Tissue distribution, expression, and antimicrobial activity of Anas platyrhynchos avian ß-defensin 6.

In this study, a novel avian ß-defensin (AvBD) was isolated from the Chaohu duck. The complete nucleotide sequence of the gene contained a 204-bp open reading frame that encoded 67 amino acids (aa), including a signal peptide of 20 aa, a propiece of 5 aa, and a mature peptide of 42 aa. The homology, characterization, and comparison of this gene with AvBD from other avian species confirmed that it was duck AvBD6. Also, the preproprotein of AvBD6 from chicken, goose, and duck was highly conserved with 100% aa homology. The AvBD6 mRNA was widely expressed in the investigated tissues of healthy 5-mo-old ducks, with the exception of the skin, kidney, and bursa. The AvBD6 mRNA was highly expressed in the spleen, lung, stomach, tongue, and egg yolk, successively; moderately expressed in the bone marrow and liver; and expressed to lower degrees in the trachea, heart, intestine, muscle, esophagus, and testis. We produced recombinant AvBD6 by expressing the gene in Escherichia coli. The yield of soluble glutathione S-transferees (GST)-AvBD6 in the inclusion bodies increased significantly as the incubation temperature was decreased from 37 to 30°C. As expected, the GST-AvBD6 exhibited strong bactericidal properties [minimum inhibitory concentration (MIC) = 0.5 to 2 µM] against the Aeromonas veronii biovar sobria strain BJCP-5, E. coli, and Enterococcus faecalis [ATCC 29212); it possessed medium bactericidal properties (MIC = 4 to 8 µM) against Staphylococcus aureus, Salmonella enteritidis, Pseudomonas aeruginosa (ATCC 27853), and Bacillus subtilis (CMCC 63501;; and it possessed low bactericidal properties (MIC = 16 µM) against Candida albicans (ATCC 10231). Additionally, the antimicrobial activity of GST-AvBD6 proved to be the same as that of synthetic AvBD6. The A. veronii biovar sobria strain BJCP-5 cells that were treated with GST-AvBD6 showed lysis and shrinkage under scanning electron microscopy. The mechanisms of AvBD6-mediated killing of A. veronii biovar sobria involved both cell lysis and nonlysis. Our results indicate that AvBD6 plays an important role in the innate immunity of the Chaohu duck.

Effects of pig antibacterial peptides on growth performance and intestine mucosal immune of broiler chickens.

Currently, substitutions for antibiotic growth promoters in animals are attracting interest. This study investigated the effects of pig antibacterial peptides (PABP) on growth performance and small intestine mucosal immune responses in broilers. Three hundred 1-d-old Arbor Acre male broiler chickens were randomly allocated to 5 groups with 60 birds per group. The groups were control group; PABP administered in drinking water at 20 and 30 mg/L of water; or PABP supplemented in feed at 150 and 200 mg/kg of diet. The birds were fed a corn-soybean based diet for 6 wk. Chickens were weighed weekly and killed after 42 d of feeding, and growth performance was measured. Samples of the duodenum and jejunum were collected. The villus height, mucosa thickness, alkaline phosphatase activity, and numbers of secreting IgA and goblet cells were evaluated. The PABP-treated groups had greater BW and average daily gain, greater height of villus and thickness of gut mucosa, greater activity of alkaline phosphatase, higher ratio of secreting IgA, and a greater number of goblet cells compared with the control group (P<0.05). In conclusion, PABP can improve the growth performance, increase the intestinal ability to absorb nutrients, and improve the mucosal immunity of the intestine.