78 research outputs found
A novel approach to antibiofilm susceptibility testing using a thermo-reversible matrix
Method:
Pseudomonas aeruginosa (NCIMB 8626) was cultured in medium containing poloxamer 407 at 37°C for 24 hours to generate biofilms. The preparation was cooled to liquefy the poloxamer and allow recovery of the biofilm cells, which were then stained with SYTO9 to determine viability following exposure to four antimicrobials: polyhexanide, octenadine dihydrochloride, povidone-iodine and silver carbonate. Over an 8-minute time period, fluorescence levels were spectrophotometrically measured and compared with bacterial controls, cultured in the absence of poloxamer and without antimicrobial.
Results:
Untreated cells showed no reduction in viability over this period. Importantly, planktonic cells were more susceptible to test agents compared with those of a ‘biofilm’ phenotype cultured in poloxamer. Antibiofilm activity was evident for all of the test agents, with highest relative activity seen with octenadine dihydrochloride.
Conclusion:
In summary, a novel and relatively rapid approach to screen compounds for antibiofilm activity has been described. The method uses standard laboratory equipment and can be readily adapted to test a wide range of microorganisms and other antibiofilm compounds
A discretized integral hydrodynamics
Using an interpolant form for the gradient of a function of position, we
write an integral version of the conservation equations for a fluid. In the
appropriate limit, these become the usual conservation laws of mass, momentum
and energy. We also discuss the special cases of the Navier-Stokes equations
for viscous flow and the Fourier law for thermal conduction in the presence of
hydrodynamic fluctuations. By means of a discretization procedure, we show how
these equations can give rise to the so-called "particle dynamics" of Smoothed
Particle Hydrodynamics and Dissipative Particle Dynamics.Comment: 10 pages, RevTex, submitted to Phys. Rev.
Thermodynamically admissible form for discrete hydrodynamics
We construct a discrete model of fluid particles according to the GENERIC
formalism. The model has the form of Smoothed Particle Hydrodynamics including
correct thermal fluctuations. A slight variation of the model reproduces the
Dissipative Particle Dynamics model with any desired thermodynamic behavior.
The resulting algorithm has the following properties: mass, momentum and energy
are conserved, entropy is a non-decreasing function of time and the thermal
fluctuations produce the correct Einstein distribution function at equilibrium.Comment: 4 page
Optical Observations of GRO J1655-40 in Quiescence I: A Precise Mass for the Black Hole Primary
We report photometric and spectroscopic observations of the black hole binary
GRO J1655-40 in complete quiescence. In contrast to the 1995 photometry, the
light curves from 1996 are almost completely dominated by ellipsoidal
modulations from the secondary star. Model fits to the light curves, which take
into account the temperature profile of the accretion disk and eclipse effects,
yield an inclination of i=69.50 +/- 0.08 degrees and a mass ratio of Q=2.99 +/-
0.08. The precision of our determinations of i and Q allow us to determine the
black hole mass to an accuracy of approximately 4% (7.02 +/- 0.22 solar
masses). The secondary star's mass is 2.34 +/- 0.12 solar masses. The position
of the secondary on the Hertzsprung-Russell diagram is consistent with that of
a 2.3 solar mass star which has evolved off the main sequence and is halfway to
the start of the giant branch. Using the new spectra we present an improved
value of the spectroscopic period (2.62157 +/- 0.00015 days), radial velocity
semiamplitude (228.2 +/- 2.2 km/sec), and mass function (3.24 +/- 0.09 solar
masses). Evolutionary models suggest an average mass transfer rate for such a
system of 3.4E-9 solar masses per year (2.16E+17 grams per second), which is
much larger than the average mass transfer rates implied in the other six
transient black hole systems, but still barely below the critical mass transfer
rate required for stability.Comment: 30 pages, 12 figures, LaTeX (uses orosztwo.sty), to appear in ApJ,
vol. 474 (March 10, 1997
New Complexities in the Low-State line profiles of AM Herculis
When accretion temporarily ceases in the polar AM Her, the emission line
profiles are known to develop several distinct components, whose origin remains
poorly understood. The new low-state spectra reported here have a more
favorable combination of spectral resolution (R~4500), time resolution (~3-min
exposures), and S/N than earlier work, revealing additional details of the
orbital dependence of the line profiles. The central strong feature of H-alpha
is found to be composed of two components of similar strength, one having K~100
km/sec and phased with the motion of the secondary star, the other having
little or no detectable radial velocity variations. We attribute the central
line component to gas near the coupling region, perhaps with a contribution
from irradiation of the secondary star. The two satellite components have RV
offsets of ~+/-250 km/sec on either side of the central strong H-alpha peak.
