RESUMO
Brucella melitensis primarily affects sheep, goats and is associated with brucellosis in humans, which is one of the world's most widespread neglected zoonotic disease. The current study attempted the determination of genetic diversity through comparative genome analysis of B. melitensis strains reported from India with other countries. The study also reports the isolation and identification of B. melitensis BMNDDB8664 from a cow with a history of abortion, whole-genome sequencing (WGS), determination of virulence factors, genotyping, and comparative genome analysis. Multilocus sequence typing, Multiple locus variable number of tandem repeats analysis (MLVA), and WGS based phylogeny revealed the predominance of ST-8 and genotypes (116 and II respectively) that clustered to the East Mediterranean lineage. Identification of hitherto unreported genotypes by MLVA also indicated the existence and circulation of West Mediterranean and American lineages in India. Though the AMOS-PCR results suggest the BMNDDB8664 isolate as Brucella abortus, the outcomes from multiplex PCR, ribosomal multilocus sequence typing, and WGS analysis confirmed it as B. melitensis. The analysis revealed the presence of adeF gene (aids conferring resistance to fluoro-quinolone and tetracyclines). The isolate lacked two important T4SS genes virB2 and virB7 genes (roles in infection and rifampicin resistance respectively) and also lacked the Brucella suis mprF gene that aids intracellular survival. Further, BMNDDB8664 lacked some of the genes associated with LPS synthesis (wbkB, wbkC) and transport (wzm, wzt) and hence, is most likely a rough strain. WGS-based phylogenetic analysis revealed close genetic relatedness of this BMNDDB8664 with a sheep isolate and two human isolates. The results prompt systematic, broad-based epidemiological studies on brucella infection at the species level. For effective control of human brucellosis, a concerted One Health approach with studies encircling the identification of aetiology at species, strain level to find their prevalence, spread, and inter-host transmission patterns need to be understood, for better design and implementation of effective control strategies in India and other endemic regions. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-023-01081-w.
RESUMO
In this paper, we describe the growth and characterization of ≈530 nm thick superlattices (100 periods) of AlxGa1-xN/AlN (0 ⩽ x ⩽ 0.1) Stranski-Krastanov quantum dots (QDs) for application as the active region of electron-beam pumped ultraviolet lamps. Highly dense (>1011 cm-2) QD layers are deposited by molecular beam epitaxy, and we explore the effect of the III/V ratio during the growth process on their optical performance. The study considers structures emitting in the 244-335 nm range at room temperature, with a relative linewidth in the 6%-11% range, mainly due to the QD diameter dispersion inherent in self-assembled growth. Under electron pumping, the emission efficiency remains constant for acceleration voltages below ≈9 kV. The correlation of this threshold with the total thickness of the SL and the penetration depth of the electron beam confirms the homogeneity of the nanostructures along the growth axis. Below the threshold, the emission intensity scales linearly with the injected current. The internal quantum efficiency (IQE) is characterized at low injection, which reveals the material properties in terms of non-radiative processes, and high injection, which emulates carrier injection in operation conditions. In QDs synthesized with III/V ratio <0.75, the IQE remains around 50% from low injection to pumping power densities as high as 200 kW cm-2, being the first kind of nanostructure that present such stable behaviour.
RESUMO
In this paper, we describe the design and characterization of 400 nm long (88 periods) Al x Ga1-x N/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW cm-2. We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage V A = 5 kV. At such V A, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW cm-2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm.
