Bacillus cereus var. Toyoi modulates the immune reaction and reduces the occurrence of diarrhea in piglets challenged with Salmonella Typhimurium DT1041

Abstract

A feeding trial with sows and their piglets was performed with the probiotic feed additive Bacillus cereus var. Toyoi in two consecutive experimental periods. Sows (n = 8) were allocated into treatment (Bc) and control (CO) groups. Sows of Bc group (n = 4) were fed 3.14 × 10(5) cfu/g Bacillus cereus var. Toyoi with the diet from d 87 of pregnancy on. Their piglets received Bacillus cereus var. Toyoi supplemented feed (8.7 × 10(5) cfu/g) starting on d 14 of life and further on after weaning (6.5 × 10(5) cfu/g), whereas sows and piglets of the CO group remained untreated. One day after weaning, piglets from both groups (n = 24 each) were challenged orally with Salmonella Typhimurium DT104 (3 × 10(9) viable bacteria). Health status, shedding of B. cereus in the feces, and performance of the piglets were monitored. At 24 h, 72 h, 6 d, and 28 d postinfection (PI), six piglets from each group were euthanized and cell counts of Salmonellae were determined in the colon contents, mesenteric lymph nodes, and tonsils. Peripheral blood mononuclear cells and jejunal intraepithelial lymphocytes (IEL) were analyzed by flow cytometry. The incidence of scours was lower in the Bc group than in the CO group (P = 0.004). In addition, the fecal shedding of Salmonella was significantly lower in the Bc group at 25 d PI (P = 0.004). Shortly after infection, the γδ T cells were significantly less frequent in the blood of Bc piglets. For both CD8-positive γδ T cells (P = 0.033) and CD8-negative γδ T cells (P = 0.028), significant differences were observed. Furthermore, 28 d PI piglets from the treated group showed lower numbers of γδ T cells in the jejunal epithelium (P = 0.036). To investigate the role of intestinal γδ T cells during the infection with S. Typhimurium, IEL were gained from six healthy 40-d-old piglets and infected in vitro with S. Typhimurium. CD8β cells and γδ T cells were detected by flow cytometry and the infection rates of both populations in the cell suspensions were compared. The infection rate (IR) of γδ T cells was higher in all six cell suspensions than the IR of CD8β expressing T cells (P = 0.002). In conclusion, B. cereus var. Toyoi supplementation of sows and their piglets had a positive impact on the health status of the piglets after a challenge with Salmonella, likely due to an altered immune response marked by reduced frequencies of CD8+ γδ T cells in the peripheral blood and the jejunal epithelium.