RESUMO
Based on the search for new biodegradable materials that are low cost and easy to synthesize by environmentally friendly methods, we report the use of carrageenan membranes (mixture of κ and λ carrageenans) with different concentrations of titanium dioxide nanoparticles (TiO2 NPs) and Ni/CeO2 (10 wt % Ni) for the fabrication of a novel fuel cell electrode for the oxidation of ethanol. Each membrane was characterized to determine its physicochemical properties using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. Using impedance spectroscopy (IS), a maximum value of 2.08 × 10-4 S/cm in ionic conductivity was found for the carrageenan nanocomposite with a concentration of 5 wt % TiO2 NPs (CR5%). Due to its high conductivity values, the CR5% membrane was mixed with Ni/CeO2 to prepare the working electrode for cyclic voltammetry measurements. Using a solution of 1 M ethanol and 1 M KOH, the oxidation of ethanol over CR5% + Ni/CeO2 resulted in peak current density values at forward and reverse scan voltages of 9.52 and 12.22 mA/cm2, respectively. From our results, the CR5% + Ni/CeO2 membrane proves to be more efficient in the oxidation of ethanol compared with commercially available Nafion membranes containing Ni/CeO2.
RESUMO
The purpose of this study was to determine the effects of plant products on the growth, swarming motility, biofilm formation and virulence gene expression in enterohemorrhagic Escherichia coli O157:H7 and enteroaggregative E. coli strain 042 and a strain of O104:H4 serotype. Extracts of Lippia graveolens and Haematoxylon brassiletto, and carvacrol, brazilin were tested by an antimicrobial microdilution method using citral and rifaximin as controls. All products showed bactericidal activity with minimal bactericidal concentrations ranging from 0.08 to 8.1 mg/ml. Swarming motility was determined in soft LB agar. Most compounds reduced swarming motility by 7%-100%; except carvacrol which promoted motility in two strains. Biofilm formation studies were done in microtiter plates. Rifaximin inhibited growth and reduced biofilm formation, but various concentrations of other compounds actually induced biofilm formation. Real time PCR showed that most compounds decreased stx2 expression. The expression of pic and rpoS in E. coli 042 were suppressed but in E. coli O104:H4 they varied depending on compounds. In conclusion, these extracts affect E. coli growth, swarming motility and virulence gene expression. Although these compounds were bactericidal for pathogenic E. coli, sublethal concentrations had varied effects on phenotypic and genotypic traits, and some increased virulence gene expression.
Assuntos
Biofilmes/efeitos dos fármacos , Escherichia coli Êntero-Hemorrágica/efeitos dos fármacos , Escherichia coli Êntero-Hemorrágica/fisiologia , Escherichia coli O157/efeitos dos fármacos , Extratos Vegetais/farmacologia , Escherichia coli Shiga Toxigênica/efeitos dos fármacos , Proteínas de Bactérias/genética , Biofilmes/crescimento & desenvolvimento , Escherichia coli Êntero-Hemorrágica/genética , Escherichia coli Êntero-Hemorrágica/patogenicidade , Escherichia coli O157/genética , Escherichia coli O157/patogenicidade , Escherichia coli O157/fisiologia , Proteínas de Escherichia coli/genética , Expressão Gênica , Genótipo , Testes de Sensibilidade Microbiana , Origanum , Fenótipo , Folhas de Planta/química , Reação em Cadeia da Polimerase em Tempo Real , Rifamicinas/farmacologia , Rifaximina , Serina Endopeptidases/genética , Toxina Shiga II/genética , Escherichia coli Shiga Toxigênica/crescimento & desenvolvimento , Escherichia coli Shiga Toxigênica/patogenicidade , Escherichia coli Shiga Toxigênica/fisiologia , Fator sigma/genética , Virulência/efeitos dos fármacos , Virulência/genéticaRESUMO
Escherichia coli productor de toxina Shiga (STEC), es un patógeno transmitido por alimentos. El serotipo O157:H7 se considera clínicamente el más importante, pero un 50% de las infecciones por STEC corresponden a serotipos no O157. En Venezuela, la presencia de cepas STEC no O157 en productos cárnicos no ha sido reportada, lo que motivó este trabajo. Se analizaron 70 muestras de carne molida (35 bovinas y 35 porcinas). El aislamiento de E. coli se llevó a cabo en agar MacConkey sorbitol, suplementado con cefixima y la identificación bioquímica según pautas de la FDA. Se realizó la extracción del ADN y ensayos de PCR para la identificación de cepas STEC O157:H7 y STEC no O157. De 70 muestras analizadas, 50 (71,4%) resultaron positivas al aislamiento de E. coli, lográndose identificar 47 cepas sorbitol positivas y 3 cepas sorbitol negativas. La PCR demostró ausencia de STEC O157:H7 y presencia de STEC no O157 productor de toxina Shiga Stx1 y Stx2 en el 4,3% de las muestras analizadas. Se demuestra, por primera vez en el país, la circulación de cepas STEC no O157 en productos cárnicos, lo que permite sugerir el establecimiento de estrategias de prevención asociadas a este patógeno.
Shiga toxin producing Escherichia coli (STEC) is a food-transmitted pathogen. Serotype O157:H7 is considered the most clinically important, but 50% of STEC infections correspond to non-O157 serotypes. In Venezuela, presence of non-O157 STEC strains in meat products has not been reported, which was the reason for this study. Seventy ground meat samples were analyzed (35 bovine and 35 porcine). E. coli isolation was done in MacConkey sorbitol agar, supplemented with cefixim, and the biochemical identification was done according to FDA guidelines. DNA extraction and PCR assays were used for the identification of STEC O157:H7 and not O157 strains. Of the 70 samples analyzed, 50 (71.4%) were positive for E. coli isolation, and 47 sorbitol positive and 3 sorbitol negative strains were identified. PCR showed absence of STEC O157:H7 and presence of non-O157 STEC Shiga toxin Stx1 and Stx2 producers in 4.3% of the samples analyzed. This is the first time that the circulation of non-O157 STEC strains in meat products is demonstrated in this country, which suggests that prevention strategies associated to this pathogen should be established.