resolution and noise in experimental and uncertainty in CFD modeling of cardiovascular flows. The accuracy of the method was assessed with 1D Womersley flow, 2D idealized aneurysm, and 3D patient-specific cerebral aneurysm models. Synthetic experimental data were used to enable direct quantification of errors using benchmark datasets. The accuracy of ROM-KF in reconstructing near-wall hemodynamics was assessed by applying the method to problems where near-wall blood flow data were missing in the experimental dataset. The ROM-KF method provided blood flow data that were more accurate than the computational and synthetic experimental datasets and improved near-wall hemodynamics quantification.

Data-driven cardiovascular flow modelling: examples and opportunities.

High-fidelity blood flow modelling is crucial for enhancing our understanding of cardiovascular disease. Despite significant advances in computational and experimental characterization of blood flow, the knowledge that we can acquire from such investigations remains limited by the presence of uncertainty in parameters, low resolution, and measurement noise. Additionally, extracting useful information from these datasets is challenging. Data-driven modelling techniques have the potential to overcome these challenges and transform cardiovascular flow modelling. Here, we review several data-driven modelling techniques, highlight the common ideas and principles that emerge across numerous such techniques, and provide illustrative examples of how they could be used in the context of cardiovascular fluid mechanics. In particular, we discuss principal component analysis (PCA), robust PCA, compressed sensing, the Kalman filter for data assimilation, low-rank data recovery, and several additional methods for reduced-order modelling of cardiovascular flows, including the dynamic mode decomposition and the sparse identification of nonlinear dynamics. All techniques are presented in the context of cardiovascular flows with simple examples. These data-driven modelling techniques have the potential to transform computational and experimental cardiovascular research, and we discuss challenges and opportunities in applying these techniques in the field, looking ultimately towards data-driven patient-specific blood flow modelling.

Brain Α-Tocopherol Concentration is Inversely Associated with Neurofibrillary Tangle Counts in Brain Regions Affected in Earlier Braak Stages: A Cross-Sectional Finding in the Oldest Old.

Objectives: Higher vitamin E status has been associated with lower risk of Alzheimer's disease (AD). However, evidence of the association of vitamin E concentration in neural tissue with AD pathologies is limited. Design: The cross-sectional relationship between the human brain concentrations of α- and γ-tocopherol and the severity of AD pathologies - neurofibrillary tangle (NFT) and neuritic plaque (NP) - was investigated. Setting & Participants: Brains from 43 centenarians (≥ 98 years at death) enrolled in the Phase III of the Georgia Centenarian Study were collected at autopsy. Measurements: Brain α- and γ-tocopherol concentrations (previously reported) were averaged from frontal, temporal, and occipital cortices. NP and NFT counts (previously reported) were assessed in frontal, temporal, parietal, entorhinal cortices, amygdala, hippocampus, and subiculum. NFT topological progression was assessed using Braak staging. Multiple linear regression was performed to assess the relationship between tocopherol concentrations and NP or NFT counts, with and without adjustment for covariates. Results: Brain α-tocopherol concentrations were inversely associated with NFT but not NP counts in amygdala (ß = -2.67, 95% CI [-4.57, -0.79]), entorhinal cortex (ß = -2.01, 95% CI [-3.72, -0.30]), hippocampus (ß = -2.23, 95% CI [-3.82, -0.64]), and subiculum (ß = -2.52, 95% CI [-4.42, -0.62]) where NFT present earlier in its topological progression, but not in neocortices. Subjects with Braak III-IV had lower α-tocopherol (median = 69,622 pmol/g, IQR = 54,389-72,155 pmol/g) than those with Braak I-II (median = 72,108 pmol/g, IQR = 64,056-82,430 pmol/g), but the difference was of borderline significance (p = 0.063). γ-Tocopherol concentrations were not associated with either NFT or NP counts in any brain regions assessed. Conclusions: Higher brain α-tocopherol level is specifically associated with lower NFT counts in brain structures affected in earlier Braak stages. Our findings emphasize the possible importance of α-tocopherol intervention timing in tauopathy progression and warrant future clinical trials.

