A Comprehensive Phenotypic Screening Strategy to Identify Modulators of Cargo Translocation by the Bacterial Type IVB...

Area of Science:

• Microbiology and Molecular Pathogenesis
• Drug Discovery and Development

Background:

• Bacterial type IV secretion systems (T4SSs) are crucial virulence factors, essential for translocating effector proteins into host cells.
• T4SSs are attractive drug targets due to their dispensability for bacterial survival in vitro, offering a 'pathogen's Achilles heel' strategy.
• Conventional antibiotics have limitations, necessitating the development of pathogen-selective therapeutics to combat multi-drug resistant infections.

Purpose of the Study:

• To develop and implement a high-throughput screening (HTS) approach to identify small molecules inhibiting T4SS function.
• To discover compounds that specifically interfere with effector protein delivery by T4SSs from key human pathogens.
• To validate identified compounds for their efficacy and specificity in cell-based assays and against multiple bacterial species.

Main Methods:

• Designed an automated HTS assay using a fluorescence resonance energy transfer (FRET)-based detection system in a bacteria/macrophage coculture model.
• Screened a library of over 18,000 compounds against Legionella pneumophila effector delivery into RAW264.7 macrophages.
• Conducted in vitro and cell-based secondary screens to validate hit compounds, assessing effects on bacterial growth and T4SS-dependent virulence.

Main Results:

• Identified several hit compounds that effectively inhibited T4SS-mediated effector delivery and virulence processes (e.g., intracellular proliferation, lysosomal avoidance).
• Confirmed that hit compounds did not affect bacterial growth in standard culture media, indicating target specificity.
• Demonstrated that the same compounds attenuated effector delivery by the T4SS of Coxiella burnetii, showing broader applicability.

Conclusions:

• Interference with bacterial T4SS function is a viable therapeutic strategy against bacterial pathogens.
• The identified compounds serve as valuable tools for further research into T4SS regulation and dynamics.
• This study represents a significant step towards developing precision therapeutics that target pathogens selectively, minimizing harm to the host microbiota.