Effect of Parenteral Antibiotic Administration on Persistence of Vancomycin-Resistant Enterococcus faecium in the Mouse Gastrointestinal Tract

A mouse model of vancomycin-resistant Enterococcus faecium (VRE) intestinal colonization was used to study the effect of different subcutaneous antibiotics on persistence and density of VRE colonization. Gastric inoculation of a clinical VanB VRE isolate, in conjunction with oral vancomycin in drinking water (250 μg/mL), resulted in high-level VRE colonization (mean, 9.5 log 10 cfu/g) in all 169 experimental mice. After discontinuation of oral vancomycin, the level of VRE in the stool specimens of mice receiving subcutaneous saline steadily decreased (mean, 3.59 log 10 cfu/g at day 19). Subcutaneous vancomycin, clindamycin, piperacillintazobactam, ticarcillin-clavulanic acid, metronidazole, cefotetan, ampicillin, and ampicillinsulbactam all promoted persistent high levels of stool VRE. Subcutaneous ceftriaxone, cefepime, ciprofloxacin, and aztreonam promoted increased VRE density to a lesser degree or not at all. Thus, in a mouse model, vancomycin and antibiotics with potent antianaerobic activity promoted persistent high-density intestinal VRE colonization, whereas antibiotics lacking potent antianaerobic activity did not.