Effect of antibiotic therapy on the density of vancomycin-resistant enterococci in the stool of colonized patients.

Background: Colonization and infection with vancomycin-resistant enterococc i have been associated with exposure to antibiotics that are active against anaerobes. In mice that have intestinal colonization with vancomycin-resis tant enterococci, these agents promote high-density colonization, whereas a ntibiotics with minimal antianaerobic activity do not. Methods: We conducted a seven-month prospective study of 51 patients who we re colonized with vancomycin-resistant enterococci, as evidenced by the pre sence of the bacteria in stool. We examined the density of vancomycin-resis tant enterococci in stool during and after therapy with antibiotic regimens and compared the effect on this density of antianaerobic agents and agents with minimal antianaerobic activity. In a subgroup of 10 patients, culture s of environmental specimens (e.g., from bedding and clothing) were obtaine d. Results: During treatment with 40 of 42 antianaerobic-antibiotic regimens ( 95 percent), high-density colonization with vancomycin-resistant enterococc i was maintained (mean [+/-SD] number of organisms, 7.8+/-1.5 log per gram of stool). The density of colonization decreased after these regimens were discontinued. Among patients who had not received antianaerobic antibiotics for at least one week, 10 of 13 patients who began such regimens had an in crease in the number of organisms of more than 1.0 log per gram (mean incre ase, 2.2 log per gram), whereas among 10 patients who began regimens of ant ibiotics with minimal antianaerobic activity, there was a mean decrease in the number of enterococci of 0.6 log per gram (P=0.006 for the difference b etween groups). When the density of vancomycin-resistant enterococci in sto ol was at least 4 log per gram, 10 of 12 sets of cultures of environmental specimens had at least one positive sample, as compared with 1 of 9 sets fr om patients with a mean number of organisms in stool of less than 4 log per gram (P=0.002). Conclusions: For patients with vancomycin-resistant enterococci in stool, t reatment with antianaerobic antibiotics promotes high-density colonization. Limiting the use of such agents in these patients may help decrease the sp read of vancomycin-resistant enterococci. (N Engl J Med 2000;343:1925-32.) (C) 2000, Massachusetts Medical Society.