Abstract
The BT/TAMUS 2032 (BT) cationic peptides are a group of related cationic peptides produced by a Gram-positive soil bacterium, Brevibacillus texasporus. Cationic amphiphilic peptides produced by host cells have been found to stimulate or prime the innate immune responses in mammals, but little information is available on the effects of bacterial-produced peptides on host immunity. We have previously shown that BT, provided as a feed additive for 4 days after hatch, significantly induced protection against extraintestinal colonization by Salmonella enterica serovar Enteritidis. We also found that feeding BT significantly upregulated the functional efficiency of heterophils, the avian equivalent to mammalian neutrophils. The objective of the present study was to further evaluate the effect of BT as a nonantibiotic, antibacterial compound and a stimulator of the innate immune response of young chickens. BT, provided as a feed additive at three different concentrations (12, 24, or 48 ppm) for 4 days after hatch, significantly increased protection against Salmonella enterica serovar Enteritidis cecal colonization in a concentration-dependent manner. We also confirmed our previous results that the functional activities of heterophils from chickens fed the BT rations were significantly upregulated. In addition, we also found that the functional activities of peripheral blood monocytes were significantly increased in a concentration-dependent manner when compared with monocytes isolated from chickens fed a control diet. This is the first report of bacterial cationic peptides providing protection against Salmonella cecal colonization. The significance of these data is that the orally delivered cationic peptides stimulate the innate response during the first week after hatch, normally a time of immunologic inefficiency and increased susceptibility to bacterial infections. We speculate that BT given as a feed additive during the first week after hatch could provide increased protection against a variety of bacterial pathogens because of the nonspecific nature of the innate response.