A High-throughput, High-content, Liquid-based C. elegans Pathosystem
July 1st, 2018
14.4K views
Here we describe a protocol that is an adaptable, whole host, high-content screening tool that can be utilized to study host-pathogen interactions and be used for drug discovery.
Overview
This article describes a protocol for a high-content screening tool that studies host-pathogen interactions and aids in drug discovery. The method emphasizes the use of small volumes in a liquid format, making it adaptable for various experiments.
Key Study Components
Area of Science
- Host-pathogen interactions
- Drug discovery
- Microbial virulence factors
Background
- Understanding host-pathogen interactions is crucial for developing new therapeutics.
- Virulence factors play a significant role in pathogen behavior and infection.
- Small molecules can potentially mitigate pathogenic effects.
- High-content screening allows for efficient analysis of multiple factors simultaneously.
Purpose of Study
- To develop a protocol for studying host-pathogen interactions.
- To facilitate drug discovery through high-content screening.
- To evaluate the impact of virulence factors and small molecules.
Methods Used
- Streaking P. aeruginosa from frozen stock onto LB Agar plates.
- Incubating plates at 37 degrees C for 16 to 24 hours.
- Inoculating sterile LB broth with a single colony for culture preparation.
- Conducting assays in a BSL 2 biosafety cabinet.
Main Results
- The method allows for the assessment of various virulence factors.
- Small molecules can be tested for their ability to ameliorate pathogenic effects.
- Liquid format with small volumes enhances experimental efficiency.
- Results can inform future drug development strategies.
Conclusions
- This protocol provides a versatile tool for studying host-pathogen dynamics.
- It supports the identification of potential therapeutic agents.
- Future applications may expand to other pathogens and drug classes.
Frequently Asked Questions
What is the main advantage of this screening method?
The main advantage is its liquid format with small volumes, allowing for efficient high-content screening.
What type of pathogens can be studied using this protocol?
The protocol is designed for studying host-pathogen interactions, specifically with P. aeruginosa.
How long should the P. aeruginosa plates be incubated?
The plates should be incubated at 37 degrees C for 16 to 24 hours.
What is the purpose of using a BSL 2 biosafety cabinet?
The BSL 2 biosafety cabinet is used to ensure safe handling of pathogens during the experiment.
How can small molecules be tested in this method?
Small molecules can be introduced during the assay to evaluate their effects on pathogen behavior.
Executive Industry Relevance
This liquid-based C. elegans pathosystem enables high-throughput phenotypic screening in a liquid format, reducing false positives by eliminating toxic or bio-unavailable compounds early in discovery. The assay supports rapid interrogation of host-pathogen interactions and virulence factors, accelerating target validation and lead identification in antimicrobial discovery. Its compatibility with RNAi screening and small molecule testing provides a scalable, reproducible platform for de-risking therapeutic hypotheses before costly biochemical purification or animal model studies.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Interrogates host factors in pathogen killing via RNAi screens in 24- or 96-well formats to clarify therapeutic targets.
- Operational Value: Enables whole-genome screens in months, reducing time to identify host-directed drug targets.
- Predictive Value: Supports phenotypic readouts that reflect in vivo-like host-pathogen dynamics, improving target confidence.
Screening & Assay Development
- Scientific Value: Uses liquid format with small volumes to enable high-content, high-throughput screening in 384-well plates.
- Operational Value: Requires as few as four wells for statistically significant data, improving assay efficiency and reagent conservation.
- Assay Readiness: Compatible with automated imaging and spectrophotometry for quantitative, reproducible readouts.
Translational & Preclinical Research
- Translational Value: Adapts to Gram-positive pathogens like E. faecalis without preinfection, improving safety and reducing contamination risk.
- Disease Relevance: Models time-dependent killing relevant to chronic infection phenotypes.
- Preclinical Continuity: Supports screening of small molecules that ameliorate pathogenesis, informing lead optimization.
