FIG. 1.

Inhibition of lethal intestinal STEC infection by B. breve colonization in SM-treated mice. SM sulfate at a concentration of 5 mg/ml in drinking water was given to 28 mice from day −6 until day 16. B. breve strain Yakult (1 × 10⁸ to 3 × 10⁸ CFU/mouse/day) in 0.1 ml of saline was administered to half of the mice once a day from day −5 to −3, and the other half of the mice were administered saline on the same schedule as that for the B. breve treatment. Mice were infected orally with STEC (5 × 10³ CFU) on day 0 and then treated with MMC at an inoculum dose of 0.25 mg/kg of body weight three times at 18, 21, and 24 h after the STEC infection. (A) Feces for bacteriological analysis were obtained from 6 randomly selected mice in each group on days 0 (at 3, 6, 9, 12, 15, and 18 h), 1, 3, 4, 7, 10, and 16 after the STEC infection, with the exception of the control group on days 10 to 16 (n = 2). Viable counts of STEC and B. breve were examined as described in the text. Symbols: •, number of STEC organisms in the STEC-infected control mice; ○, number of STEC organisms in the B. breve-treated mice; ▵, number of B. breve organisms in B. breve-treated mice. (B) All 14 mice in each group were weighed every day until day 8. Symbols: •, STEC-infected control; ○, B. breve-treated mice. (C) The STEC-infected control mice (•) and B. breve-treated mice (○) were observed for survival for 14 days after the challenge infection. **, a significant difference was observed between the B. breve-treated and the untreated control groups (P < 0.01).