Transferable Capacity for Gastrointestinal Colonization in Enterococcus faecium in a Mouse Model

A high level of gastrointestinal colonization frequently precedes invasive infection due to Enterococcus faecium. Factors other than antimicrobial resistance that promote gastrointestinal colonization by E. faecium have not been identified. We tested the ability of a colonization-proficient clinical E. faecium isolate (C68) to transfer colonizing ability to noncolonizing E. faecium recipient strains. Transconjugants derived frommatings that used E. faeciumD344SRF as a recipient strain colonizedmouse gastrointestinal tracts in high numbers under selective pressure fromclindamycin or vancomycin, comparedwith control strains that lackedDNA transferred fromC68. We transferred DNA into a second recipient strain (E. faecium GE-1), which also colonized mice in significantly greater numbers under selective pressure from clindamycin, compared with a control strain. These results indi-cate that E. faecium clinical isolates express transmissible factors other than antimicrobial resistance that pro-mote colonization of the mouse gastrointestinal tract. A high level of gastrointestinal colonization by entero-cocci is a frequent predecessor of serious enterococcal infection and such is promoted by the use of systemic or local antimicrobial agents [1–3]. Over the past decade, it has been recognized that the worldwide hospital out