Since antibiotic resistance is a major threat to global health, recent observations that the traditional test of minimum inhibitory concentration (MIC) is not informative enough to guide effective ...antibiotic treatment are alarming. Bacterial heteroresistance, in which seemingly susceptible isogenic bacterial populations contain resistant sub-populations, underlies much of this challenge. To close this gap, here we developed a droplet-based digital MIC screen that constitutes a practical analytical platform for quantifying the single-cell distribution of phenotypic responses to antibiotics, as well as for measuring inoculum effect with high accuracy. We found that antibiotic efficacy is determined by the amount of antibiotic used per bacterial colony forming unit (CFU), not by the absolute antibiotic concentration, as shown by the treatment of beta-lactamase-carrying Escherichia coli with cefotaxime. We also noted that cells exhibited a pronounced clustering phenotype when exposed to near-inhibitory amounts of cefotaxime. Overall, our method facilitates research into the interplay between heteroresistance and antibiotic efficacy, as well as research into the origin and stimulation of heterogeneity by exposure to antibiotics. Due to the absolute bacteria quantification in this digital assay, our method provides a platform for developing reference MIC assays that are robust against inoculum-density variations.
•Calorimetric measurements of binary Ga-Zn system.•Integral molar mixing enthalpies of liquid Ga-Zn alloys.•Thermodynamic properties of liquid Ga-Zn alloys.
This paper contains the results of the ...integral molar mixing enthalpy of Ga-Zn liquid alloys, measured calorimetrically at two temperatures: 722K over the entire concentration range and 923K for the concentration range of Zn lower than 0.5at.%. Experimental values obtained in this range of temperatures indicate that the integral molar enthalpy of liquid alloys of this binary system is temperature independent. The available experimental values of the partial or molar Gibbs energies, together with the enthalpy of mixing, were used for the elaboration of the equation in the form proposed by Redlich and Kister, which describes the dependence of the excess Gibbs energy on the concentration and temperature. The experimental thermodynamic values of the excess Gibbs energy, mixing enthalpy change and activity were compared with those calculated with the use of the elaborated Redlich-Kister equation. Moreover, the partial structure factors and short-range order parameter were calculated and discussed in relation to the thermodynamic properties and the phase diagram of the Ga-Zn system.
•Calorimetric measurements of liquid Ga–Li alloys.•Integral enthalpies of mixing of liquid Ga–Li alloys at T=873K, 992K and 1039K.•Thermodynamic properties of liquid Ga–Li alloys.•Calorimetric ...measurements vs. Miedema’s model.
The integral molar enthalpy of mixing was determined by the drop calorimetric method for binary Ga–Li liquid alloys. The measurements were conducted at three temperatures, i.e. 873K, 992K and 1039K, and in the following concentration ranges: XLi=0.7030 to 0.9801, 0.0908 to 0.3748 and 0.4284 to 0.8282, respectively. A strong negative deviation from the ideal solution was observed, with the minimum value equal to −21.2kJ/mol for XLi=0.5421. The analysis of the experimental data suggests that the integral mixing enthalpy of the Ga–Li liquid solutions is independent of temperature. The values calculated from the Miedema’s model are more positive in comparison to the measured ones, and the maximum difference of about 12.5kJ/mol is observed for the 0.5mol fraction of Li. By way of applying the calorimetric data from this work and the electromotive force measurements of Wen and Huggins and Yatsenko et al., the Redlich–Kister relation was worked out for the excess Gibbs energy of the liquid Ga–Li liquid solutions. The calculated Scc(0) partial structure factor points to the GaLi associates in liquids.
Traumatic disruption of the acromioclavicular joint capsule is associated with pain and instability after the injury and may lead to degenerative joint disease. The objective of this study was to ...quantify the effect of transection of the acromioclavicular joint capsule on the kinematics and the in situ forces in the coracoclavicular ligaments in response to external loading conditions.
Eleven fresh-frozen human cadaveric shoulders were tested with use of a robotic/universal force-moment sensor testing system. The shoulders were subjected to three loading conditions (an anterior, posterior, and superior load of 70 N) in their intact state and after transection of the acromioclavicular joint capsule.
