Replication rates of Mycobacterium tuberculosis in human macrophages do not correlate with mycobacterial antibiotic susceptibility

PLoS One. 2014 Nov 11;9(11):e112426. doi: 10.1371/journal.pone.0112426. eCollection 2014.

Abstract

The standard treatment of tuberculosis (TB) takes six to nine months to complete and this lengthy therapy contributes to the emergence of drug-resistant TB. TB is caused by Mycobacterium tuberculosis (Mtb) and the ability of this bacterium to switch to a dormant phenotype has been suggested to be responsible for the slow clearance during treatment. A recent study showed that the replication rate of a non-virulent mycobacterium, Mycobacterium smegmatis, did not correlate with antibiotic susceptibility. However, the question whether this observation also holds true for Mtb remains unanswered. Here, in order to mimic physiological conditions of TB infection, we established a protocol based on long-term infection of primary human macrophages, featuring Mtb replicating at different rates inside the cells. During conditions that restricted Mtb replication, the bacterial phenotype was associated with reduced acid-fastness. However, these phenotypically altered bacteria were as sensitive to isoniazid, pyrazinamide and ethambutol as intracellularly replicating Mtb. In support of the recent findings with M. smegmatis, we conclude that replication rates of Mtb do not correlate with antibiotic tolerance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antitubercular Agents / pharmacology*
  • Antitubercular Agents / therapeutic use
  • Bacterial Load*
  • Cell Proliferation
  • DNA Replication
  • Drug Resistance, Bacterial*
  • Humans
  • Macrophages / microbiology*
  • Mycobacterium tuberculosis / drug effects
  • Mycobacterium tuberculosis / growth & development*
  • Mycobacterium tuberculosis / pathogenicity
  • Phenotype
  • Time Factors
  • Tuberculosis / drug therapy
  • Tuberculosis / microbiology

Substances

  • Antitubercular Agents

Grants and funding

The project was funded by the Bill & Melinda Gates Foundation (www.gatesfoundation.org), the Swedish Research Council (grant numbers 2009-3821 and 2012-3349, www.vr.se), the Swedish International Development Cooperation Agency (www.sida.se), the Swedish Heart-Lung Foundation (www.hjart-lungfonden.se), King Oscar II Foundation, Carl Trygger Foundation (www.carltryggersstiftelse.se), and the Clas Groschinsky Foundation (www.groschinsky.org). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.