Mechanisms of low susceptibility to the disinfectant benzalkonium chloride in a multidrug-resistant environmental isolate of Aeromonas hydrophila

Excessive discharge of quaternary ammonium disinfectants such as benzalkonium chloride (BAC) into aquatic systems can trigger several physiological responses in environmental microorganisms. In this study, we isolated a less-susceptible strain of Aeromonas hydrophila to BAC, designated as INISA09, from a wastewater treatment plant in Costa Rica. We characterized its phenotypic response upon exposure to three different concentrations of BAC and characterized mechanisms related to its resistance using genomic and proteomic approaches. The genome of the strain, mapped against 52 different sequenced A. hydrophila strains, consists of approximately 4.6 Mb with 4,273 genes. We found a massive genome rearrangement and thousands of missense mutations compared to the reference strain A. hydrophila ATCC 7966. We identified 15,762 missense mutations mainly associated with transport, antimicrobial resistance, and outer membrane proteins. In addition, a quantitative proteomic analysis revealed a significant upregulation of several efflux pumps and the downregulation of porins when the strain was exposed to three BAC concentrations. Other genes related to membrane fatty acid metabolism and redox metabolic reactions also showed an altered expression. Our findings indicate that the response of A. hydrophila INISA09 to BAC primarily occurs at the envelop level, which is the primary target of BAC. Our study elucidates the mechanisms of antimicrobial susceptibility in aquatic environments against a widely used disinfectant and will help better understand how bacteria can adapt to biocide pollution. To our knowledge, this is the first study addressing the resistance to BAC in an environmental A. hydrophila isolate. We propose that this bacterial species could also serve as a new model to study antimicrobial pollution in aquatic environments.

Occurrence of pathogenic microorganisms in small drinking-water systems in Costa Rica

This study describes the quality of drinking water sampled over 2 years (2018 and 2019) from 20 ASADAS (Spanish acronym for Administrative Associations for Water and Sewer Systems) in Costa Rica. The analysis included Rotavirus (RV), somatic coliphages, fecal coliforms, and Escherichia coli. The ASADAS were categorized into three regions as temperate rainy (region 1), tropical rainy (region 2), and tropical rainy and dry (region 3) according to biogeographic classification. The concentrations of fecal coliforms and E. coli were higher in samples from surface water sources from the ASADAS in region 3 compared to regions 1 and 2. RV-positive samples (24/296) were detected in drinking-water samples from regions 2 and 3 during dry and transition seasons, with higher concentrations more frequently in the dry season. In addition, somatic coliphages were detected in samples from the three regions, with higher concentrations in region 2. Furthermore, a statistically significant relationship was found between somatic coliphages and diarrheal cases, classified as outbreaks or alerts in the region. Thus, the results confirmed that somatic coliphages are a good indicator of the presence of diarrhea cases in a specific region.

Fully kinetic simulations of strong steady-state collisional planar plasma shocks

We report on simulations of strong, steady-state collisional planar plasma shocks with fully kinetic ions and electrons, independently confirmed by two fully kinetic codes (an Eulerian continuum and a Lagrangian particle-in-cell). While kinetic electrons do not fundamentally change the shock structure as compared with fluid electrons, we find an appreciable rearrangement of the preheat layer, associated with nonlocal electron heat transport effects. The electron heat-flux profile qualitatively agrees between kinetic- and fluid-electron models, suggesting a certain level of "stiffness," though substantial nonlocality is observed in the kinetic heat flux. We also find good agreement with nonlocal electron heat-flux closures proposed in the literature. Finally, in contrast to the classical hydrodynamic picture, we find a significant collapse in the "precursor" electric-field shock at the preheat layer leading edge, which correlates with the electron-temperature gradient relaxation.

