Multi-population dissolution in confined active fluids

Autonomous out-of-equilibrium agents or cells in suspension are ubiquitous in biology and engineering. Turning chemical energy into mechanical stress, they generate activity in their environment, which may trigger spontaneous large-scale dynamics. Often, these systems are composed of multiple populations that may reflect the coexistence of multiple species, differing phenotypes, or chemically varying agents in engineered settings. Here, we present a new method for modeling such multi-population active fluids subject to confinement. We use a continuum multi-scale mean-field approach to represent each phase by its first three orientational moments and couple their evolution with those of the suspending fluid. The resulting coupled system is solved using a parallel adaptive level-set-based solver for high computational efficiency and maximal flexibility in the confinement geometry. Motivated by recent experimental work, we employ our method to study the spatiotemporal dynamics of confined bacterial suspensions and swarms dominated by fluid hydrodynamic effects. Our in silico explorations reproduce observed emergent collective patterns, including features of active dissolution in two-population active-passive swarms, with results clearly suggesting that hydrodynamic effects dominate dissolution dynamics. Our work lays the foundation for a systematic characterization and study of collective phenomena in natural or synthetic multi-population systems such as bacteria colonies, bird flocks, fish schools, colloid swimmers, or programmable active matter.

Size-Dependent Diffusion and Dispersion of Particles in Mucin

Mucus, composed significantly of glycosylated mucins, is a soft and rheologically complex material that lines respiratory, reproductive, and gastrointestinal tracts in mammals. Mucus may present as a gel, as a highly viscous fluid, or as a viscoelastic fluid. Mucus acts as a barrier to the transport of harmful microbes and inhaled atmospheric pollutants to underlying cellular tissue. Studies on mucin gels have provided critical insights into the chemistry of the gels, their swelling kinetics, and the diffusion and permeability of molecular constituents such as water. The transport and dispersion of micron and sub-micron particles in mucin gels and solutions, however, differs from the motion of small molecules since the much larger tracers may interact with microstructure of the mucin network. Here, using brightfield and fluorescence microscopy, high-speed particle tracking, and passive microrheology, we study the thermally driven stochastic movement of 0.5-5.0 μm tracer particles in 10% mucin solutions at neutral pH, and in 10% mucin mixed with industrially relevant dust; specifically, unmodified limestone rock dust, modified limestone, and crystalline silica. Particle trajectories are used to calculate mean square displacements and the displacement probability distributions; these are then used to assess tracer diffusion and transport. Complex moduli are concomitantly extracted using established microrheology techniques. We find that under the conditions analyzed, the reconstituted mucin behaves as a weak viscoelastic fluid rather than as a viscoelastic gel. For small- to moderately sized tracers with a diameter of lessthan 2 μm, we find that effective diffusion coefficients follow the classical Stokes-Einstein relationship. Tracer diffusivity in dust-laden mucin is surprisingly larger than in bare mucin. Probability distributions of mean squared displacements suggest that heterogeneity, transient trapping, and electrostatic interactions impact dispersion and overall transport, especially for larger tracers. Our results motivate further exploration of physiochemical and rheological mechanisms mediating particle transport in mucin solutions and gels.

Response to the COVID-19 pandemic in the legally deprived population of liberty in Cali (Colombia)

 

With the COVID-19 pandemic, the challenge of reducing the transmission of the disease has led to new challenges in decision-making. The vulnerability of persons deprived of liberty led to the design of contagion mitigation alternatives. Since February 2020, at the Villahermosa Penitentiary and Prison Center in Cali, the Secretaría de Salud Pública (SSP) began a series of actions that intensified on March 11, when the WHO declared COVID -19 as a pandemic. The SSP, in an articulated work; configured a series of strategies aimed at mitigating the impact and speed of contagion, infectious disease doctors and internists were also summoned who provided recommendations and contributed to decision-making. An intervention model was designed, which was guided by two main processes: promotion and prevention actions and service provision actions. The articulated work and the high commitment of the actors involved, the development of strategies for biosecurity, hygiene, isolation, rapid detection, and, above all, immediate control of symptoms and medical care on-site with adjustments that allowed managing patients inside the institution; It has meant that to date mortality is below 1% and that for the time being the situation is under control.

Key messages

• The humanization of health service provision is essential to achieve effective results.

• The rapid and articulated responses made it possible to maintain a mortality of less than 1% in this population.

Mass and stiffness spectrometry of nanoparticles and whole intact bacteria by multimode nanomechanical resonators

The identification of species is a fundamental problem in analytical chemistry and biology. Mass spectrometers identify species by their molecular mass with extremely high sensitivity (<10⁻²⁴ g). However, its application is usually limited to light analytes (<10⁻¹⁹ g). Here we demonstrate that by using nanomechanical resonators, heavier analytes can be identified by their mass and stiffness. The method is demonstrated with spherical gold nanoparticles and whole intact E. coli bacteria delivered by electrospray ionization to microcantilever resonators placed in low vacuum at 0.1 torr. We develop a theoretical procedure for obtaining the mass, position and stiffness of the analytes arriving the resonator from the adsorption-induced eigenfrequency jumps. These results demonstrate the enormous potential of this technology for identification of large biological complexes near their native conformation, a goal that is beyond the capabilities of conventional mass spectrometers.

Mass spectrometry can accurately identify species by molecular mass, but measuring large species can be difficult. Here the authors show that nanomechanical resonators can identify both the mass and stiffness of larger analytes, demonstrating it for gold nanoparticles and E. Coli bacteria.

