Amazon deforestation alters small stream structure, nitrogen biogeochemistry and connectivity to larger rivers

Human activities that modify land cover can alter the structure and biogeochemistry of small streams but these effects are poorly known over large regions of the humid tropics where rates of forest clearing are high. We examined how conversion of Amazon lowland tropical forest to cattle pasture influenced the physical and chemical structure, organic matter stocks and N cycling of small streams. We combined a regional ground survey of small streams with an intensive study of nutrient cycling using (15)N additions in three representative streams: a second-order forest stream, a second-order pasture stream and a third-order pasture stream. These three streams were within several km of each other and on similar soils. Replacement of forest with pasture decreased stream habitat complexity by changing streams from run and pool channels with forest leaf detritus (50% cover) to grass-filled (63% cover) channel with runs of slow-moving water. In the survey, pasture streams consistently had lower concentrations of dissolved oxygen and nitrate (NO(3) (-)) compared with similar-sized forest streams. Stable isotope additions revealed that second-order pasture stream had a shorter NH(4) (+) uptake length, higher uptake rates into organic matter components and a shorter (15)NH(4) (+) residence time than the second-order forest stream or the third-order pasture stream. Nitrification was significant in the forest stream (19% of the added (15)NH(4) (+)) but not in the second-order pasture (0%) or third-order (6%) pasture stream. The forest stream retained 7% of added (15)N in organic matter compartments and exported 53% ((15)NH(4) (+) = 34%; (15)NO(3) (-) = 19%). In contrast, the second-order pasture stream retained 75% of added (15)N, predominantly in grasses (69%) and exported only 4% as (15)NH(4) (+). The fate of tracer (15)N in the third-order pasture stream more closely resembled that in the forest stream, with 5% of added N retained and 26% exported ((15)NH(4) (+) = 9%; (15)NO(3) (-) = 6%). These findings indicate that the widespread infilling by grass in small streams in areas deforested for pasture greatly increases the retention of inorganic N in the first- and second-order streams, which make up roughly three-fourths of total stream channel length in Amazon basin watersheds. The importance of this phenomenon and its effect on N transport to larger rivers across the larger areas of the Amazon Basin will depend on better evaluation of both the extent and the scale at which stream infilling by grass occurs, but our analysis suggests the phenomenon is widespread.

Biodegradable nanosize particles of poly(L,L-lactide)-b-poly(ethylene glycol)-b-poly(L,L-lactide)

Two series of poly(L,L-lactide-b-ethylene glycol-b-L,L-lactide) copolymers, PLA-PEO-PLA, were synthesized by polymerization Of L,L-lactide using a dihydroxy-terminated poly(ethylene glycol) (PEG) (M-n = 4000 or 600 g/mol) as coinitiator and stannous 2-ethylhexanoate, Sn(Oct)(2), as initiator. The synthesized copolymers have shown high stereoregularity as observed by C-13 NMR analyses. The nanoparticles were prepared by using a solvent diffusion method and the self-assemblage process and were characterized by NMR and SEM. It was possible to conclude that the self-assembled particles presented a core-shell structure characterized by a hydrophobic PLA core and a hydrophilic PEG shell, thus the NMR of the aqueous solutions indicated a quasi-solid behavior for the particles` interior. The diameters of the spherical particles as observed by SEM were in the 50-250 nm range, depending on the copolymer composition and the preparation procedure.

Microbiological Assay for Apramycin Soluble Powder

The aim of this study was to validate an agar diffusion method through the parameters linearity, precision and accuracy, to quantify apramycin in soluble powder. The calibration curve of apramycin was constructed by plotting log of concentrations (mu g ml(-1)) versus zone diameter (mm) and shows good linearity in the range of 1.0-4.0 mu g.ml(-1). The precision of the assay was determined by assaying samples at the same day (repeatability - R.S.D. = 2.00%) and on different days (intermediate precision - R.S.D. = 5.06%) and indicate good precision. The accuracy expresses the agreement between the accepted value and the value found. The mean recovery was found to be 100.49 % for apramycin soluble powder. The results indicated that the microbiological assay proposed in this work hold linearity, precision and accuracy being an acceptable alternative method for routine quality control of apramycin in the pharmaceutical dosage form studied.

