# Confinement-Induced Drug-Tolerance in Mycobacteria Mediated by an Efflux Mechanism

## TL;DR

This study shows that mycobacteria become more resistant to drugs when they grow in confined spaces, like inside immune cells, due to an efflux mechanism.

## Contribution

The study identifies a novel epigenetic drug-tolerance mechanism in mycobacteria caused by physical confinement.

## Key findings

- Mycobacteria in confined bioreactors show increased drug tolerance.
- Efflux mechanisms are activated in confined growth environments.
- Drug tolerance disappears in larger volume growth conditions.

## Abstract

Tuberculosis (TB) is the world’s deadliest curable disease, responsible for an estimated 1.5 million deaths annually. A considerable challenge in controlling this disease is the prolonged multidrug chemotherapy (6 to 9 months) required to overcome drug-tolerant mycobacteria that persist in human tissues, although the same drugs can sterilize genetically identical mycobacteria growing in axenic culture within days. An essential component of TB infection involves intracellular Mycobacterium tuberculosis bacteria that multiply within macrophages and are significantly more tolerant to antibiotics compared to extracellular mycobacteria. To investigate this aspect of human TB, we created a physical cell culture system that mimics confinement of replicating mycobacteria, such as in a macrophage during infection. Using this system, we uncovered an epigenetic drug-tolerance phenotype that appears when mycobacteria are cultured in space-confined bioreactors and disappears in larger volume growth contexts. Efflux mechanisms that are induced in space-confined growth environments contribute to this drug-tolerance phenotype. Therefore, macrophage-induced drug tolerance by mycobacteria may be an effect of confined growth among other macrophage-specific mechanisms.