2,466 research outputs found
Dermatophytes’ identification by Matrix-assisted laser desorption ionization-time of flight mass spectrometry. (MALDI-TOF MS) - the experience of a clinical laboratory
Objectives:
Dermatophytes are a challenging group of fungi that infect the keratinized tissues. The taxonomy of these
fungi has changed recently with the reclassification of some species and description of new ones. However,
many clinical laboratories still base the identification of dermatophytes on their phenotype. Since
dermatophytes are very pleomorphic, macro and micromorphology are often insufficient to reach a correct
classification and may lead to misidentifications. The identification based on MALDI-TOF relies on the protein
profile of the microorganism. Thus, this study aims to summarize our current laboratorial experience of
dermatophyte identification using MALDI-TOF MS.
Methods:
From january to april 2018, 95 dermatophytes isolates, collected from human keratinized samples and also
from quality control programs were characterized by phenotypic analysis, and by VITEK MS V3.2 bioMerieux.
Before identification procedure, isolates were inoculated on Sabouraud Dextrose agar plates and incubated at
27°C during 5 to 10 days. Species were identified taking into account clinical features, as well as cultural,
microscopic and physiological characteristics. Prior to MALDI-TOF MS analysis, the samples were pre-treated
according to the manufacturer’s protocol for filamentous fungi. Molecular identification by sequencing of the
internal transcribed spacer 1 (ITS1) was performed in 34 of those isolates
Results:
Through phenotypic analysis eight different species were identified (54 Trichophyton rubrum; 4 T.soudanense;
22 T.interdigitale; 1 T.mentagrophytes; 3 T.tonsurans; 7 Microsporum canis; 3 M.audouinii; 1 Microsporum
spp.- (non canis or audouinii). MALDI-TOF analysis showed an identification agreement in 80 cases (84,2%)
with a confidence level of 99,9%. Eight isolates showed divergent identification results: three T.rubrum were
identified as T.violaceum, three T.soudanense were identified as T.rubrum, one T.mentagrophytes was
identified as T.interdigitale and one T.tonsurans was identified as T.rubrum. In four cases MALDI-TOF analysis
did not get a profile. The ITS sequencing analysis of discrepant results corroborated the MALDI-TOF
identification in five of them. On the other hand, T.soudanense was only identified by phenotypic analysis since
MALDI-TOF and ITS sequencing result was T.rubrum. MALDITOF identification of T.violaceum was not
confirmed by ITS sequencing that identified T. rubrum instead, in accordance with the phenotypic
identification.
Conclusion:
Correct identification of dermatophytes to species level requires sequencing of the ITS, LSU, and/or betatubulin
regions. The implementation of this methodology in a clinical laboratory is expensive and time
consuming. MALDI-TOF identification is a good option for dermatophytes’ identification performed in
laboratory routine, since costs of consumables as well as time of sample preparation are lower than for PCR
analysis and doesn’t require long training period as phenotypic identification does. In this study, however, both
methods failed to identify some species variants like Trichophyton soudanense or T. violaceum. The combined
use of both MALDI-TOF and phenotypic methods seems to be the better approach for dermatophytes’
identification since some species show significant phenotypic and clinical differences.info:eu-repo/semantics/publishedVersio
The bispectrum of redshifted 21-cm fluctuations from the dark ages
Brightness-temperature fluctuations in the redshifted 21-cm background from
the cosmic dark ages are generated by irregularities in the gas-density
distribution and can then be used to determine the statistical properties of
density fluctuations in the early Universe. We first derive the most general
expansion of brightness-temperature fluctuations up to second order in terms of
all the possible sources of spatial fluctuations. We then focus on the
three-point statistics and compute the angular bispectrum of
brightness-temperature fluctuations generated prior to the epoch of hydrogen
reionization. For simplicity, we neglect redshift-space distortions. We find
that low-frequency radio experiments with arcmin angular resolution can easily
detect non-Gaussianity produced by non-linear gravity with high signal-to-noise
ratio. The bispectrum thus provides a unique test of the gravitational
instability scenario for structure formation, and can be used to measure the
cosmological parameters. Detecting the signature of primordial non-Gaussianity
produced during or right after an inflationary period is more challenging but
still possible. An ideal experiment limited by cosmic variance only and with an
angular resolution of a few arcsec has the potential to detect primordial
non-Gaussianity with a non-linearity parameter of f_NL ~ 1. Additional sources
of error as weak lensing and an imperfect foreground subtraction could severely
hamper the detection of primordial non-Gaussianity which will benefit from the
use of optimal estimators combined with tomographic techniques.Comment: 15 pages, 4 figures, revised version accepted for publication in ApJ
(contains an improved discussion of gas temperature fluctuations
Multidimensional Quasi-Monte Carlo Malliavin Greeks
We investigate the use of Malliavin calculus in order to calculate the Greeks
of multidimensional complex path-dependent options by simulation. For this
purpose, we extend the formulas employed by Montero and Kohatsu-Higa to the
multidimensional case. The multidimensional setting shows the convenience of
the Malliavin Calculus approach over different techniques that have been
previously proposed. Indeed, these techniques may be computationally expensive
and do not provide flexibility for variance reduction. In contrast, the
Malliavin approach exhibits a higher flexibility by providing a class of
functions that return the same expected value (the Greek) with different
accuracies. This versatility for variance reduction is not possible without the
use of the generalized integral by part formula of Malliavin Calculus. In the
multidimensional context, we find convenient formulas that permit to improve
the localization technique, introduced in Fourni\'e et al and reduce both the
computational cost and the variance. Moreover, we show that the parameters
employed for variance reduction can be obtained \textit{on the flight} in the
simulation. We illustrate the efficiency of the proposed procedures, coupled
with the enhanced version of Quasi-Monte Carlo simulations as discussed in
Sabino, for the numerical estimation of the Deltas of call, digital Asian-style
and Exotic basket options with a fixed and a floating strike price in a
multidimensional Black-Scholes market.Comment: 22 pages, 6 figure
Pricing and Hedging Asian Basket Options with Quasi-Monte Carlo Simulations
In this article we consider the problem of pricing and hedging
high-dimensional Asian basket options by Quasi-Monte Carlo simulation. We
assume a Black-Scholes market with time-dependent volatilities and show how to
compute the deltas by the aid of the Malliavin Calculus, extending the
procedure employed by Montero and Kohatsu-Higa (2003). Efficient
path-generation algorithms, such as Linear Transformation and Principal
Component Analysis, exhibit a high computational cost in a market with
time-dependent volatilities. We present a new and fast Cholesky algorithm for
block matrices that makes the Linear Transformation even more convenient.
Moreover, we propose a new-path generation technique based on a Kronecker
Product Approximation. This construction returns the same accuracy of the
Linear Transformation used for the computation of the deltas and the prices in
the case of correlated asset returns while requiring a lower computational
time. All these techniques can be easily employed for stochastic volatility
models based on the mixture of multi-dimensional dynamics introduced by Brigo
et al. (2004).Comment: 16 page
The burden of serious fungal infections in Portugal
Using published data, we were able to estimate the incidence or prevalence of the above referred fungal infections and ~194 293 (1.8%) people in Portugal suffer from those fungal infections each year
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