B-Vitamin Therapy for Kidney Transplant Recipients Lowers Homocysteine and Improves Selective Cognitive Outcomes in the Randomized FAVORIT Ancillary Cognitive Trial.

BACKGROUND: Objectives: Elevated plasma total homocysteine (tHcy) is associated with increased risk of cardiovascular disease, stroke and dementia. Results of clinical trials using B-vitamins to reduce the cognitive risks attributed to tHcy have been inconsistent. The high prevalence of both hyperhomocysteinemia and cognitive impairment among kidney transplant recipients makes them an important population in which to evaluate the effect of lowering homocysteine on cognitive function. We therefore evaluated whether B-vitamin therapy to lower tHcy would prevent cognitive-decline in a cohort of stable kidney transplant recipients. DESIGN: The study was a longitudinal ancillary of the FAVORIT trial, a randomized, placebo-controlled multi-site trial of high-dose B vitamins to reduce cardiovascular and cerebrovascular events in clinically stable kidney transplant recipients with elevated tHcy. PARTICIPANTS: 584 participants from 18 sites across North America. INTERVENTION: The intervention consisted of a daily multivitamin containing high-doses of folate (5.0 mg), vitamin B12 (1.0 mg) and vitamin B6 (50 mg). The placebo consisted of a daily multi-vitamin containing no folate and recommended daily allowances of vitamins B12 and B6 (0 mg folate; 2.0 µg vitamin B12; 1.4 mg vitamin B6). MEASUREMENTS: Annual neuropsychological assessment for up to 5 years (mean 3.3 years) using a standardized test battery. Efficacy was analyzed on an intention-to-treat basis using end-of-trial data. Subgroup analyses included stratification for baseline plasma B-vitamin and tHcy concentrations. RESULTS: At baseline, cognitive impairment was common with 61% of participants falling more than one standard deviation below published norms for at least one cognitive test. Fewer than 1% of participants had insufficient plasma folate < 5 ng/ml or vitamin B12 < 148 pmol/L. However, 44.6% had plasma B6 concentrations < 30 nmol/L. At follow-up, processing speed and memory scores were modestly but significantly better in the B-vitamin supplement group than in controls (p≤0.05). There was no interaction between baseline tHcy, B-vitamin status and treatment on the cognitive outcomes. CONCLUSIONS: High-dose B-vitamin supplementation provided modest cognitive benefit for kidney transplant recipients with elevated baseline tHcy. Since nearly all participants were folate and vitamin B12 sufficient at baseline, the potential cognitive benefits of folate and B12 supplementation in individuals with poor B-vitamin status remains to be determined.

Indicator microbes correlate with pathogenic bacteria, yeasts and helminthes in sand at a subtropical recreational beach site.

AIMS: Research into the relationship between pathogens, faecal indicator microbes and environmental factors in beach sand has been limited, yet vital to the understanding of the microbial relationship between sand and the water column and to the improvement of criteria for better human health protection at beaches. The objectives of this study were to evaluate the presence and distribution of pathogens in various zones of beach sand (subtidal, intertidal and supratidal) and to assess their relationship with environmental parameters and indicator microbes at a non-point source subtropical marine beach. METHODS AND RESULTS: In this exploratory study in subtropical Miami (Florida, USA), beach sand samples were collected and analysed over the course of 6 days for several pathogens, microbial source tracking markers and indicator microbes. An inverse correlation between moisture content and most indicator microbes was found. Significant associations were identified between some indicator microbes and pathogens (such as nematode larvae and yeasts in the genus Candida), which are from classes of microbes that are rarely evaluated in the context of recreational beach use. CONCLUSIONS: Results indicate that indicator microbes may predict the presence of some of the pathogens, in particular helminthes, yeasts and the bacterial pathogen Staphylococcus aureus including methicillin-resistant forms. Indicator microbes may thus be useful for monitoring beach sand and water quality at non-point source beaches. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of both indicator microbes and pathogens in beach sand provides one possible explanation for human health effects reported at non-point sources beaches.

