Application of Silver and Phage on Bacterial Populations Significantly Decreases Its Size

Student Classification


Faculty Mentor

Liesl Jeffers-Francis, Ph.D.


Department of Biology

Document Type


Publication Date

Spring 2019




Introduction: The massive failure of traditional antibiotics over the 20th century is well known. This has led to researchers attempting new approaches to controlling multi-drug resistant (MDR) bacteria including ionic and nanoparticle metals and phage therapy. However, it is clear that no matter what single approach is deployed against bacteria, that they can rapidly evolve resistance. Therefore, combination therapies have been developed for treatment of pathogenic bacteria and viruses. The goal of our research is to find combination therapies which are antagonistic, which means that they must result in evolutionary trade-offs. Our long-term goal is to determine if the application of two complementary antibacterial treatments, nanoparticle metal and bacteriophage, can successfully inhibit bacterial infections. Methods: Escherichia coli will be used to evolve T4 and T7 bacteriophage and silver resistant bacterial colonies. Once colonies of resistant bacteria are established, the colonies will be allowed to co-evolve in the presence of bacteriophage and/or 2-5ug/ml of silver ions. To isolate phage resistant mutants, classic "spot tests" will be performed whereby individual colonies would indicate bacterial resistance to phage versus visible lawn clearing indicative of phage sensitivity. Confirmation of phage resistance will be measured by performing a "streak test". These phage/metal resistant colonies will then be serially passaged in 50 ml conical flasks. The passages will be repeated for the duration of the experiment (~20 days). Growth rates will be evaluated by measuring optical density throughout the experiment. We will also be able to monitor the genomic changes that occur in conjunction with the phenotypic changes by whole genome sequencing of the bacterial and bacteriophage populations during the course of the experiment. Additionally, we will assess the effect of metal/phage trade-offs on antibiotic resistance/susceptibility. Results: Thus far we have isolated phage resistant Escherichia coli using the spot test and are confirming phage resistance using the steak test. We have also determined the optimal concentration of silver ions that we will use for the coevolution experiment by performing a minimum inhibitory concentration test (MIC). Experiments are ongoing. Conclusion: If an antagonistic trade-off is observed between silver and bacteriophage resistance in Escherichia coli, then this can be used as a means of sustainable antimicrobial combination therapy.

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