How two-dimensional bending can extraordinarily stiffen thin sheets

Curved thin sheets are ubiquitously found in nature and manmade structures from macro- to nanoscale. Within the framework of classical thin plate theory, the stiffness of thin sheets is independent of its bending state for small deflections. This assumption, however, goes against intuition. Simple experiments with a cantilever sheet made of paper show that the cantilever stiffness largely increases with small amounts of transversal curvature. We here demonstrate by using simple geometric arguments that thin sheets subject to two-dimensional bending necessarily develop internal stresses. The coupling between the internal stresses and the bending moments can increase the stiffness of the plate by several times. We develop a theory that describes the stiffness of curved thin sheets with simple equations in terms of the longitudinal and transversal curvatures. The theory predicts experimental results with a macroscopic cantilever sheet as well as numerical simulations by the finite element method. The results shed new light on plant and insect wing biomechanics and provide an easy route to engineer micro- and nanomechanical structures based on thin materials with extraordinary stiffness tunability.

Comparison of International Reference Values for Bone Speed of Sound in Pediatric Populations: Meta-analysis

The aim of this study was to compare international reference values (RV) for tibial and radial speed of sound (SoS) assessed by quantitative ultrasound (QUS) in pediatric populations. These values were compared by age and country of origin in a systematic review with meta-analysis from studies published on QUS (Sunlight Omnisense). A search was carried out in electronic databases. Nine studies with 6963 patients were included in the meta-analysis. For the newborn populations, 3 studies (from Italy, Portugal, and Israel) were used. These studies included subjects with 27-42 wk gestational age. The mean difference (Portugal-Israel) was found to be 23.62 m/s [95% confidence interval [CI] 6.29, 40.95]. Additionally, no difference was found between Italy-Portugal (p = 0.69), or Italy-Israel (p = 0.28). In pediatric populations, we compared 8 studies from Canada, Mexico, Israel, Greece, Portugal, and Turkey. No significant differences found for SoS RV between Israel-Turkey, Israel-Greece, or Israel-Canada (p > 0.05). Significant differences were found in Mexico-Israel -105.29 m/s (95% CI -140.05, -70.54) (p < 0.001); Mexico-Portugal -115.14 m/s (95% CI -164.86, -65.42) (p < 0.001); Mexico-Greece: -239.14 m/s (95% CI -267.67, -210.62) (p < 0.001); Mexico-Turkey: -115.14 m/s (95% CI -164.86, -65.42) (p < 0.001); Mexico-Canada: -113.51 m/s (95% CI -140.25, -86.77) (p < 0.001).This study demonstrates that there are differences in SoS-RV obtained by tibial and radial QUS in pediatric populations between Mexico and other countries (Israel, Portugal, Greece, Turkey, and Canada).

Development and Validation of a Lateral Flow Immunoassay Test Kit for Dual Detection of Casein and β-Lactoglobulin Residues

Allergies to cow's milk are very common and can present as life-threatening anaphylaxis. Consequently, food labeling legislation mandates that foods containing milk residues, including casein and/or β-lactoglobulin, provide an indication of such on the product label. Because contamination with either component independent of the other can occur during food manufacturing, effective allergen management measures for containment of milk residues necessitates the use of dual screening methods. To assist the food industry in improving food safety practices, we have developed a rapid lateral flow immunoassay test kit that reliably reports both residues down to 0.01 μg per swab and 0.1 ppm of protein for foods. The assay utilizes both sandwich and competitive format test lines and is specific for bovine milk residues. Selectivity testing using a panel of matrices with potentially interfering substances, including commonly used sanitizing agents, indicated reduction in the limit of detection by one-to fourfold. With food, residues were easily detected in all cow's milk-based foods tested, but goat and sheep milk residues were not detected. Specificity analysis revealed no cross-reactivity with common commodities, with the exception of kidney beans when present at high concentrations (> 1%). The development of a highly sensitive and rapid test method capable of detecting trace amounts of casein and/or β-lactoglobulin should aid food manufacturers and regulatory agencies in monitoring for milk allergens in environmental and food samples.

Detection of cancer biomarkers in serum using a hybrid mechanical and optoplasmonic nanosensor

Blood contains a range of protein biomarkers that could be used in the early detection of disease. To achieve this, however, requires sensors capable of detecting (with high reproducibility) biomarkers at concentrations one million times lower than the concentration of the other blood proteins. Here, we show that a sandwich assay that combines mechanical and optoplasmonic transduction can detect cancer biomarkers in serum at ultralow concentrations. A biomarker is first recognized by a surface-anchored antibody and then by an antibody in solution that identifies a free region of the captured biomarker. This second antibody is tethered to a gold nanoparticle that acts as a mass and plasmonic label; the two signatures are detected by means of a silicon cantilever that serves as a mechanical resonator for 'weighing' the mass of the captured nanoparticles and as an optical cavity that boosts the plasmonic signal from the nanoparticles. The capabilities of the approach are illustrated with two cancer biomarkers: the carcinoembryonic antigen and the prostate specific antigen, which are currently in clinical use for the diagnosis, monitoring and prognosis of colon and prostate cancer, respectively. A detection limit of 1 × 10(-16) g ml(-1) in serum is achieved with both biomarkers, which is at least seven orders of magnitude lower than that achieved in routine clinical practice. Moreover, the rate of false positives and false negatives at this concentration is extremely low, ∼10(-4).

Horizontally patterned Si nanowire growth for nanomechanical devices

We report a method to pattern horizontal vapor-liquid-solid growth of Si nanowires at vertical sidewalls of Si microstructures. The method allows one to produce either single nanowire structures or well-ordered nanowire arrays with predefined growth positions, thus enabling a practical development of nanomechanical devices that exploit the singular properties of Si nanowires. In particular, we demonstrate the fabrication of doubly clamped nanowire resonators and resonator arrays whose mechanical resonances can be measured by optical or electrical readout. We also show that the fabrication method enables the electrical readout of the resonant mode splitting of nanowire resonators in the VHF range, which allows the application of such an effect for enhanced nanomechanical sensing with nanowire resonators.