Short-term exposure to benzalkonium chloride in bacteria from activated sludge alters the community diversity and the antibiotic resistance profile

The continuous introduction of cleaning products containing benzalkonium chloride (BAC) from household discharges can mold the microbial communities in wastewater treatment plants (WWTPs) in a way still poorly understood. In this study, we performed an in vitro exposure of activated sludge from a WWTP in Costa Rica to BAC, quantified the changes in intI1, sul2, and qacE/qacEΔ1 gene profiles, and determined alterations in the bacterial community composition. The analysis of the qPCR data revealed elevated charges of antibiotic resistance genes in the microbial community; after BAC's exposure, a significant increase in the qacE/qacEΔ1 gene, which is related to ammonium quaternary resistance, was observed. The 16S rRNA gene sequences' analysis showed pronounced variations in the structure of the bacterial communities, including reduction of the alpha diversity values and an increase of the relative abundance of Alphaproteobacteria, particularly of Rhodospseudomonas and Rhodobacter. We confirmed that the microbial communities presented high resilience to BAC at the mg/mL concentration, probably due to constant exposure to this pollutant. They also presented antibiotic resistance-related genes with similar mechanisms to tolerate this substance. These mechanisms should be explored more thoroughly, especially in the context of high use of disinfectant.

Oral Findings in Patients With COVID-19

The aim of this study was to describe oral lesions in a group of patients with COVID-19. We recruited 55 patients, 25 women (45.5%) and 30 men (54.5%), aged between 1 and 89 years with confirmed COVID-19 at different stages of severity. After obtaining informed consent, we examined their mouths and recorded clinical findings. Forty percent of the patients had at least 1 oral lesion. The most common lesions were candidiasis and ulcers (7 patients each); 2 patients had enanthems. Geographic tongue and caviar tongue were also observed. Altered taste, dry mouth, and painful/burning mouth were noted in 60%, 27.3%, and 36.4% of patients, respectively. Oral mucosal alterations and lesions were prevalent in this series of COVID-19 patients. Altered taste and a painful/burning mouth were common symptoms.

Wastewater-Based Epidemiology of Enteric Viruses and Surveillance of Acute Gastrointestinal Illness Outbreaks in a Resource-Limited Region

Acute gastrointestinal illness (AGI) continues to be an important cause of morbidity and mortality among all ages. This study applied the principles of wastewater-based epidemiology for the preventive identification of potential outbreaks of acute viral gastroenteritis and hepatitis A by analyzing the presence of human enteric viruses in influents of small municipal wastewater treatment plants (WWTPs) handling domestic sewage, together with public health reports of acute diarrheal and hepatitis A disease in Costa Rica during 2013. Raw wastewater samples were collected during four seasonal periods with different rainfall levels. The presence of five human enteric viruses (rotavirus A, norovirus GI, norovirus GII, enterovirus, and hepatitis A virus) was studied by endpoint and real-time polymerase chain reaction in influents of five WWTPs. Cases of AGI were analyzed using historical public health reports of endemic levels and quartile ranges for each administrative and territorial area where the WWTPs are located and for its surrounding counties. A tendency for a higher rate of positive viral tests was present 1 week before an increase of AGI cases. Epidemiological weeks categorized as Outbreak (above the 75th percentile) and Success (below the 25th percentile) showed statistically significant differences in terms of positive viral test rates (Wilcoxon test, P = 0.05). Virological monitoring of wastewater in small WWTPs is an appropriate model for epidemiological surveillance of diarrheal and hepatitis A diseases in low- and middle-resource countries.

A Somatic Coliphage Threshold Approach To Improve the Management of Activated Sludge Wastewater Treatment Plant Effluents in Resource-Limited Regions

