Antibiotics | Notable Study: How T4 Phage Resistance Influences Escherichia coli B's Response to Iron(III) Stress

This study reveals the significant impact of T4 phage resistance on Escherichia coli B's adaptation to iron(III) stress, emphasizing the importance of environmental stress order in resistance evolution. Through experimental evolution and whole-genome sequencing, the authors demonstrate that phage resistance can alter subsequent metal resistance genetic and phenotypic trajectories, highlighting the necessity of considering evolutionary constraints in phage-metal combination therapy design.

 

Literature Overview
This article, 'Phage Resistance Modulates Escherichia coli B Response to Metal-Based Antimicrobials' published in Antibiotics, reviews T4 phage and iron(III) stress effects on Escherichia coli B resistance evolution through experimental evolution and genomic analysis under different selection pressures.

Background Knowledge
With rapid development of multidrug-resistant bacteria, phage therapy and metal-based antimicrobials have emerged as promising anti-infection strategies. Iron(III), an essential bacterial nutrient at low concentrations but toxic at high levels, exerts toxicity through oxidative stress and metabolic dysfunction. Phage resistance typically develops via cell surface receptor modifications or membrane permeability changes, which may interact with metal resistance mechanisms. While prior studies show iron adaptation can affect phage resistance, how phage pre-adaptation influences subsequent iron resistance evolution remains unclear. This research systematically evaluates phenotypic and genomic changes under different stress sequences through experimental evolution, elucidating adaptive phenotype-genotype interactions to establish evolutionary biological foundations for combined antimicrobial strategies.

 

 

Research Methods and Experiments
The study employed Escherichia coli B as a model strain, establishing four experimental evolution conditions: control group (LB medium), T4 phage selection group, iron(III) selection group, and sequential phage-iron(III) selection group. Each condition included ten independent populations undergoing 35-day continuous passage. Phage resistance was evaluated via plaque assays, iron(III) tolerance through growth experiments under varying iron(III) sulfate concentrations, and cross-resistance testing against antibiotics and heavy metals. Whole-genome sequencing analyzed mutation patterns and gene frequency changes in final populations.

Key Conclusions and Perspectives

• Phage resistance evolved rapidly within 24 hours, with all phage-exposed populations achieving complete resistance while iron(III)-exposed groups showed no phage resistance.
• Iron(III)-adapted populations demonstrated tolerance at 1000–1750 mg/L concentrations but remained sensitive to iron(II) and antibiotics (tetracycline).
• Sequentially adapted phage-iron(III) populations maintained phage resistance while showing reduced iron(II) tolerance and distinct antibiotic sensitivity patterns compared to iron(III)-adapted groups.
• Whole-genome sequencing revealed large-fragment deletions in LPS synthesis-related genes (waaA, waaG) in phage-adapted groups, versus selective clearance in regulatory genes (qseB, basR, cpxP) for iron(III)-adapted groups.
• New SNPs emerged in transcription regulation genes (rpoC, infC) in phage/iron(III) adapted populations that weren't observed in phage-only groups, indicating historical constraints on evolutionary pathways.
• The research uncovered significant historical dependence in mutation pathways, demonstrating adaptive interactions between phage and metal resistance mechanisms where evolutionary trajectories are non-independent.

Research Significance and Prospects
This work highlights the importance of historical dependence and adaptive phenotype interactions in evolutionary biology, providing genomic and phenotypic foundations for phage-metal combination therapies. Future research should evaluate adaptive impacts of different metal-phage combinations across pathogens to explore clinical applications of evolutionary-informed antimicrobial strategies.

 

 

Conclusion
Through experimental evolution and genomic analysis, this study systematically evaluated T4 phage and iron(III) stress effects on Escherichia coli B resistance pathways. Results demonstrate that phage resistance evolution substantially alters subsequent iron resistance adaptation's genetic mechanisms and phenotypic characteristics, indicating profound historical constraints from stress sequence. These findings have significant implications for designing phage-metal combination therapies and expand understanding of adaptive interactions and historical dependencies in bacterial evolution. Future studies should explore adaptive impacts of other metal-phage combinations across bacterial species to provide broader evolutionary guidance for antimicrobial treatments.

 

Franklin C Ezeanowai, Akamu J Ewunkem, Ugonna C Morikwe, Jr, and Liesl K Jeffers-Francis. Phage Resistance Modulates Escherichia coli B Response to Metal-Based Antimicrobials. Antibiotics.