Drug Gradient Selection
Drug Gradient Selection - Related Videos
08:42
Density Gradient Ultracentrifugation
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2023
Density gradient ultracentrifugation is a common technique used to isolate and purify biomolecules and cell structures. This technique exploits the fact that, in suspension, particles that are more dense than the solvent will sediment, while those that are less dense will float. A high-speed ultracentrifuge is used to accelerate this process in order to separate biomolecules within a density gradient, which can be established by layering liquids of decreasing density in a centrifuge tube. The...
10:50
Design and Use of a Low Cost, Automated Morbidostat for Adaptive Evolution of Bacteria Under Antibiotic Drug Selection
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Cited by 14 •
2016
We describe a low cost, configurable morbidostat that enables the characterization of antibiotic drug resistance by dynamically adjusting the drug concentration. The device can be integrated with a multiplexed microfluidic platform. The approach can be scaled up for laboratory antibiotic drug resistance studies.
09:01
Mutagenesis and Functional Selection Protocols for Directed Evolution of Proteins in E. coli
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Cited by 12 •
2011
Here we demonstrate a simple protocol to create a random mutant library for a given target sequence. We show how this method, which is performed in vivo in Escherichia coli, can be coupled with functional selections to evolve new enzymatic activities.
06:03
Pancreatic Duct Infusion: An Effective and Selective Method of Drug and Viral Delivery
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Cited by 1 •
2021
Pancreatic duct infusion is an important technique that can allow for lineage tracing, gene introduction, and cell line-specific targeting. A pancreatic duct infusion technique for drug and viral delivery to pancreatic cells is presented here.
03:36
Purification of Bacteriophages Using a Sucrose Density Gradient
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2026
Source: Rustad, M., et.al. Synthesis of Infectious Bacteriophages in an E. coli-based Cell-free Expression System. J. Vis. Exp. (2017)This video demonstrates the purification of bacteriophages from a suspension containing host bacterial debris using a sucrose density gradient. It shows how the density gradient separates phages by buoyant density, enabling recovery of a visible band for resuspension and further analysis.
FAQs
Selection pressure acts across successive exposure stages: a concentration that allows only limited survival narrows the population, and later increases test whether survivors can persist under stronger pressure. Continued expansion under selection makes the surviving phenotype experimentally observable rather than treating all cells as equally affected. The resulting culture is enriched for drug tolerance or resistance.
Survival may reflect altered drug uptake, increased efflux, modification of the drug target, or adaptation to cellular stress. These mechanisms provide different explanations for a similar resistant or tolerant phenotype. Comparing surviving cultures with untreated or differently selected populations can help investigators connect the observed response to a particular biological process.
Stepwise increases allow cells that survive an initial, limited-pressure condition to expand before they encounter stronger selection. This creates successive tests of persistence and enriches populations according to their ability to tolerate increasing drug concentrations. The approach therefore supports comparison of responses across selection stages rather than producing only a single survival outcome.
The starting concentration, the size of each concentration increase, and continued exposure during survivor expansion directly shape the selected population. A starting level that permits limited survival establishes the initial filter, while later concentrations determine how strongly persistence is tested. These choices influence whether the final culture represents relatively tolerant or more strongly resistant cells.
Cells first encounter a concentration that permits limited survival. Susceptible cells are then eliminated while surviving cells expand under continued selection. The drug concentration is subsequently increased in steps, and the population is evaluated for continued survival at each stage. This sequence produces cultures enriched through repeated selection rather than a single exposure event.
Selected cultures can reveal whether a population develops a drug-tolerant or resistant phenotype and can support comparisons of responses under different selection conditions. Investigators can also examine whether survival is associated with altered uptake, efflux, target modification, or stress adaptation. These outcomes help connect population-level drug responses with possible cellular mechanisms.
In antimicrobial research, the method supports studies of populations that persist during compound exposure. In cancer biology, it helps generate cultures for examining drug-tolerant or resistant behavior. Across both areas, the resulting comparisons can contribute to research on treatment design and resistance monitoring by showing how surviving populations respond as selection pressure increases.