Effective wastewater management is crucial to ensure the safety of water reuse projects and effluent discharge into surface waters. Multiple studies have demonstrated that municipal wastewater treatment with conventional activated sludge processes is inefficient for the removal of a wide spectrum of viruses in sewage. In this study, a well-accepted statistical approach was used to investigate the relationship between viral indicators and human enteric viruses during wastewater treatment in a resource-limited region. Influent and effluent samples from five urban wastewater treatment plants (WWTPs) in Costa Rica were analyzed for somatic coliphage and human enterovirus, hepatitis A virus, norovirus genotypes I and II, and rotavirus. All WWTPs provide primary treatment followed by conventional activated sludge treatment prior to discharge into surface waters that are indirectly used for agricultural irrigation. The results revealed a statistically significant relationship between the detection of at least one of the five human enteric viruses and somatic coliphage. Multiple logistic regression and receiver operating characteristic curve analysis identified a threshold of 3.0 × 103 (3.5 log10) somatic coliphage PFU per 100 ml, which corresponded to an increased likelihood of encountering enteric viruses above the limit of detection (>1.83 × 102 virus targets/100 ml). Additionally, quantitative microbial risk assessment was executed for farmers indirectly reusing WWTP effluent that met the proposed threshold. The resulting estimated median cumulative annual disease burden complied with World Health Organization recommendations. Future studies are needed to validate the proposed threshold for use in Costa Rica and other regions.IMPORTANCE Effective wastewater management is crucial to ensure safe direct and indirect water reuse; nevertheless, few countries have adopted the virus log reduction value management approach established by the World Health Organization. In this study, we investigated an alternative and/or complementary approach to the virus log reduction value framework for the indirect reuse of activated sludge-treated wastewater effluent. Specifically, we employed a well-accepted statistical approach to identify a statistically sound somatic coliphage threshold value which corresponded to an increased likelihood of human enteric virus detection. This study demonstrates an alternative approach to the virus log reduction value framework which can be applied to improve wastewater reuse practices and effluent management.

Spontaneous transport barriers quench turbulent resistivity in two-dimensional magnetohydrodynamics

This Rapid Communication identifies the physical mechanism for the quench of turbulent resistivity in two-dimensional magnetohydrodynamics. Without an imposed, ordered magnetic field, a multiscale, blob-and-barrier structure of magnetic potential forms spontaneously. Magnetic energy is concentrated in thin, linear barriers, located at the interstices between blobs. The barriers quench the transport and kinematic decay of magnetic energy. The local transport bifurcation underlying barrier formation is linked to the inverse cascade of 〈A^{2}〉 and negative resistivity, which induce local bistability. For small-scale forcing, spontaneous layering of the magnetic potential occurs, with barriers located at the interstices between layers. This structure is effectively a magnetic staircase.

Observations of Multiple Nuclear Reaction Histories and Fuel-Ion Species Dynamics in Shock-Driven Inertial Confinement Fusion Implosions

Fuel-ion species dynamics in hydrodynamiclike shock-driven DT^{3}He-filled inertial confinement fusion implosion is quantitatively assessed for the first time using simultaneously measured D^{3}He and DT reaction histories. These reaction histories are measured with the particle x-ray temporal diagnostic, which captures the relative timing between different nuclear burns with unprecedented precision (∼10  ps). The observed 50±10  ps earlier D^{3}He reaction history timing (relative to DT) cannot be explained by average-ion hydrodynamic simulations and is attributed to fuel-ion species separation between the D, T, and ^{3}He ions during shock convergence and rebound. At the onset of the shock burn, inferred ^{3}He/T fuel ratio in the burn region using the measured reaction histories is much higher as compared to the initial gas-filled ratio. As T and ^{3}He have the same mass but different charge, these results indicate that the charge-to-mass ratio plays an important role in driving fuel-ion species separation during strong shock propagation even for these hydrodynamiclike plasmas.

Enterococci as a key parameter for water quality index: Purires River, Costa Rica

This study used the Canadian Water Quality Index (CWI) to characterize water sampled at three points within the Purires River micro basin, Costa Rica. The first sampling point is located in a high zone with domestic agricultural activities, the second point around the mid-point of the flow of the river, and the third point at the lowest zone with extensive agricultural activities mainly centered on the production of fresh vegetables. Eleven physicochemical parameters (As, Cd, Cr, biochemical oxygen demand (BOD), chemical oxygen demand (COD), NH₄ ⁺, NO₃ ^-, Pb, pH, percent saturation of dissolved oxygen (PSO), and total suspended solids (TSS)) and two microbiological parameters (fecal coliforms and enterococci) were evaluated. We evaluated three different Canadian Water Quality Indexes (CWIs): CWI-1 included only physicochemical parameters, CWI-2 included CWI-1 parameters plus fecal coliforms, and CWI-3 included CWI-2 in addition to enterococci. Statistical analysis of individual parameters showed significant differences between sampling sites. CWI-1 was unable to discriminate between the three sampling points, and characterized the water quality as 'fair'. CWI-2 was only able to discriminate when the water contained high levels of chemical and microbiological contaminants, while CWI-3 adequately discriminated water quality at each of the sampling points. The evaluation of enterococci together with more traditional water quality parameters enabled better categorization of surface water quality.

