Identification and characterisation of Staphylococcus aureus on low cost screen printed carbon electrodes using impedance spectroscopy.

Staphylococcus aureus infections are a cause of significant morbidity and mortality, in addition to representing a considerable economic burden. The aim of this study was to explore a low cost screen printed electrode as a sensor for the detection of S. aureus using impedance spectroscopy. S. aureus was incubated in chambers containing the electrodes and the results analysed using a novel normalisation approach. These results show that it is possible to detect the presence of S. aureus in LB media after 30 min incubation of a 1% growth culture, in addition to being able to see immediate cell concentration dependant changes in 0.9% NaCl. These observations imply that a number of electrochemical mechanisms cause a change in the impedance as a result of the presence of S. aureus, including adsorption to the electrode surface and the metabolism of the bacteria during growth. The study suggests that this detection approach would be useful in a number of clinical scenarios where S. aureus leads to difficult to treat infections.

Mechanism of transcriptional regulation by the Escherichia coli nitric oxide sensor NorR.

Nitric oxide (NO) is a highly reactive water-soluble gas encountered by bacteria endogenously as an intermediate of denitrification and exogenously as one of the radical species deployed by macrophages against invading pathogens. Bacteria therefore require a mechanism to detoxify NO. Escherichia coli flavorubredoxin and its associated oxidoreductase, encoded by the norV and norW genes respectively, reduces NO to nitrous oxide under anaerobic conditions. Transcription of the norVW genes is activated in response to NO by the sigma(54)-dependent regulator NorR, a member of the prokaryotic enhancer binding protein family. NorR binds co-operatively to three enhancer sites to regulate transcription of both norVW and the divergently transcribed norR gene. In the present paper, we show that disruption of any one of the three GT-(N(7))-AC NorR binding sites in the norR-norVW intergenic region prevents both activation of norVW expression and autogenous repression of the norR promoter by NorR. We have recently demonstrated that the N-terminal GAF (cGMP-specific and -stimulated phosphodiesterases, Anabaena adenylate cyclases and Escherichia coli FhlA) domain of NorR contains a non-haem mononuclear iron centre and senses NO by formation of a mono-nitrosyl iron complex. Site-directed mutagenesis has identified candidate protein ligands to the ferrous iron centre in the GAF domain.

Photoemission Study of CO Adsorption on Gd.

Angle-resolved UV photoemission spectroscopy has been used to investigate the interaction of CO with Gd films, grown on W(110). The results suggest the CO absorbs dissociatively, initially forming Gd(2)O(3), with subsequent catalytic oxidation of CO to form carbonate.

Utilization of Photoemission Cross-Section Effects for Monitoring Thin-Film Growth in UHV.

Given the tunability of synchrotron radiation, photoemission spectroscopy can be used to monitor the growth modes of thin films in UHV. Cross-section effects such as Cooper minima and resonant photoemission can be exploited to maximize the adsorbate signal and minimize that from the substrate. Under favourable circumstances growth can be monitored in real time at coverages of <1%. As an example the growth of Gd on W(110) is investigated.

Gd/W(110) interface formation studied by w 4f surface core-level spectroscopy.

W 4f core-level spectra of Gd films on W(110) show components which can be identified as being due to bulk and interface W. The results suggest that the W/Gd interface is abrupt, i.e. no interface alloying occurs. At submonolayer coverages a further component is seen which is attributable to intermediate (n x 2) phases.