25-Hydroxyvitamin D, dementia, and cerebrovascular pathology in elders receiving home services.

BACKGROUND: Vitamin D deficiency has potential adverse effects on neurocognitive health and subcortical function. However, no studies have examined the association between vitamin D status, dementia, and cranial MRI indicators of cerebrovascular disease (CVD). METHODS: Cross-sectional investigation of 25-hydroxyvitamin D [25(OH)D], dementia, and MRI measures of CVD in elders receiving home care (aged 65-99 years) from 2003 to 2007. RESULTS: Among 318 participants, the mean age was 73.5 +/- 8.1 years, 231 (72.6%) were women, and 109 (34.3%) were black. 25(OH)D concentrations were deficient (<10 ng/mL) in 14.5% and insufficient (10-20 ng/mL) in 44.3% of participants. There were 76 participants (23.9%) with dementia, 41 of which were classified as probable AD. Mean 25(OH)D concentrations were lower in subjects with dementia (16.8 vs 20.0 ng/mL, p < 0.01). There was a higher prevalence of dementia among participants with 25(OH)D insufficiency (< or =20 ng/mL) (30.5% vs 14.5%, p < 0.01). 25(OH)D deficiency was associated with increased white matter hyperintensity volume (4.9 vs 2.9 mL, p < 0.01), grade (3.0 vs 2.2, p = 0.04), and prevalence of large vessel infarcts (10.1% vs 6.9%, p < 0.01). After adjustment for age, race, sex, body mass index, and education, 25(OH)D insufficiency (< or =20 ng/mL) was associated with more than twice the odds of all-cause dementia (odds ratio [OR] = 2.3, 95% confidence interval [CI] 1.2-4.2), Alzheimer disease (OR = 2.5, 95% CI 1.1-6.1), and stroke (with and without dementia symptoms) (OR = 2.0, 95% CI 1.0-4.0). CONCLUSIONS: Vitamin D insufficiency and deficiency was associated with all-cause dementia, Alzheimer disease, stroke (with and without dementia symptoms), and MRI indicators of cerebrovascular disease. These findings suggest a potential vasculoprotective role of vitamin D.

Simultaneous concentration of Enterococci and coliphage from marine waters using a dual layer filtration system.

Concentrating diverse microbes in a time and cost effective manner is an essential component in water quality monitoring of recreational beaches. Historically, detection of bacteria and viruses requires two different capture methods to detect both types of organisms in a given water sample. The purpose of this present study was to evaluate a newly devised dual layered filtration system, which was developed to simultaneously concentrate both viruses and bacteria in one step from marine waters. An apparatus was designed to accommodate two 90-mm diam., 0.45 microm pore size membranes in series, one on top of the other. The top polyvinylidene fluoride (PVDF) membrane was used to filter bacteria by physical straining while the bottom HA membrane retained viruses through adsorption. Results indicated that the dual layer filtration system recovered 83+/-14% of the test bacteria (Enterococcus fecalis) and 81+/-28% of the test virus (MS2 coliphage) on the top and bottom membranes, respectively. This research demonstrates the potential of using a dual layered filtration system for the simultaneous concentration of both bacteria and viruses on separate filters from recreational beach waters. This system is relatively simple to use, inexpensive, and has the potential to be suitable for routine monitoring. This study serves as a proof of concept for the technique. Additional experiments are needed to evaluate the system on a variety of different bacteria and viruses as well as on water with different physical and chemical parameters.

Multivitamin use and B vitamin status in a homebound elderly population.