Formation and evolution of target patterns in Cahn-Hilliard flows

We study the evolution of the concentration field in a single eddy in the two-dimensional (2D) Cahn-Hilliard system to better understand scalar mixing processes in that system. This study extends investigations of the classic studies of flux expulsion in 2D magnetohydrodynamics and homogenization of potential vorticity in 2D fluids. Simulation results show that there are three stages in the evolution: (A) formation of a "jelly roll" pattern, for which the concentration field is constant along spirals; (B) a change in isoconcentration contour topology; and (C) formation of a target pattern, for which the isoconcentration contours follow concentric annuli. In the final target pattern stage, the isoconcentration bands align with stream lines. The results indicate that the target pattern is a metastable state. The band merger process continues on a time scale exponentially long relative to the eddy turnover time. The band merger process resembles step merger in drift-ZF staircases; this is characteristic of the long-time evolution of phase-separated patterns described by the Cahn-Hilliard equation.

Role of Ion Kinetic Physics in the Interaction of Magnetic Flux Ropes

To explain many natural magnetized plasma phenomena, it is crucial to understand how rates of collisionless magnetic reconnection scale in large magnetohydrodynamic (MHD) scale systems. Simulations of isolated current sheets conclude such rates are independent of system size and can be reproduced by the Hall-MHD model, but neglect sheet formation and coupling to MHD scales. Here, it is shown for the problem of flux-rope merging, which includes this formation and coupling, that the Hall-MHD model fails to reproduce the kinetic results. The minimum sufficient model must retain ion kinetic effects, which set the ion diffusion region geometry and give time-averaged rates that reduce significantly with system size, leading to different global evolution in large systems.

Experimental-like helical self-organization in reversed-field pinch modeling

We report the first nonlinear three-dimensional magnetohydrodynamic (MHD) numerical simulations of the reversed-field pinch (RFP) that exhibit a systematic repetition of quasisingle helicity states with the same dominant mode in between reconnection events. This distinctive feature of experimental self-organized helical RFP plasmas is reproduced in MHD simulations at low dissipation by allowing a helical modulation of the plasma magnetic boundary similar to the experimental one. Realistic mode amplitudes and magnetic topology are also found.

Flux pileup in collisionless magnetic reconnection: bursty interaction of large flux ropes

Using fully kinetic simulations of the island coalescence problem for a range of system sizes greatly exceeding kinetic scales, the phenomenon of flux pileup in the collisionless regime is demonstrated. While small islands on the scale of λ ≤ 5 ion inertial length (d(i)) coalesce rapidly and do not support significant flux pileup, coalescence of larger islands is characterized by large flux pileup and a weaker time averaged reconnection rate that scales as √(d(i)/λ) while the peak rate remains nearly independent of island size. For the largest islands (λ = 100d(i)), reconnection is bursty and nearly shuts off after the first bounce, reconnecting ~20% of the available flux.

Local and nonlocal parallel heat transport in general magnetic fields

A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.

