Antimicrobial peptides refer to a variety of peptides with inhibitory or bactericidal activity in vivo, usually containing 20-60 amino acid residues with a molecular weight of 2000-7000 Da. Most of antimicrobial peptides are alkaline as well as with a good thermal stability. Currently, the single drug target, long-term widespread use and drug resistance of antibiotics have hindered their applications in clinical infection management. More and more studies have shown that antimicrobial peptides from synthetic and natural sources have broad-spectrum antibacterial activity, high specificity and low toxicity, and are expected to be the excellent alternatives of antibiotics to overcome drug resistance, thus being widely used in the pharmaceutical field, food industry and agricultural engineering.
Classification of Antimicrobial Peptides
Antimicrobial peptides are manifold according to their structural features. Statistics show that the highest percentage of antimicrobial peptides are those containing disulfide bridge structures, followed by those with α-helix and β-fold as well as both structures. However, the structures of a considerable proportion of antimicrobial peptides remain unknown. Among them, α-helical peptides are widely distributed and diverse, with amphiphilic structures in the molecule, and mainly achieve bactericidal effects by changing the permeability and barrier function of the phospholipid bilayer of cell membranes, or by penetrating the membrane interface to destroy the membrane structure. β-folded peptides usually are more structural complex than α-helical antimicrobial peptides, presenting as ring-like molecules with structures of intramolecular disulfide bonds.
Applications of Antimicrobial Peptides
Since antimicrobial peptides differ from antibiotics in their bactericidal mechanism which shield from producing resistant strains and drug resistance，they have become an ideal substitute for antibiotics. Moreover, the combination of antimicrobial peptides and antibiotics can largely reduce or bypass the occurrence of antibiotic-resistant behavior. Combination therapy with the antimicrobial peptide DP7 eradicates drug resistance to vancomycin and azithromycin in Staphylococcus aureus and Escherichia coli. Antimicrobial peptides exhibit synergistic effects not only with antibiotics, but also with components of the immune system.
2. Food industry
Antimicrobial peptides with strong germicidal effect on many kinds of Gram-positive and negative bacteria in food, and has no toxic side effects on human and storage, so it can be applied to new food preservative. For example, Nisin is a polycyclic antibacterial peptide produced by Lactococcus lactis, with antagonistic effect on Gram-positive bacteria. Currently, Nisin is widely applied as a natural preservative in food industry.
3. Agricultural engineering
The use of insect antimicrobial peptides to cultivate crops with antibacterial varieties can greatly reduce the number of pesticides, and produce green agricultural products. Insect antimicrobial peptides are considered as the most promising green feed additive, which can promote animal growth, improve animal disease resistance, and is not easy to produce drug resistance.