OBJECTIVE: Homebound elderly are at increased risk for micronutrient deficiencies and nutritional status in this population has not been adequately described. There is evidence for beneficial effects of multivitamin use and a greater understanding of their nutritional contribution could identify behaviors that may help alleviate excess chronic disease. The purpose of this analysis is to investigate, in a racially diverse group of homebound elders, the association of multivitamin use with measures of plasma B vitamin concentrations. DESIGN: We examined the cross-sectional association between multivitamin use and plasma concentrations of B vitamins and homocysteine in 236 white and 182 black homebound elders (65-99y). Dietary intake was assessed and demographic and health information was ascertained. RESULTS: White and black elders had a high prevalence of dietary intakes below the Estimated Average Requirement for folate (38.1 and 40.7%), vitamin B6 (16.9 and 19.2%.), and vitamin B12 (3 and 3.9%) respectively. Multivitamin use was associated with higher mean plasma B vitamin concentrations in each group. In whites, multivitamin users had higher concentrations of vitamin B6 (64.6 vs. 32.4 nmol/L; p < 0.001), vitamin B12 (398 vs. 324 pmol/L;p < 0.001) and folate (39.4 vs. 30.4 nmol/L;p < 0.001). Black multivitamin users had higher concentrations of vitamin B6 (53.7 vs. 29.5 nmol/L; p < 0.001), B12 (427 vs. 372 pmol/L; p < 0.05) and folate (35.7 vs. 25.4 nmol/L; < 0.001) than non-users. CONCLUSIONS: Multivitamin supplementation was associated with higher mean plasma concentrations of vitamins B6, B12, and folate and lower prevalence of low plasma B vitamin status in a biracial homebound elderly.

Confirmation of putative stormwater impact on water quality at a Florida beach by microbial source tracking methods and structure of indicator organism populations.

The effect of a stormwater conveyance system on indicator bacteria levels at a Florida beach was assessed using microbial source tracking methods, and by investigating indicator bacteria population structure in water and sediments. During a rain event, regulatory standards for both fecal coliforms and Enterococcus spp. were exceeded, contrasting with significantly lower levels under dry conditions. Indicator bacteria levels were high in sediments under all conditions. The involvement of human sewage in the contamination was investigated using polymerase chain reaction (PCR) assays for the esp gene of Enterococcus faecium and for the conserved T antigen of human polyomaviruses, all of which were negative. BOX-PCR subtyping of Escherichia coli and Enterococcus showed higher population diversity during the rain event; and higher population similarity during dry conditions, suggesting that without fresh inputs, only a subset of the population survives the selective pressure of the secondary habitat. These data indicate that high indicator bacteria levels were attributable to a stormwater system that acted as a reservoir and conduit, flushing high levels of indicator bacteria to the beach during a rain event. Such environmental reservoirs of indicator bacteria further complicate the already questionable relationship between indicator organisms and human pathogens, and call for a better understanding of the ecology, fate and persistence of indicator bacteria.

Geographical variation in antibiotic resistance profiles of Escherichia coli isolated from swine, poultry, beef and dairy cattle farm water retention ponds in Florida.

AIMS: The aim of this study was to assess geographical variation in multiple antibiotic resistance (MAR) profiles of livestock Escherichia coli as well as to evaluate the ability of MAR profiles to differentiate sources of faecal pollution. METHODS AND RESULTS: More than 2000 E. coli isolates were collected from water retention ponds and manure of swine, poultry, beef and dairy farms in south, central and north Florida, and analysed for MAR using nine antibiotics. There were significant differences in antibiotic resistance of E. coli by season and livestock type for more than one antibiotic, but regional differences were significant only for ampicillin. Over the three regions, discriminant analysis using MAR profiles correctly classified 27% of swine, 49% of poultry, 56% of beef and 51% of dairy isolates. CONCLUSIONS: Regional variations in MAR combined with moderate discrimination success suggest that MAR profiles of E. coli may only be marginally successful in identifying sources of faecal pollution. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates the existence of regional and seasonal differences in MAR profiles as well as the limited ability of MAR profiles to discriminate among livestock sources.

Assessment of virulence-factor activity relationships (VFARs) for waterborne diseases.

