Filterability of staphylococcal species through membrane filters following application of stressors

<p>Abstract</p> <p>Background</p> <p>Passage of bacterial cells through filter pores has been reported for a number of bacterial species. In this investigation, we tested the filterability of staphylococcal cultures that were exposed to several environmental stress conditions by passing them through 0.22 and 0.45 μm sterile filters, which are industry standards.</p> <p>Findings</p> <p>Results showed repeated passage of viable staphylococcal cells through both pore sizes, although more passage was seen through the 0.45 μm pore size. Of the three staphylococcal species, <it>S. lugdunensis </it>showed the best passage at relatively higher numbers regardless of the treatment, while both <it>S. aureus </it>and <it>S. epidermidis </it>showed limited passage or complete inhibition.</p> <p>Conclusion</p> <p>The data showed that staphylococcal bacteria were capable of passing through sterile filters in a viable state. There was better passage through 0.45 μm sterile filters than through the 0.22 μm sterile filters. Application of a stress condition did not appear to enhance filterability of these bacterial cultures.</p

Impedance spectroscopy study of the unipolar and bipolar resistive switching states of atomic layer deposited polycrystalline ZrO 2_{2} thin films

The polarity of the resistive switching (RS) characteristic of metal-oxide-metal devices from atomic layer deposited polycrystalline ZrO2 films was studied by means of impedance spectroscopy. Pt/ZrO2/Ti/Pt cells made with 10 nm Ti and 30 nm Pt capping top electrodes, served as unipolar switching (US) devices. Bipolar switching (BS) devices were represented by Pt/ZrO2/30 nm TiN cells. Temperature measurements of the ON-state resistances clearly show metallic and semiconducting behavior for the US and BS cells, respectively. The pristine and the ON and OFF states of the devices were analyzed by means of impedance spectroscopy. All ZrO2 based RS devices exhibited similar impedance characteristics in the pristine states. In contrast, after electroforming clear differences in the Nyquist-plots of the US and BS devices were observed. The effect of the device structure on the RS polarity is discussed under consideration of the pillar-shaped grainy microstructure of the ZrO2 thin films. An empirical model based on redox reactions between ZrO2 and the non-noble metal electrode is proposed emphasizing defect formation prior at the ZrO2 grain boundaries