Optomechanics with silicon nanowires by harnessing confined electromagnetic modes

The optomechanical coupling that emerges in an optical cavity in which one of the mirrors is a mechanical resonator has allowed sub-Kelvin cooling with the prospect of observing quantum phenomena and self-sustained oscillators with very high spectral purity. Both applications clearly benefit from the use of the smallest possible mechanical resonator. Unfortunately, the optomechanical coupling largely decays when the size of the mechanical system is below the light wavelength. Here, we propose to exploit the optical resonances associated to the light confinement in subwavelength structures to circumvent this limitation, efficiently extending optomechanics to nanoscale objects. We demonstrate this mechanism with suspended silicon nanowires. We are able to optically cool the mechanical vibration of the nanowires from room temperature to 30-40 K or to obtain regenerative mechanical oscillation with a frequency stability of about one part per million. The reported optomechanical phenomena can be exploited for developing cost-optimized mass sensors with sensitivities in the zeptogram range.

High throughput optical readout of dense arrays of nanomechanical systems for sensing applications

We present an instrument based on the scanning of a laser beam and the measurement of the reflected beam deflection that enables the readout of arrays of nanomechanical systems without limitation in the geometry of the sample, with high sensitivity and a spatial resolution of few micrometers. The measurement of nanoscale deformations on surfaces of cm(2) is performed automatically, with minimal need of user intervention for optical alignment. To exploit the capability of the instrument for high throughput biological and chemical sensing, we have designed and fabricated a two-dimensional array of 128 cantilevers. As a proof of concept, we measure the nanometer-scale bending of the 128 cantilevers, previously coated with a thin gold layer, induced by the adsorption and self-assembly on the gold surface of several self-assembled monolayers. The instrument is able to provide the static and dynamic responses of cantilevers with subnanometer resolution and at a rate of up to ten cantilevers per second. The instrumentation and the fabricated chip enable applications for the analysis of complex biological systems and for artificial olfaction.

Stress and DNA assembly differences on cantilevers gold coated by resistive and e-beam evaporation techniques

Changes in the sign of differential surface stress of gold-coated cantilevers produced by thiol-derivatized single-stranded DNA immobilization are observed, depending on the method used to deposit the gold. While the DNA immobilization on e-beam gold-coated cantilevers produces a compressive differential surface stress in the metallic layer, the opposite is observed for resistively coated cantilevers under the same immobilization conditions. The gold films exhibit quite a similar morphology, and the immobilization differences seem to be related to the charge state of the metallic layer surface. This in turn produces a different distribution of the orientation of the DNA strands on the gold layer. A tentative explanation for the observed effect is proposed.

160 FREEZABILITY OF ELECTROEJACULATED AND EPIDIDYMAL SPERMATOZOA FROM BLUE WILDEBEEST (CONNOCHAETES TAURINUS)

Maintenance of population viability, especially endangered species, requires preservation of as much genetic variability as possible, therefore genetic resource banks are very important. For male gametes, preservation of all available sources (ejaculates and epididymal) are useful. Information regarding sperm characteristics of most wild ruminant species is limited compared to that from domestic species. The objective of this work was to characterize the freezability of electroejaculated and epididymal spermatozoa from a wildebeest (5 year old; housed in Cabárceno Nature Park, Cantabria, Spain) that was castrated because of behavioral problems. After general anesthesia (ethorfine + xilazine, 1.8 mL + 0.5 mg kg–1) with dart, semen was collected by electroejaculation (3 V and 75 mA). Sperm concentration was 250 × 106 mL–1 (total spermatozoa: 1128.6 × 106). After castration, epididymides were disected and spermatozoa were collected by making several incisions in the caudal epididymis. Concentration was 12 441 × 106 spermatozoa mL–1 (total spermatozoa: 24 882 × 106). Samples were diluted to 200 × 106 spermatozoa mL–1 (TesT-Fructose-Egg yolk-Glycerol-Antibiotics) and chilled to 5°C during 2 h. Diluted semen was packaged in 0.25-mL straws and frozen from 5°C to –100°C (–20°C min–1) in a programmable cell freezer (Kryo 10, Planer). Straws were plunged into liquid nitrogen until analysis and thawed in a water bath (65°C, 6 s). Fresh, pre-freezing and post-thawed samples were analysed for motility (total motility TM, %; progressive motility PM, %; path velocity VAP, μm s–1; track speed VCL, μm s–1; progressive velocity VSL, μm s–1) using a CASA (ISAS, Proiser, Valencia, Spain). Viability (VIAB %) (SYBR-14 and propidium iodide) and mitochondrial membrane potential (MIT %) (JC1) were assessed by flow cytometry. Post-thawing results for electroejaculated v. epididymal samples were, respectively: TM: 87.0 v. 64.6%; PM: 68.7 v. 33.4%; VAP: 95.9 v. 49.8 μm s–1; VCL: 108.3 v. 71.6 μm s–1; VSL: 86.7 v. 40.2 μm s–1; VIAB: 57.0 v. 73.9%; MIT: 59.5 v. 77.5%. Motility parameters were higher for the electroejaculated sample; however, viability was higher for the epididymal sample. Recovery rates (post-thawed value/pre-freezing value × 100) for electroejaculated v. epididymal samples were: TM: 97.2 v. 93.4%; PM: 113.3 v. 103.2%; VAP: 88.9 v. 122.0 μm s–1; VCL: 87.5 v. 126.0 μm s–1; VSL: 93.4 v. 125.3 μm s–1; VIAB: 75.0 v. 97.7%; MIT: 69.2 v. 95.9%). These rates suggest a good freezability of electroejaculated and epididymal spermatozoa in blue wildebeest. This work was supported in part by Cantur. 3 Supported by Juan de la Cierva program (MICINN, Spain).

Direct costs of osteoporosis and hip fracture: an analysis for the Mexican healthcare system

This study reports the direct costs related to osteoporosis and hip fractures paid for governmental and private institutions in the Mexican health system and estimates the impact of these entities on Mexico. We conclude that the economic burden due to the direct costs of hip fracture justifies wide-scale prevention programs for osteoporosis (OP).