23 EFFECT OF HISTONE ACETYLATION LEVELS ON THE IN VITRO DEVELOPMENT OF CLONED BOVINE EMBRYOS

The epigenetic status of donor cells is an important factor for their successful reprogramming during somatic cell nuclear transfer (SCNT). Environmental factors partly influence DNA methylation and histone modifications (Fraga et al. 2005 PNAS USA 102, 10 604–10 609; Ke et al. 2006 Carcinogenesis 27, 1481–1488; Rodenhiser and Mann 2006 CMAJ 174, 341–348); low temperatures have altered epigenetic events in plants (Amasino 2004 Plant Cell; Hao et al. 2002 Cryo Letters 23, 37–46). Because cryopreservation alters histone acetylation levels in donor cells and subsequent viability of cloned embryos (Gómez et al. 2008 Cloning Stem Cells, in press), similar alterations may occur in bovine cloned embryos reconstructed with donor cells thawed immediately before SCNT. The objectives of the present study were (1) to measure the relative levels of nuclear histone acetylation in bovine fibroblasts immediately after thawing (frozen/thawed) or following a period of culturing (cultured) and (2) to determine the influence of the epigenetic status of donor cells on the in vitro development of reconstructed, cloned bovine embryos by gauging blastocyst development. Cell cultures lines were derived from the skin of 3 adult cows and analyzed at passage 1 (P1), 2 (P2), and 10 (P10). For each of 3 passages, cells were cultured until reaching 100% confluence, followed by an additional 3 days of culture during which time acetylation levels were measured in cultured and frozen/thawed cells. For cryopreservation, cells at P1, P2, and P10 were disaggregated and resuspended in CryoStor™ (CS10; BioLife Solutions, Bothell, WA, USA) and cooled at 1.0°C min–1 to –80°C prior to storage in liquid nitrogen. Cells were fixed with ethanol for 12 h and incubated for 30 min with antibody directed against acetylated lysine 9 on histone 3 (H3K9). The cells were then incubated with a fluorescein isothiocyanate conjugated secondary antibody and DNA stain and evaluated by flow cytometry. Cloned embryos were reconstructed with cultured or frozen/thawed cells at P1, P2, and P10 as described by Vajta et al. 2005 (Reprod. Fertil. Dev. 17, 791–797). Derived embryos were cultured until Day 8, and cleavage and development to the blastocyst stage were evaluated. Histone acetylation levels for all 3 cell lines, either fresh or frozen/thawed, were significantly higher at P1 than at P2 and P10 (Table 1), and cryopreservation reduced histone acetylation levels only in cell culture line 2 at P1. Higher development to the blastocyst stage (25%) was observed when embryos were reconstructed with cultured cells at P2 and with cells that had lower histone acetylation levels (Pearson correlation, r = –0.55; P = 0.01) Table 1.Relative levels of histone acetylation in bovine fibroblast culture and percentages of development to blastocyst stage after cloning

Evolution in the resistance of Mycobacterium tuberculosis to anti-tuberculosis drugs in Nicaragua

SETTING

Nicaragua, a country where the DOTS strategy has been successfully implemented since 1984.

OBJECTIVE

To estimate the prevalence and trends of Mycobacterium tuberculosis resistance to first-line anti-tuberculosis drugs.

DESIGN

A prospective national survey carried out in 2004 according to the standardised model developed by the World Health Organisation and the International Union Against Tuberculosis and Lung Disease.

RESULTS

A total of 423 M. tuberculosis strains were studied. Among the 320 strains evaluated for initial resistance, 13.1% displayed resistance to any drug, lower than the 1998 figure of 15.6%. Overall initial resistance to isoniazid (INH), rifampicin (RMP) and multidrug resistance (MDR) was respectively 6.6%, 0.9% and 0.6%. Initial resistance was higher in older age groups. Overall acquired resistance was 35.9% (n = 103); resistance to INH was 29.3% and to RMP 8.9%, while MDR was 7.9%. The acquired MDR rate was clearly higher in Category I failures (44.4%) than in relapses (3.8%) and retrieved defaulters (2.7%). All resistance rates found in this study were lower than those detected in 1998.

CONCLUSION

This study shows low rates of resistance and MDR and a downward trend in all rates, undoubtedly related to the proper implementation of the National Tuberculosis Programme.

Quantitative, comprehensive, analytical model for magnetic reconnection in Hall magnetohydrodynamics

Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}.

Fast reconnection in nonrelativistic 2D electron-positron plasmas

In this Letter, we put forth (and validate numerically) a fluid-based analytical theory, which predicts that fast reconnection in nonrelativistic, low-beta pair plasmas is possible in collisionless regimes. This novel theoretical result complements recent kinetic computational evidence and challenges the accepted understanding, which considers fast dispersive waves (not supported in pair plasmas) as the key enabling physics ingredient for fast reconnection. The implications of this theory for the understanding of fast reconnection in standard electron-proton plasmas are discussed.

