Immune modulation by Bacillus subtilis-based direct-fed microbials in commercial broiler chickens

Abstract

Direct-fed microbials (DFMs), also known as probiotics, have been successfully used to improve the balance of gut microbiota. Spores of Bacillus subtilis, have been used as DFMs for food animals and humans and our previous studies showed that dietary supplementation of broiler chickens with a B. subtilis DFM from hatch enhanced innate immunity and improved protection against avian coccidiosis. In two experiments, we investigated the effects of dietary B. subtilis-based DFM on growth performance and host humoral immune response to Eimeria spp. and Clostridium perfringens, and evaluated B. subtilis-induced global gene expression changes in broiler chickens. Day-old broiler chickens were fed diets with or without DFMs for 28 days starting from hatch. At 14 and 28 days post-hatch, broiler chickens fed the DFM-enriched diet gained significantly more weight (P<0.05) compared with the control diet-fed chickens. Broiler chickens fed diet containing DFM exhibited a significant decrease (P=0.033) in Eimeria- and C. perfringens necrotic enteritis B-like (NetB) toxin-specific serum antibodies compared with those fed a control diet at day 28. The levels of transcripts encoding interleukin (IL) 1β, IL12 and interferon-γ were greater (P=0.004) in the DFM-fed chickens compared with the control chickens. In order to better understand B. subtilis-induced molecular changes associated with improved innate immunity, mRNA was isolated from mid-intestine of DFM-fed chickens for global microarray analysis. Dietary DFMs induced considerable changes in transcriptional expression in intestine, and biofunctional analysis identified 37 genes related with “Inflammatory Response”. These results indicate that dietary B. subtilis DFM is an effective growth-promoting dietary supplement to increase growth and augment innate immune response in broiler chickens. Further study is needed to investigate the mechanism mediated by dietary DFMs to enhance protective innate immunity in a disease model (i.e., necrotic enteritis) which causes considerable economic impact in the poultry industry worldwide.