In vivo and in silico determination of essential genes of Campylobacter jejuni

<p>Abstract</p> <p>Background</p> <p>In the United Kingdom, the thermophilic <it>Campylobacter </it>species <it>C. jejuni </it>and <it>C. coli </it>are the most frequent causes of food-borne gastroenteritis in humans. While campylobacteriosis is usually a relatively mild infection, it has a significant public health and economic impact, and possible complications include reactive arthritis and the autoimmune diseases Guillain-Barré syndrome. The rapid developments in "omics" technologies have resulted in the availability of diverse datasets allowing predictions of metabolism and physiology of pathogenic micro-organisms. When combined, these datasets may allow for the identification of potential weaknesses that can be used for development of new antimicrobials to reduce or eliminate <it>C. jejuni </it>and <it>C. coli </it>from the food chain.</p> <p>Results</p> <p>A metabolic model of <it>C. jejuni </it>was constructed using the annotation of the NCTC 11168 genome sequence, a published model of the related bacterium <it>Helicobacter pylori</it>, and extensive literature mining. Using this model, we have used <it>in silico </it>Flux Balance Analysis (FBA) to determine key metabolic routes that are essential for generating energy and biomass, thus creating a list of genes potentially essential for growth under laboratory conditions. To complement this <it>in silico </it>approach, candidate essential genes have been determined using a whole genome transposon mutagenesis method. FBA and transposon mutagenesis (both this study and a published study) predict a similar number of essential genes (around 200). The analysis of the intersection between the three approaches highlights the shikimate pathway where genes are predicted to be essential by one or more method, and tend to be network hubs, based on a previously published <it>Campylobacter </it>protein-protein interaction network, and could therefore be targets for novel antimicrobial therapy.</p> <p>Conclusions</p> <p>We have constructed the first curated metabolic model for the food-borne pathogen <it>Campylobacter jejuni </it>and have presented the resulting metabolic insights. We have shown that the combination of <it>in silico </it>and <it>in vivo </it>approaches could point to non-redundant, indispensable genes associated with the well characterised shikimate pathway, and also genes of unknown function specific to <it>C. jejuni</it>, which are all potential novel <it>Campylobacter </it>intervention targets.</p

How long do nosocomial pathogens persist on inanimate surfaces? A systematic review

BACKGROUND: Inanimate surfaces have often been described as the source for outbreaks of nosocomial infections. The aim of this review is to summarize data on the persistence of different nosocomial pathogens on inanimate surfaces. METHODS: The literature was systematically reviewed in MedLine without language restrictions. In addition, cited articles in a report were assessed and standard textbooks on the topic were reviewed. All reports with experimental evidence on the duration of persistence of a nosocomial pathogen on any type of surface were included. RESULTS: Most gram-positive bacteria, such as Enterococcus spp. (including VRE), Staphylococcus aureus (including MRSA), or Streptococcus pyogenes, survive for months on dry surfaces. Many gram-negative species, such as Acinetobacter spp., Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, Serratia marcescens, or Shigella spp., can also survive for months. A few others, such as Bordetella pertussis, Haemophilus influenzae, Proteus vulgaris, or Vibrio cholerae, however, persist only for days. Mycobacteria, including Mycobacterium tuberculosis, and spore-forming bacteria, including Clostridium difficile, can also survive for months on surfaces. Candida albicans as the most important nosocomial fungal pathogen can survive up to 4 months on surfaces. Persistence of other yeasts, such as Torulopsis glabrata, was described to be similar (5 months) or shorter (Candida parapsilosis, 14 days). Most viruses from the respiratory tract, such as corona, coxsackie, influenza, SARS or rhino virus, can persist on surfaces for a few days. Viruses from the gastrointestinal tract, such as astrovirus, HAV, polio- or rota virus, persist for approximately 2 months. Blood-borne viruses, such as HBV or HIV, can persist for more than one week. Herpes viruses, such as CMV or HSV type 1 and 2, have been shown to persist from only a few hours up to 7 days. CONCLUSION: The most common nosocomial pathogens may well survive or persist on surfaces for months and can thereby be a continuous source of transmission if no regular preventive surface disinfection is performed