METHODS

To estimate the total direct costs of OP and hip fractures in the Mexican Health care system, a sample of governmental and private institutions were studied. Information was gathered through direct questionnaires in 275 OP patients and 218 hip fracture cases. Additionally, a chart review was conducted and experts' opinions obtained to get accurate protocol scenarios for diagnoses and treatment of OP with no fracture. Microcosting and activity-based costing techniques were used to yield unit costs.

RESULTS

The total direct costs for OP and hip fracture were estimated for 2006 based on the projected annual incidence of hip fractures in Mexico. A total of 22,233 hip fracture cases were estimated for 2006 with a total cost to the healthcare system of US$ 97,058,159 for the acute treatment alone ($4,365.50 per case). We found considerable differences in costs and the way the patients were treated across the different health sectors within the country.

CONCLUSION

Costs of the acute treatment of hip fractures in Mexico are high and are expected to increase with the predicted increment of life expectancy and the number of elderly in our population.

Detection of bacteria based on the thermomechanical noise of a nanomechanical resonator: origin of the response and detection limits

We have measured the effect of bacteria adsorption on the resonant frequency of microcantilevers as a function of the adsorption position and vibration mode. The resonant frequencies were measured from the Brownian fluctuations of the cantilever tip. We found that the sign and amount of the resonant frequency change is determined by the position and extent of the adsorption on the cantilever with regard to the shape of the vibration mode. To explain these results, a theoretical one-dimensional model is proposed. We obtain analytical expressions for the resonant frequency that accurately fit the data obtained by the finite element method. More importantly, the theory data shows a good agreement with the experiments. Our results indicate that there exist two opposite mechanisms that can produce a significant resonant frequency shift: the stiffness and the mass of the bacterial cells. Based on the thermomechanical noise, we analyse the regions of the cantilever of lowest and highest sensitivity to the attachment of bacteria. The combination of high vibration modes and the confinement of the adsorption to defined regions of the cantilever allows the detection of single bacterial cells by only measuring the Brownian fluctuations. This study can be extended to smaller cantilevers and other biological systems such as proteins and nucleic acids.

Activity of ertapenem and other antimicrobials against ESBL-producing enterobacteria isolated from urine in patients from Madrid

The objective of this study was to evaluate the activity of ertapenem and other antimicrobials against extended-spectrum beta-lactamase (ESBL)-producing enterobacteria isolated from patients' urine samples at 4 community healthcare centers in the Madrid (Spain) area and to determine the prevalence of ESBL-producing enterobacteria in community-acquired urinary tract infections. The antibiotic susceptibility results were compared by patient age and sex. A total of 293 strains were studied. The minimum inhibitory concentration (MIC) for each antibiotic was determined using the agar dilution method. The tested carbapenems were the antibiotics with the greatest activity (ertapenem MIC(90)=0.06 mg/l; imipenem MIC(90)=0.5 mg/l), with no intermediate or resistant strains being observed. High rates of resistance to ciprofloxacin (80.9%) and cotrimoxazole were observed (62.1%). The global prevalence of ESBL-producing enterobacteria was 3.6% (293/8,139). Prevalence according to areas was 5.3% in Getafe, 3.45% in Arguelles, 3.02% in Alcala de Henares and 3.56% in Mostoles. The global prevalence of ESBL-producing Escherichia coli was 4.15% (279/6,721). The analysis of resistance according to patient sex (males versus females) showed no significant differences. The analysis of resistance according to patient age (<50 years versus > or = 50 years) showed statistically significant differences (more resistance among subjects > or = 50 years old) for cotrimoxazole (OR=0.43, 95%CI: 0.20-0.93, p=0.018) and ciprofloxacin (OR=0.32, 95%CI: 0.14-0.74, p=0.0027). In view of the good activity shown by ertapenem, and the continuous increase in the prevalence of ESBL strains, this antibiotic and some of the others could be a good choice for the treatment of community-acquired urinary tract infections produced by such bacteria in Spain.

[Biological cost associated with fosfomycin resistance in Escherichia coli isolates from urinary tract infections]

Resistance to fosfomycin develops rapidly in experimental conditions, although despite its frequent use in UTI, resistance in E. coli, the main uropathogen, is very low (1-3%), and has remained so for many years. The objective of this study was to ascertain whether E. coli fosfomycin-resistant strains have less fitness than those that are fosfomycin-sensitive in competing, and would therefore tend to disappear in their competition with fosfomycin-sensitive strains in the absence of antibiotics. Fosfomycin-resistant strains (n=11) with different phenotypes of resistance to other antibiotics were used. All but one were lactose (+). Fosfomycin-susceptible strains (n=15) that had the same phenotypes of resistance to other antibiotics as the resistant strains and which had the opposite pattern of lactose fermentation were also used. Thirty-three (33) competition experiments by pairs of strains were conducted in nutrient broth. Equal amounts of the strains were challenged (approx. 50% and approx. 50%) for 4 days, with a daily change to a new medium. Five differential counts were performed on days 0, 1, 2, 3 and 4. In 20 experiments (60.6%) there was a relative increase in the fosfomycin-sensitive strain. In 6 experiments (18.2%) there was a relative increase in the fosfomycin-resistant strain. In 7 experiments (21.2%), on the fourth day none of the strains reached 60%. When the data of the 26 (20+6) experiments in which there were changes were analyzed by the chi2 test there was a statistically significant difference (p=0.044). Resistance to fosfomycin could entail a biological cost (less fitness) for the majority of the E. coli strains assayed.

