A 21-year survey of from bloodstream infections (BSIs) in a tertiary hospital reveals how community-hospital dynamics, influence local BSI rates, the trends of the B2 phylogroup and the STc131 pandemic clone

Escherichia coli is overrepresented in all bloodstream infections (BSIs) series, mostly associated with a few clonal lineages. Its population structure has been analyzed but the dynamics remains to be fully understood. We analyze the dynamics of E. coli-BSIs in a sample of 649 isolates, representing all 7165 E. coli BSI episodes recorded in a tertiary hospital (1996-2016) according to clonal identification (phylogenetic groups/subgroups, STc131 subclades), antibiotic susceptibility (13 antibiotics), and virulence-associated genes (VAGs, 29 genes). Patient data were obtained from the laboratory system and clinical charts. The incidence of BSI-EC doubled from 1996 to 2016 (5.5 to 10.8 BSI episodes/1000 hospitalizations). Intertwined waves of community-acquired (CA) and hospital-acquired isolates (HA) episodes of both B2 and non-B2 phylogroups, occurred until B2 overtook non-B2 BSI episodes. ST131 contributed to increasing the B2 rates, but only transiently altered the population structure. B2 isolates predominate (53%), overrepresented by subgroups B2-I (STc131), B2-II, B2-IX, and B2-VI (25%, 25%, 14%, and 9%). We observed a remarkable increase only for B2-I-STc131 (C1/C2 subclades), a decreasing trend for phylogroup D, and oscillations for other B2 subgroups throughout the years. According to VAG patterns, B2 strains exhibit a population structure compatible with the niche specialization theory. A reservoir of B2 and non-B2 strains represented in human microbiota, flows from the community to the hospital and vice-versa, where they can either be selected or coexist. The increase of BSI is determined by waves of CA that predate the amplification of HA episodes of both B2 and non-B2 phylogroups in various time periods, influenced by FQR and microbiota composition.