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Updated: Jan 1, 2026
Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43
Published on: September 11, 2020
Microscale insights into pneumococcal antibiotic mutant selection windows
Robin A Sorg1, Jan-Willem Veening1
1Molecular Genetics Group, Groningen Biomolecular Sciences and Biotechnology Institute, Centre for Synthetic Biology, University of Groningen, Nijenborgh 7, Groningen 9747 AG, The Netherlands.
Abstract:
The human pathogen Streptococcus pneumoniae shows alarming rates of antibiotic resistance emergence. The basic requirements for de novo resistance emergence are poorly understood in the pneumococcus. Here we systematically analyse the impact of antibiotics on S. pneumoniae at concentrations that inhibit wild type cells, that is, within the mutant selection window. We identify discrete growth-inhibition profiles for bacteriostatic and bactericidal compounds, providing a predictive framework for distinction between the two classifications. Cells treated with bacteriostatic agents show continued gene expression activity, and real-time mutation assays link this activity to the development of genotypic resistance. Time-lapse microscopy reveals that antibiotic-susceptible pneumococci display remarkable growth and death bistability patterns in response to many antibiotics. We furthermore capture the rise of subpopulations with decreased susceptibility towards cell wall synthesis inhibitors (heteroresisters). We show that this phenomenon is epigenetically inherited, and that heteroresistance potentiates the accumulation of genotypic resistance.
Insights
Emerging antibiotic resistance in Streptococcus pneumoniae is a major concern. This study reveals how bacteriostatic antibiotics promote resistance by allowing gene expression and epigenetic inheritance of reduced susceptibility, aiding further genotypic resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pneumoniae is a significant human pathogen with increasing antibiotic resistance.
- The fundamental mechanisms driving the de novo emergence of resistance in pneumococci remain unclear.
- Understanding resistance development is crucial for combating infectious diseases.
Purpose of the Study:
- To systematically analyze the impact of antibiotics on Streptococcus pneumoniae within the mutant selection window.
- To differentiate between bacteriostatic and bactericidal antibiotic effects on pneumococcal growth and gene expression.
- To investigate the mechanisms underlying the emergence of antibiotic heteroresistance and its role in promoting genotypic resistance.
Main Methods:
- Systematic analysis of antibiotic effects on Streptococcus pneumoniae at sub-inhibitory concentrations.
- Identification of distinct growth-inhibition profiles for bacteriostatic and bactericidal compounds.
- Real-time mutation assays and time-lapse microscopy to observe cellular responses and resistance development.
- Epigenetic analysis to understand the inheritance of heteroresistance.
Main Results:
- Discrete growth-inhibition profiles were identified, enabling prediction of bacteriostatic vs. bactericidal activity.
- Bacteriostatic agents promoted continued gene expression, linked to genotypic resistance development.
- Antibiotic-susceptible pneumococci exhibited growth and death bistability.
- Subpopulations with decreased susceptibility (heteroresisters) to cell wall synthesis inhibitors were observed.
- Heteroresistance was found to be epigenetically inherited and potentiated genotypic resistance accumulation.
Conclusions:
- Antibiotic concentration within the mutant selection window is critical for resistance emergence.
- Bacteriostatic antibiotics facilitate resistance development through sustained gene expression and epigenetic mechanisms.
- Heteroresistance is an epigenetically inherited trait that primes pneumococci for further genotypic resistance, posing a significant clinical challenge.