25 CRYOPRESERVATION AND IN VITRO CULTURE AFFECT HISTONE ACETYLATION LEVELS OF BOVINE FIBROBLASTS

Long-term culture of bovine fibroblasts increases histone acetylation levels (Enright et al. 2003 Biol. Reprod. 69, 1525–1530), and blastocyst development and pregnancy rates are enhanced by using donor cells having high levels of histone acetylation (Yang et al. 2007 Reproduction 133, 219–230; Yang et al. 2006 Biol. Reprod. 76, 36–42). When histone acetylation levels are increased in amino acid residues, the nucleosome is less tightly bound to DNA and, as a consequence, relaxation of the chromatin structure occurs (Zlatanova et al. 2000 FASEB J. 14, 1697–1704). Exposure of the donor cell with relaxed chromatin structure to oocyte cytoplasm factors after nuclear transfer (NT) may be effective for nuclear reprogramming (Tóth et al. 2004 J. Cell Sci. 117, 4277–4287). Bovine embryos can be reconstructed with donor cells thawed immediately before NT, but it is not known if epigenetic changes arise during cell cryopreservation, and if NT efficiency is affected. The acetylated form of histone H3-lysine 9-lysine 14 (acH3K9/14) is associated with active chromatin configuration (Rice and Allis 2001 Curr. Opin. Cell Biol. 13, 263–273) and active transcription (Fuks 2005 Curr. Opin. Genet. Dev. 15, 490–495) and, thus, can be used as a marker to determine epigenetic changes in somatic cells. The purpose of our study was to evaluate histone acetylation levels of cultured and cryopreserved bovine fibroblasts. Cells were derived from skin of three adult cows and cultured in GMEM for 15 days. Fibroblasts from each of the three cell lines were analyzed at passage 1 (P1), 2 (P2), and 10 (P10). At each of the three passages, cells were cultured until reaching 100% confluence, followed by an additional 3 days in culture during which time acetylation levels were measured in fresh and frozen cells. For cryopreservation, cells at P1, P2, and P10 were disaggregated with accutase, resuspended in CryoStor™ (CS10; BioLife Solutions, Bothell, WA, USA), and cooled at 1.0°C min–1 to –80°C prior to storage in liquid nitrogen. Cells were fixed with ethanol for 12 h and incubated for 30 min with antibody directed against acetylated lysine 9 on histone 3 (H3K9). Then, cells were incubated with a fluorescein isothiocyanate (FITC) conjugated secondary antibody and DNA stain and evaluated by flow cytometry. Overall, histone acetylation levels in frozen cells (70%) were lower than levels in fresh cells (86%; P < 0.05), and all cell lines, whether fresh or frozen, showed lower acetylation levels at P1 (61%) than at P2 and P10 (88% and 85%, respectively; P < 0.001). No significant differences were observed between individual cell lines for fresh and frozen treatments. However, frozen cells from cell line 3 showed lower histone acetylation levels than fresh cells from cell line 3 and cell lines 1 and 2 at each passage. In summary, histone acetylation levels were lower in cryopreserved bovine fibroblasts and were higher in cell lines cultured for longer times. Table 1. Flow cytometrically detected acetylation levels of lysine 9 on histone 3 in cultured or cryopreserved bovine fibroblast cell lines passed for 1, 2, or 10 times

Steady-state properties of driven magnetic reconnection in 2D electron magnetohydrodynamics

We formulate a rigorous nonlinear analytical model that describes the dynamics of the diffusion (reconnection) region in driven systems in the context of electron magnetohydrodynamics (EMHD). A steady-state analysis yields allowed geometric configurations and associated reconnection rates. In addition to the well-known open X-point geometry, elongated configurations are found possible. The model predictions have been validated numerically with two-dimensional EMHD nonlinear simulations, and are in excellent agreement with previously published work.

112 VIABILITY AND APOPTOSIS OF BOVINE FIBROBLASTS FROZEN IN A CONVENTIONAL ( - 20°C) OR LOW-TEMPERATURE ( - 80°C) FREEZER

