RESUMEN
We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure-a magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.
Asunto(s)
Escherichia coli/efectos de los fármacos , Escherichia coli/crecimiento & desarrollo , Estudiantes de Medicina , beta-Lactamasas/biosíntesis , Farmacorresistencia Bacteriana , Escherichia coli/enzimología , Escherichia coli/aislamiento & purificación , Heces/microbiología , Femenino , Humanos , Masculino , Factores de Tiempo , Adulto JovenRESUMEN
The study shows for the first time the presence of the Klebsiella oxytoca strain fp10 coproducing plasmid-mediated KPC-2 and IMP-8 carbapenemases. The strain was obtained from the fecal sample of an inpatient and showed high-level resistance to imipenem and ertapenem (MICs > 32 µg/ml). Conjugation experiments demonstrated the transferability of the carbapenem-resistant determinants. The results of plasmid analysis and Southern hybridization revealed that the bla(KPC-2) gene was located on transferable plasmid pFP10-1 (â¼54 kb), whereas the bla(IMP-8) gene was on transferable plasmid pFP10-2 (â¼180 kb). Analysis of the genetic environment of these two genes has demonstrated that ISKpn6 and ISKpn8 are involved in the spread of the bla(KPC-2) gene, while the transposable elements IS26, intI1, and tniC might contribute to the dissemination of the bla(IMP-8) gene. The chimera of several transposon-associated elements indicated a novel genetic environment of IMP-type metallo-ß-lactamase gene in Enterobacteriaceae from China.
Asunto(s)
Klebsiella oxytoca/enzimología , beta-Lactamasas/biosíntesis , Conjugación Genética , Klebsiella oxytoca/efectos de los fármacos , Klebsiella oxytoca/genética , Pruebas de Sensibilidad Microbiana , Plásmidos , Análisis de Secuencia de ADN , beta-Lactamasas/genéticaRESUMEN
BACKGROUND: The community could be a reservoir of antibiotic resistance genes. The aim of this study was to investigate the prevalence and genetic environments of bla(CTX-M) among faecal Escherichia coli obtained from healthy persons in a region of China. METHODS: Bacteria in stool specimens were screened for extended-spectrum ß-lactamase (ESBL) production on 2 MacConkey agars, one with cefotaxime and one with ceftazidime. bla(CTX-M) and their genetic environments, as well as phylogenetic analysis and detection of the O25b-ST131 clone of E. coli, were characterized by polymerase chain reaction and sequencing. Pulsed field gel electrophoresis and conjugation assays were performed by standard procedures. RESULTS: A surprisingly high number (50.5%, 55/109) of faecal samples showed the presence of ESBL-producing E. coli. bla(CTX-M) genes were detected in all of these strains. The CTX-M-9 group (41/55, 74.5%) was found most frequently, followed by the CTX-M-1 group (16/55, 29.1%). CTX-M-14 (n = 39) was the predominant CTX-M enzyme in this study. However, the genes for the CTX-M-2 and CTX-M-8 groups were not observed. ISEcp1 was detected in 90.9% of the strains, while IS26 was observed upstream from bla(CTX-M) in only 1 strain. Phylogenetic groups A and D were found to predominate in commensal E. coli. High clonal diversity was observed and most bla(CTX-M) genes were transferable. The O25b-ST131 clone was found in 4 strains. CONCLUSIONS: This study reveals the wide dissemination of CTX-M ESBL-producing E. coli in the gut flora of healthy individuals in China.
Asunto(s)
Escherichia coli/enzimología , Escherichia coli/aislamiento & purificación , Heces/microbiología , beta-Lactamasas/biosíntesis , Adolescente , Adulto , Anciano , China , ADN Bacteriano/química , ADN Bacteriano/genética , Escherichia coli/genética , Femenino , Genotipo , Humanos , Masculino , Pruebas de Sensibilidad Microbiana/métodos , Persona de Mediana Edad , Filogenia , Reacción en Cadena de la Polimerasa , Prevalencia , Análisis de Secuencia de ADN , Adulto JovenRESUMEN
The study of phylogenetic groups and pathogenicity island (PAI) markers in commensal Escherichia coli strains from asymptomatic Chinese people showed that group A strains are the most common and that nearly half of all fecal strains which were randomly selected harbor PAIs.