GASTROINTESTINAL-TRACT COLONIZATION WITH VANCOMYCIN-RESISTANT ENTEROCOCCUS-FAECIUM IN AN ANIMAL-MODEL

Vancomycin-resistant enterococci have become important nosocomial path ogens in many institutions, The gastrointestinal tract of susceptible hosts serves as the likely reservoir from which the organism is dissem inated. To study factors promoting colonization and the efficacy of de contamination therapy,vith antimicrobial agents, a model of gastrointe stinal colonization with vancomycin-resistant Enterococcus faecium was developed in CF1 mice. At baseline, all animals were colonized with n on-vancomycin-resistant enterococci (5.0 log(10) CFU/g), but vancomyci n-resistant organisms were not detectable. Following gastric inoculati on,vith 5 x 10(8) CFU of a clinical isolate of vancomycin-resistant E. faecium, the strain transiently colonized the gastrointestinal tract of 100% of mice but was undetectable by Day 14 (less than or equal to 2.7 log(10) mean CFU/g). In animals who received 5 mg of streptomycin per mi or 250 mu g of vancomycin per mi in drinking water, colonizatio n with the organism occurred at significantly higher bacterial counts than in controls at 7 days following inoculation (9.4 for vancomycin, 9.2 for streptomycin, and 5.1 log(10) mean CFU/g for controls; P < 0.0 5), Fecal concentrations of vancomycin-resistant E. faecium persisted at high counts through Day 22 in mice receiving these antibiotics, but low counts were also still detected in 3 of 10 control animals. In mi ce with previously established vancomycin-resistant E. faecium coloniz ation, oral administration of ramoplanin, a lipoglycodepsipeptide to w hich the strain was susceptible, suppressed growth of all enterococci in feces, including the vancomycin-resistant strain after 7 days of th erapy (less than or equal to 3.1 and less than or equal to 3.3 log(10) mean CFU/g for vancomycin and streptomycin groups, respectively). All mice had a recurrence of colonization with vancomycin-resistant E. fa ecium after the ramoplanin was discontinued, In summary, this animal m odel demonstrates the importance of antibiotics in predisposing to gas trointestinal colonization with vancomycin-resistant Enterococcus spp, Although treatment with ramoplanin temporarily suppressed the organis m, recurrence of colonization due to relapse or reinfection occurred.