High-throughput Screening of Chemical Compounds to Elucidate Their Effects on Bacterial Persistence
February 23rd, 2021
In this method paper, we present a high-throughput screening strategy to identify chemical compounds, such as osmolytes, that have a significant impact on bacterial persistence.
The protocol described here makes it possible to identify conditions that can significantly impact bacterial persistence in a high-throughput manner. This method is readily adaptable to screen for various areas, such as drug panels, gene libraries and more. As the method includes various sub steps, which are to be conducted simultaneously, visual demonstration can aid researchers to manage their timing to obtain precise results.
Begin by preparing microarray cell cultures. Transfer 250 microliters of exponential phase cells to 25 milliliters of fresh modified LB medium in a 50 milliliter centrifuge tube. Then gently mix the cell suspension to make it homogenous.
Transfer the diluted cell suspension into a sterile 50 milliliters reservoir. Using a multi-channel pipette, transfer 150 microliters of the cell suspension to each well of a microarray plate containing various chemicals. Microarrays can also be generated manually following the method described in the text manuscript.
Cover the microarray plate with a gas permeable ceiling membrane and incubate it in an orbital shaker at 37 degrees Celsius and 250 RPM for 24 hours. To make persister assay plates, prepare 25 milliliters of modified LB medium containing five micrograms per milliliter of Ofloxacin in a 50 milliliter centrifuge tube and transfer this medium to a sterile reservoir. Transfer 190 microliters of the modified LB medium into each well of a generic flat bottom 96 well plate.
After the 24 hour incubation, remove the microarray from the shaker and transfer 10 microliters of cell cultures from the microarray to the wells of the persister assay plate containing modified LB medium with Ofloxacin. Take 10 microliters of cell suspensions from the persister essay plate and serially dilute it three times in 290 microliters of PBS solution using a round bottom 96 well plate and a multi-channel pipette. Then spot 10 microliters of all serially diluted cell suspensions on antibiotic free fresh agar plates.
Cover the persister assay plate with a gas permeable ceiling membrane and incubate it in an orbital shaker at 37 degrees Celsius and 250 RPM for six hours. After the six hour incubation, repeat the serial dilution and spotting on agar plates. Incubate the agar plates for 16 hours at 37 degrees Celsius.
Then count the colony forming units or CFUs. Use the CFU levels before and six hours after the antibiotic treatment to calculate the persister fraction in each well. The CFU counts before the OFX treatment also help assess the effects of osmolites on e coli viability.
Transfer 250 microliters of exponential phase cells to 25 milliliters of fresh modified LB medium containing the osmolite identified from the microarray screening. Incubate the flask in an orbital shaker at 250 RPM and 37 degrees Celsius for 24 hours. After 24 hours, remove the flask from the shaker and transfer 250 microliters of the cell culture to 25 milliliters of fresh modified LB medium in a 250 milliliter baffled flask.
Add 25 microliters of Ofloxacin stock solution to the cell suspension and shake the flask gently to make the assay culture homogenous. Incubate the flask in a shaker at 37 degrees Celsius and 250 RPM. At every hour during the treatment, including a time point before addition of Ofloxacin, transfer one milliliter of the assay culture from the flask to a 1.5 milliliter micro centrifuge tube and centrifuge it at 17, 000 times G for three minutes.
Remove 950 microliters of supernatant and wash the cells three times with 950 microliters of PBS. After the final wash, re-suspend the cell pellet in 100 microliters of PBS solution. Take 10 microliters of the cell suspension and serially dilute it six times with 90 microliters of PBS inside a 96 well round bottom plate.
Spot 10 microliters of the diluted cell suspensions on an antibiotic free agar plate. To increase the limit of detection, plate the remaining 90 microliters of cell suspension on a fresh agar plate. Incubate the plates at 37 degrees Celsius for 16 hours, then count CFUs.
A representative image of agar plates used to determine CFU levels of cell cultures before and after OFX treatment is shown here. The first column is the control group. The second column has cells that were cultured in 100 millimolar sodium nitrate and the third column contains cells that were cultured in 60 millimolar sodium nitrate.
For simplicity, only two osmolites are focused on here. A graphical representation of the CFU data from the plates and persister fractions of the cell cultures tested in 96 well plates are shown here. To calculate the fractions, persister counts were normalized to the cell counts obtained before the antibiotic treatment.
To generate byphasic kill curves, the cells were cultured in 25 milliliters of modified LB medium with the indicated osmolites and baffled flasks for 24 hours, then transferred to persister assay flasks for persister enumeration. When attempting this protocol, keep in mind that spotting the cells on agar plate is labor intensive and requires focus. An error during the step can lead to cross-contamination among the conditions being tested.
