Antibiotics have long provided effective treatment against bacterial infections. The creation of drugs like penicillin, streptomycin, and tetracycline allowed doctors to treat common bacterial infections that were once debilitating and even fatal. As antibiotic use has grown over the past several decades, bacteria have developed modes of resistance that have rendered some antibiotics useless. As these “super bugs” have become more resilient and resistant to treatment, researchers have begun to explore new ways of treating infections. Research has turned toward the use of antimicrobial peptides as an alternative to traditional antibiotics in treating drug resistant bacteria.
Antimicrobial peptides, also referred to as defensins, are short chains of amino acids that act against microorganisms. In plants and animals these peptides are made up of anywhere between 15 and 45 amino acid residues, and they are usually cationic, meaning that they contain higher amounts of lysine and arginine (Hancock and Lehrer 82). The peptides are produced as part of the body’s innate immune system, and they may be continuously present or produced in response to injury and infection. Because antimicrobial peptides are incorporated in innate immunity and are considered part of the body’s second line of defense against infection, they are often found in areas that may have close contact with environmental pathogens. These areas include, “the skin, ear, and eye, on epithelial surfaces, including the tongue, trachea, lungs, and gut, and in the bone marrow and testes” (Hancock and Scott 8856).
Antimicrobial peptides fall into two major categories based on the length of the peptide sequences between cysteine residues, with subfamilies of - and -defensins. Both families of antimicrobial peptides have “characteristic -sheet-rich fold and a framework of six disulphide-linked cysteines” (Ganz 710). Though - and -defensins display differences in cysteine placement and arrangement, the identical folds indicate that these defensins are, “branches of a single gene family that has undergone repeated duplications” (Hancock and Lehrer 83).
Antimicrobial peptides act against microbes by interfering with cellular membranes and interrupting internal signaling and cell metabolism. While antibiotics work similarly to antimicrobial peptides by breaking down the cell walls of bacteria or interfering with DNA, RNA, and protein synthesis in the cell, some bacteria that have developed antibiotic resistance can rid themselves of antibiotics, thus resuming normal function. Antimicrobial peptides actually insert themselves in the cytoplasmic membrane and create pores or transmembrane channels. These channels allow small molecules to cross into the bacteria, and this permeability coincides with, “the inhibition of RNA, DNA, and protein synthesis and decreased bacterial viability” (Ganz 714). This unique mode of action helps inhibit bacteria from developing resistance or...