Enteric Populations of Escherichia coli are Likely to be Resistant to Phages Due to O Antigen Production

There is a surfeit of bioinformatic data showing that bacteriophages abound in the enteric microbiomes of humans. What is the contribution of these viruses in shaping the bacterial strain and species composition of the gut microbiome and how are these phages maintained over time? To address these questions, we performed experiments with Escherichia coli and phages isolated from four fecal microbiota transplantation (FMT) doses as representative samples of non-dysbiotic enteric microbiota and develop and analyze the properties of a mathematical model of the population and evolutionary dynamics of bacteria and phage. Our models predict and experiments confirm that due to production of the O antigen, E. coli in the enteric microbiome are likely to be resistant to infection with co-occurring phages. Furthermore, our modeling suggests that the phages can be maintained in the population due to the high rates of host transition between resistant and sensitive states, which we call leaky resistance. Based on our observations and model predictions, we postulate that the phages found in the human gut are likely to play little role in shaping the composition of E. coli at the strain level in the enteric microbiome in healthy individuals. How general this is for other species of bacteria in the enteric flora is not yet clear, although O antigen expression is common across many taxa. ImportanceBioinformatic data shows that bacteriophages are ubiquitous in the gut, however little is known about the role these bacterial viruses play in shaping the bacterial species and strain composition in the human gut microbiome or how they are maintained over time in this dynamic environment. Here we show that Escherichia coli isolated from fecal samples are likely to be resistant to their co-existing phages due to production of the O antigen. Based on these results, we postulate that bacteriophages are likely playing little role of shaping the abundance and diversity of bacteria in the human gut microbiome in healthy individuals.