[The intercontinental schizophrenia outpatient health outcomes study (IC-SOHO): initial 6 month findings of the sample in Latin America]

The IC-SOHO study was designed to supply information on antipsychotic treatments in the real clinical practice by assessment of a large and diverse sample population with schizophrenia. This document describes the findings of the first 6 months of IC-SOHO in Latin America. To date, this is the largest observational study of its type in this region. In this observational and prospective study, those out-patients with schizophrenia, who require a change or initiation of antipsychotic medication are hospitalized. Effectiveness was evaluated using the Clinical Global Impression-Seriousness (CGI-S) grading scale. Tolerability was assessed by questionnaires on adverse events and weight measurements. Herein, the comparisons between olanzapine (monotherapy), risperidone (monotherapy) and conventional antipsychotics (monotherapy and combined therapy) are presented. As a whole, 7,658 patients participated in the ICSOHO; n=2,671 from 11 countries of Latin America that were included in this report. At 6 months, the proportion of patients who responded to olanzapine was significantly greater than those who responded to risperidone or conventional antipsychotics (p<0.001). Patients from the olanzapine group had greater improvements in all the symptom domains, including general, positive, negative, depressive and cognitive symptoms in comparison with risperidone (p<0.05) or conventional antipsychotics (p < 0.001). Extrapyramidal symptoms (EPS) and tardive dyskinesia (TD) decreased from baseline in the groups treated with olanzapine and risperidone, but increased in the conventional group. The adverse events related with the sexual function were more prominent in the conventional group. Weight gain was observed in each treatment group, although the patients from the olanzapine group had greater weight grain followed by those of risperidone and then by those of conventional antipsychotics. Our findings in this population of the Latin American sample emulate the results of other studies in different samples, where it was found that olanzapine was more effective and better tolerated than risperidone or conventional antipsychotics.

Highly sensitive polymer-based cantilever-sensors for DNA detection

We present a technology for the fabrication of cantilever arrays aimed to develop an integrated biosensor microsystem. The fabrication process is based on spin coating of the photosensitive polymer and near-ultraviolet exposure. Arrays of up to 33 microcantilevers are fabricated in the novel polymer material SU-8. The low Young's modulus of the polymer, 40 times lower than that of silicon, enables to improve the sensitivity of the sensor device for target detection. The mechanical properties of SU-8 cantilevers, such as spring constant, resonant frequency and quality factor are characterized as a function of the dimensions and the medium. The devices have been tested for measurement of the adsorption of single stranded DNA and subsequent interstitial adsorption of lateral spacer molecules. We demonstrate that sensitivity is enhanced by a factor of six compared to that of commercial silicon nitride cantilevers.

Resistance to macrolides, clindamycin and telithromycin in Streptococcus pyogenes isolated in Spain during 2004

OBJECTIVES

To study the antimicrobial susceptibility and prevalence of the different phenotypes and genotypes of macrolide resistance in group A streptococci isolated in Spain in 2004, and to compare the results with those obtained in 1998 and 2001 using the same methodology and centres.

METHODS

A total of 530 unique isolates of Streptococcus pyogenes collected in 21 laboratories from 16 geographic areas (regions) in Spain were used. Antimicrobial susceptibility testing was performed using the agar dilution method. Discs containing erythromycin or clindamycin were used to recognize the phenotypes of macrolide-lincosamide-streptogramin (MLS) resistance. Genes encoding macrolide-lincosamide resistance were detected by PCR.

RESULTS

Resistance to erythromycin was 21.7% [95% confidence interval (CI) 16.5-26.3]. The resistance to azithromycin was 21.5%, whereas the resistance to miocamycin and to clindamycin was 6.6% (95% CI 3.0-8.9). Thirty-one (5.8%) of the isolates were resistant to telithromycin. Of the 115 erythromycin-resistant isolates, 67.8% had the M phenotype, representing 14.7% of all the isolates tested. Thirty-five isolates (30.5% of the erythromycin-resistant strains and 6.6% of all the isolates) had the MLS(B) constitutive phenotype. There was a high prevalence of resistance to telithromycin (88.6%) among the 35 strains with the MLS(B) constitutive phenotype. When we compared these results with those from previous studies (1998 and 2001), we found a significant increase in the MLS(B) constitutive phenotype (P < 0.001), and a significant decrease in the M phenotype (P < 0.005) was noted.

CONCLUSIONS

The significant increase in the prevalence of resistance to clindamycin and miocamycin, and the prevalence of resistance to telithromycin reached in a short period of time from the introduction of its use, underscore the need for continuous surveillance of antimicrobial resistance in S. pyogenes in Spain.

Bioelectrical impedance vector analysis in haemodialysis patients: relation between oedema and mortality

In this work, bioelectrical impedance vector analysis (BIVA) method is used in a sample of haemodialysis patients in stable (without oedema) and critical (hyperhydrated and malnutrition) states, in order to establish the relation between hyperhydration (oedema) and mortality. The measurements obtained were single frequency (50 kHz), tetrapolar (hand-foot) complex impedance measurements (vector components are: resistance R and reactance Xc). The impedance components were standardized by the height H of the subjects, (R/H and Xc/H) to obtain de impedance vector Z/H, that is represented in the RXc plot (abscise R/H, ordinate Xc/H). Measurements were performed on a sample of 74 patients (30 men and 44 women, 18-70 year, body mass index (BMI), 19-30 kg m(-2)) at the Saturnino Lora University Hospital in Santiago de Cuba. The 46 stable patients comprised 28 men and 18 women; the 28 critical patients 16 men and 12 women. The reference population consisted of 1196 healthy adult subjects living in Santiago de Cuba (689 men and 507 women, 18-70 year, BMI 19-30 kg m(-2)). We used the RXc plot with the BIVA method to characterize the reference population using the 50%, 75% and 95% tolerance ellipses. Student's t-test and Hotelling's T2-test were used to analyse the separation of groups obtained by means of clinical diagnosis and those obtained by BIVA. We obtained a significant difference (P < 0.05) in R/H, Xc/H and phase angle (PA) in men as in women between the location of Z/H vectors in the RXc graph and the separation made by the doctors between stable and critical patients. Critical (hyperhydrated) patients were located below the inferior pole of the 75% tolerance ellipse, whereas stable patients were within the tolerance ellipses. Some cases classified as stable by the clinic were classified as hyperhydrated by BIVA with 100% sensitivity and 48% specificity. In conclusion, the BIVA method could be used to classify patients by hydration state and to predict survival. Advantages of the method are its simplicity, objectivity and that it does not require the definition of patient dry weight.

