Long-term clonal dynamics ofEnterococcus faeciumstrains causing bloodstream infections (1995–2015) in Spain

OBJECTIVES: To investigate the population structure of Enterococcus faecium causing bloodstream infections (BSIs) in a tertiary Spanish hospital with low glycopeptide resistance, and to enhance our knowledge of the dynamics of emergence and spread of high-risk clonal complexes. METHODS: ) and clonal relationship (SmaI-PFGE, MLST evaluated by goeBURST and BAPS). RESULTS: The increased incidence of BSIs caused by enterococci [2.3‰ of attended patients (inpatients and outpatients) in 1996 to 3.0‰ in 2014] significantly correlated with the increase in BSIs caused by E. faecium (0.33‰ of attended patients in 1996 to 1.3‰ in 2014). The BSIs Enterococcus faecalis:E. faecium ratio changed from 5:1 in 1996 to 1:1 in 2014. During the last decade an increase in E. faecium BSIs episodes in cancer patients (10.9% in 1995-2005 and 37.1% in 2006-15) was detected. Ampicillin-susceptible E. faecium (ASEfm; different STs/BAPS) and ampicillin-resistant E. faecium (AREfm; ST18/ST17-BAPS 3.3a) isolates were recovered throughout the study. Successive waves of BAPS 2.1a-AREfm (ST117, ST203 and ST80) partially replaced ASEfm and ST18-AREfm since 2006. CONCLUSIONS: Different AREfm clones (belonging to BAPS 2.1a and BAPS 3.3a) consistently isolated during the last decade from BSIs might be explained by a continuous and dense colonization (favouring both invasion and cross-transmission) of hospitalized patients. High-density colonization by these clones is probably enhanced in elderly patients by heavy and prolonged antibiotic exposure, particularly in oncological patients.