Expression, purification, crystallization, and NMR studies of the helicase interaction domain of Escherichia coli DnaG primase

in Escherichia coli, the DnaG primase is the RNA polymerase that synthesizes RNA primers at replication forks. It is composed of three domains, a small N-terminal zinc-binding domain, a larger central domain responsible for RNA synthesis, and a C-terminal domain comprising residues 434-581 [DnaG(434-581)] that interact with the hexameric DnaB helicase. Presumably because of this interaction, it had not been possible previously to express the C-terminal domain in a stably transformed E coli strain. This problem was overcome by expression of DnaG(434-581) under control of tandem bacteriophage gimel-promoters, and the protein was purified in yields of 4-6 mg/L of culture and studied by NMR. A TOCSY spectrum of a 2 mM solution of the protein at pH 7.0, indicated that its structured core comprises residues 444-579. This was consistent with sequence conservation among most-closely related primases. Linewidths in a NOESY spectrum of a 0.5 mM sample in 10 mM phosphate, pH 6.05, 0.1 M NaCl, recorded at 36 degreesC, indicated the protein to be monomeric. Crystals of selenomethionine-substituted DnaG(434-581) obtained by the hanging-drop vapor-diffusion method were body-centered tetragonal, space group I4(1)22, with unit cell parameters a = b 142.2 Angstrom, c = 192.1 Angstrom, and diffracted beyond 2.7 Angstrom resolution with synchrotron radiation. (C) 2003 Elsevier Inc. All rights reserved.

Synthesis, spectroscopic characterization, DFT studies and biological assays of a novel gold(I) complex with 2-mercaptothiazoline

A new gold(I) complex with 2-mercaptothiazoline (MTZ) with the coordination formula [AuCN(C(3)H(5)NS(2))] was synthesized and characterized by chemical and spectroscopic measurements, OFT studies and biological assays. Infrared (IR) and (1)H, (13)C and (15)N nuclear magnetic resonance (NMR) spectroscopic measurements indicate coordination of the ligand to gold(I) through the nitrogen atom. Studies based on OFT confirmed nitrogen coordination to gold(I) as a minimum of the potential energy surface with calculations of the hessians showing no imaginary frequencies. Thermal decomposition starts at temperatures near 160 degrees C, leading to the formation of Au as the final residue at 1000 degrees C. The gold(I) complex with 2-mercaptothiazoline (Au-MTZ) is soluble in dimethyl sulfoxide (DMSO), and is insoluble in water, methanol, ethanol, acetonitrile and hexane. The antibacterial activities of the Au-MTZ complex were evaluated by an antibiogram assay using the disc diffusion method. The compound showed an effective antibacterial activity against Staphylococcus aureus (Gram-positive) and Escherichia coli and Pseudomonas aeruginosa (Gram-negative) bacterial cells. Biological analysis for evaluation of the cytotoxic effect of the Au-MTZ complex was performed using HeLa cells derived from human cervical adenocarcinoma. The complex presented a potent cytotoxic activity, inducing 85% of cell death at a concentration of 2.0 mu mol L(-1). (C) 2011 Elsevier Ltd. All rights reserved.

Direct and transdentinal antibacterial activity of chlorhexidine

Purpose: To evaluate the antibacterial effect of different chlorhexidine (CHX) concentrations against Streptococcus mutans using the agar-diffusion method with and without human dentin discs placed between the bacteria and the test substances. Methods: For the direct application (agar-well technique), a base layer containing 15 mL of BHI agar and 300 mu L. of S. mutans inoculum (10(9) cfu/mL) was prepared in Petri dishes. Six wells per dish were made at equidistant points and immediately filled with CHX gels (0.12%, 0.2%, 1% and 2%), 35% phosphoric acid and pure natrosol (n=6 wells/substance). Paper discs soaked in sterile distilled water served as control group (n=6). For the indirect application (transdentinal diffusion), 0.2 mm- and 0.5 mm-thick human dentin discs (36 discs/thickness) had the hydraulic conductance determined, which allowed the homogeneous allocation of them to the experimental and control groups. The discs were placed at equidistant points on the Petri dishes containing BHI with the S. mutans inoculum (six discs per dish; one per substance) with the pulpal side in contact with the bacteria. In the discs treated with CHX gels, dentin surface was etched with H(3)PO(4) and rinsed with distilled water before CHX gel application for 1 minute. After both direct and indirect application, the dishes were incubated for 24 hours and the bacterial growth inhibition zones formed around the wells and dentin discs were measured. Data were analyzed statistically by the non-parametric Kruskal-Wallis and Mann-Whitney tests at 5% significance level. Results: In the direct test, all CHX concentrations presented a dose-dependent antibacterial activity against S. mutans. In the indirect test, there were statistically significant differences (P< 0.05) among all groups and the largest microbial growth inhibition zones were observed when 2% CHX was applied on 0.2 mm-thick discs (P< 0.05). It was concluded that all evaluated CHX gels exhibited both direct and transdentinal antibacterial activity against S. mutans. This effect of CHX was strongly influenced by the CHX concentration as well as the dentin barrier thickness. (Am J Dent 2010;23:255-259).