Nanomechanics of the formation of DNA self-assembled monolayers and hybridization on microcantilevers

Biomolecular interactions over the surface of a microcantilever can produce its bending motion via changes of the surface stress, which is referred to nanomechanical response. Here, we have studied the interaction forces responsible for the bending motion during the formation of a self-assembled monolayer of thiolated 27-mer single-stranded DNA on the gold-coated side of a microcantilever and during the subsequent hybridization with the complementary nucleic acid. The immobilization of the single-stranded DNA probe gives a mean surface stress of 25 mN/m and a mean bending of 23 nm for microcantilevers with a length and thickness of about 200 microm and 0.8 microm, respectively. The hybridization with the complementary sequence could not be inferred from the nanomechanical response. The nanomechanical response was compared with data from well-established techniques such as surface plasmon resonance and radiolabeling, to determine the surface coverage and study the intermolecular forces between neighboring DNA molecules anchored to the microcantilever surface. From both techniques, an immobilization surface density of 3 x 10(12) molecules/cm(2) and a hybridization efficiency of 40% were determined. More importantly, label-free hybridization was clearly detected in the same conditions with a conventional sensor based on surface plasmon resonance. The results imply that the nanomechanical signal during the immobilization process arises mainly from the covalent attachment to the gold surface, and the interchain interactions between neighboring DNA molecules are weak, producing an undetectable surface stress. We conclude that detection of nucleic acid hybridization with nanomechanical sensors requires reference cantilevers to remove nonspecific signals, more sensitive microcantilever geometries, and immobilization chemistries specially addressed to enhance the surface stress variations.

High-Q dynamic force microscopy in liquid and its application to living cells

We present a new dynamic force microscopy technique for imaging in liquids in the piconewton regime. The low quality factor (Q) of the cantilever is increased up to three orders of magnitude by the implementation of a positive feedback control. The technique also includes a phase-locked loop unit to track the resonance of the cantilever. Experiments and computer simulations indicate that the tip-sample forces are below 100 pN, about two orders of magnitude lower than in conventional tapping mode atomic force microscopy. Furthermore, the spectroscopic ability is greatly enhanced. Either the phase shift or the resonant frequency shows a high sensitivity to variations in either the energy dissipation or conservative interactions between the tip and the sample, respectively. The potential of this technique is demonstrated by imaging living cells.

Chemical sensors and biosensors in liquid environment based on microcantilevers with amplified quality factor

A new technique is presented for bio/chemical sensors, based on microcantilevers, for detection in liquid environment. The low quality factor of the cantilever in liquid is increased up to three orders of magnitude by using Q-control. This enables AC detection that is immune to the long-term drift of the DC cantilever response in liquids, and to temperature variations. This technique has been applied for the detection of ethanol in aqueous solution by using the microbalance method, and for antibody/antigen recognition by the surface stress method. The results show the feasibility and very high sensitivity of these novel devices.

Human chromosome structure studied by scanning force microscopy after an enzymatic digestion of the covering cell material

In standard preparations, metaphase human chromosomes are covered by a cell material film composed mainly of proteins and RNA. This film (approximately 30 nm thickness) hides the chromosome structure to the tip of a scanning force microscope. In this work, a mild enzymatic treatment is applied to remove the cell material film. After treatment, the individual chromatin fibers at the surface were resolved. Furthermore, the chromosome shows a thickness modulation, in which thicker/thinner regions could be associated with G/R bands. Finally, the topography of the chromosomes in solution is presented. The chromosome volume swelled about five-fold and chromatin packaging in bands and coils was observed.

Selective cleaning of the cell debris in human chromosome preparations studied by scanning force microscopy

The chromosome structure is one of most challenging biological structures to be discovered. Most evidence about the structure comes from optical microscopy. Scanning force microscopy (SFM) can achieve molecular resolution and allows imaging in liquids. However, little information about the chromosome structure has been revealed by SFM. In this work, a mild enzymatic treatment is applied to the chromosomes to remove selectively the RNA and proteins coming from the cell. The resulting SFM images indicate that a protein film with embedded RNA molecules covers chromosomes in standard cytogenetic preparations. The thickness of the protein layer is 15-35 nm and the RNA adheres preferentially to the chromosome surface. The cell material film results in a quite smooth chromosome surface without evidence of any structural detail. After treatment, the chromosome was cleaned from cell residues and individual chromatin fibers at the surface were resolved. Furthermore, insights about the higher order structure of the chromosome can be inferred.

Effect of the menstrual cycle in ethanol pharmacokinetics

Differences in ethanol pharmacokinetics within the menstrual cycle have previously been reported and attributed to variations in body composition, hormonal influences and gastric emptying. To establish the role of the menstrual cycle in ethanol pharmacokinetics associated with changes in body composition, ethanol blood concentrations were measured in nine healthy women during the midfollicular (P1, days 8-10) and midluteal (P2, days 22-24) phases of the menstrual cycle after a postprandial oral ethanol dose (0.3 g kg(-1)). Total body water was assessed by dual-energy x-ray densitometry (DEXA) on both occasions. Median total body water did not vary during either phase of the menstrual cycle (P1 = 54.54%, P2 = 54.66%; P = 0.9296). Median area under the ethanol concentration-time curve (AUC) was lower during P1 (215.33 mg.h dl(-1)) than during P2 (231.33 mg.h dl(-1))(P = 0.8253). No significant differences were found on ethanol pharmacokinetics in either phase of the menstrual cycle.