Pipeline & Workflow Integration
The assay fits within early discovery workflows, supporting hypothesis testing in host-pathogen interactions and enabling progression from target identification to phenotypic lead screening.
- Discovery Biology: Facilitates interrogation of virulence factors and host genetic contributions to pathogenesis.
- Screening: Enables standardized, liquid-based phenotypic screening with quantitative worm survival readouts.
- Analytics: Generates time- and concentration-dependent killing curves amenable to statistical analysis and hit selection.
- Translational Research: Connects host-target modulation to pathogen attenuation, supporting mechanistic de-risking.
- Enterprise Reuse: Platform adaptable to multiple pathogens, supporting broad antimicrobial target discovery programs.
Operational & Enterprise Impact
- Scientific Value: Reduces false positives by removing cytotoxic or bio-unavailable compounds early in screening.
- Operational Value: Liquid format with small volumes increases throughput and reduces hands-on time to 60–75 minutes per 384-well plate.
- Strategic Value: Improves go/no-go decisions by providing phenotypic efficacy data in a whole-organism context.
- Portfolio Impact: Enables risk-adjusted prioritization of host-directed or virulence-targeting antimicrobial candidates.
Implementation Considerations
- Requires expertise in C. elegans handling, RNAi feeding, and pathogen culture under BSL-2 conditions.
- Depends on access to worm sorters, multichannel pipettes, microplate washers, and automated imagers or spectrophotometers.
- Needs standardization of worm sorting, bacterial seeding, and incubation timing across teams and sites.
- Adaptation to alternative pathogens requires validation of killing kinetics and liquid compatibility.
- Limitations include dependency on synchronized worm staging and potential variability in RNAi feeding efficiency.
Biopharma FAQs
Why does worm settling matter before liquid killing assay setup?
Incomplete worm settling can lead to inaccurate worm counts per well, increasing variability in survival readouts and reducing assay reproducibility. Proper gravitational settling ensures consistent worm distribution, which is critical for reliable phenotypic scoring in high-throughput screens. This step minimizes technical noise and supports detection of weak genetic or chemical hits.
How does OD 600 normalization of P. aeruginosa affect assay consistency?
Normalizing bacterial suspension to OD 600 = 0.09 ensures standardized inoculum across wells, enabling time- and concentration-dependent killing curves. The protocol tolerates a wide range of initial OD (as low as 0.025), but consistent normalization supports reproducible kinetics and comparability across experiments. This control reduces false variability in pathogen exposure during screening.
What enables statistically significant data from as few as four wells in this assay?
High signal-to-noise ratio in the liquid killing assay allows clear discrimination between positive and negative conditions, even with low replicate numbers. When worm survival differences are robust, as shown in the protocol, minimal replication is sufficient for confident hit calling. This improves screening efficiency without compromising statistical confidence in early-stage target validation.
Why is the two-step incubation (37°C then 25°C) for P. aeruginosa dispensable in this liquid assay?
Unlike conventional slow killing assays, this liquid-based pathosystem does not require the two-step temperature shift to observe time-dependent killing of C. elegans. The assay functions effectively at a single incubation temperature (25°C), simplifying workflow and reducing hands-on time. This adaptation enhances compatibility with automated screening platforms while maintaining phenotypic relevance.
How does substituting E. faecalis for P. aeruginosa improve the safety and usability of the assay?
The E. faecalis variant does not require preinfection, eliminating a step that risks contaminating liquid-handling equipment and increases biosafety concerns. This modification improves safety profile and operational ease while maintaining robust killing (~95% death at 96 h). It enables broader application in antimicrobial discovery without compromising assay integrity.
Chapters in this video
0:04
Title
0:25
Preparation and Maintenance of P. aeruginosa and RNAi Bacteria
2:34
Maintenance and Preparation of C. elegans
3:21
Liquid Killing Assay Setup
5:56
Adaptation for Screening Multiple C. elegans Strains or Knockdowns
7:06
Results: C. elegans-P. aeruginosa Liquid Killing Pathosystem
8:37
Conclusion