PHB-PEO electrospun fiber membranes containing chlorhexidine for drug delivery applications

Fiber meshes of poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate)/ poly(ethylene oxide) (PHB/PEO) with different concentrations of chlorhexidine (CHX) were prepared by electrospinning, for assessment as a polymer based drug delivery system. The electrospun fibers were characterized at morphological, molecular and mechanical levels. The bactericidal potential of PHB and PHB/PEO electrospun fibers with and without CHX was investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by disk diffusion susceptibility tests. Electrospun fibers containing CHX exhibited bactericidal activity. PHB/PEO-1%CHX displayed higher CHX release levels and equivalent antibacterial activity when compared to PHB/PEO with 5 and 10 wt% CHX. Bactericidal performance of samples with 1 wt% CHX was assessed by Colony Forming Units (CFU), where a reduction of 100 % and 99.69 % against E. coli and S. aureus were achieved, respectively.

Extração e caracterização de extratos de Jatropha gossypiifolia L.: avaliação da sua atividade antimicrobiana e antioxidante

Trabalho Final de Mestrado para obtenção do grau de mestre em Engenharia Química e Biológica

Genetic relationships of Corynebacterium diphtheriae strains isolated from a diphtheria case and carriers by restriction fragment length polymorphism of rRNA genes

In the present study we report the results of an analysis, based on ribotyping of Corynebacterium diphtheriae intermedius strains isolated from a 9 years old child with clinical diphtheria and his 5 contacts. Quantitative analysis of RFLPs of rRNA was used to determine relatedness of these 7 C.diphtheriae strains providing support data in the diphtheria epidemiology. We have also tested those strains for toxigenicity in vitro by using the Elek's gel diffusion method and in vivo by using cell culture method on cultured monkey kidney cell (VERO cells). The hybridization results revealed that the 5 C.diphtheriae strains isolated from contacts and one isolated from the clinical case (nose case strain) had identical RFLP patterns with all 4 restriction endonucleases used, ribotype B. The genetic distance from this ribotype and ribotype A (throat case strain), that we initially assumed to be responsible for the illness of the patient, was of 0.450 showing poor genetic correlation among these two ribotypes. We found no significant differences concerned to the toxin production by using the cell culture method. In conclusion, the use of RFLPs of rRNA gene was successful in detecting minor differences in closely related toxigenic C.diphtheriae intermedius strains and providing information about genetic relationships among them.

Epidemiological characterization, antimicrobial resistance and virulence mechanisms of human and animal streptococci

Dissertação para obtenção do Grau de Doutor em Biologia

Indications of carbapenem resistance evolution through heteroresistance as an intermediate stage in Acinetobacter baumannii after carbapenem administration

We describe an in vivo evolution of an antimicrobial profile from susceptibility to full-resistance to carbapenems, with heteroresistance as an intermediate stage, in an Acinetobacter baumannii strain. Heteroresistance was characterized by the growth of sub-populations within the susceptibility halo in both disk-diffusion and Etest. PCRs for the main A. baumannii carbapenemases were negative. The exact resistance mechanism, diagnostic methods and clinical relevance of heteroresistance in A. baumannii warrant further investigations. This is the first description of such phenomenon in vivo and the second report of heteroresistance to carbapenems in A. baumannii.