LARGE PENETRATION DEPTH OFF ATOMS COMBINED WITH ACCUMULATION AND DETECTION IN RARE GAS INTERFACES

Author Institution: Fachbereich Physik, FU Berlin, Arnimallee 14The penetration of photomobilized F atoms is studied by a sandwich experiment using a stack of three rare gas layers. In the top layer photomobile F atoms are prepared, the spacer layer of variable thickness serves as a drift distance and the bottom layer is used for detecting the penetrating atoms. F atoms with a mean kinetic energy of 4.3 eV are generated in the top layer by photodissociating $F_{2}$ with 10.15 eV on a repulsive potential surface and ejected into the spacer layer composed of either Ar or Ne. F atoms arriving at the interface between the spacer layer and the Kr detection layer are identified by the characteristic $Kr_{2} ^{-}F^{-}$ emission and its intensity after complete $F_{2}$ dissociation delivers the amount of pencetrated atoms. The F atom content at this interface is kept below 1/20 of a monolayer by exploiting energy transfer from Kr excions. The penetration depths of about monolayer similar for Ar and Ne matrices and show no distinct dependence on temperature. They exceed those for $F^{+}$ and $F^{-}$ ions by am order of mangnitude, but are in accordance with those molecular dynamics calculation which predict a rectilinear motion in channels of the lattice. The penetration depth delivers an upper limit for the average length of travel of 14 monolayers and is consistent with a mean free path between large angle scattering collisions of 4 monolayers and less than 7 collisions per trajectory. The synchrotron radiation setup providing the VUV photones has been complmented with an FTIR spectrometer with a beam path which uses the same mirror for imaging at the sample and thus guarantees a coincidence of the irradiated volumes by VUV and IR light. Results for transients will be presented with a special emphasis on reactions of F atoms at the interface with molecules condensed in this interface

PENETRATION DEPTHS OF PHOTOMOBILIZED F ATOMS FROM A SANDWICH EXPERIMENT

[1] R. Alimi. R.B. Gerber, V.A. Apkarian, J. Chem. Phys., 92, 3551 (1990) [2] C. Bressler, N. Schwentner, Phys. Rev. Lett., 22, 648 (1996)Author Institution: Institut f\""{u}r Experimentalphysik, Freie, Universit\""{a}t BerlinElectronic excitation of an insulator leads in general to a significant rearrangement of the lattice which can induce even a displacement of atoms like in the color center formation. For even stronger changes in the equilibrium coordinates an atom in the excited center can gain significant energy thus being photomobilized. The distance where it comes at rest again due to dissipation of its kinetic energy corresponds to its penetration depth and a mean range can be derived. Exceptionally large penetration depths were predicted for photomobilized F atoms in a rare gas lattice [1] and a new direct and reliable technique will be presented for the determination of the mean range [2]. $F_{2}$ molecules are dissociated in a doped Ar layer of typical 5nm thickness by means of synchrotron radiation with a photon energy of 10.15 eV. F atoms gain a kinetic energy of about 4.2 eV and part of them can cross a spacer layer of pure Ar and some of them will reach the interface between the Ar spacer and the Kr substrate. The thickness of the Ar spacer is varied with monolayer accuracy from 0 up to 10 nm and the penetration depths are derived from the decreasing number of F atoms at the interface with increasing spacer thickness for a complete dissociation of $F_{2}$. The intensity of the $Kr_{2}$ F emission, which is characteristic for the interface, delivers the amount of F atoms and the sensitivity is enhanced considerably by using energy transfer from excitons of the Kr substrate. Indeed, larger penetration depths with mean values corresponding to eight nearest neighbor distances are observed and the results are discussed with respect to the molecular dynamics simulations, angular distributions in the plan as system, homogenity and ordering of the sample structure and temperature effects