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Updated: Jun 12, 2026
Assay Development for High-Throughput Drug Screening Against Mycobacteria
Published on: October 25, 2024
Transport assays and permeability in pathogenic mycobacteria
Marie-Antoinette Lanéelle1, Mamadou Daffé
1Department of Molecular Mechanisms of Mycobacterial Infections, Institut of Pharmacology and Structural Biology, UMR 5089 of the National Centre for Scientific Research and University Paul Sabatier Toulouse III, Toulouse III, France.
Abstract:
Mycobacteria produce an effective permeability layer that consists of a mycolic acid-containing cell wall. This protection confers a natural resistance to many chemical agents and results in a low permeability toward both hydrophilic and lipophilic agents. The permeability of cells is classically measured using methods that generally need cell suspensions and are hazardous with pathogens (e.g., nutrient and antibiotic uptake). A major problem encountered with mycobacteria is their propensity to form aggregates; the addition of detergent to the cell suspension is not recommended as this disorganizes the cell envelope, rendering it more permeable to antibiotics. To circumvent this problem, growing cells are uniformly labeled with [(3)H]-uracil, allowing a quantification of the aliquots; then, the uptake of [(14)C]-labeled probes is followed during the first minutes. To avoid the generation of aerosols associated with the commonly used filtration methods, centrifugation through an oil mixture is the preferred alternative technique for use with Mycobacterium tuberculosis.
Insights
Mycobacteria possess a unique cell wall that limits permeability, posing challenges for traditional drug efficacy testing. A novel method using radiolabeled probes and oil centrifugation overcomes these challenges for Mycobacterium tuberculosis.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Mycobacteria feature a mycolic acid-rich cell wall, creating a low-permeability barrier.
- This natural resistance complicates standard permeability assays, often requiring hazardous methods or cell-disrupting detergents.
- Mycobacterial aggregation further complicates cell suspension-based measurements.
Purpose of the Study:
- To develop a safe and effective method for measuring mycobacterial cell envelope permeability.
- To overcome challenges associated with mycobacterial aggregation and hazardous assay conditions.
- To provide a reliable technique for assessing the uptake of substances by Mycobacterium tuberculosis.
Main Methods:
- Growing cells uniformly labeled with [(3)H]-uracil for aliquot quantification.
- Tracking the uptake of [(14)C]-labeled probes over short incubation periods.
- Employing centrifugation through an oil mixture to separate cells from the external medium, avoiding aerosol generation.
Main Results:
- The developed method allows for the quantification of probe uptake in intact mycobacterial cells.
- Oil centrifugation effectively replaces hazardous filtration methods, enhancing safety.
- This technique is suitable for studying the permeability of Mycobacterium tuberculosis without disorganizing the cell envelope.
Conclusions:
- A novel, safe, and efficient method for assessing mycobacterial permeability has been established.
- This technique is particularly valuable for working with pathogenic Mycobacterium tuberculosis.
- The method facilitates accurate measurement of substance uptake, crucial for understanding drug efficacy and resistance.
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