Transection of the capsule resulted in a significant (p < 0.05) increase in anterior translation (6.4 mm) and posterior translation (3.6 mm) but not in superior translation (1.6 mm). The effect of capsule transection on the forces in the coracoclavicular ligaments was also significant (p < 0.05) in response to anterior and posterior loading but not in response to superior loading. However, differences were found between the forces in the trapezoid and conoid ligaments. Under an anterior load, the mean in situ force (and standard deviation) in the trapezoid increased from 14 +/- 14 N to 25 +/- 19 N, while the mean force in the conoid increased from 15 +/- 14 N to 49 +/- 23 N, or 227%. In contrast, in response to a posterior load, the mean in situ force in the trapezoid increased from 23 +/- 15 N to 38 +/- 23 N, or 66% (p < 0.05), while the mean force in the conoid increased only 9%.
The large differences in the change of force in the conoid and trapezoid ligaments suggest that these ligaments should not be considered as one structure when surgical treatment is considered. Furthermore, transection of the capsule resulted in a shift of load to the coracoclavicular ligaments, which may render the intact coracoclavicular ligaments more likely to fail with anterior or posterior loading. The results of the present study also suggest that the intact coracoclavicular ligaments cannot compensate for the loss of capsular function during anterior-posterior loading as occurs in type-II acromioclavicular joint injuries.
We explain how to design classic digital assays, comprising identical partitions, in order to obtain the required precision of the estimate within a defined range of concentrations. The design, ...including the number and volume of partitions, depends significantly on whether the assay is to assess the concentration of the target analyte in the sample or in the source of the sample (e.g. a patient body) with a given precision. We also show how to translate the result referring to the concentration in the sample into the concentration in the source of the sample, including the significant change in the breath of the confidence intervals.
Background: The focus of most anterior cruciate ligament reconstructions has been on replacing the anteromedial bundle and not the posterolateral
bundle.
Hypothesis: Anatomic two-bundle ...reconstruction restores knee kinematics more closely to normal than does single-bundle reconstruction.
Study Design: Controlled laboratory study.
Methods: Ten cadaveric knees were subjected to external loading conditions: 1) a 134-N anterior tibial load and 2) a combined rotatory
load of 5-N·m internal tibial torque and 10-N·m valgus torque. Resulting knee kinematics and in situ force in the anterior
cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for
1) intact, 2) anterior cruciate ligament deficient, 3) single-bundle reconstructed, and 4) anatomically reconstructed knees.
Results: Anterior tibial translation for the anatomic reconstruction was significantly closer to that of the intact knee than was
the single-bundle reconstruction. The in situ force normalized to the intact anterior cruciate ligament for the anatomic reconstruction
was 97%± 9%, whereas the single-bundle reconstruction was only 89%± 13%. With a combined rotatory load, the normalized in
situ force for the single-bundle and anatomic reconstructions at 30° of flexion was 66%± 40%and 91%± 35%, respectively.
Conclusions: Anatomic reconstruction may produce a better biomechanical outcome, especially during rotatory loads.
Clinical Relevance: Results may lead to the use of a two-bundle technique.
Emerging microfluidic technology has introduced new precision controls over reaction conditions. Owing to the small amount of reagents, microfluidics significantly lowers the cost of carrying a ...single reaction. Moreover, in two-phase systems, each part of a dispersed fluid can be treated as an independent chemical reactor with a volume from femtoliters to microliters, increasing the throughput. In this work, we propose a microfluidic device that provides continuous recirculation of droplets in a closed loop, maintaining low consumption of oil phase, no cross-contamination, stabilized temperature, a constant condition of gas exchange, dynamic feedback control on droplet volume, and a real-time optical characterization of bacterial growth in a droplet. The channels (tubing) and junction cubes are made of Teflon fluorinated ethylene propylene (FEP) to ensure non-wetting conditions and to prevent the formation of biofilm, which is particularly crucial for biological experiments. We show the design and operation of a novel microfluidic loop with the circular motion of microdroplet reactors monitored with optical sensors and precision temperature controls. We have employed the proposed system for long term monitoring of bacterial growth during the antibiotic chloramphenicol treatment. The proposed system can find applications in a broad field of biomedical diagnostics and therapy.
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