Two lytic bacteriophages that depend on the Escherichia coli multi-drug efflux gene tolC and differentially affect bacterial growth and selection

Abstract

Bacterial pathogens are increasingly evolving drug resistance under natural selection from antibiotics in medicine, agriculture, and nature. Meanwhile, bacteria ubiquitously encounter bacteriophages and can rapidly evolve phage resistance. However, the role of phages in interacting with drug-resistant and drug-sensitive bacteria remains unclear. To gain insight into such relationships, we screened for and characterized phages that rely on the multi-drug efflux pump gene tolC. First, we screened a collection of 33 environmental and commercial Escherichia coli phages for their ability to infect cells that lacked tolC. Our screen revealed two phages that had reduced efficiency of plating (EOP) on the tolC knockout compared to wild type. We further characterized these phages with bacterial growth curves, transmission electron microscopy, and analysis of phage-resistant mutants. Phage U136B is a curly-tailed virus in family Siphoviridae with no ability to infect a tolC knockout, suggesting TolC is the U136B receptor. Phage 132 is a contractile-tailed virus in family Myoviridae with reduced EOP on cells lacking ompF and its positive regulators tolC and ompR. U136B and 132 differentially effect bacterial growth and lysis, and U136B-resistant mutants contain mutations of the tolC gene. Together, these results show that the tolC gene involved in drug resistance can modify bacteria-phage interactions in multiple ways, altering bacterial lysis and selection. These new phages offer utility for studying evolution, tradeoffs, and infection mechanisms.\n\nImportanceBacteria face strong selection by antibiotics in medicine and agriculture, resulting in increasing levels of drug resistance among bacterial pathogens. Slowing this process will require an understanding of the environmental contexts in which drug resistance evolutionarily increases or decreases. In this study, we investigate two newly-isolated bacteriophages that rely on a bacterial antibiotic resistance gene. These bacteriophages vary in their interactions with drug-resistant bacteria, with one of the phages selecting for phage-resistant mutants that have mutations in the antibiotic resistance gene. Further study of these new phages will be useful to understanding evolutionary tradeoffs and how phages might be applied in natural settings to reverse the problem of drug resistance.