Population Dynamics of a Two Phages–One Host Infection System Using Escherichia coli Strain ECOR57 and Phages vB_EcoP_SU10 and vB_EcoD_SU57

In this study, we looked at the population dynamics of a two phages-one host system using phages vB_EcoP_SU10 (SU10) and vB_EcoD_SU57 (SU57) and the bacteria Escherichia coli, strain ECOR57. Phage-specific growth curves were observed where infections by SU10 resulted in a moderate production of phages and infections by SU57 resulted in a fast and extensive production of phage progeny. Sequentially adding SU10 followed by SU57 did not produce a significant change in growth rates, whereas adding SU57 followed by SU10 resulted in a decrease in SU10 titer The efficiency of the plating assays showed that ECOR57 exhibited a resistance spectrum after infection by both the single and combined phages. Phage-resistant bacteria exhibited four different morphotypes (i.e., normal, slimy, edgy, and pointy). The normal and edgy morphotypes had a high frequency of developing resistance. Bacterial growth and biofilm assays indicated that the edgy and pointy morphotypes reached a stationary phase faster and produced more biofilm compared to the wild type. These findings suggest that the dynamic structure of phage–bacteria communities dictate resistance evolution and development. Understanding when and how resistances arise and phage(s)–hosts interactions could aid in the design of phage therapy treatments.