Fibroblasts are commonly frozen in dimethyl sulfoxide (DMSO, 10% v/v) at a cooling rate of 1°C min−1 in cryo-containers placed in a low-temperature (−80°C) freezer (LTF) overnight before storage in liquid nitrogen (LN2). LTFs are not always available and cell viability may be altered by freezing at different cooling rates. Therefore, the purpose of the present study was to evaluate apoptosis and viability of bovine fibroblasts frozen at different cooling rates in a −80°C freezer or conventional −20°C freezer. Fibroblasts were generated from skin tissue collected from an adult female cow. Tissue was cut and cultured in DMEM for 7 to 10 days and passaged 2 or 3 times before being cryopreserved. Cells were frozen by one of 6 procedures; cells that were not frozen served as a control. To be frozen, cells were resuspended in DMEM + 10% FBS and 10% DMSO in 2-mL cryo-vials before being placed into freezing containers (Mr. Frosty, Nalgene). For groups 1 and 2, the container was placed in a −20°C freezer and cooled at ≈0.6°C min−1 to −7°C; ice formation was induced by seeding, after which cooling was continued at ≈0.6°C min−1 to −20°C. Vials in groups 1 and 2 were placed in LN2 after 1 h and 16 to 18 h, respectively. Group 3 and 4 vials were also cooled to −20°C at 0.6°C min, except that these samples were not seeded. After being held at −20°C for 16 to 18 h, group 3 vials were thawed; group 4 vials were stored in LN2. Vials in groups 5 and 6 were placed into a Mr. Frosty container and cooled at ≈1°C min−1 in a −80°C freezer. After being held at −80°C for 16 to 18 h, group 5 vials were thawed, and group 6 vials were placed into LN2. Group 1, 2, 3, and 4 vials were thawed in a 37°C water bath; group 5 and 6 vials were thawed in a 40°C water bath. Cell viabilities were quantified by using TB exclusion (TB) with microscopy. At least 20 000 cells from each group were thawed, and caspase 3, a key enzyme involved in apoptotic processes, was detected using a Caspase 3-FLICA apoptosis detection kit; propidium iodide-stained nuclei were assessed with cytometry (FCM) to determine viability (Table 1). Data were analyzed by ANOVA (P &lt; 0.05). Although there were viability differences among groups, freezer type, seeding, holding time, and LN2 had no significant impact, as assessed by TB or FCM; however, no LN2 significantly increased the percentage of viable cells displaying apoptosis. In summary, bovine fibroblasts were successfully frozen in a conventional (−20°C) freezer before storage in LN2. Table 1. Viability and apoptosis of bovine fibroblasts frozen at −20°C or −80°C

Evaluation of a rapid culture method for tuberculosis diagnosis: a Latin American multi-center study

SETTINGS

Tuberculosis (TB) diagnostic laboratories in Latin America.

OBJECTIVES

Evaluation of thin-layer agar (TLA) compared to Löwenstein-Jensen (LJ) culture for the diagnosis of TB.

DESIGN

Phase II prospective study in six laboratories. Samples included sputum and extra-pulmonary specimens from patients with a clinical diagnosis of TB. Respiratory samples were decontaminated using NaOH/ NALC; all samples were centrifuged, stained with Ziehl-Neelsen for acid-fast bacilli (AFB), cultured on LJ and TLA and identified according to recommended procedures. Sensitivity and likelihood ratios (LR), growth detection time and contamination rate were calculated for both media.

RESULTS

A total of 1118 clinical specimens were studied. Cultures detected Mycobacterium tuberculosis in all AFB-positive samples, whereas for AFB-negative specimens LJ detected 3.2% and TLA 4.4%. Sensitivity was 92.6% (95%CI 87.9-95.9) and 84.7% (95%CI 78.8-89.0) for TLA and LJ, respectively. Positive and negative LRs were similar. Contamination was 5.1% for TLA and 3.0% for LJ. Median time to detection of a positive culture was 11.5 days (95%CI 9.3-15.0) for TLA and 30.5 days (95%CI 26.9-39.0) for LJ (P < 0.0001).

CONCLUSION

Difference in the characteristics of the participating laboratories, the disease prevalence and the number and type of specimens processed did not affect the overall performance of TLA as compared to LJ, supporting the robustness of the method and its feasibility in different laboratory settings.

Coalescence of magnetic islands in the low-resistivity, Hall-MHD regime

The coalescence of magnetic islands in the low-resistivity eta, Hall-MHD regime is studied. The interaction between the ion inertial length d(i) and the dynamically evolving current sheet scale length deltaJ is established. Initially, d(i) << deltaJ. If eta is such that deltaJ dynamically thins down to d(i) prior to the well-known sloshing phenomena, then sloshing is avoided. This results in eta independent peak reconnection rates. However, if d(i) is small enough that deltaJ cannot be thinned down to this scale prior to sloshing, then sloshing proceeds as in the resistive MHD model.