The interaction of DNA with bacteriophage phi 29 connector: a study by AFM and TEM

The connector of bacteriophage phi 29 is involved in DNA packaging during viral morphogenesis and we have studied its in vitro binding to DNA using either linear or circular DNA. The protein-DNA complexes have been analyzed by transmission electron microscopy (TEM) and by atomic force microscopy (AFM) of samples directly deposited on mica. TEM showed the presence of a specific binding due to the interaction of the protein with the free ends of the DNA. The study of these samples by AFM showed two major types of morphologies: The interaction of the connector with circular DNA revealed that the strands of DNA that enter and exit the protein complex form an angle with a mean value of 132 degrees. Nevertheless, when the connector was incubated with linear DNA (and later circularized), there was an additional bend angle of about 168 degrees. Further morphological analysis of the latter samples by AFM revealed a structure of the protein-DNA complex consistent with the DNA traversing the connector, probably through the inner channel. On the other hand, images from the samples obtained by incubation of the connector with circular DNa were consistent with an interaction of the DNA with the outer side of the connector.

[The labor migration sending regions in the state of Zacatecas]

"In a preliminary survey in the state of Zacatecas, [Mexico,] we identified those municipalities which contribute most to the migration of Mexican workers to the United States; later, we corroborated our findings in situ and drew up an approximation of the geographic and economic characteristics of those municipalities, which make up 'migration sending zones or regions' in the state." (SUMMARY IN ENG)

Binding and effects of catecholestrogens on adenylate cyclase activity, and adrenoceptors, benzodiazepine and GABA receptors in guinea-pig hypothalamic membranes

Catecholestrogen (CE) binding to guinea-pig hypothalamic membranes was assessed by using [3H]2-hydroxyestrone (2-OHE1) as a ligand. Binding was maximal at pH 7.4 and 37 degrees C, and after 10 min incubations. A high affinity binding site with dissociation constant (KD) = 0.20 +/- 0.02 nM and site concentration (Bmax) = 38 +/- 2 fmol/mg protein, and a low affinity binding site with KD = 235 +/- 10 nM and Bmax = 4.2 +/- 1.0 pmol/mg protein (n = 7) were detected. The order of affinity (Ki, microM) for displacement of 10 nM [3H]2-OHE1 from hypothalamic binding sites was 2-OHE1 (0.8), 2-hydroxyestradiol (2-OHE2) (1.0), epinephrine (5.9), norepinephrine (NE) (7.7), dopamine (270), estradiol, estrone, propranolol, phentolamine, domperidone (greater than 10 000). NE inhibition of 2-OHE1 binding was non-competitive, Only 0.5 mM 2-OHE2 depressed in a non-competitive way the hypothalamic beta-adrenoceptor binding (measured by using [3H]dihydroalprenolol) without affecting alpha-adrenoceptor binding (measured by using [3H]dihydroergocryptine). Both 2-OHE2 and 2-OHE1 impaired NE-stimulated adenylate cyclase activity in hypothalamic membranes with EC50 of about 5 and 10 microM, respectively. CE decreased [3H]gamma-aminobutyric acid binding by hypothalamic membranes with Ki = 8 microM (2-OHE2) and 50 microM (2-OHE1). The binding of [3H]flunitrazepam to the same membrane preparation was not affected by CE. These results support the existence of significant CE binding and effects in guinea-pig hypothalamic membranes.

Uncoupling of the parathyroid hormone receptor-adenylate cyclase system of canine kidney during dietary phosphorus deprivation

The mechanisms involved in the renal resistance to the phosphaturic action of PTH during dietary phosphorus deprivation remain ill defined. Previous studies in dogs from our laboratory demonstrated that baseline excretion of cAMP and the increment after administration of parathyroid extract were markedly reduced during dietary phosphorus deprivation. The present studies examine the initial events in the actions of PTH, namely receptor binding and adenylate cyclase activation, in renal cortical membranes from normal and phosphorus-deprived animals. Mongrel dogs were fed a diet deficient in phosphorus for 4-6 weeks. Plasma phosphorus fell from 4.2 +/- 0.4 to 1.4 +/- 0.3 mg/dl. In renal cortical membranes from these animals, basal adenylate cyclase activity was not different from that in control normal animals. However, PTH-stimulated enzyme activity was markedly reduced (5785 +/- 303 pmol cAMP/mg protein X 30 min in controls vs. 2612 +/- 406 pmol cAMP/mg protein X 30 min; P less than 0.01). Kact (PTH concentration for half-maximal enzyme activation) was unchanged. PTH receptor binding assessed with [Nle8,Nle18,Tyr34]bovine PTH-(1-34) NH2 was not different in the two groups. The decreased PTH-stimulated adenylate cyclase activity was not corrected by GTP. Activation of adenylate cyclase by NaF was reduced in membranes from the phosphorus-deprived animals, whereas enzyme activation by guanylylimidodiphosphate was similar in both groups. Enzyme activity in the presence of Mn++ was not different from the control value. These data indicate that during dietary phosphorus deprivation there is uncoupling of the PTH receptor-adenylate system of canine kidney. This abnormality may play a role in the renal resistance to PTH during dietary phosphorus deprivation.

