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Metabolism and Metabolic Studies
Abbreviations: ADEE, apparent digestibility of diethyl ether extract; ADG, average daily weight gain; AGP, antibiotic growth promoter; AME, apparent metabolisable energy; AMP, antimicrobial peptides; CADN, cecropin A(1-11)-D(12-37)-Asn; CADNL, cecropin A(1-11)-D(12-37)-Asn liquid sample; F, feed intake; F:G, feed:gain ratio; G, weight gain; GIT, gastrointestinal tract; MEMP, dietary apparent metabolisable energy:apparent metabolisable protein ratio; NR, nitrogen retention; PB, phosphate buffer; YPCT, yeast fermentation broth containing yeast extract, peptone, maize steep powder and trisodium phosphate
Antimicrobial peptides (AMP) are evolutionarily conserved components of the innate immune response, found among all classes of life ranging from prokaryotes to humans, and a promising family of natural alternatives to antibiotic growth promoters (AGP) with vast diversity in terms of sources, structures, functionalities, antimicrobial spectra and modes of action(1-3). Currently, 1711 AMP have been identified from a wide range of organisms (http://aps.unmc.edu/AP/main.php; accessed February 2011). Recent research demonstrated that AMP could improve the growth performance of piglets(4,5), growing-finishing pigs(6), chickens(7)and fishes(8), and the integrity of intestinal surfaces and intestinal mucosal response of chickens(7,9,10). It seems that AMP are suited to be alternatives to AGP, but the use of AMP from natural sources is not at present cost-effective. Those AMP consisting of a single polypeptide chain of common amino acids are well suited for large-scale production by recombinant expression methods using micro-organisms that are resistant to the produced AMP.
Cecropins A (K W K L F K K I E K V G Q N I R D G I I K A G P A V A V V G Q A T Q I A K) and D (W N P F K E L E K V G Q R V R D A V I S A G P A V A T V A Q A T A L A K) belong to the cecropin family of AMP. They were originally isolated from the insect Hyalophora cecropia, and exerted strong antibiotic activity against Gram-positive and Gram-negative bacteria at micromolar concentrations(11)