Fig 6.

Effects of exogenous XO and hypoxanthine on the outcome of STEC infection in a ligated rabbit ileal loop model of infection. Ten-centimeter segments of ileum were ligated as described in Materials and Methods and infected with 4 × 10⁸ CFU of rabbit STEC E22-stx2 plus XO and hypoxanthine. Twenty hours after infection, loops were collected and photographed and the contents were analyzed. (A) Gross appearance of an ileal loop infected with E22-stx2 but without any other additives, showing distention with fluid but absence of necrosis. (B) One of 2 intestinal loops receiving E22-stx2 plus XO and hypoxanthine (hypoxnth) showed overt necrotic mottling (loop 6, left arrow), while the other loop showed only one small spot of necrosis at the site of the injection (right arrow). (C) Hemoglobin concentrations in loop fluids were assayed after centrifugation of the samples at 16,000 × g for 10 min to remove intact cells and debris. In the presence of STEC bacteria, addition of 1 U/ml XO seemed to reduce the bloody character of the loop fluids, but this did not reach statistical significance. *, in the presence of STEC, XO, and 400 μM hypoxanthine, hemoglobin in the loop fluids was significantly higher than that with the pathogen and XO. (D) Fluid secretion into the loops, as measured by the volume-to-length ratio. hypo, hypoxanthine. (E) Comparison of the numbers of bacteria recovered from each loop (expressed as the logarithm of the number of bacteria recovered per loop), showing the lack of any decrease in CFU in loops receiving hypoxanthine (hypo) and XO. (F) Shiga toxin protein (Stx) content of the loops by enzyme immunoassay, expressed in ng per loop. *, significantly increased compared to E22-stx2 alone. hypo, hypoxanthine.