Effect of parathyroid hormone on Na+-dependent phosphate transport and cAMP-dependent 32P phosphorylation in brush border vesicles from isolated perfused canine kidneys

Concentrative uptake of 32Pi induced by the dissipation of a Na+ gradient (overshoot) was demonstrated in brush border membrane vesicles obtained from isolated perfused canine kidneys. Na+-dependent 32Pi transport was decreased in brush border vesicles from isolated kidneys perfused with parathyroid hormone (PTH) for 2 h compared to uptake measured in vesicles from kidneys perfused without PTH. Cyclic AMP-dependent 32P phosphorylation of a 62,000 Mr protein band was demonstrable on autoradiograms of sodium dodecyl sulfate-polyacrylamide gels of membrane suspensions from kidneys perfused +/- PTH. Evidence that perfusion with PTH resulted in cAMP-dependent phosphorylation in isolated kidneys from parathyroidectomized dogs (decreased cAMP-dependent 32P phosphorylation of the 62,000-Mr band in brush border vesicles) was obtained after 2-h perfusion with PTH. Decreased 32P phosphorylation was not observed if membranes were allowed to dephosphorylate prior to 32P phosphorylation in vitro. We conclude that brush border vesicles from isolated perfused canine kidneys can be used to study the action of PTH on Na+-Pi cotransport in brush border membranes and on cAMP-dependent phosphorylation of the membrane. It is strongly suggested that PTH effects changes in Na+-dependent 32Pi transport in isolated brush border vesicles and changes in 32P phosphorylation of vesicles via a direct action on the renal cortical cell rather than as a consequence of extrarenal actions of the hormone.

Effects of dietary-induced hyperparathyroidism on the parathyroid hormone-receptor-adenylate cyclase system of canine kidney. Evidence for postreceptor mechanism of desensitization

The present studies were designed to examine the consequences of chronic mild elevations of endogenous parathyroid hormone (PTH) in vivo on the PTH receptor-adenylate cyclase system of canine kidney cortex. Hyperparathyroidism was induced in normal dogs by feeding a diet low in calcium, high in phosphorus to the animals for a period of 6-9 wk. This maneuver resulted in a two to threefold increase in the plasma levels of carboxy-terminal immunoreactive PTH. This degree of hyperparathyroidism is similar to that seen in patients with hyperparathyroidism and normal renal function. After 6-9 wk on the diet the animals were killed and basolateral renal cortical membranes prepared for the study of the PTH receptor-adenylate cyclase system in vitro. The dietary hyperparathyroidism resulted in desensitization of the PTH-responsive adenylate cyclase (Vmax 3,648 +/- 654 pmol cyclic (c)AMP/mg protein per 30 min in hyperparathyroid animals vs. 5,303 +/- 348 in normal controls). The Kact (concentration of PTH required for half-maximal enzyme activation) was unchanged. However, PTH receptor binding (125I-norleucyl8-norleucyl18-tyrosinyl34, 125I[Nle8, Nle18, Tyr34] bPTH (1-34) NH2 as radioligand) was not different in the two groups of animals. Thus, dietary hyperparathyroidism resulted in an uncoupling of the PTH receptor-adenylate cyclase system. This defect was not corrected by guanyl nucleotides in vitro, and the effects of guanyl nucleotides on PTH binding and enzyme activation appeared normal. NaF-stimulated enzyme activity was reduced in the hyperparathyroid animals (8,285 +/- 607 pmol cAMP/mg protein per 30 min vs. 10,851 +/- 247 in controls). These data indicate that desensitization of the PTH-responsive adenylate cyclase system of canine kidney as a result of mild chronic elevations of endogenous PTH is due to a postreceptor defect, demonstrable by NaF activation, not corrected by guanyl nucleotides, leading to abnormal PTH-receptor adenylate cyclase coupling.

Cholera-like enterotoxin produced by Campylobacter jejuni. Characterisation and clinical significance

The presence and clinical significance of enterotoxins produced by Campylobacter jejuni were investigated. The supernatant of a prototype virulent strain grown in supplemented medium induced intraluminal fluid secretion in rat ileal loop but not in rabbit ileal loop or the infant mouse assay. It induced elongation and increased intracellular cyclic AMP levels in Chinese hamster ovary cells. Toxin activity was blocked by cholera antitoxin and was destroyed by heat and high or low pH; its molecular weight is in the range 10(4)-10(5) daltons. Toxin production was detected in 24 of 32 C jejuni strains from patients with diarrhoea and 1 of 6 from carriers. Antibody response to autologous C jejuni somatic antigen was investigated in 19 subjects for whom serial serum specimens were available. A fourfold rise was observed in all 10 patients with enterotoxigenic C jejuni diarrhoea, in 1 of 3 patients with non-enterotoxigenic C jejuni, and in none of the symptomless carriers of non-enterotoxigenic strains. These findings demonstrate that C jejuni produces an enterotoxin that may be important in pathogenesis of diarrhoea.

Regulation of PTH receptor-adenylate cyclase system of canine kidney: influence of Mn2+ on effects of Ca2+, PTH, and GTP

Metal ions play important roles in the regulation of the activation of adenylate cyclase. Previous studies have suggested that an important site of action of metal ions is at or closely related to the nucleotide regulatory protein. The present studies examine the nature of the regulation of enzyme activity by divalent cations and the influence of Mn2+ on hormone binding and stimulation of adenylate cyclase. Studies were performed in canine renal cortical membranes. Substitution of Mg2+ by Mn2+ was associated with a progressive decline in the ability of GTP or PTH to stimulate adenylate cyclase activity. Mn2+ did not alter specific binding of an iodinated PTH analogue. However, in spite of the loss of guanine nucleotide stimulation of enzyme activity, the effects of guanine nucleotide on PTH binding were not altered in the presence of Mn2+. Substitution of Mg2+ by Mn2+ abolished the inhibitory effect of Ca2+ on basal adenylate cyclase activity. Similarly, the effects of GTP or PTH to enhance the inhibitory effects of Ca2+ on enzyme activity were abolished in the presence of Mn2+. Since Mg2+ and Ca2+ compete for a common allosteric site and Mn2+ abolished the effects of these cations, it would appear that Mn2+ also competes for the binding site of Mg2+ and Ca2+. The present studies demonstrating that Mn2+ does not affect hormone binding or the actions of guanine nucleotides on hormone binding yet totally eliminates the effect of GTP on enzyme activity indicate that the effect of Mn2+ occurs at the level of the interactions of the nucleotide regulatory component with the catalytic unit. In addition, these data suggest that there are two functionally distinct sites of guanine nucleotides with different ionic requirements.