An investigation, using an in-vitro alginate biofilm model, into locally delivered antibiotic combinations to treat staphylococcal prosthetic infection

INTRODUCTION Joint replacement is a common and effective procedure but unfortunately, a small proportion of patients develop Prosthetic joint Infection (PJI). The bacteria responsible for these infections exist within a surface -associated community known as a biofilm. When this biofilm phenotype is expressed, it allows the organisms to resist phagocytic host defenses, tolerate the stresses induced by antimicrobials and colonize peri- prosthetic niches. PJI is invariably refractory to standard therapies and clinicians are required to use a combination of systemic and local antimicrobials, repeated debridement and prosthesis exchange to treat the patient resulting in significant morbidity. Standard antibiotic sensitivity tests offer little insight into bacterial susceptibilities in the biofilm state. Furthermore, they neither test at the higher levels, nor in the combinations of antibiotics that are commonly locally delivered during surgery. The aim of this thesis was to develop and validate a biofilm model, and to use it to test staphylococcal biofilms with clinically achievable concentrations of antibiotics in combination.METHODS Sodium alginate gel was chelated with a calcium chloride solution to form bullet shaped beads with a surface area of 161mm2 These beads were then removed and their surface inoculated with either a methicillin sensitive Staphylococcus aureus (ATCC 29213) or a clinical strain of coagulase negative staphylococcus. After being incubated aerobically for 20 hours in a 48 -well micro -titre plate, growth controls were sampled and enumerated. The remaining beads were washed to remove non - adherent bacteria and placed into fresh broth containing antibiotics. After 3 hours of antibiotic challenge, they were removed, washed and the biofilm detached by dissolving the bead in a citric acid and Na2CO3 solution. Viable organisms were enumerated after micro -dilution and Miles Misra plating onto agar.RESULTS Cryo -scanning electron microscopy demonstrated the model allowed a biofilm to develop on the surface of alginate beads. Overall the technique performed with satisfactory resemblance of the control data and acceptable responsiveness after disinfection. The repeatability of disinfection was found to be most variable around the level used to define bacterial eradication. The model was used to compare the minimum inhibitory (MIC) and biofilm eradication concentrations (MBEC) of seven commonly used antibiotics. Poor correlation was found between the susceptibility of the standard planktonic cultures to antibiotics and those that were effective against organisms in biofilm. Gentamicin and daptomycin were found to be the only mono -therapies that were effective against the biofilm at clinically achievable levels. Combining antibiotics that were ineffective as single agents did not confer additional benefit.Interestingly despite gentamicin being effective when tested alone, combining it with clindamycin, rifampacin or linezolid reduced the bactericidal effect markedly in both strains. This phenomenon was investigated further by varying the concentration of antibiotics within the combinations. Combining the bactericidal antibiotics tested with gentamicin had an additive or synergistic effect. More importantly, a strong antagonistic effect was observed, with between 8 and 32 times more gentamicin being required, when it was combined with antibiotics considered bacteriostatic.CONCLUSION Standard microbiology laboratory testing is inadequate to guide clinical treatment of PJI. Testing of biofilm susceptibility to combinations of antimicrobials at high concentrations should be included in the laboratory testing of PJI. Further research should be directed towards understanding the mechanisms in which bacteriostatic antibiotics induce the organisms to become more tolerant to other antibiotics. If the antagonistic effect is confirmed in -vivo then it is logical to study a two stage antimicrobial strategy, avoiding potential antagonism by only introducing bacteriostatic agents when the bactericidal drugs dip below their minimum biofilm eradication concentration

Observation of transverse interference fringes on an atom laser beam

Using the unique detection properties offered by metastable helium atoms we have produced high resolution images of the transverse spatial profiles of an atom laser beam. We observe fringes on the beam, resulting from quantum mechanical interference between atoms that start from rest at different transverse locations within the outcoupling surface and end up at a later time with different velocities at the same transverse position. Numerical simulations in the low output-coupling limit give good quantitative agreement with our experimental data

Spinaxinus (Bivalvia: Thyasiroidea) from sulfide biogenerators in the Gulf of Mexico and hydrothermal vents in the Fiji Back Arc: Chemosymbiosis and Taxonomy