So it is important to practice spotting multiple samples simultaneously prior to the experiment. Following this protocol, drug panels and mutant cell libraries can be screened to study the impacts on the persistence. With this screening, we have identified a number of osmolites and PS conditions that have a significant impact on bacterial persistence.
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Overview
This method paper presents a high-throughput screening strategy to identify chemical compounds that significantly impact bacterial persistence. The protocol is adaptable for various applications, including drug panels and gene libraries.
Key Study Components
Area of Science
- Microbiology
- High-throughput screening
- Chemical compounds
Background
- Bacterial persistence is a critical factor in infection management.
- Identifying compounds that affect persistence can lead to new therapeutic strategies.
- High-throughput methods allow for efficient screening of multiple conditions.
- Visual demonstrations can enhance the execution of complex protocols.
Purpose of Study
- To develop a method for screening compounds affecting bacterial persistence.
- To provide a protocol that can be adapted for various research needs.
- To facilitate simultaneous execution of multiple experimental steps.
Methods Used
- Preparation of microarray cell cultures.
- Transfer of exponential phase cells to modified LB medium.
- Homogenization of cell suspension.
- Simultaneous execution of various sub-steps for efficiency.
Main Results
- The method allows for the identification of significant chemical compounds.
- Demonstrated adaptability for different screening applications.
- Visual aids improve timing and accuracy in experiments.
- High-throughput capabilities enhance research efficiency.
Conclusions
- This high-throughput screening method is effective for identifying compounds that impact bacterial persistence.
- The protocol's adaptability makes it valuable for various research contexts.
- Visual demonstrations are beneficial for managing complex experimental procedures.
Frequently Asked Questions
Executive Industry Relevance
High-throughput screening of chemical compounds for effects on bacterial persistence addresses a critical bottleneck in anti-infective discovery by enabling systematic interrogation of phenotypic resistance mechanisms. This approach supports predictive confidence in early-stage target validation and informs portfolio triage by identifying modulators of persistence that may underlie chronic infection relapse. Adaptability to drug panels and gene libraries positions this workflow as a reusable asset across discovery and preclinical pipelines.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables systematic evaluation of chemical and genetic modulators of bacterial persistence.
- Supports functional target validation by quantifying phenotypic switching under defined conditions.
- Facilitates biological de-risking by clarifying persistence mechanisms relevant to chronic infection models.
- Provides data for predictive confidence in advancing anti-persistence strategies.
Screening & Assay Development
- Delivers validated, quantitative readouts of persister fractions across diverse chemical conditions.
- Standardizes assay conditions for reproducibility and cross-study comparability.
- Enables scalable, parallelized screening of compound libraries or genetic variants.
- Prepares robust biological systems for downstream mechanistic or translational studies.
Translational & Preclinical Research
- Aligns in vitro persistence modulation with disease-relevant bacterial phenotypes.
- Supports continuity from discovery through preclinical validation of anti-persistence interventions.
- Informs risk-adjusted advancement of candidates targeting persistence mechanisms.
- Provides mechanistic de-risking for chronic infection models.
Pipeline & Workflow Integration
This high-throughput screening method integrates at the interface of early discovery and lead identification, supporting both hypothesis-driven and unbiased compound evaluation for persistence modulation.
- Discovery Biology: Enables hypothesis testing of environmental and chemical triggers of persistence.
- Screening: Provides reproducible, quantitative outputs for compound or gene library evaluation.
- Analytics: Generates colony forming unit (CFU) data and persister fraction calculations for comparative analysis.
- Translational Research: Bridges in vitro findings to preclinical models of chronic infection when supported by downstream validation.
- Enterprise Reuse: Adaptable to diverse screening arrays, supporting multiple R&D programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in anti-persistence target validation and mechanistic de-risking.
- Operational Value: Standardizes high-throughput workflows for reproducibility and scalability.
- Strategic Value: Enables informed go/no-go decisions and reduces late-stage biological risk in anti-infective portfolios.
- Portfolio Impact: Supports risk-adjusted prioritization of candidates targeting persistence mechanisms.
Implementation Considerations
- Requires expertise in high-throughput microbiological assays and quantitative CFU analysis.
- Demands multi-channel pipetting, microarray plate handling, and colony counting infrastructure.
- Necessitates rigorous cross-team standardization to minimize cross-contamination and ensure data integrity.
- Adaptable to various model systems, but labor-intensive steps such as agar spotting require practice and precision.
- Throughput and detection limits are constrained by manual handling and colony enumeration capacity.
