First application of a transcutaneous optical single-port glucose monitoring device in patients with type 1 diabetes mellitus.

The combination of continuous glucose monitoring (CGM) and continuous subcutaneous insulin infusion can be used to improve the treatment of patients with diabetes. The aim of this study was to advance an existing preclinical single-port system for clinical application by integrating the sensors of a phosphorescence based CGM system into a standard insulin infusion set. The extracorporeal optical phase fluorimeter was miniaturised and is now comparable with commercial CGM systems regarding size, weight and wear comfort. Sensor chemistry was adapted to improve the adhesion of the sensor elements on the insulin infusion set. In-vitro tests showed a linear correlation of R2=0.998 between sensor values and reference glucose values in the range of 0-300mg/dl. Electrical and cytotoxicity tests showed no negative impact on human health. Two single-port devices were tested in each of 12 patients with type 1 diabetes mellitus in a clinical set-up for 12h. Without additional data processing, the overall median absolute relative difference (median ARD) was 22.5%. For some of the used devices the median ARD was even well below 10%. The present results show that individual glucose sensors performance of the single-port system is comparable with commercial CGM systems but further improvements are needed. The new system offers a high extent of safety and usability by combining insulin infusion and continuous glucose measurement in a single-port system which could become a central element in an artificial pancreas for an improved treatment of patients with type 1 diabetes mellitus.

Motility of Marichromatium gracile in response to light, oxygen, and sulfide.

The motility of the purple sulfur bacterium Marichromatium gracile was investigated under different light regimes in a gradient capillary setup with opposing oxygen and sulfide gradients. The gradients were quantified with microsensors, while the behavior of swimming cells was studied by video microscopy in combination with a computerized cell tracking system. M. gracile exhibited photokinesis, photophobic responses, and phobic responses toward oxygen and sulfide. The observed migration patterns could be explained solely by the various phobic responses. In the dark, M. gracile formed an approximately 500-microm-thick band at the oxic-anoxic interface, with a sharp border toward the oxic zone always positioned at approximately 10 microM O(2). Flux calculations yielded a molar conversion ratio S(tot)/O(2) of 2.03:1 (S(tot) = [H(2)S] + [HS(-)] + [S(2-)]) for the sulfide oxidation within the band, indicating that in darkness the bacteria oxidized sulfide incompletely to sulfur stored in intracellular sulfur globules. In the light, M. gracile spread into the anoxic zone while still avoiding regions with >10 microM O(2). The cells also preferred low sulfide concentrations if the oxygen was replaced by nitrogen. A light-dark transition experiment demonstrated a dynamic interaction between the chemical gradients and the cell's metabolism. In darkness and anoxia, M. gracile lost its motility after ca. 1 h. In contrast, at oxygen concentrations of >100 microM with no sulfide present the cells remained viable and motile for ca. 3 days both in light and darkness. Oxygen was respired also in the light, but respiration rates were lower than in the dark. Observed aggregation patterns are interpreted as effective protection strategies against high oxygen concentrations and might represent first stages of biofilm formation.

True chemotaxis in oxygen gradients of the sulfur-oxidizing bacterium Thiovulum majus.

Observations of free-swimming Thiovulum majus cells show that these bacteria exhibit a phobic response as well as true chemotaxis in oxygen gradients. Both phenomena of their chemotactic behavior are integrated into a single model of helical klinotaxis, which is demonstrated by computer simulations.

Fiber-optic fluorometer for microscale mapping of photosynthetic pigments in microbial communities.

Microscale fluorescence measurements were performed in photosynthetic biofilms at a spatial resolution of 100 to 200 microm with a new fiber-optic fluorometer which allowed four different excitation and emission wavelengths and was configured for measuring phycobiliproteins, chlorophylls, and bacteriochlorophylls. We present details of the measuring system and describe examples of applications in different microbial communities.

A new system for three-dimensional tracking of motile microorganisms.

A new three-dimensional (3D)-tracking system with optimized dark-field illumination is presented. It allows simultaneous 3D tracking of several free-swimming microorganisms with diameters of >10 microm. Resolution limits and illumination efficiencies for different size classes of microorganisms are treated analytically. First applications for 3D tracking of protists are demonstrated.