Protein synthesis inhibitor - Wikipedia
Inhibition of Nucleic Acid Synthesis by Antibiotics
Antimicrobial peptides: Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs) are small peptides (30-60 s) and can be isolated from all living organisms. They are essential components of the innate immune system and possess antimicrobial and immunomodulatory properties (; ). These can directly kill broad range of microbes including bacteria, fungus and viruses (). Till date more than 700 antimicrobial peptides have been identified. After identification, some of these peptides are synthesized and tested for their antimicrobial and immunomodualtory functions. Studies have been conducted on fowlicidin 1 and 3 peptides (; ). These antimicrobial peptides interact with surface membrane of bacteria either by forming discrete pores or by disrupting the membrane bilayer, leading to loss of membrane function, resulting in cell leakage and, consequently, cell death (; ; ). In relation to the full length peptide fowl-1(6-26), an analog from which five-amino terminal residues have been omitted, has helped in maintaining the antibacterial potency against a wide range of Gram-negative as well as Gram-positive bacteria that include strains which are resistant to antibiotic (). Recently, other modes of action like inhibition of the synthesis of , proteins, cell-wall components and essential enzymatic activities have also been proposed (). AMPs can be obtained from natural sources, chemical synthesis or by recombinant technology (). Some of the antimicrobial peptides such as colicin and cecropin, particularly cecropin A (1-11)-D (12-37)-Asn (CADN), act as growth promoter in poultry and have been suggested as possible alternate to antibiotic growth promoters ().
ANTIBIOTICS - PROTEIN SYNTHESIS, NUCLEIC ACID SYNTHESIS AND ..
Organic acids: In recent years, the use of acidifiers has been increased many fold and are found to have the ability to reduce many pathogenic and spoilage organisms by lowering the gut pH. Because of the development and emergence of antibiotic resistant microbes (), the utilization of s has been increased as growth promoters in animal agriculture, which could help in providing protection from adverse human health implications. In poultry diets, the use of s elicits a positive response in performance of broiler growth. In order to inhibit growth of bacteria of intestine (those which compete with host for the nutrients that are available) there is requirement of dietary acidification thereby causing reduced possibility of availability of bacterial metabolites which are toxic in nature. In the ceaca as well as small intestine it has been suggested by a number of studies that s affect the bacterial concentration. In the crop of the poultry birds they are bactericidal for (; ; ). In the young ones, acid production in the gut is insufficient and acidifiers are sometimes used in feeds to compensate it. The use of s such as formic, lactic, propionic, citric, sorbic and phosphoric acids optimizes the balance of the microflora of the gastrointestinal tract (; ; ; ; ). They lower the pH, at which the activity of proteases and beneficial bacteria is optimized and proliferation of is minimized by a direct antibacterial effect destroying their cell membranes (; ; ). In experimental studies, s have been found suitable growth promoters in pigs (; ; ) and poultry (). Supplementation of organic acid also increases intestinal colonization of spp. in chicks (). They are widely used to inhibit pathogens like salmonellae and in their undissociated forms are able to pass through their cell membrane. Inside the bacterial cell, the acid dissociates to produce H+ ions, which lower the pH causing the organism to use its energy in trying to restore the normal balance. It also disrupts DNA and protein synthesis and thus the bacteria are unable to replicate or its replication slows down. Lower pH conditions thus protect the bird from infection especially at young ages. In addition to direct microbial action, recent studies have shown that salt form of s including butyrate, propionate and acetate have shown their ability in reducing colonization in chicken cecum by enhancing innate immune defense via increased synthesis of host defense peptides (, ). Furthermore, s also reduce the contamination of litter with the harmful microorganisms, neutralize ammonia production and diminish the risk of re-infection. The effectiveness of organic acids in poultry may also depend on the composition of the diet and its buffering capacity. The combination of citric, lactic, formic and orthophosphoric acid at doses of 2-8 kg ton-1 of feed are found effective. Propionic acid suppresses the growth of moulds and prevents the formation of mycotoxins. Short-chain s such as butyrate are considered potential alternatives to antibiotic growth promoters. Butyric acid at 0.2% level of incorporation can help to maintain the performance and carcass quality of broilers (). The Medium-chain Fatty Acids (MCFA), caproic, caprylic and capric acid, are also capable of inhibiting the growth of at low concentrations . The ifiers are thus considered effective and recognized as safe, with no concern over getting into human food chain.