Isolation and antifungal susceptibility testing of Trichosporon asahii in Ceará, Brazil

Trichosporon spp. are yeasts capable of causing invasive disease, which mainly affect immunocompromised patients. A clinical strain of T. asahii was isolated from the blood cultures of patients admitted to the General Hospital of Fortaleza. Susceptibility tests were conducted by disk diffusion and broth microdilution. The isolated strain of T. asahii was resistant to fluconazole. The patient used amphotericin B and caspofungin in order to facilitate the microbiological cure. It was the first isolation and identification of T. asahii in blood culture in Ceará, Brazil.

Preliminary study of community-acquired Staphylococcus aureus infection in Manaus Hospital, Amazonia Region, Brazil

Methicillin resistant Staphylococcus aureus is considered a public health problem with a strong potential for dissemination and high rates of morbidity and mortality. In this study we describe bacteriological and epidemiological characteristics of Staphylococcus aureus in Manaus (Amazon region). During the one-year study period (2000-2001), sixteen cases of acute pyogenic multiple abscess were evaluated. Community-acquired S. aureus was identified as causative agent in 10 (62.5%) patients. The strains tested with antimicrobials by discs diffusion method, exhibited a high rate of sensitivity to cephalexin (100%), erythromycin (90%). Oxacillin-susceptible Staphylococcus aureus was 90%. No isolate was resistant to Vancomycin. To our knowledge, no series of community-acquired Staphylococcus aureus in Manaus hospital has been published. Our partial results showed a high rate of antimicrobial sensitivity among community-acquired Staphylococcus aureus in the hospital of Tropical Medicine Institute of Manaus, Amazon Region.

Evaluation of bacterial growth inhibition by mercaptopropionic acid in metallo-β-lactamase detection on multidrug-resistant Acinetobacter baumannii

INTRODUCTION: Metallo-β-lactamase (MBL) has been reported all over the world. METHODS: The inhibitory effect of mercaptopropionic acid (MPA) on bacterial growth was evaluated by comparison between disk diffusion and broth dilution methodology with determination of the minimum inhibitory concentration (MIC) for multidrug-resistant Acinetobacter baumanni strains. RESULTS: MPA significantly inhibited growth of the strains. CONCLUSIONS: The use of MPA can affect the results in phenotypic methods of MBL detection.

Prevalence of resistance phenotypes in Staphylococcus aureus and coagulase-negative isolates of venous ulcers of primary healthcare patients

INTRODUCTION: In venous ulcers, the presence of Staphylococcus aureus and coagulase-negative staphylococcus resistance phenotypes can aggravate and limit the choices for treatment. METHODS: Staphylococcus isolated from 69 patients (98 ulcers) between October of 2009 and October of 2010 were tested. The macrolide, lincosamide, streptogramin B (MLS B) group resistance phenotype detection was performed using the D-test. Isolates resistant to cefoxitin and/or oxacillin (disk-diffusion) were subjected to the confirmatory test to detect minimum inhibitory concentration (MIC), using oxacillin strips (E-test®). RESULTS: The prevalence of S. aureus was 83%, and 15% of coagulase-negative staphylococcus (CoNS). In addition were detected 28% of methicillin-resistant Staphylococcus aureus (MRSA) and 47% of methicillin-resistant coagulase-negative staphylococcus (MRCoNS). Among the S. aureus, 69.6% were resistant to erythromycin, 69.6% to clindamycin, 69.6% to gentamicin, and 100% to ciprofloxacin. Considering the MRSA, 74% were highly resistant to oxacillin, MIC ≥ 256µg/mL, and the MLS Bc constitutive resistance predominated in 65.2%. Among the 20 isolates sensitive to clindamycin, 12 presented an inducible MLS B phenotype. Of the MRCoNS, 71.4%were resistant to erythromycin, ciprofloxacin and gentamicin. Considering the isolates positive for β-lactamases, the MIC breakpoint was between 0.5 and 2µg/mL. CONCLUSIONS: The results point to a high occurrence of multi-drug resistant bacteria in venous ulcers in primary healthcare patients, thus evidencing the need for preventive measures to avoid outbreaks caused by multi-drug resistant pathogens, and the importance of healthcare professionals being able to identifying colonized versus infected venous ulcers as an essential criteria to implementing systemic antibacterial therapy.