Virulence-factor activity relationship (VFAR) is a concept that was developed as a way to relate the architectural and biochemical components of a microorganism to its potential to cause human disease. Development of these relationships requires specialised bioinformatics databases that do not exist at present. A pilot-scale VFAR database was designed for three different waterborne organisms: Escherichia coli, Norovirus and Cryptosporidium, to evaluate VFAR relationships. For the web-based database, each organism has separate pages containing virulence genes, occurrence genes, primer sets and probes, taxonomy, outbreaks, and serotype/species/genogroup/genotype. As the database continues to grow, it will be possible to relate the occurrence and prevalence of certain genes in various microorganisms to outbreak data and, subsequently, to establish the utility of using a combination of specific genes as markers of virulence and in establishing virulence-factor activity relationships (VFARs). The database and the VFARs established will be of use to the regulatory community as a way to assist with prioritising those organisms, which need to be regulated.

Assessment of methods for detection of infectious Cryptosporidium oocysts and Giardia cysts in reclaimed effluents.

This study evaluates the occurrence of Cryptosporidium oocysts and Giardia cysts in reclaimed effluents if method 1623 with the Envirochek capsule filters (standard and high-volume [HV] filters) and a modified version of the Information Collection Rule method (ICR) with the polypropylene yarn-wound cartridge filter are used. The recovery efficiency of the analytical methods was evaluated with samples of reagent, tap, and reclaimed water by using flow cytometer-sorted spike suspensions. (Oo)cyst recovery efficiency determined filter performance and method reproducibility in the water matrix tested. Method 1623 with the Envirochek HV capsule filter generated significantly higher recovery rates than did the standard Envirochek filter and the modified ICR method. Notwithstanding, large variations in recovery rates (>80%) occurred with samples of reclaimed water, and none of the water quality parameters analyzed in the reclaimed effluents could explain such variability. The highest concentrations of indigenous oocysts were detected by method 1623 with the HV filter, which provided a sufficient number of oocysts for further confirmation of infectious potential. Confirmation of species and potential infectivity for all positive protozoan samples was made by using a nested PCR restriction fragment polymorphism assay and the focus detection method most-probable-number assay, respectively. The methodology and results described in the present investigation provide useful information for the establishment of pathogen numeric standards for reclaimed effluents used for unrestricted irrigation.

Elution, detection, and quantification of polio I, bacteriophages, Salmonella montevideo, and Escherichia coli O157:H7 from seeded strawberries and tomatoes.

This study compared the effect of different physical and chemical treatments of strawberries and tomatoes to determine their ability to recover seeded viral and bacterial pathogens from produce surfaces. Solutions of salts, amino acids, complex media, and detergents were compared as eluants. Phosphate-buffered saline (PBS) containing 0.1% Tween 80 eluted the highest number of seeded microorganisms. Elution with this defined solution was then compared under different conditions of physical agitation. Rotary shaking for 20 min at 36 degrees C eluted higher numbers of viruses and bacteria than did low- or high-speed stomaching. Commercially available and laboratory prepared bacteriological differential media were compared for their ability to recover and distinguish eluted Salmonella Montevideo and Escherichia coli O157:H7 strains from seeded produce. The recovery of seeded bacterial pathogens was low when differential media containing selective ingredients were used (MacConkey sorbitol agar, XLD agar, MacConkey agar). Highest recoveries were obtained on a medium consisting of tryptic soy agar supplemented with sodium thiosulfate and ferric ammonium citrate compared with selective media that inhibited up to 50% of the growth of the eluted microorganisms.

Influence of salts on virus adsorption to microporous filters.