Magnetic reconnection in the two-dimensional Kelvin-Helmholtz instability

Magnetic reconnection in the two-dimensional Kelvin-Helmholtz instability is studied. The flow is modeled by the reduced MHD equations with constant resistivity and viscosity. For super-Alfvénic flow, localized transient reconnection is observed on the Kelvin-Helmholtz time scale (this is not new). We study this transient reconnection and consider the peak reconnection rate which occurs with the initial vortex formation. Over the range of resistivities considered, it is shown that this peak reconnection rate is not a function of resistivity, and is a function of the initial flow shear. Additionally, it is demonstrated that there is a fundamental difference between the evolution of a problem at S = 200 and S = 10,000.

[Knowledge, opinions, and practices regarding Aedes aegypti]

The active participation of the community is indispensable for reducing Aedes aegypti mosquito populations so causes leading to their growth, actions taken, effects on the health and the people in charge of controlling such mosquitoes are all dealt with in this paper. 210 persons were interviewed from June 25 to 27, 1997. The causes of the growth of the mosquito population were: excessive garbage (59%), dirty waters (58%), open water reservoirs (50%) and lack of fumigation (21%). 40% of interviewed people did not know that these vectors can breed even in clean waters. They mentioned some effects on the health due to the mosquito bites. 51% said that mosquitoes should be jointly controlled by the State and the community but 35% believed that the State should be the sole responsible for this task. These opinions may determine that steps are not properly taken to avoid proliferation of vector and that the activities of the anti-vector program are not really understood since they do not meet the expectations.

Chick embryo development can be irreversibly altered by early exposure to weak extremely-low-frequency magnetic fields

Several reports have shown that weak, extremely-low-frequency (ELF), pulsed magnetic fields (PMFs) can adversely affect the early embryonic development of the chick. In this study, freshly fertilized chicken eggs were exposed during the first 48 h of postlaying incubation to PMFs with 100 Hz repetition rate, 1.0 microT peak-to-peak amplitude, and 500 microseconds pulse duration. Two different pulse waveforms were used, having rise and fall times of 85 microseconds (PMF-A) or 2.1 microseconds (PMF-B). It has been reported that, with 2 day exposure, these fields significantly increase the proportion of developmental abnormalities. In the present study, following exposure, the eggs were allowed to incubate for an additional 9 days in the absence of the PMFs. The embryos were taken out of the eggs and studied blind. Each of the two PMF-exposed groups showed an excess in the percentage of developmental anomalies compared with the respective sham-exposed samples. This excess of anomalies was not significant for the PMF-A-treated embryos (P = 0.173), whereas it was significant for the PMF-B-exposed group (P = 0.007), which showed a particularly high rate of early embryonic death. These results reveal that PMFs can induce irreversible developmental alterations and confirm that the pulse waveform can be a determinant factor in the embryonic response to ELF magnetic fields. The data also validate previous work based on the study of PMFs' effects at day 2 of embryonic development under field exposure.

Clomipramine actions on firing rate in septal nuclei of the rat are not related to anaesthesia (urethane)

An increased firing rate in lateral septal nuclei (LSN) appears in urethane-anesthetized rats after several acute drug and non-drug human antidepressant treatments. A still more pronounced increase in firing rate is produced in LSN after clomipramine (CMI) long-term treatment. In spite of urethane is a widely used anesthetic for single unit extracellular recordings, it modifies evoked potentials wave-form. Therefore, present study discards urethane interaction with CMI in LSN single unit extracellular recordings. CMI was acutely injected (1.25 mg/kg: IP) either to urethane-anesthetized, or non-anesthetized encephale-isolé rats. The CMI treated groups showed higher rates of firing in LSN regardless of the use of general anesthesia during recordings. Another group of urethane-anesthetized rats received intracerebroventricular (ICV) microinjections of CMI (100 micrograms/10 microliters/1 min). An amount of 42.8% of LSN-recorded neurons responded with a long-lasting increased firing rate. Results discard urethane and CMI interactions. Additionally, systemic actions of CMI on firing rate of LSN are reproduced by ICV/route microinjections.