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 from matings that used E. faecium D344SRF as a recipient strain colonized mouse gastrointestinal tracts in high numbers under selective pressure from clindamycin or vancomycin, compared with control strains that lacked DNA transferred from C68. 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 indicate that E. faecium clinical isolates express transmissible factors other than antimicrobial resistance that promote colonization of the mouse gastrointestinal tract.