Staphylococcus epidermidis is the main cause of bacteremia and infections of indwelling catheters, glycopeptide antibiotics are often considered as the choice of empirical drugs for the treatment of staphylococcal infections. In the present study, 12 teicoplanin nonsusceptible S. epidermidis isolates were collected between January and October 2013. All strains carried the mecA gene, displayed multiple drug resistance, and showed heterogeneous resistance to vancomycin using the population analysis profiling/area under the curve method. Multilocus sequence typing revealed four different sequence types among these isolates; eight isolates belonged to the same ST type (ST267). Pulsed-field gel electrophoresis (PFGE) with SmaI endonuclease showed four distinct pulsotypes. Six isolates that belonged to ST267 shared the same PFGE bands, indicating that they were clonally related. In addition, cell wall thickening and decreased autolysis were found in these isolates. Our study demonstrated that ST267 was the most epidemic clone among teicoplanin nonsusceptible S. epidermidis and identified a potential endemic clone in this region, which was believed to be the first report that the ST267 clone has spread in China. Our findings revealed that strengthened monitoring of S. epidermidis for drug resistance to glycopeptide antibiotics is urgently needed, and heightened measures should be taken to control the further spread of the ST267 clone.
Chinese water chestnut (CWC) is popular among consumers due to its unique flavor and crisp and sweet taste. Thus far, the key substances affecting the taste compound of CWC are still unclear. In this study, we used UPLC-MS/MS and an electronic tongue system to study the effects of four typical steaming and cooking methods, cooking without peel for 10 min (PC), steaming without peel for 15 min (PS), cooking with peel for 30 min (WPC), steaming with peel for 30 min (WPS), on the taste compound generation and variation of CWC, and revealed the secret of its crisp and sweet taste. The results show that the electronic tongue can effectively identify the taste profile of CWC, and the effective tastes of CWC were umami, bitterness, saltiness, and sweetness. We screened 371 differential compounds from 640 metabolic species. Among them, nucleotides and their derivatives, carbohydrates, organic acids and their derivatives, and amino acids and their derivatives are closely related to the key taste of CWC, and these compounds affected the taste of CWC through six related metabolic pathways: oxidative phosphorylation and purine metabolism; alanine, aspartate, and glutamate; bile secretion; amino sugar and nucleotide sugar metabolism; the phenylpropane pathway; and toluene degradation. This study reveals the potential metabolic causes of taste compound generation and variation in the taste of CWC.
The white pulp of the Chinese water chestnut (CWC) is crisp and sweet with delicious flavours and is an important ingredient in many Chinese dishes. Phenylacetaldehyde is a characteristic flavoured substance produced in the steaming and cooking process of CWC. The steaming process and conditions were simulated to construct three Maillard reaction systems which consisted of glucose and phenylalanine, and of both alone. The simulation results showed that glucose and phenylalanine were the reaction substrates for the formation of phenylacetaldehyde. The intermediate α-dicarbonyl compounds (α-DCs) and the final products of the simulated system were detected by solid-phase microextraction (SPME) and gas chromatography–mass spectrometry (GC-MS) methods. Through the above methods the formation mechanism of phenylacetaldehyde is clarified; under the conditions of the steaming process, glucose is caramelized to produce Methylglyoxal (MGO), 2,3-Butanedione (BD), Glyoxal (GO) and other α-DCs. α-DCs and phenylalanine undergo a Strecker degradation reaction to generate phenylacetaldehyde. The optimal ratio of the amount of substance of glucose to phenylalanine for Maillard reaction is 1:4. The results can provide scientific reference for the regulation of flavour substances and the evaluation of flavour quality in the steaming process of fruits and vegetables.
The Chinese water chestnut (CWC) is among the most widespread and economically important vegetables in Southern China. There are two different types of cultivars for this vegetable, namely, big CWC (BCWC) and small CWC (SCWC). These are used for different purposes based on their metabolic profiles. This study aimed to investigate the metabolite profile of CWC and compare the profiles of peels collected in different harvest years using ultraperformance liquid chromatography/mass spectrometry (UPLC–MS)‐based metabolomics analysis. Three hundred and twenty‐one metabolites were identified, of which 87 flavonoids, 25 phenylpropanoids, and 33 organic acids and derivatives were significantly different in the content of the two varieties of BCWC and SCWC. The metabolite profiles of the two different cultivars were distinguished using principle component analysis (PCA) and orthogonal projections to latent structures discriminant analysis, and the results indicated differences in the metabolite profile of Eleocharis dulcis (Burm. f.) Trin. ex Hensch. Three isomers of hydroxycoumarin, namely, O‐feruloyl‐4‐hydroxycoumarin, O‐feruloyl‐3‐hydroxycoumarin, and O‐feruloyl‐2‐hydroxycoumarin, exhibited increased levels in BCWC, while p‐coumaric acid and vanillic acid did not show any significant differences in their content in BCWC and SCWC peels. This study, for the first time, provides novel insights into the differences among metabolite profiles between BCWC and SCWC.
Gold-doped carbon dots (CDAu) were simply and quickly prepared via microwave procedure using fullerene as a precursor, a rapid detection method for chlorpyrifos was established using surface enhanced Raman scattering (SERS) combined with aptamer (Apt) controlled gold-doped
carbon dots catalytic reaction. As the result, the SERS intensity decreased due to the aptamer inhibited the CDAu catalytic reduction of chlorauric acid by glucose. However, in the presence of chlorpyrifos, SERS intensity increased linearly with the concentration of chlorpyrifos
in the range of 12.8–432.8 ng/L, the correlation coefficient was R2 = 0.9961.
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