Serving Two Masters; The Role of Trade-Offs in the Evolution of Bacteriophage/Metal Resistance in Escherichia Coli

Antimicrobial resistance (AMR) is a major public health challenge that portends danger in healthcare delivery, as scientific reviews on antibiotic resistance predicted a likelihood of 10 million mortalities per year by 2050. Post-antibiotic era, which was brought about by the spread of resistance to traditional antibiotics, has prompted the quest for new antimicrobial substances.

Interest in metallic antimicrobial materials such as Ag, Cu, Zn, and excess Fe (II, III) are growing due to their potential to control pathogenic and multi-drug resistant bacteria. However, we do not know if utilizing these materials can lead to genetic adaptations that produce even more dangerous bacterial strains. Early studies that proposed ionic and nanoparticle metals as new antimicrobials were deficient because they did not consider the evolutionary dynamics of populations exposed to toxic materials.

Another alternative to traditional antibiotics are bacteriophages, which are viruses that infect and kill bacteria. Bacteriophage therapy recently gained more attention because of the emergence of multi-drug resistant bacteria. Our preliminary findings suggest that experimental evolution of E. coli in Fe (III) yielded variants which were better fitted in antibiotics.

If trade-offs exist in pattern of resistance, we expected our Fe (III) + T7 phage variant to trade T7 phage resistance for susceptibility to antibiotics. The goals of the present proposed study are to unravel the evolutionary dynamics of potential trade-offs between Fe (III) and phage resistance in E. coli. This project will contribute to ongoing recruitment and retention of underrepresented undergraduate and graduate minority students in STEM, including bioinformatics, genomics, microbiology, evolutionary biology and engineering.

Opportunities will include technical training, professional development activities, presentations at national conferences, and educating and recruiting their peers. Also, community science outreach activities are planned, including participation in the North Carolina Science Olympiad at a local K-12 school as well as recruitment of a high school student to perform research on this project as part of their senior science project.

The mechanism of trade-offs in antibacterial resistance evolution under multi-selective pressures, including bacteriophages, antibiotics and heavy metals is incompletely understood. Therefore, the long-term goal of this project is to evaluate bacterial evolution under multi-selective pressures, specifically heavy metal (iron) and bacteriophage. The central hypothesis is that evolution of resistance to iron will consequently confer susceptibility to bacteriophage infection and evolution of bacteriophage resistance will confer susceptibility to iron and a combination of iron and bacteriophage resistance will affect susceptibility of evolutionary resistance to either.

This trade-off mechanism is well known in evolutionary studies as a fitness epistasis or genetic background effect and is implicated in driving evolution of extensively drug resistant microbes. Understanding how bacteria evolve resistance to biocides is an important aspect of the sustainability of any control measure. For example, if the bacteria develop completely independent responses to iron and bacteriophage then this has profound implications for how any biocide should be deployed.

If there are trade-offs associated with multi-selective pressures then the sustainability of each resistant strain may be enhanced by the use of combination approaches.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.