Diversity, transmission and persistence of Escherichia coli in a cohort of mothers and their infants.

Despite that Escherichia coli is one of the most important bacteria in early infant colonization and immune modulation, we have limited knowledge about diversity, transmission and persistence within human populations for this bacterium. Here we have utilized a novel, growth-independent, direct typing approach to describe E. coli mother-to-child transmission and persistence within infants in a well-defined cohort of 86 mothers and their infants in Norway. Seven gene multilocus sequence typing of 28 study isolates, three probiotic strains, eight Norwegian pathogenic isolates and the ECOR strain collection added a phylogenetic framework to the direct sequencing data. We found that a type B2 subpopulation of the maternal E. coli strains was the main group transmitted to the infants and that the proportion of children carrying their mothers' strain decreased as the children age. Using species richness estimates we also found a limited number of strains within the cohort compared with total E. coli diversity, constraints on infant colonization, and that infant strain diversity levels increased towards maternal diversity levels over time. This knowledge about inheritance and diversity forms a foundation for future understanding of E. coli in human health and disease.