Host population structure and treatment frequency maintain balancing selection on drug resistance

J R Soc Interface. 2017 Aug;14(133):20170295. doi: 10.1098/rsif.2017.0295.

Abstract

It is a truism that antimicrobial drugs select for resistance, but explaining pathogen- and population-specific variation in patterns of resistance remains an open problem. Like other common commensals, Streptococcus pneumoniae has demonstrated persistent coexistence of drug-sensitive and drug-resistant strains. Theoretically, this outcome is unlikely. We modelled the dynamics of competing strains of S. pneumoniae to investigate the impact of transmission dynamics and treatment-induced selective pressures on the probability of stable coexistence. We find that the outcome of competition is extremely sensitive to structure in the host population, although coexistence can arise from age-assortative transmission models with age-varying rates of antibiotic use. Moreover, we find that the selective pressure from antibiotics arises not so much from the rate of antibiotic use per se but from the frequency of treatment: frequent antibiotic therapy disproportionately impacts the fitness of sensitive strains. This same phenomenon explains why serotypes with longer durations of carriage tend to be more resistant. These dynamics may apply to other potentially pathogenic, microbial commensals and highlight how population structure, which is often omitted from models, can have a large impact.

Keywords: antimicrobial resistance; epidemiology; infectious disease ecology.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Anti-Bacterial Agents / therapeutic use*
  • Drug Resistance, Bacterial / physiology*
  • Host-Pathogen Interactions / physiology*
  • Humans
  • Models, Biological*
  • Pneumococcal Infections* / drug therapy
  • Pneumococcal Infections* / metabolism
  • Pneumococcal Infections* / transmission
  • Streptococcus pneumoniae / physiology*

Substances

  • Anti-Bacterial Agents