These satellites most likely arise in large loops of magnetically confined gas
near the secondary star due to magnetic activity on the donor star and/or
interactions of the magnetic fields of the two stars. Doppler maps show that
these two satellite features have concentrations at velocities that match the
velocity locations of L4 and L5 in the system.Comment: 15 pages, 14 figures, 2 tables, ApJ in pres
The effects of changes in the order of verbal labels and numerical values on children's scores on attitude and rating scales
Research with adults has shown that variations in verbal labels and numerical scale values on rating scales can affect the responses given. However, few studies have been conducted with children. The study aimed to examine potential differences in children’s responses to Likert-type rating scales according to their anchor points and scale direction, and to see whether or not such differences were stable over time. 130 British children, aged 9 to 11, completed six sets of Likert-type rating scales, presented in four different ways varying the position of positive labels and numerical values. The results showed, both initially and 8-12 weeks later, that presenting a positive label or a high score on the left of a scale led to significantly higher mean scores than did the other variations. These findings indicate that different arrangements of rating scales can produce different results which has clear implications for the administration of scales with children
Enterococcus faecalis demonstrates pathogenicity through increased attachment in an ex vivo polymicrobial pulpal infection
This study investigated the host response to a polymicrobial pulpal infection consisting of Streptococcus anginosus and Enterococcus faecalis, bacteria commonly implicated in dental abscesses and endodontic failure, using a validated ex vivo rat tooth model. Tooth slices were inoculated with planktonic cultures of S. anginosus or E. faecalis alone or in co-culture at ratios of 50:50 and 90:10 S. anginosus to E. faecalis. Attachment was semi-quantified by measuring area covered by fluorescently labelled bacteria. Host response was established by viable histological cell counts and inflammatory response using RT-qPCR and immunohistochemistry. A significant reduction in cell viability was observed for single and polymicrobial infections, with no significant differences between infection types (≈2000cells/mm2 for infected pulps compared to ≈4000cells/mm2 for uninfected pulps). E. faecalis demonstrated significantly higher levels of attachment (6.5%) compared to S. anginosus alone (2.3%) and mixed species infections (3.4% for 50:50 and 2.3% for 90:10), with a remarkable affinity to the pulpal vasculature. Infections with E. faecalis demonstrated the greatest increase in TNF-α (47.1 fold for E. faecalis, 14.6 fold for S. anginosus, 60.1 fold for 50:50 and 25.0 fold for 90:10) and IL-1β expression (54.8 fold for E. faecalis, 8.8 fold for S. anginosus, 54.5 fold for 50:50 and 39.9 fold for 90:10) when compared to uninfected samples. Immunohistochemistry confirmed this with the majority of inflammation localised to the pulpal vasculature and odontoblast regions. Interestingly, E. faecalis supernatant and heat killed E. faecalis treatment was unable to induce the same inflammatory response, suggesting E. faecalis pathogenicity in pulpitis is linked to its greater ability to attach to the pulpal vasculature
The age patterns of severe malaria syndromes in sub-Saharan Africa across a range of transmission intensities and seasonality settings
BACKGROUND: A greater understanding of the relationship between transmission intensity, seasonality and the age-pattern of malaria is needed to guide appropriate targeting of malaria interventions in different epidemiological settings. METHODS: A systematic literature review identified studies which reported the age of paediatric hospital admissions with cerebral malaria (CM), severe malarial anaemia (SMA), or respiratory distress (RD). Study sites were categorized into a 3 × 2 matrix of Plasmodium falciparum transmission intensity and seasonality. Probability distributions were fitted by maximum likelihood methods, and best fitting models were used to estimate median ages and to represent graphically the age-pattern of each outcome for each transmission category in the matrix. RESULTS: A shift in the burden of CM towards younger age groups was seen with increasing intensity of transmission, but this was not the case for SMA or RD. Sites with 'no marked seasonality' showed more evidence of skewed age-patterns compared to areas of 'marked seasonality' for all three severe malaria syndromes. CONCLUSIONS: Although the peak age of CM will increase as transmission intensity decreases in Africa, more than 75% of all paediatric hospital admissions of severe malaria are likely to remain in under five year olds in most epidemiological settings
Importance of strategic management in the implementation of private medicine retailer programmes: case studies from three districts in Kenya
BACKGROUND: The home-management of malaria strategy seeks to improve prompt and effective anti-malarial drug use through the informal sector, with a potential channel being the Private Medicine Retailers (PMRs). Previous evaluations of PMR programmes focused on their impact on retailer knowledge and practices, with limited evidence about the influence of implementation processes on the impacts at scale. This paper examines how the implementation processes of three PMR programmes in Kenya, each scaled up within a district, contributed to the outcomes observed. These were a Ministry of Health programme in Kwale district; and two programmes supported by non-governmental organizations in collaboration with government in Kisii Central and Bungoma districts. METHODS: The research methods included 24 focus group discussions with clients and PMRs, 19 in-depth interviews with implementing actors, document review and a diary of events. The data were analysed using the combination of a broad policy analysis framework and more specific scaling up/diffusion of innovations frameworks. RESULTS: The Kisii programme, a case study of successful implementation, was underpinned by good relationships between district health managers and a "resource team", supported by a memorandum of understanding which enabled successful implementation. It had flexible budgetary and decision making processes which were responsive to local contexts, and took account of local socio-economic activities. In contrast, the Kwale programme, which had implementation challenges, was characterised by a complex funding process, with lengthy timelines, that was tied to the government financial management system which constrained implementation Although there was a flexible funding system in Bungoma, a perceived lack of transparency in fund management, inadequate management of inter-organisational relationships, and inability to adapt and respond to changing circumstances led to implementation difficulties. CONCLUSIONS: For effective scaling up of PMR programmes, the provision of technical support and adequate resources are vital, but not sufficient on their own. An active strategy to manage relationships between implementing actors through effective communication mechanisms is essential. Successful outcomes may be realised if a strong and transparent management system, including management of financial resources, is put in place. This study provides evidence of the value of assessing implementation processes as part of impact evaluation for public health programmes
Pandemic gardening:A narrative review, vignettes and implications for future research
There is a significant amount of evidence highlighting the health, wellbeing and social benefits of gardening during previous periods of crises. These benefits were also evident during the COVID-19 pandemic. This paper presents a narrative review exploring gardening during the early stages of the COVID-19 pandemic to understand the different forms of gardening that took place during this crisis and key elements of this activity. Research about gardening during the pandemic focused on food (in)security and disrupted food systems, the health and wellbeing benefits of gardening, and the social dimensions of gardening. We offer three vignettes of our own research to highlight key insights from local, national and international perspectives of gardening during the pandemic. The paper's conclusion outlines how researchers, policy makers and public health practitioners can harness what has been learned from gardening during the pandemic to ensure these benefits are more widely available and do not exacerbate already entrenched health inequalities in society.</p
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