After 1-wk habituation in the animal facility, animals were randomly assigned for antibiotic-treated or control groups (n = 4 or 5 per cage). As previously reported (50 (link)), a broad-spectrum antibiotic mixture consisting of ampicillin (1 g/L, A9518; Sigma-Aldrich), neomycin (1 g/L, N1876; Sigma-Aldrich), vancomycin (500 mg/L, 94747; Sigma-Aldrich), and metronidazole (1 g/L, M3761; Sigma-Aldrich) was added to the drinking water of the antibiotic-treated group for 4 wk. Due to the large body loss observed in mice treated with metronidazole in drinking water (51 (link)), we opted to gradually increase the concentration of metronidazole over time. In this regime, no metronidazole was added in the first day of treatment; on treatment day 2 metronidazole was introduced in a mass concentration of 250 mg/L, on day 6 the concentration was increased to 500 mg/L, and on day 9 the full concentration (1 g/L) was used. Bottles with antibiotic solution were refilled every week. The control group received regular autoclaved water. Body weight was measured three times per week.