We investigated the direct and indirect effects of mono-, di-, and trivalent salts (NaCl, MgCl(2), and AlCl(3)) on the adsorption of several viruses (MS2, PRD-1, phiX174, and poliovirus 1) to microporous filters at different pH values. The filters studied included Millipore HA (nitrocellulose), Filterite (fiberglass), Whatman (cellulose), and 1MDS (charged-modified fiber) filters. Each of these filters except the Whatman cellulose filters has been used in virus removal and recovery procedures. The direct effects of added salts were considered to be the effects associated with the presence of the soluble salts. The indirect effects of the added salts were considered to be (i) changes in the pH values of solutions and (ii) the formation of insoluble precipitates that could adsorb viruses and be removed by filtration. When direct effects alone were considered, the salts used in this study promoted virus adsorption, interfered with virus adsorption, or had little or no effect on virus adsorption, depending on the filter, the virus, and the salt. Although we were able to confirm previous reports that the addition of aluminum chloride to water enhances virus adsorption to microporous filters, we found that the enhanced adsorption was associated with indirect effects rather than direct effects. The increase in viral adsorption observed when aluminum chloride was added to water was related to the decrease in the pH of the water. Similar results could be obtained by adding HCl. The increased adsorption of viruses in water at pH 7 following addition of aluminum chloride was probably due to flocculation of aluminum, since removal of flocs by filtration greatly reduced the enhancement observed. The only direct effect of aluminum chloride on virus adsorption that we observed was interference with adsorption to microporous filters. Under conditions under which hydrophobic interactions were minimal, aluminum chloride interfered with virus adsorption to Millipore, Filterite, and 1MDS filters. In most cases, less than 10% of the viruses adsorbed to filters in the presence of a multivalent salt and a compound that interfered with hydrophobic interactions (0.1% Tween 80 or 4 M urea).

Dynamic susceptibility contrast MR imaging of regional cerebral blood volume in Alzheimer disease: a promising alternative to nuclear medicine.

BACKGROUND AND PURPOSE: The goal of our study was to evaluate the sensitivity and specificity for Alzheimer disease of semiquantitative dynamic susceptibility contrast (DSC) MR imaging as compared with results of qualitative single-photon emission computed tomography (SPECT) in the same patients and with previously published semiquantitative SPECT results. METHODS: Fifty subjects were studied: 19 patients with probable Alzheimer disease with moderate cognitive impairment, eight mildly impaired patients with possible or probable Alzheimer disease, 18 group-matched elderly healthy comparison subjects, and five elderly comparison patients with psychiatric diagnoses. Relative values of temporoparietal regional cerebral blood volume (rCBV) were measured as a percentage of cerebellar rCBV, and group classification was assessed with logistic regression. The DSC MR imaging results were compared with SPECT scans in these same subjects and with previously published semiquantitative SPECT data. RESULTS: Temporoparietal rCBV ratios were reduced 20% bilaterally in the patients with Alzheimer disease. Using left and right temporoparietal rCBV as index measures, sensitivity was 95% in moderately affected patients with Alzheimer disease and 88% in patients with mild cases. Specificity was 96% in healthy comparison subjects and in psychiatric comparison subjects. Sensitivity with DSC MR imaging was considerably better than with visual clinical readings of SPECT scans (74% in moderate and 50% in mild Alzheimer disease cases), and was similar to previous published SPECT temporoparietal measurements (90%). Specificity with SPECT was 100% visually and 87% based on previous temporoparietal measurements. CONCLUSIONS: DSC MR imaging of rCBV is promising as a safe, potentially lower-cost alternative to nuclear medicine imaging for the evaluation of patients with dementia.

Isolation of an amoeba naturally harboring a distinctive Legionella species.

There are numerous in vitro studies documenting the multiplication of Legionella species in free-living amoebae and other protozoa. It is believed that protozoa serve as host cells for the intracellular replication of certain Legionella species in a variety of environmental settings. This study describes the isolation and characterization of a bacterium initially observed within an amoeba taken from a soil sample. In the laboratory, the bacterium multiplied within and was highly pathogenic for Acanthamoeba polyphaga. Extracellular multiplication was observed on buffered charcoal yeast extract agar but not on a variety of conventional laboratory media. A 16S rRNA gene analysis placed the bacterium within the genus Legionella. Serological studies indicate that it is distinct from previously described species of the genus. This report also describes methods that should prove useful for the isolation and characterization of additional Legionella-like bacteria from free-living amoebae. In addition, the characterization of bacterial pathogens of amoebae has significant implications for understanding the ecology and identification of other unrecognized bacterial pathogens.