National laboratory-based surveillance system for antimicrobial resistance: a successful tool to support the control of antimicrobial resistance in the Netherlands

An important cornerstone in the control of antimicrobial resistance (AMR) is a well-designed quantitative system for the surveillance of spread and temporal trends in AMR. Since 2008, the Dutch national AMR surveillance system, based on routine data from medical microbiological laboratories (MMLs), has developed into a successful tool to support the control of AMR in the Netherlands. It provides background information for policy making in public health and healthcare services, supports development of empirical antibiotic therapy guidelines and facilitates in-depth research. In addition, participation of the MMLs in the national AMR surveillance network has contributed to sharing of knowledge and quality improvement. A future improvement will be the implementation of a new semantic standard together with standardised data transfer, which will reduce errors in data handling and enable a more real-time surveillance. Furthermore, the

Preparative LC separation and isolation of enantiomerically pure olefins

Diastereomer formation by the reaction of chiral olefins with optically active platinum complexes followed by LC separation of the diastereomers, and on-line or off-line release of the olefins from the complexes by ligand exchange yield optically pure enantiomers. The 100% dextrostetatory enantiomer of exo-2-vinylbicyclo[2.2.1]heptane (vinylnorbornane) could be isolated by an off-line method and was used for polarimetric measurements before and after preparative scale gas chromatographic clean-up. The initial valuable platinum complex could be easily recovered without loss

Gas-and liquid chromatographic separation of naphthalenophanes of the [2.2] and [3.3] type

Separations of various isomeric naphthalenophanes have been performed in different LC-systems, including those containing Ag+ in the mobile phase, and also by high temperature capillary GC. Ag+-complexation in the mobile phase of LC-systems can be observed with several of the strained aromatic systems, but most of the separations of practical interest can also be achieved without Ag+-complexation. For solubility reasons purification and isolation of certain isomeric species have been performed in normal phase LC-systems only

Circular dichroism as a detection method in the screening of enantioselective catalysts

The combination of liquid chromatography (HPLC), UV/Vis-spectroscopy and circular dichroism (CD) can be used to construct a high-throughput screening system to determine the enantioselectivity of enzyme- or metal-catalyzed reduction of acetophenone with formation of (S)- and (R)-1-phenylethanol. Prerequisite for the viability of this system is the experimental finding that the anisotropy factor g is linearly related to the enantiomeric excess (ee) and that it is independent of concentration, thereby excluding possible aggregation effects

Stationary phases for reversed-phase liquid chromatography : Coating of silica by polymers of various polarities

The possibilities of syntheses and the chromatographic properties of reversed-phase materials achieved by polymer coating have been investigated. Special alkylpolysiloxanes, which were to be immobilized on different types of silica, have been synthesized by equilibration of different mixtures of methylhydropolysiloxanes with octamethyltetrasiloxane and subsequent hydrosilylation of 1-alkenes of different chain length. The polymers obtained can easily be immobilized on silica by the usual methods, such as thermal treatment with dicumyl peroxide, γ-radiation, etc. The immobilization is even more effective if the polymer contains a low concentration of SiH bonds. The chromatographic behaviour of such phases in regard to efficiency, selectivity, adsorptivity, and stability has extensively been tested also in comparison with reversed-phase materials obtained by silanization of SiOH groups

Purification and analysis of partially alkylated cyclodextrins by liquid and gas chromatography

Complex mixtures of partially alkylated cyclodextrins can be analyzed by both HPLC and high temperature capillary GC. Because of the limited efficiency of LC, suitable analytical and preparative separations can be achieved only with systems of carefully optimized selectivity. Using LC it has been possible to isolate and purify single cyclodextrin species from very complex mixtures of components which contain unreacted hydroxyl groups in addition to the alkoxy groups. Analysis of the reaction mixtures and of fractions taken from LC separations can be performed with advantage by high resolution capillary GC at high temperatures between 300 and 400 °C. The thermal stability of partially alkylated cyclodextrins in high temperature GC is considerably increased by trimethylsilylation of the free hydroxyl groups. Fast atom bombardment mass spectrometry and proton NMR were used to identify species isolated from the preparative LC separations

Design and performance of a microchip electrophoresis instrument with sensitive variable-wavelength fluorescence detection

A modular instrument for high-speed microchip electrophoresis (MCE) equipped with a sensitive variable-wavelength fluorescence detection system was developed and evaluated. The experimental setup consists mainly of a lamp-based epifluorescence microscope for variable-wavelength fluorescence detection and imaging and a programmable four-channel bipolar high-voltage source capable of delivering up to +/- 10 W per channel. The optical unit was equipped with a high-sensitivity photomultiplier tube and an adjustable aperture. The system was applied to MCE separations of flurescein isothiocyanate (FITC)- labelled amines utilizing blue light (450-480 nm) for excitation as well as for the separation of rhodamines utilizing excitation light in the green spectral region (531- 560 nm). At optimized conditions baseline separation of four FITC-labelled amines could be obtained in less than 50 s at a detection limit of 460 ppt (1 nM) with a signal-to-noise ratio of 3:1. Three rhodamines could be baseline-separated in less than 6 s at a detection limit of 240 ppt (500 pm). The relative standard deviations of absolute migration times determined in repetitive MCE separations of FITC-labelled amines were below 2.5% (n= 25). By the application of cyclodextrin-modified electrolytes, chiral separation of FITC-labelled amines could be performed in seconds demonstrating the potential of microchip electrophoresis for chiral high-throughput screening

Poly(vinyl alcohol)-coated microfluidic devices for high- performance microchip electrophoresis

The channels of microfluidic glass chips have been coated with poly(vinyl alcohol) (PVA). Applied for microchip electrophoresis, the coated devices exhibited a suppressed electroosmotic flow and improved separation performance. The superior performance of PVA-coated channels could be demonstrated by electrophoretic separations of labeled amines and by video microscopy. While a distorted sample zone is injected using uncoated channels the application of PVA-coated channels results in an improved shape of the sample zone with less band broadening. Applying PVA-coated microchips for the separation of amines labeled with Alexa Fluor 350(TM) even sub- second separations, utilizing a separation length of only 650 mum, could be obtained, while this was not possible using uncoated devices. By using PVA-coated devices rather than an uncoated chip a threefold increase in separation efficiencies could be observed. As the electroosmotic flow (EOF) was suppressed, the anionic compounds were detected at the anode whereas the dominant EOF in uncoated devices resulted in an effective mobility to the cathode. Besides improved separation performance another important feature of the PVA-coated channels was the suppressed adsorption of fluorescent compounds in repetitive runs which results in an improved robustness and detection sensitivity. Applying PVA-coated channels, rinsing or etching steps could be omitted while this was necessary for a reliable operation of uncoated devices