The presence of metal resistance determinants in bacteria usually is attributed to geological or anthropogenic metal contamination in different environments or associated with the use of antimicrobial metals in human healthcare or in agriculture. While this is certainly true, we hypothesize that protozoan predation and macrophage killing are also responsible for selection of copper/zinc resistance genes in bacteria. In this review, we outline evidence supporting this hypothesis, as well as highlight the correlation between metal resistance and pathogenicity in bacteria. In addition, we introduce and characterize the Bcopper pathogenicity island^identified in Escherichia coli and Salmonella strains isolated from copper-and zinc-fed Danish pigs.
The
solubility of azithromycin monohydrate in ethanol, propan-2-ol,
butan-1-ol, ethyl ethanoate, and 2-propanone from 278.15 K to 323.15
K was measured by a synthetic method. The measured solubility data
were correlated by van’t Hoff equation, modified Apelblat equation, λh equation, Wilson, and NRTL models. It was found
that the Wilson equations give the best correlation results. The mixing
properties including the mixing free Gibbs energy, enthalpy, and entropy
of azithromycin monohydrate were also calculated based on the Wilson
model parameters. The results indicate that the dissolution process
of azithromycin monohydrate in all tested solvents is spontaneous
and endothermic.
In
research on coalbed methane, there is no accurate and reasonable
description of the gas transport behavior in a coal matrix over the
entire time and pressure scale. The classical Fick diffusion model
is inadequate to describe the transport behavior of methane in a coal
matrix. It is also very controversial to use the Darcy flow model
to simulate the gas migration in a coal matrix. In this study, experiments
involving methane desorption in coal particles were conducted under
variable-pressure boundary conditions. Based on previous research,
a new theoretical model of free gas density gradient (FGDG) is proposed
in which the mass flux of the gas is proportional to the FGDG, and
the key parameter is defined as the microchannel diffusion coefficient
(D
m). Based on this new theoretical model,
a mathematical model for the gas desorption flow in a coal matrix
is developed, and the numerical solution is obtained by the dimensionless
finite-difference method. It is shown that the simulation results
for methane desorption based on the FGDG model and the Darcy flow
model are consistent with the experimental data on the entire desorption
time scale. The permeability coefficient of the Darcy flow model is
independent of time but dependent on pressure, while the microchannel
diffusion coefficient in the FGDG model can eliminate its dependence
on time and pressure, which makes the modeling and solution of methane
desorption easier and more convenient. A comprehensive investigation
shows that the newly proposed FGDG model is more reasonable than the
Fick diffusion model and the Darcy flow model and can be used preferentially
to describe the gas transport in a coal matrix. These findings can
provide a theoretical basis for further simulating and predicting
coal production and gas transport behavior.
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