Two new species of the thyasirid genus Spinaxinus (S. emicatus Oliver n. sp. and S. phrixicus Oliver n. sp.) are described from the Gulf of Mexico and the southwest Pacific, respectively. Both are compared with the type species of the genus, the eastern Atlantic S. sentosus Oliver and Holmes, 2006. Living specimens from the Gulf of Mexico were retrieved from artificial sulfide bio-generators on the upper Louisiana Slope. Gill morphology and molecular markers from the symbiotic bacteria confirm that Spinaxinus is chemosynthetic and that the chemoautotrophic bacteria are related to sulfide oxidizing Gammaproteobacteria. Living specimens from the southwest Pacific were retrieved from hydrothermal vent sites in the Fiji and Lau Back Arc Basins. In the Atlantic Spinaxinus is now recorded from two anthropogenic situations and appears to be generally absent from natural cold seep sites and not yet recorded at any hydrothermal sites. The primarily anthropogenic distribution of Spinaxinus in the Atlantic is discussed with reference to the natural hydrothermal vent habitat of the Pacific S. phrixicus.Spinaxinus (Bivalvia: Thyasiroidea) de bio-generadores artificiales de sulfuro situados en el Golfo de Méjico y en fuentes hidrotermales de las Islas Fiji: quimiosimbiosis y taxonomía. – En este trabajo se describen dos especies nuevas de tisárido del género Spinaxinus (S. emcatus Oliver n. sp. y S. phrixicus Oliver n. sp.) encontradas res- pectivamente en el Golfo de Méjico y en el sureste del Pacífico. Se comparan estas dos especies nuevas con la especie tipo del género, S. sentous Oliver y Holmes, 2006 descrita en el Este del Atlántico. Para describir estas dos especies, se observaron ejemplares vivos recolectados sobre bio-generadores artificiales de sulfuro situados en la parte alta de la plataforma conti- nental de Louisiana, en el Golfo de Méjico. Las observaciones realizadas de las branquias de Spinaxinus y la caracterización genética de las bacterias simbiontes en estos ejemplares confirmaron que Spinaxinus es un género quimiosintético que con- tiene bacterias quimioautótrofas cercanas a las Gammaproteobacterias responsables de la oxidación del sulfuro. También se recolectaron ejemplares vivos de fuentes hidrotermales situadas en las Islas Fiji y en ‘Lau Back Arc Basins’ ambas localiza- das en el Pacífico suroccidental. La especie atlántica de Spinaxinus se encontró en dos tipos de sustratos artificiales mientras que parece que esta especie no se encuentra en ambientes naturales equivalentes como serían las surgencias frías y las fuentes hidrotermales. La distribución aparentemente limitada de la especie atlántica se discute en relación con la distribución de S. phrixicus en las fuentes hidrotermales del Pacífico

Comparative Effectiveness of Guidelines for the Management of Hyperlipidemia and Hypertension for Type 2 Diabetes Patients

Background: Several guidelines to reduce cardiovascular risk in diabetes patients exist in North America, Europe, and Australia. Their ability to achieve this goal efficiently is unclear. Methods and Findings: Decision analysis was used to compare the efficiency and effectiveness of international contemporary guidelines for the management of hypertension and hyperlipidemia for patients aged 40-80 with type 2 diabetes. Measures of comparative effectiveness included the expected probability of a coronary or stroke event, incremental medication costs per event, and number-needed-to-treat (NNT) to prevent an event. All guidelines are equally effective, but they differ significantly in their medication costs. The range of NNT to prevent an event was small across guidelines (6.5-7.6 for males and 6.5-7.5 for females); a larger range of differences were observed for expected cost per event avoided (ranges, $117,269-$157,186 for males and $115,999-$163,775 for females). Australian and U.S. guidelines result in the highest and lowest expected costs, respectively. Conclusions: International guidelines based on the same evidence and seeking the same goal are similar in their effectiveness; however, there are large differences in expected medication costs. © 2011 Shah et al

Herbivore regulation of plant abundance in aquatic ecosystems.

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant-herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore-plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore-plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant-herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants

Copy when uncertain: lower light levels increase trail pheromone deposition and reliance on pheromone trails in ants

Animals may gather information from multiple sources, and these information sources may conflict. Theory predicts that, all else being equal, reliance on a particular information source will depend on its information content relative to other sources. Information conflicts are a good area in which to test such predictions. Social insects, such as ants, make extensive use of both private information (e.g. visual route memories) and social information (e.g. pheromone trails) when attempting to locate a food source. Importantly, eusocial insects collaborate on food retrieval, so both information use and information provision may be expected to vary with the information content of alternative information sources. Many ants, such as Lasius niger, are active both day and night. Variation in light levels represents an ecologically important change in the information content of visually-acquired route information. Here, we examine information use and information provision under high light levels (3200 lux, equivalent to a bright but overcast day), moderate light levels simulating dusk (10 lux) and darkness (0.007 lux, equivalent to a moonless night). Ants learn poorly, or not at all, in darkness. As light levels decrease, ants show decreasing reliance on private visual information, and a stronger reliance on social information, consistent with a ‘copy when uncertain’ strategy. In moderate light levels and darkness, pheromone deposition increases, presumably to compensate for the low information content of visual information. Varying light levels for cathemeral animals provides a powerful and ecologically meaningful method for examining information use and provision under varying levels of information content