In vivo transfer of the vanA resistance gene from an Enterococcus faecium isolate of animal origin to an E. faecium isolate of human origin in the intestines of human volunteers

Abstract

Transient colonization by vancomycin-resistant enterococci of animal origin has been documented in the intestines of humans. However, little is known about whether transfer of the vanA gene occurs in the human intestine. Six volunteers ingested a vancomycin-resistant Enterococcus faecium isolate of chicken origin, together with a vancomycin-susceptible E. faecium recipient of human origin. Transconjugants were recovered in three of six volunteers. In one volunteer, not only was vancomycin resistance transferred, but also quinupristin-dalfopristin resistance. This study shows that transfer of the vanA gene from an E. faecium isolate of animal origin to an E. faecium isolate of human origin can occur in the intestines of humans. It suggests that transient intestinal colonization by enterococci carrying mobile elements with resistance genes represents a risk for spread of resistance genes to other enterococci that are part of the human indigenous flora, which can be responsible for infections in certain groups of patients, e.g., immunocompromised patients.

FIG. 1.

Fecal excretion of strains by the six volunteers. (A) Donor strain (open symbols). (B) Recipient strain (open symbols) and transconjugants (solid symbols). Each curve shows the results for one volunteer. Each volunteer is represented by one color. Transconjugants were excreted by only three volunteers. Results from stool samples obtained within 48 h before ingestion of the bacteria are plotted as day zero. The minimal detectable level is shown by the dashed line. The solid black squares with open centers (days 0, 14, and 35) represent the superposition of results from all six volunteers.