Small intestinal loop challenge.

All procedures involving animals were approved by the University of California (UC-Davis) Committee for Animal Care and Use (permit 18187). Male or female, 20- to 25-g, BALB/c mice (UC-Davis) were anesthetized by intraperitoneal administration of 0.2 ml/10 g of body weight of a mix of xylazine (0.5 mg/ml) and ketamine (5 mg/ml). Immediately before surgery, the abdomen of each mouse was disinfected with iodine solution (Betadine; Purdue Pharma LP). A midline laparotomy was performed, and an ∼10- to 15-cm-long intestinal loop was prepared in the jejunum of each mouse by double ligation of the intestine without interfering with the blood supply. For each inoculation (see below), a new sterile needle and syringe were used. The incision in the peritoneum, abdominal muscles, and skin was closed in one plane using Super Glue (Henkel Corporation). This procedure was the standard for all experiments in the study.